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Speedometer Adjustments

Speedometer Adjustments

Hello all,

I have a speedometer accuracy question.

Once I get over 40 mph, mine tends to report "a possible range" of speed,
with the needle constantly flickering. I tend to go with the lower end of
the flickering, that is, if the lower end is around 55 and the upper end
peaks over 90, but everyone is still passing me on the interstate, I assume
I'm doing the speed limit.

Is this possibly just (slight hint of sarcasm) a spring replacement or an
adjustment or should I send it to one of those people in Hemmings that
repair instruments?

I assume that it will be a typical repair job if I send it off, one that
uses the quaint southern word "hunnertn," translating as some (specified)
hundreds of dollars, as in "This'll cost ya two hunnertn fifty, at least."
for those not from the South.

Jim Voorhies
XK140 FHC

Jim,
In addition to all of the other good advice you may want to check the
odometer for binding. The odometer uses the speedometer cable to turn its
gears. Momentary binding at specific points could cause the the spining
magnet to slow down at a binding point and speed up once its past (i.e. the
cable snaps back once the drag is gone). Lubricating the odometer should
cure this problem.

Cleo Bay
XK120, XK140

Jim,
Take the unit out and run it with an electric drill to determine if it is
faulty. If it is OK, then you probably have a cable bind that is causing
the wavering.

George Badger

Jim,

i haven't gone in in a while, but my recollection is that the speedo action
is a spinning magnet inside a spring balanced housing attached to the
needle. There is a small air gap....with age and storage a dusting of rust
may form causing occassional physical contact where only a magnetic pull
should exist between the spinning parts. This might explain the swinging
needle....or not-

Jim Warren XK 140dhc, XJ6 vdp

Jim,

You are correct. I had my S-type speedo apart last week. I could easily see
where the spinning magnet was striking the plate attached to the needle. I
don't know exactly what caused the air gap to close but it wasn't rust.
Perhaps warpage or a bushing wear. I tried to slide the magnet back on its
shaft. When I put it back together it worked for a while, that is it
eliminated the wild swinging, but it was reading too low.

By the time I put about 50 miles on it it was swinging wildly again.

Thank goodness for the lock up torque converter. It allows me to use the
tach to determine speed.

Jim,

I have excellent results having old british gages repaired by Nisonger
Instrument Sales in NY. 914-381-1952. Bob Nisonger is the owner, very
knowledgeable and definitely not southern (how about a Broklyn accent). I
have always been pleasantly surprised at the reasonable prices, although
$100 or so may be what it would cost to get your old speedo back in shape.
Before you do that though, have you checked the cable, fittings, etc. I'm
no mechanic, but it sounds like it might be that kind of problem.

Good luck,

Jeff Snook



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