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XJ-S Suspension & Steering

// JagWeb // XJ-S Help // Contents //

 

XJ-S Suspension & Steering

Clunks

If something in the front goes "clunk" when you drive over a bump, check the rubber bushings on the top of the front shock absorbers. British non-metallics again. Any generic rubber shock bushing will do, and will do better than the original.

Front Suspension Check

You may be confident that your front suspension is just fine, but this test is so quick and easy you might as well try it. Stand beside the car and grab the top of a front tire and shake it vigorously in and out. If everything is OK, the only thing you will feel is the flexing of the tires, and you will hear nothing.

If you feel any slop, or you hear a "clunk" back and forth, your front suspension is NOT up to snuff. You should check the following items, which are discussed in more detail below:

  1. Adjustment of the wheel bearings.
  2. Condition of the ball joints, upper and lower.
  3. Wear groove on bottom of front axle.
  4. Bushings at inner end of upper and lower swingarms.
  5. Front subframe mounts.

Perform this test and correct any problems noted before having your car aligned. The repair or replacement of ball joints, tie rod ends, swingarm bushings or subframe mounts normally requires realignment, and it's a shame to have to do it over.

It should also be noted that, contrary to common belief, a car will not periodically require realignment for no good reason. If a car was correctly aligned at one time and no longer is, it is because parts are either worn or damaged, and merely realigning without addressing those parts is unwise.

Front Hub Removal

Michael Neal suggests the brake caliper not be removed when pulling the hub, to avoid fiddling with the steering arm shims. Instead, unbolt the disk from the hub by inserting a socket through an opening in the dust shield. Then, remove the hub leaving the disk in place.

Front Wheel Bearings

According to Chad Bolles, the XJ-S uses standard front wheel bearings, available in any auto parts store. The pre-1977-1/2 XJ-S outer is an A-2, the inner is an A-6. The post-1977-1/2 car uses A-13 for the inner, A-12 for the outer.

Front Axle Wear

The inner races of the inner front wheel bearings tend to turn on the axles. As a result, they eventually wear a groove in the axle, on the bottom where the load is. This allows the wheel to wobble even when the bearings are adjusted properly, and your Jag starts driving like a Pontiac. To check:

  1. Remove the front hubs and check the stub axles for a wear groove. Run your fingernail along the bottom of the axle from the upright outward. If your fingernail catches at all, the axle should be replaced.
  2. When assembling, ensure that the inner races will not turn by using Loctite 640 or some similar high-strength bearing retaining substance. Use it on the inner race of the outer bearing, too, since it has been known to have the same problem.
  3. Adjust the front wheel bearings as described below.

Front Wheel Bearing Adjustment

Spin on the retaining nut until it seats, normally a very sudden change; continue to tighten while turning the hub until an increase in resistance in turning the hub is felt. This is usually about 1/10 of a turn after the adjustment nut starts to seat. This may seem tight, and in fact may be tighter than the official Jaguar procedure (measuring end play) would result in. Any bearing expert will tell you that proper operation of a roller bearing requires some preload. It is better to be too tight than too loose. When tight, the weight of the car is distributed among the rollers. When loose, the slop allows the load to be taken by only one or two rollers at a time, and the unloaded rollers may slide rather than roll.

Front Wheel Bearing Caps

Apparently, some bearing caps are a total seal, while others have a small hole in the middle. It is suggested that if you have wheels that don't keep dirt out of this area, put a small piece of aluminum tape over the hole. Or, just pry it off and take it down to the local auto parts store and buy a generic replacement.

Ball Joints and Tie Rod Ends

To test joints such as these, it is helpful to find a convenient way to "shake" them, or to move them in such a way that will cause them to slop one way and then the other. In the case of tie rod ends, this is easily done by moving the steering wheel back and forth just a little. With ball joints, if the front tire shaking described above caused a "clunk", that same motion will work for this test.

This test requires two people. Place a single finger on the joint in question in such a way that one side of the finger is against the hardware on one side of the joint, and the other side of the finger is against the other side. While holding this position (may be difficult, since the car should be sitting on its wheels) another person should provide the shaking motion. If the joint is OK, no motion can be felt between the two parts. If the joint is loose, a human finger will easily detect the slop. Typically, any slop at all is unacceptable, the joint should be replaced.

Swingarm Bushings

Swingarm bushings may be checked using similar methods as the ball joints, except that the bushings include some rubber so there will be some slight motion even in a perfectly good joint. Usually, the best indication that a swingarm bushing is bad is that some of the rubber is hanging out of it.

Front Subframe Mounts

If your XJ-S goes "clunk" every now and then, notably when you first start moving, one of the things you should check is the rubber mounts that hold the front suspension assembly to the frame. There are two doughnut-shaped mounts at the front, and two V-shaped mounts near the steering rack. If the rubber is torn or otherwise damaged, they should be replaced.

Grease (Zerk) Fittings

Unlike the newer American "low-maintenance" cars, the Jag has zerk fittings all over the suspension. Periodically it should be gone over with the grease gun, but please be conservative. It is tempting to grease fittings too often and to pump too much grease, which will destroy the seals or gaiters on the joint.

