Brake Bleeding
Bleeding the brakes is essential after disconnecting brake lines
in order to get air out of the system and ensure a "hard" pedal.
Bleeding is also a periodic maintenance action, sorta like changing
the oil; brake fluid absorbs moisture, either that was already within
the system or from the air in the reservoir, and this moisture is not
good for the insides of the brake cylinders. Also, the fluid
eventually becomes contaminated with tiny particles of metal from
wear within the cylinders, and the particles only serve to accelerate
the wear. So it is beneficial to occasionally bleed the brakes even
if there is no air in them, and to bleed them enough that the entire
system is filled with fresh fluid.
Two-Person Method
Bleeding the old-fashioned way requires two people. One person
sits in the car and "pumps" the pedal to get the pedal up where it
belongs, and then holds pressure on the system while the other person
opens one of the bleed screws to allow the fluid to squirt out. A
small piece of hose routed into a container helps reduce the mess.
When the bleed screw is opened, the pedal will go to the floor, and
the person in the car must KEEP it there until
the bleed screw is closed once again; if the pedal is allowed to
rise, it will draw air back in through the bleed screw. After the
bleed screw is closed, the pedal is pumped back up and the cycle is
repeated. If a clear hose is used on the bleed screw, it is easy to
see when the crud is gone and clear fluid is coming through. You must
pause every now and then to top up the reservoir with fresh fluid.
One-Person Method
If you want to make things easier or require only one person,
there are numerous gadgets available to help. Dan Welchman suggests
the "Eazi-bleed" kit
I think they're made by Gunsons but I'm not sure. This device
uses your spare tyre as a compressed air reservoir which pressurizes
a large plastic brake fluid reservoir via a hose and footpump-style
valve connector. A tube dips into the bottom of this reservoir and
feeds fluid up to an air-tight cap that screws onto your brake fluid
reservoir on the car (the kit comes with a wide range of different
caps and rubber gaskets to fit most cars).
Once you've fitted this and got it air-tight you can bleed the
brakes by just opening each of the nipples and letting the fluid flow
out until it's bubble free (or longer if you're changing the fluid).
No pumping, no assistant needed, and no worrying about having to top
up the reservoir for fear of running out of fluid and pumping air
through the system. They're extremely cheap and work pretty well.
Brake Fluid
Reservoir Connections
To make the brake fluid reservoir fit under the hood, Jaguar uses
a remote reservoir connected with metal lines and short pieces of
flexible hose. If these hoses need replacing, do not use conventional
fuel line; the brake fluid attacks the fuel line material, and the
result will be darkened fluid with lots of crud in it.
Replacement Hose
The fact is, none of the hose commonly sold at an auto parts store
will serve. Also, nylon tubing is unsuitable; the brake fluid soaks
right through it, and then it hardens and shrinks.
Of course, using Jaguar original hose is not recommended, as it is
a British non-metallic product. After all, you are now having to
replace it. But there are other cars that also use hose to connect a
remote reservoir to the master cylinder, including Mercedes and Fiat,
so you can check other dealers for suitable hose.
Non-automotive hose is also a possibility. You can visit an
industrial supply store and attempt to find a clerk who knows his
stuff, or a reference manual that lists acceptable applications for
different hose materials. Commercially available air hose works well
in this application; it is red with a black inner liner, and is sold
in many hardware stores.
Keep in mind that this application sees NO
pressure, so high-pressure brake or hydraulic hose is unnecessary and
will only make it very difficult to install over the plastic
fittings.
Brake Fluid Level Switch
Hey, it's electrical, so it's discussed in the
Electrical
section.
Brake Fluid Reservoir Cap
Failures
Apparently the cap occasionally breaks into a center portion and
an outer portion. According to Michael Neal,
This is a problem and tends to reoccur if you don't modify the
reservoir. This is on the pre-abs XJ-S brake reservoirs. Usually just
flattening the sharp vertical ridge on the reservoir with a file will
do it.
Dot 5 Brake Fluid
Many people swear by "Dot 5" silicone-based brake fluid, and
others swear at it. Silicone brake fluid does not absorb moisture,
does not harm paint when spilled, and has a very high boiling point.
It is also non-toxic.
