Yes, they do. On a conventional cable system, the cable comes into
the speedometer head and a gear train drives the odometer and
trip-meter sections. The speedometer part spins a bar magnet inside
an aluminum cup, and the eddy currents move the needle. (With damper
springs to move it back to zero, and calibrate the swing.)
If it's an electronic speedometer (which yours is probably too old
to be, but you never really know till you look) there is no cable,
only a pulse generator attached at the transmission where the cable
would normally go. The speedometer head is a simple meter movement
with an electronics module translating the electronic signal
pulses-per-second to speedometer needle deflection.
The odometer and trip-meter are moved by a little stepper motor of
some sort, the little computer module has to do a translation of X
pulses per 1/100 mile indicated advance. With an electronic motor
driven analog odometer it doesn't smoothly turn, it moves forward in a
series of small jerks like the sweep second hand on a quartz analog
(And for both speedo and odometer it's easy to re-calibrate the
electronic systems for a different tire size, and get them within 1%
accurate. On a mechanical system you have to change the transmission
drive gear which is a lot more work, and if your tire size falls
between drive gear sizes that might only get you within +/- 3%.)
Get the factory repair manual, and follow the troubleshooting tree.
I won't even venture a guess past giving you the basic explanation of
how it works. It's more likely a mechanical failure inside the speedo
head, but they are too expensive to just swap out on a guess.
Speedometer heads can be diagnosed and fixed at qualified shops.
They are delicate, but not impossibly so.
If it can't be fixed, you can usually order the new speedometer head
with the odometer mileage set to where the old one was before it died.
That way you don't have to fill out a change of indicated mileage
declaration form and file it with the DMV and disclose the odometer
swap to the next buyer - and if you don't follow your state's
proscribed procedure for this disclosure they can accuse you of
odometer tampering and make big trouble.
--<< Bruce >>--
Same as on my 94 'Boid a year or 2 ago. I think it's a
fairly common failure. If you search the archives ...
It's not mechanical. The dash cluster is all electronic.
You can pull the cluster and speedo and inspect. The speedo is
"tamper-proof". I couldn't do anything with it.
A replacement speedo with pre-set miles from a dealer was
about $250 (not installed) about 1.5 years ago here in the
midwest US. Check on your states odo-tampering laws.
Might consider a speedo from a junkyard. But your mileage
would be wrong, unless you can figger how to fiddle the
damned thang. I couldn't.
If you need more info, just ask.
"Mit der Dummheit kaempfen Goetter selbst vergebens!"
I have a 94 thunderchicken with the same issue, both the odo and trip
quit at the same time and the speedometer still works but
usually sticks until
you hit about 40mph or give the steering wheel a
light rap then it jumps into
action. I have a friend with the same year
and setup and it does the same thing.
I haven't looked into why it does
it or how to fix yet, personally could care
less about my mileage, it's
depressing enough driving 32 miles one way to work
anyway. But it is a
common problem. And from what I have found out it is all
the sending unit is doing it's job and it's with the head unit.
driving car, comfy and handles well, if only we could keep up with the
bits and pieces wearing out on them so quickly.
I have a 95 Tbird. Same issue. Had speedo gears replaced 2 years ago
and they lasted 18 mos (c$180) and I changed out the speedo. Now I
see I can buy gears and do it myself for $25-50 (depending on website
for gears). The job was waranteed for 1 year
Hard part is removing the needle. I will post when I do it and put
pictures/instructions on my website after post. I have read elsewhere
how to remove needle.
Wish me luck.
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