The following is a list of the grease fittings on the car:

  • All six universal joints -- good luck getting at the forward one on the drive shaft. The protective covers on the rear axle U-joints have openings for greasing, but they may not line up. You can relocate them as necessary.
  • All four corners of the flat plate under the differential (lower swingarm inner joints). There are holes in the plate for access to the zerk fittings.
  • The needle bearings in the lower pivot joint of the rear hub carriers; the fittings are just inside the rear wheels at the bottom.
  • Both front hubs. The fitting is on the side of the hub near the outer cap. With some wheel designs, the wheels do not need to be removed. Rumor has it these fittings have been deleted in later cars.
  • Both upper front ball joints -- remove the front wheels for access.
  • Both lower front ball joints. The fittings point inward, underneath the car.
  • Steering rack -- see the note later in this section.

Also, the rear wheel bearings should be greased by removing the small cap on the hub carrier and spooning a little grease into the hole. Don't overgrease, because the excess merely spins out and coats the inside of your wheels.

The pre-1983 Jaguars also had zerk fittings on the tie rod ends, but the later cars were fitted with "improved" tie rod ends with no such fittings.

The ball joint zerk fittings are designed with a relief system to prevent the grease gun from applying too much pressure. Under the fitting itself is a plastic washer that covers the relief hole. When the joint is full of grease, any additional greasing will force the plastic washer to bend, allowing the grease to come out adjacent to the fitting itself.

Michael Neal sends this tip on lubricating the lower ball joint:

If the grease comes out from behind the plastic washer as soon as you apply it then the passage is plugged. The best way to clean the passage is to remove the lower plate and zerk fitting. Ream out the passage and apply some grease to the cup before reassembling. The grease in the passage hardens after a relatively short amount of time and plugs the passage.

When installing the zerk fittings on these ball joints, note that overtightening the fitting onto the plastic washer will deform the washer and open the relief hole.

See the note on lubricating the water pump in the section on the Cooling System.

Don't overlook the zerk fittings themselves as a possible source of trouble. Each zerk fitting has a tiny spring-loaded ball check valve to allow grease in but not out. It is susceptible to corrosion and jamming. They are also easily damaged by impact.

Anti-Seize Compound

See the description in the Maintenance Tips. This note is to point out that many suspension components involve tapered fits, such as the ball joints and the front axle in the upright. It is suggested that anti-seize compound be used on the tapers themselves as well as the threaded nuts. It does no harm, and can make the assembly much easier to get apart in the future. In these applications, care should be taken to ensure the entire fitting is thinly coated, since the anti-seize compound will not be spread during assembly as it is on threads.

Lower Ball Joints

The original lower ball joint is a rebuildable assembly, with parts books listing the individual components. The lower ball joint from the XJ40 (the 1988-on boxy XJ6) is a one-piece throwaway item (part number CAC9937) that will replace the entire ball joint assembly on the XJ-S, and costs less than the individual parts of the original design. In fact, Jaguar no longer makes the original, rebuildable ball joint or parts to fit it; the authorized repair shops merely replace the joint with the XJ40 item.

An aftermarket parts company, Quinton Hazell, makes a rebuild kit for the original lower ball joint assembly. QH's prices for this kit are much more reasonable than the Jaguar parts prices ever were, and it is cheaper to use this kit to rebuild your ball joint than to install the new XJ40 unit.

The lower ball joint is assembled with shims to provide a properly snug fit between the ball and the socket. However, it should be noted that these shims are intended to provide a proper fit at assembly, NOT for removing the slop from a worn joint. If a joint develops slop, it should be rebuilt with new parts or replaced entirely, not merely readjusted.

When rebuilding the lower ball joint, don't lose the shims that come out. Although the QH kit includes shims, they are really intended to provide some adjustment capability from the original set; there may not be enough to provide all new shims.

When rebuilding the ball joint, thoroughly grease the ball and socket parts prior to final assembly. Although the joint has a zerk fitting, its use is no substitute for proper greasing at assembly.

Ball Joint Gaiter

The gaiter on the original Jaguar ball joint is a Rube Goldberg assembly in itself. It is a clear flexible plastic item, with a steel ring molded into it to make the small opening fit snugly around the ball shaft. The gaiter fits into a plastic ring (C22970), and a rubber ring (looks like a skinny O-ring) fits into a groove on the gaiter to hold it snugly into this plastic ring. The plastic ring then snaps onto the ball joint. Be sure that the plastic ring is oriented properly; the little ridge on the inside must be on the edge toward the joint itself.

The gaiter provided in the QH rebuild kit is different than the original. It is a more conventional solid black rubber item with no metal reinforcement. A metal clip is provided in the kit to be used in place of the rubber ring on the large opening. The kit does NOT include the plastic ring; if you boogered up the original getting it apart, it can be ordered separately. In a pinch, the gaiter seems to work just as well attached directly to the socket without the plastic ring.

If you are replacing just the gaiter itself and have neither the metal clip nor the rubber ring, you can simply tie it on with some wire. If using the QH gaiter, you can use nothing at all -- the black rubber gaiter fits quite snugly.

The original Jaguar gaiter has a life expectancy of less than five years. The clear plastic turns dark brown, then rots and falls out in crumbs. However, the gaiters in the QH kit are also British, so there's no telling if they are any better than the originals.