Some of the arguments are based on it not absorbing moisture. If
there is no water in your brake system to begin with, theoretically
none will get in by being absorbed by the fluid in the reservoir. But
if there is water in the system to begin with, the silicone fluid
will not absorb it, and it may puddle in local spots and cause
corrosion.
Silicon fluid absorbs more air than conventional fluid, meaning
that the brake pedal will feel spongier, even when fully bled. Of
course, this will not be apparent at first, since it takes some time
to absorb air within the reservoir and for the air to diffuse
throughout the system.
It is reportedly of some importance that the two types of fluid
not be mixed. Silicon fluid is less dense than normal fluid and won't
mix with it, so it is theoretically feasible to fill the reservoir
with silicon fluid while bleeding the conventional fluid out at the
wheels.
Name Confusion
There is even some misunderstanding about the name. DOT 3 and DOT
4 brake fluids are referred to as such because they conform to
Department Of Transportation standards. "Dot 5" silicon-based fluid,
however, is a trade name, not a DOT standard. There are even reports
that DOT has now issued a standard #5, and it is NOT for
silicone-based fluid but for something else.
Older Girling Systems
There are also reports that older Girling systems require DOT 4
fluid to keep the seals pliable to seal properly. Some components are
reported to get hard when exposed to silicone fluid; others are
reported to absorb too much silicone and swell so much as to jam the
works.
According to Jim Beckmeyer, who had a master cylinder resleeved:
"White Post said that the
warranty would be voided if I used DOT 5." Draw your own conclusions.
Flushing
One thing is apparent to all experts: If your car is using DOT 3
or DOT 4 brake fluid, it should be flushed according to the
maintenance schedule. If left in too long, the absorbed water will
cause corrosion throughout the system.
ABS Brake Systems
Reportedly, Pat Goss, the host of the TV show Motor Week, said the
following:
Never use silicon brake fluid in an ABS system! [Silicon] brake
fluid doesn't like the pumping action of the ABS pump. The pistons
move so rapidly that it causes the silicon to foam and all of a
sudden you have aerated fluid and you have a pedal that's on the
floor.
Power Brake Servo
The (non-ABS) servo assembly comes apart in the center, by
twisting one half until the retaining tangs line up with the cutouts.
There is a special tool for this job, but Bruce Hayes reports the
tool can be improvised. He carefully mounted the master cylinder in a
vice, and fashioned a tool to attach to the studs on the housing to
turn it.
Front Brake Rotor
Replacement
Jaguar chose to bolt the rotor to the inside of the hub flange,
rather than the outside like intelligently-designed cars. As a
result, the hub must be removed to get the rotor off.
The various manuals suggest unbolting the rotor from the hub
during this process by inserting a tool through the opening in the
dust shield. However, Nance O'Neil points out that there is no need
to unbolt the rotor before removal, and instead the hub/rotor
assembly can be removed as a unit and then disassembled on the bench.
Either way, the brake caliper must be unbolted.
Rear Brake Pad Change
The CATALOGUE passed on this tip from the Jaguar Club of
Pittsburgh. To get the old pads out, tie a piece of wire to them
connected to a turnbuckle tied to the transmission mount. Tighten the
turnbuckle while tapping the pad with a hammer to remove the pad.
Emergency Brake Pad
Change
Jan Wikström:
It's a fairly tinkery job, and definitely easier the second
time... If you have a reasonable manual with a good picture of the
system, patience is really all you need (you'll be working by feel as
you can't see the upper side of the handbrake bits). A point: the
bronze fork that positions the handbrake pads off the disk will be
bent in if the pads are seriously worn and will need to be opened out
to fit the new pads. Just tinker until it slips in easily.
Another point: the self-adjusting ratchet mechanisms in the pad
holders are quite likely to be clogged with semi-carbonized grease
and dysfunctional; open the pad holders up, clean out the ratchet
mechanism and grease very lightly with high-temp grease or
MOS2 (molybdenum disulfide). Drowning them in grease as
the factory did is just silly; the ratchets may rotate one turn every
few months and don't really need lubrication.