The ball shaft must be separated from the lower A-arm to replace the gaiter. Disconnect the upper ball joint to allow tilting the upright to get better access. Use of a fork-type ball joint separator on the lower joint will not only destroy the old gaiter, but the plastic ring and the upper ball seat as well. The fork type separator doesn't work very well here anyway; better to have the screw-type separator on hand. If the joint isn't jammed too severely, it is also possible to get the joint loose by disconnecting the tie rod and the brake line (helpful for getting the nut off anyway), jamming something between the inner edge of the hub carrier and the A-arm, and forcefully rocking the hub carrier outward.

Upper Ball Joint

The official repair manual calls for "Steering Joint Taper Separator JD.24", but we don't need no steenking separator! Put the car on jackstands and remove the wheel. Put a jack and block of wood under the lower ball joint and jack it enough that the rubber bumpers on the upper A-arm are not touching the subframe. Loosen the nut on the upper ball post several turns, but do not remove it. Lower the jack so that the rubber bumpers sit on the stops and the full spring force is applied to separating the joint. If you're lucky and the previous mechanic used anti-seize compound on the taper, you'll hear a pop as it comes loose. If more difficult, a little judicious tapping on the side of the upright may help.

Make sure to note where the shims are located between the arms and the ball joint. Even if you plan to have the car aligned, at least it will drive better on the way to the shop. The shims are supposed to lift right out, but they weren't made quite right. They tend to catch the bolt on the inner corner on the hook-shaped end. If this corner is filed slightly, reassembly will be easier.

The gaiter and associated parts on the upper ball joint are exactly the same parts as those on the lower joint -- see notes above.

Steering Arm Shim

The steering arm bolts to the hub carrier with two bolts. At the rear (longer) bolt, there is a shim (it looks like a washer) that goes between the steering arm and the brake caliper. Don't lose it! Omitting this shim at reassembly screws up your alignment and distorts your suspension parts.

If you have lost the shim already, replacements are available in 0.004" and 0.010" thicknesses. To determine the thickness required, assemble the parts and tighten all bolts except the one the shim goes on. Measure the gap between the brake caliper and the steering arm with a feeler gauge. After assembly with the appropriate shims, be sure to have the car aligned.

Front End Alignment

Randy Taylor sends a warning to be careful which alignment shop you choose to align a Jaguar:

The generic American tank has shims to align the front suspension camber and castor. These shims are placed at both the front and rear pivots of the upper control arm. By adding or subtracting shims equally at both ends, you change the camber. By adding or subtracting shims at one end only, you change the castor. Jaguars do not work this way, but look like they do to the uninitiated. The Jaguar has shims at the upper pivot just like the Chevy/Ford above, but they must be used as camber adjustment only with equal amounts of shim change at both front and rear pivots. The castor adjustment is done by a separate set of shims at the upper ball joint. If some hack jumps in there and adjusts camber and castor by staggering the pivot shims, you will end up with a car with a sort of correct alignment (dynamic castor gain will not be as Jag intended), but the car will just eat upper control arm bushings.

The good news is that the XJ front subframe is one stout critter. Unless it has been seriously whacked, it is rare for camber or castor to need adjusting. Alignment is usually just a matter of setting the toe correctly after the latest steering rack change/rebuild.

There are reports that the spec books that alignment shops have consistently list the wrong alignment specs for Jaguars. Just to be sure, take your own repair manual with you, and if the numbers that you have disagree with those they have, insist they use yours. They shouldn't care, it's your car and your money.

Tony Watts points out that there is a description of how to perform your own alignment with simple tools on the WWW at http://www.vtr.org/maintain/diy-alignment.html

Steering Wheel Alignment

If your steering wheel is cockeyed when driving in a straight line, your problem may be in the relationship between the steering wheel and the rack, or between the rack and the wheels. Jaguar has provided a nifty method of determining which. If you remove the grease fitting from the steering rack, a dowel (or special Jaguar tool no. 12279) can be inserted to engage a notch in the rack. When the notch is lined up with the grease fitting hole, the rack is centered. The steering wheel can then be lined up properly. Once this is done, a misalignment when driving straight (be sure you're on a level road, and not in the right lane of a road that is crowned) calls for correction at the tie rods. If the correction is minor and you are confident that the alignment is otherwise OK, this can be done by carefully marking both tie rods and adjusting both of them the same amount.

Ride Height

XJ-S owners are often concerned about whether the car is actually supposed to sit that low, or if something is wrong. The Jaguar XJ-S Repair Operation Manual describes a check, but it assumes you have original tires with full tread. It also assumes you have "slip plates", devices you set the front tires on so they can slide around and not bind the suspension travel. The following is a derived procedure that subtracts the tire rolling diameter out of the equation in order to determine if your car is sitting at the "correct" ride height for the tires you have on it, and all it requires is a level section of concrete.

Position the car on level ground with nobody in it, no heavy stuff inside or in the trunk, a full tank of gas, the emergency brake off and the shifter in N. Push the car back and forth a few feet. When pushing rearwards, push on the front bumper and deliberately bounce the front of the car a little while pushing. When pushing forwards, push the rear bumper and deliberately bounce that end as well. This is to make sure the car is fully settled in its position.

Measure the height to the center of the front wheels. With any luck, they should be the same, but if they vary slightly determine the average.

Subtract 6-3/8" from this height. This gives you the correct height above the ground for the flat bottom of the cross member between the front wheels.

Using the same front wheel center measurement (do NOT measure the height of the center of the rear wheels), subtract 4-7/8." This will give you the correct height above the ground for the edges of the plate between the rear wheels with a full tank of gas.

So much for the "correct" ride height. Now, to describe what you actually have, a story from B. J. Kroppe:

My former supervisor (a Jaguar employee) did vehicle packaging for the F-Type. He started with XJ-S drawings and came across some things which didn't add up. So he went to the assembly plant and measured some XJ-S vehicles and compared them to the drawings. He discovered that the cars being produced (this was mid-late 1980's) were very much lower than the drawings said they should be.

After some investigating he learned that over the years more features had been put on the car, making it heavier, but springs had not been changed to accommodate for the added weight, thus causing the lower ride height in the actual cars vs. what the drawings were saying.

In practice, it appears the XJ-S may ride about a half inch lower than the "correct" ride height, even when new. If yours is significantly lower than that, however, it's probable that either the shocks or the springs need replacing.

Sagging Front End

If your Jag seems to be riding low on the nose end, a likely culprit to check is the front shock absorbers. The XJ-S uses gas shocks, in which the damping fluid is held under pressure by a small amount of gas within the chamber. A side effect is that the pressure causes the shock to try to extend. This extending force helps raise the car a little, especially when the suspension is soft. The Jag was designed for these shocks, and if they lose pressure, the nose sags. Since the pressure may be lost while the fluid is still present, the low nose may be the first sign of failing shocks. Of course, the rear shocks are also gas type and may cause the same problem, but it doesn't seem to happen as often.

Shock Absorbers

The mail-order catalogs seem to offer only original shocks or big-bucks performance shocks. However, NAPA, Monroe, and Gabriel offer serviceable, reasonably-priced gas shocks for the XJ-S.

To check the front shocks, jack up the car and remove the front wheel. From inside the engine compartment, remove the locknut, nut, rubber doughnut and seat from the top of the shock absorber. Then reach into the wheel well, grab the top portion of the shock and pull it downward. If it is in good shape, it should move downward smoothly with a hiss, and when released should move smoothly but forcefully back to its full extended position by itself. If the motion is not smooth, or the shock compresses easily and quickly with no damping effect, or fails to extend itself when released, replace the shocks.

The traditional tests of shock absorbers involving pushing the car down and noting its recovery or noting the car's reactions over bumps are not entirely applicable to modern gas shocks. If a gas shock loses its gas charge, it may still appear to pass these tests; if it still has fluid in it, it will still provide some damping. The damping effectiveness is greatly reduced, however, and will get much worse over a series of bumps. And, as noted above, the car's ride height will be affected. There seems to be no substitute for disconnecting the shocks and checking them by hand. Checking the rear shocks will require a spring compressor to remove the springs from the shocks.

The front shocks should be checked before having the car aligned. The front end of the car sitting lower than it should has an effect on the camber, and will alter alignment settings.

Steering Column Installation

If you have lowered your steering column, Rob Reilly sends this tip for reinstallation:

When putting back the steering column use a little rubber cement to hold all the washers in place. Leave the bolts loose and pull the column back about 1/4" before you tighten them; if you don't, you will get binding in the lower column universal joint and bumpy steering.

Steering Rack Lubrication

According to the John's Cars catalog, using the zerk fitting on the steering rack does more harm than good, and they remove them during their rebuilds. Others have reported no problems, but obviously one would be well advised not to get carried away with the grease gun.

Steering Rack Lowering

Any time the steering rack is lowered for inspection or repair, it is wise to disconnect the bolts mounting the power steering cooler to the subframe. The pipes on this unit are very fragile, the hoses are short and often stiffened by age and heat, and a new cooler is of course more than US$100. It can generally be repaired by any reputable radiator shop, however.

Steering Rack Mount Bushings

The mount bushings in the steering rack are parallel to the axis of the rack itself. Since the forces caused by steering are also parallel to the rack, the elastomer in the bushings is subjected to shear. This is a really lousy design; sound engineering practice is to avoid shear or tensile stresses in elastomers, and subject them to compressive loads only.

This book is organized such that this section covers maintenance only, modifications are later in the book. Many people probably feel that they do not wish to modify their car, and may not even read through that section. Please, PLEASE, go to the section on Suspension & Steering Modifications and take the advice on replacing these rack mount bushings. Even if the stock bushings have not yet failed, even if the car is brand new, it is advised to replace them with alternative design bushings.

Contrary to the instructions in the manual, the steering rack can be lowered far enough to work on the mount bushings without disconnecting either the hydraulic lines, the tie rods or the steering column. The only difficult part is access to both ends of the three mounting bolts.

John's Cars offers a rental tool for removing the original bushings from the rack. It is extremely helpful, especially when working with the rack hanging under the car where a bench press won't help. Or, you can improvise such a tool using two 3/8" drive sockets (one deep), a long 5/16" bolt or piece of threaded rod, and nuts and washers.

Be sure that all rack mount parts fit snugly when assembled. Do not use the bolts to pull the frame in to meet the sides of the bushings. If necessary, buy some 5/16" fender washers and insert them alongside the mounts to make them fit properly.

Steering Rack Mount Bolts

If you happen to be working on the rack with either the engine or the front subframe out of the car, you may be able to put the bolts in any way you wish. But for the benefit of those who work on the car later, please install the upper mount bolt on the driver's side from the outside inward, and the lower bolts on both sides from the inside outward. This makes it much easier to install or remove the rack with the engine and front suspension in the way.