Rear Brake Rotors
According to Michael Neal, the rear brake rotors on the XJ-S are a
"sandwich" construction:
The stock rear rotors have the actual thin outer rotor surface
attached to a solid core. These thin outer surfaces are very brittle
and break easily.
If problems occur, Neal recommends the use of aftermarket solid
disks. Apparently, when you order disks from some suppliers like
Special Interest Car Parts, they will send you the solid rotors
rather than even asking; the aftermarket parts are what they stock.
Rear Brake Disassembly
John Himes found out that both the Haynes manual and the Jaguar
manual described incorrect procedures for this job, at least on his
1988.
They are wrong on how the calipers mount. Both manuals tell you
to break the wire and remove the bolts that are shown on the outside
of the calipers. There is no wire and the bolts are on the inside of
the calipers. You must move the wheel to align a hold in the rotor to
remove / replace these 2 bolts.
Randy K. Wilson says this problem is caused by the difference
between the Salisbury and Dana differential units.
Brake Caliper Overhaul
Before removal, see the comments regarding the steering arm shims
in the section on Suspension/Steering.
On the rear calipers, brake fluid communicates from one side of
the caliper to the other via a "bridge pipe" a short piece of brake
line that connects to each side with threaded fittings. The front
calipers, however, have no such pipe; fluid communicates between the
two sides via a drilled passage through the caliper halves
themselves. Hence, there must be a seal between the two halves to
prevent leakage.
The official Jaguar repair manual starts: "CAUTION: Under no circumstances must the caliper
halves be separated." Apparently good advice; the seal between the
halves is difficult to find, and the caliper overhaul kit does
not include it.
So; you took the calipers apart and THEN
checked this manual! Shame on you. According to Rob Reilly, you can
get the seals from John Farrell.
Other possibilities include a Chevy dealer.
Brake Caliper Restoration
Old brake calipers are often restored to usable condition by the
fitting of brass or stainless steel sleeves. Thomas L. Felts sends
his experience:
I had all of my brake cylinders rebuilt several years ago...
they were rebuilt using a brass sleeve, which, three out of the four
wheels had the sleeves separate. Two earlier on. I have had a number
of people tell me to never use brass as a sleeve.
ABS Brake Pad Change
If the car has ABS brakes and the calipers are pressed back, fluid
within the calipers is forced back up the lines and into the master
control system. Since the fluid that has been within the calipers for
some time often has a high degree of contamination (wear particles
from the cylinder walls, etc.), when this fluid is backed into the
controls it tends to cause problems. It is suggested that when
pressing the calipers back (like when installing new pads) to open
the bleed port and allow the fluid to drain rather than pushing it
back up the lines.
Perhaps this isn't a bad idea with ANY
brakes.
Testing ABS Brakes
Michael Neal writes:
I do extreme situation ABS test on cars during on major
services. I get quite a few surprises. Even from a moderate speed of
45 mph I've had cars yank the steering wheel out of my hands and the
car ends up rotating 30 or 40 degrees. This is usually caused by a
sticking piston or slide on a caliper.
Pat Goss, the host of the TV show Motor Week, reportedly advised
to exercise the ABS at least once a month on a gravel road or
in a wet parking lot. (Meaning, jam the brakes and let the ABS kick
in.)
Dirty Front Wheels
Dust from the front brakes tends to get the wheels dirty,
especially if you use them hard. There is a device available to
prevent this problem. It's called Kleenwheels, and it's essentially a
disk that seals the wheel on the inside so the dust can't come out
through the openings. They are available at many auto parts stores.
It would be logical to assume that cutting off this airflow path
would result in a reduction in brake cooling, and therefore poorer
braking performance under severe, repeated braking. However, most
users don't notice any detriment (perhaps because they never use
their brakes hard enough for overheating to be a problem). The
primary cooling airflow is from the inboard side of the brakes to the
inside of the hub and outward through the ventilated disk. The warmed
air can then go either out through the wheel or inward under the car.
The use of Kleenwheels prevents the first exit, so all the air goes
inward. So, the use of Kleenwheels won't reduce the airflow to the
brakes, but it may cause more of the warmed air to recirculate back
through the brake again. Considering the airflow underneath the car
during any activity where hot brakes are a concern, this is probably
insignificant.
On to the Suspension
& Steering
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