If you must replace the mounting bolts, be careful not to use bolts that are too long. When complete, be sure the upper bolt on the driver's side does not protrude too close to the engine block, since the engine moves on its mounts and will beat against the bolt. And the lower bolts should not protrude too closely to the lower A-arms, since they are likewise mounted on rubber and may move during operation.

Steering Rack Removal

If you have to remove the steering rack, one problem is how to remove the pinch bolt that connects the steering column swivel joint to the tower shaft. Remove the oil filter first, then turn the steering wheel until the pinch bolt is positioned where you can get at it.

Also note that the pinch bolt must be completely removed for the swivel joint to be disconnected from the tower shaft. The tower shaft has a recess the bolt fits through; merely loosening it will not permit removal.

Steering Rack Tower Shaft Seal

This seal is prone to leakage. John's Cars offers an aftermarket seal that is supposedly better than the original. It better be, it's quite expensive.

Reportedly, one problem associated with this seal is incorrect installation by driving it too far into the housing. Be sure not to drive it any deeper than it needs to go.

Steering Rack Rebuilding

There is a "seal kit" available for the steering rack. Note that reportedly the tower shaft seal is NOT included in this kit; check with your source and order the tower shaft seal separately if necessary.

A high percentage of people who have rebuilt their own steering racks have reported failure on the first try, and all for the same reason: when installing the rack bar through the seal on the driver's side end of the rack, the teeth on the rack bar ruined the seal. This typically results in ordering an entire new seal kit to obtain this one seal, and greater care the next time. The repair manual calls for wrapping the rack with tape prior to sliding the seal over it; apparently this is the minimal precaution, experience says to lube it up as well and exercise extreme caution during assembly. It has also been suggested that the seal and the part it mounts into be slid over the rack separately and then assembled, since installation in the housing makes the seal more difficult to work with.

Power Steering Pump

The XJ-S power steering pump is a standard GM Saginaw unit. However, it is uncertain whether the Jaguar system operates at the same pressure as a GM; so, if you replace the original unit, it is suggested that you remove the pressure control valve from the Jaguar unit and install it in the new one. The pressure control valve is easily removed by removing the outlet fitting and shaking the unit until it falls out.

Power Steering Fluid

You're supposed to put the same type fluid into the power steering unit that you put into the automatic transmission. This is interesting, since the early cars with the Borg Warner automatics called for Type F fluid while the later cars with GM 400 automatics call for Dexron II/III, and the power steering system didn't change. Apparently any ATF will do in the power steering system.

Apparently Type G fluid was called out in some owner's manuals for the power steering. "Type G is an obsolete designator for Dexron. It's so obsolete that nobody remembers what it was."

See the discussion on Dexron ATF's in the Drivetrain section.

Rear End Alignment

There's no such thing as castor on non-steering wheels, and toe-in is not adjustable on the rear of the XJ-S; if it's off, something is bent. The only alignment adjustment available at the rear is the camber, adjusted by replacing shims between the inner end of the axle and the brake disk. The more shims put in, the more the top of the rear wheel tilts outward.

Note that there are usually some shims between the brake disk and the differential unit. These are to locate the disk properly between the calipers, but also affect the camber as well. If working in this area, always make sure all shims are reinstalled properly.

Randy Taylor offers this advice:

Camber is not a constant. The camber control is taken on two pivoted arms (of unequal length) so that the camber can change on a predetermined curve based on suspension position.

It is very unlikely for the camber to change from factory specs unless one of three things happens: either something is bent, someone left some shims out during a differential or brake service, or the ride height is wrong. The #1 cause is the last: sagged rear springs. So, when you are told that the rear camber is off, investigate the static ride height before investing a lot of time/money in shim swapping.

Rear Suspension Subframe/Differential Removal

To work on the differential, as well as many major tasks relating to the rear brakes, it is necessary to lower the entire rear suspension assembly out the bottom of the car. Fortunately, this is nowhere near as difficult as it appears. Jan Wikström says:

You need two good stands and a small garage jack, as well as a friend to stabilise the subframe as you move it down and up (and help you lift it to the workbench; that sucker is heavy). To make the job a lot easier, take the spring/shock units out first and refit them last. You'll need to shift the subframe in two lifts, as the stroke of the jack won't be long enough. I use a 5" thick wooden block on the jack and rest the unit on two cement blocks halfway up.

Some others have reported good results with putting the wheels back on during removal; that way, the assembly can be rolled out from under the car. It will require positioning the car on even taller stands, though.

Rear Spring/Damper Disassembly

The obvious way to disassemble the springs from the dampers on the rear end is to remove the damper with the spring installed, then use a spring compressor on the bench to separate them. However, Ian Macfarlane provides an alternative procedure:

To change the rear shock absorbers without using a spring compressor, the springs can be held in the compressed state by fitting four elongated "C" shaped brackets (two per spring) over the centre 80% of the spring with the car jacked up under the suspension (preferably with a load in the rear of the car to maximize spring compression). Then, when the car is jacked up under the body, the springs will remain partly compressed and the shock absorbers can be replaced relatively easily.

Rear Wheel Bearings

According to Chad Bolles, the bearings in the rear wheel carriers are a Bower/BCA part number 18590-18520 for the inner, and 18690-18620 for the outer; available in any auto parts store.

Rear Axle Failure

Jan Wikström reports on his problem and solution:

The stub axle in the hub carrier (the bit that turns in the rear wheel bearings) is splined for the hub and has a large thread and castellated nut on its outer end. This thread comes right down to the splined part with no fillet whatever and creates a horrendous stress concentration at the end of the thread. Mine suffered a fatigue fracture in consequence; my local parts pusher tells me this is not uncommon, as one would expect from such an elementary error, especially if the nut is overtightened. Accordingly, I ground and polished a shallow rounded groove at the base of the thread of the new part... (see Figure 3 and Figure 4, illustrations graciously provided by Jan Wikström).


Figure 3 - Rear Stub Axle Failure Location


Figure 4 - Rear Stub Axle Modification

The next time you do the rear wheel bearings or U-joints, I strongly recommend having the stub axles checked and modified; any competent engineering shop will know about stress relief. Modifying parts of the Jaguar may be sacrilege to some of us, but fine as the design is, it isn't perfect...

If the stub axle has already broken, it is possible to fix it by drilling and tapping a hole in the end and using a bolt and washer instead of the nut. GT Jaguar offers a grade 8 bolt and a specially designed washer for this purpose, although you could conceivably come up with suitable parts from local sources. This fix may also be used as a preventative measure, since cutting off the stub and drilling for the bolt eliminates the stress concentration in the original part as well as the shallow groove does.

Perhaps one thing to note is that GTJ offers these parts at all; that would seem a serious indicator of just how common this problem is, and how important it is to address it.

Rear Hub Carrier Cracking

Joe Bunik reports that the cast aluminum hub carriers on his car cracked in the area just above and outward of the fulcrum shaft. The crack was parallel to the fulcrum shaft, but just far enough above it to be in the structural portion between the fulcrum shaft bearings and the wheel bearings. According to his mechanic, this is not an unusual problem.

Folks, if this part breaks at speed, you will be taking the Lord's name in vain! These parts are expensive, but if a crack is found one would be foolish indeed not to address it.

What with the rough surface on the cast aluminum combined with the dirt and grime normally covering it, it is entirely too easy not to notice a crack like this. Whenever a rear wheel is removed, it is recommended that the hub carrier be cleaned up a little and inspected for cracks, especially in the area just above the fulcrum shaft.

Spoke Wheels

Yes, a Jaguar with real spoke wheels really looks good. Unfortunately, it generally doesn't drive worth a hoot. The spoke wheels available have a reputation for trouble. Spoke wheels were a good idea in the 1950s when Jaguars needed to maximize air flow to cool their brakes. Since that time, two changes have conspired against spoke wheels:

  1. The advent of tubeless tires. Many spoke wheels won't work with tubeless tires, so you must install a tube. A tube installed in a speed-rated tire (the XJ-S should be fitted with V-rated tires) completely negates the rating, and renders the tire unsafe at speed. Don't drive fast with inner tubes in your tires!
  2. The advent of low, wide tires. A spoke wheel is a reasonable structure when it's tall and skinny, like a bicycle wheel or the automobile wheels of the 1950s. But it is a structurally poor design for modern low, wide wheels.

Furthermore, modern Jaguar wheels need an offset (distance from mounting surface to centerline of wheel) of around 1-1/2" which is not conducive to spoke wheel strength.

Maintenance

Spoke wheels tend to need truing on a regular basis. This is not a job for the home mechanic, and finding someone who can do it is a challenge. Often the wheels must be returned to the manufacturer for truing. Obviously, whoever does it, this process will also require rebalancing because the wheel is not the same shape as it was.

Rust Problems

Spoke wheels generally have chrome-plated steel rims, leading to rust problems, flaking chrome, and associated leakage at the tire/rim seal.

Weight

By the way, if it's a weight reduction you expect, forget it. There is nothing lightweight about spoke wheels.

It should also be noted that since the spoke wheels are more flexible than alloy, the handling will suffer somewhat. With a car this heavy, the difference in the way the car corners is noticeable. You may even get sounds, as the spokes strain and creak with the load.

Alloy Wheels

The specified torque on lug nuts on earlier Jaguar alloy wheels is 45-50 ft-lb., and 75 ft-lb. on later ones. This impresses some people as not being very tight. However, higher torque is unnecessary and causes damage to the aluminum wheels; this is true of all alloy wheels, and in this day and age your tire store should know better. If the shop installs your wheels with an air wrench, tell them where to get off and take your business elsewhere.

There are now machines in better tire stores that mount tires by gripping the wheel from the inside with soft grippers and never touch the wheel's pretty outside surface. Check out the price lists for new Jaguar alloy wheels and decide for yourself if it's worth finding a store with this equipment.

You might also want to watch how the wheels are mounted on the balance machine.

Anti-Seize Compound Again

Believe it or not, one of the places where Jaguars are known to have seizing problems is between the alloy wheel and the hub. Robert Woodling suggests use of anti-seize compound on the mating surfaces, especially at the hole in the center of the wheel. It can be disconcerting to have a flat tire and be unable to get the wheel off.

Wheel Balancing

Incompetence is rampant in the retail tire industry -- at least in Florida. Left to their own devices, most of the meatheads in a tire store will happily static balance your Jaguar alloy wheels, then beat the weights onto the rim with a hammer.

Static Balance

There are two basic types of imbalance. The old-fashioned bubble balancing, which engineers refer to as static balancing, only corrects one type of imbalance -- the type that causes the wheels to hop. This is generally adequate only for wheels that are very narrow, and should be considered unsatisfactory for any modern automobile.

Dynamic Balance

The other type of imbalance, dynamic imbalance, is the type that causes wobble. A wheel that is statically balanced may still be dynamically imbalanced by having a heavy area on the outside edge of the wheel and an equivalent heavy area 180 degrees away on the inside edge. Although the wheel would appear balanced on a bubble machine, when spinning the two diagonally opposite heavy areas cause the wheel to wobble. It's usually not too noticeable on the rear wheels, but on the front wheels it can cause steering wheel shudder. And you may eventually want to rotate the rear wheels to the front, so it's kind of nice to have them all correct.

To correct a dynamic imbalance requires that weights be placed in two separate planes -- usually (but not necessarily) the inside and outside edges of a wheel. It requires more lead than static balancing. It also requires a machine that actually spins the wheel; the bubble balancer is out. Use of these machines has come to be called "computer balancing." However, note that a switch on the machine allows the operator to specify a static balance only, so asking for "computer balancing" does not guarantee a proper dynamic balance.

The meatheads generally understand that the owner of alloy wheels is not thrilled about balance weights on the visible outside surface of the wheel. The standard response is simple: he sets the balance machine on "static" and applies all the balance weights to the inside rim of the wheel. This actually makes the dynamic imbalance worse, since even in the days of the bubble balancer the operator knew to put half the weight on the inside edge and half on the outside.

Insist on watching what is going on. There is a button marked "static" usually at the top left on the machine, with a red indicator light. When on, the machine will read imbalance values on the left indicator and a blank display on the right indicator. If you see this happening, I highly recommend you have your wheels put back on your car and take your business elsewhere.

The balance weights needed are part of the problem. Steel wheels commonly use "clip-on" weights that are hammered onto the rim. Some alloy wheels are designed with a rim that can accommodate clip-on weights, but they may not attach as well to the thicker aluminum. And use of a hammer to install is not good for aluminum, especially if the meathead responds to difficulty with a bigger swing.

Clearance

When the steering on an XJ-S is turned full lock, the clearance between the inside edge of the wheel rim and the front anti-sway bar is very small. If wider-than-original wheels are used, clip-on balance weights may actually hit the bar, resulting in a blip-blip-blip as you roll around a tight turn.

The proper balance weights to use on alloy wheels are called "stick-on" and are attached to the inner surface of the wheel with a layer of foam tape attached to the back side of the lead weight. One problem is that they are not reusable; once peeled off, the tape is not reusable, and the shops customarily throw them away. I guess using generic foam tape has not occurred to them, or just isn't worth it, even though they often complain loudly that these weights are expensive and charge the customer accordingly.

The problem is exacerbated by the meathead not knowing how to use the machine properly and having to do a by-guess-or-by-gosh balance job. With the clip-on weights, he can just keep prying them off and reinstalling them until he gets it right, but he can waste a lot of stick-on weights. An intelligent operator, of course, will be able to set the machine up properly and get the correct weight applied the first try.

The older computer balance machines were really designed for steel wheels. They have a setting for the width of the wheel and assume you will be putting clip-on weights on the edge. While the machines have a setting labeled "Mag", it is unlikely the operator will know how to use it. If you are using stick-on weights (which are located radially inward and on different planes than clip-on), the machine must be set up properly in order to read the correct amount of weight required. Simply setting the same width, offset and diameter info as used on the steel wheels will indicate if the wheel is imbalanced but will give incorrect data on the size balance weights needed, so the operator will be making several attempts.

There are newer balance machines that better accommodate alloy wheels. They can properly balance the tires by applying weights in any two planes, not necessarily the outer edges; the desired location for the weights is a separate setting in the balance procedure. They also can "split" a large balance weight requirement into two smaller weights, telling the operator where to put them both. This is helpful for two reasons: first, a large stick-on weight means a LONG stick-on weight, and as it curls around the rim its effective radius reduces somewhat, and the balance becomes inaccurate. Second, using two smaller weights may allow the operator to hide them behind spokes on some wheels.

Owners of alloy wheels should always insist on dynamic balancing using stick-on weights in two planes within the wheel -- one near the inner edge, and one just inside of the outer face of the wheel. Since these planes are closer together than the edges of the wheel, even more lead will be required to correct imbalances. But the weights won't show, and nobody will need to use a hammer to install them. Always insist that the balance machine shows 0.00 on both indicators before the balance is acceptable.

The only real problem with stick-on weights is a reputation for getting lost. Since clumps of mud and other debris sometimes gets dragged around the inside of the wheel, the foam tape can be ripped away. Two suggestions are in order, and neither is likely to be done by the tire shop, so the owner should bring the materials necessary and do them himself while the wheels are off: First, mark the locations of the stick-on weights with a permanent marker. Then, secure them with a piece of aluminum tape (available at air conditioning shops). Duct tape is not good; it quickly dries up and falls off, often taking the balance weight with it. The aluminum tape appears to be light enough to not affect the balance when added.

Wheel Interchangability

A few years back when Jaguar introduced the Anti-lock Braking System (ABS), they also introduced the new faux spoke pattern alloy wheels. Some reports at the time suggest these changes were related; apparently, the older wheels (a domed 5-spoke alloy design) interfered with the ABS hardware. The bolt pattern, offset, width, and other dimensions remained unchanged, so the later wheels can be used on earlier cars. But if the reports are true, the earlier wheels cannot be used on later cars.

Tires

When replacing tires as a set, you don't have to stick with the brand of tire that came on the car. In fact, it may be better to change brands according to Michael Neal, who works on Jaguars for a living:

I've seen hundreds of the 215/70 Pirelli P5s rip out at the sidewall near the bead. These are the original equipment tires on the U.S. spec XJ6 Series IIIs and early XJ-S. Sorry, but I would not even consider buying a set of these. The 235/60 P600s had the same problem.

Speed Rating

You should insist on at least a V-rating (a speed rating of 220 Km/h, or 137 mph) unless you always obey the U.S. speed limits. In some countries, you are required by law to use V-rated tires on these cars. You will find V-rated tires expensive. The rating is either indicated within the tire size, as in 215/70VR-15, or elsewhere on the sidewall, as in a 98V adjacent to the tire size. Other ratings include S (180 Km/h or 112 mph), T (190 Km/h or 118 mph), H (200 Km/h or 124 mph), and Z (250 Km/h, or 155 mph), and new speed ratings higher than Z seem to be introduced on a regular basis. In the U.S., if there is no indication of speed rating, the tire is S-rated.

These ratings are intended to indicate suitability for Autobahn-style driving -- continuous high speed. Generally, the limiting factor is heat buildup in the tire. High-speed-rated tires either run cooler or are made of higher-temperature material, or both. Much of the heat generated is dissipated to the air inside the tire and away through the rim, so inner tubes invalidate the ratings (the flexing of the inner tubes themselves adds to the heat buildup).

Since the flexing of the tire is what generates the heat, tire manufacturers usually achieve a high speed rating by making the sidewalls stiff. Therefore, the high-speed-rated tires drive differently than normal tires, even at low speed. For this reason, many recommend the V-rated tires even to those who don't drive fast. This is especially true for the XJ6 and XJ-S, because the soft suspensions get downright mushy with the softer, lower rated tires. There are reports that S-rated tires used on these heavy cars will flex so much that they will wear out quickly.

The heat buildup due to tire flexing is also the reason you must have fully inflated tires when driving fast, as indicated in the XJ-S glovebox.

As the tread wears, the speed rating of the tire will actually improve. A thinner carcass generates less heat when flexing, and dissipates heat better. There have been promotions claiming street tires were successfully used for racing; in these cases, typically the outer half of the tread was shaved off before the tire was even put on the car.

Tire Design

One other thing to consider when replacing tires is the intentions of the tire design. The original Pirelli P5's were designed for a soft ride, and the 235/60 Goodyears fitted to the later XJ-S reportedly also provide an excellent ride -- actually an impressive achievement when maintaining a V rating. However, most V-rated tires are designed more for performance than ride, and replacement with such tires is likely to result in vastly better performance and road feel but a less luxurious ride. A set of Dunlop SP Sport D40 M2 235/60-15's (unidirectional tread, max pressure 44 psi) convert the XJ-S from a luxury coupe into a GT. Similar results have been reported with Yokohama performance tires.

Tire Codes

For those who'd like to know, the rest of the tire size code works like this: The first three digits, such as 215, is the width (mm) of the tire at the widest point -- the middle of the sidewall. It is always rounded to a number ending in 5. The two digits after the slash, along with an implied decimal point, gives the aspect ratio: the height of the tire above the rim divided by the width described above. For the 215/70VR-15, this is 0.70. If there is no such number, the aspect ratio is 0.80. The R in the tire size merely indicates it is a radial tire; it is sometimes omitted. The -15 indicates it fits a 15" wheel.

Overall Diameter

The one thing you normally don't want to change is the overall diameter of the tire, since this would affect your speedometer and odometer readings as well as your ride height. Changing the ride height can have adverse effects on the suspension geometry, even if you don't mind the altered ground clearance. To maintain overall diameter when you go to a wider tire, you also have to change the aspect ratio to a lower value. Tire manufacturers also usually list a "loaded radius", the distance from the ground to the center of the wheel with weight on it. This measurement is meant to include the deformation of the tire under load so the consumer can determine the actual ride height.

The early XJ-S was fitted with 215/70VR-15, and the later models with 235/60VR-15 tires. The later tires are slightly smaller in diameter than the earlier, but there is no indication that Jaguar altered the speedometer or suspension. Both sizes are very suitable for the car, and there is normally no reason to select tires beyond these sizes.

Mixing Tires

DO NOT mix tire types, sizes or makes on a Jaguar. The XJ-S and the XJ6 have a suspension design in which the entire suspension assemblies are attached to the car with flexible mounts, and the relative stiffness of the mounts is premised on all the tires being the same. Mixing tire types, even outwardly similar ones, can result in dangerous instabilities in this suspension system. This is no joke; having one type of perfectly good tire on one end and another type of perfectly good tire on the other can result in you being rudely introduced to a tree when you aren't even traveling that fast.

 

On to the Body

 


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