Odometers stopped turning (and I don't think it's the gears)

[DaddyBear]

Hi guys... I just had the back-light of the OBC replaced with the LED type and after I got the car back I noticed that both odometers were not turning anymore. Mechanic said that he didn't remove the instrument cluster and thinks that it could be the worn gears... I only have 52K miles on it and there were no prior sign of trouble.

I suspect that he disconnected something when he disassembled the center console... Any ideas are appreciated :)

[hornhospital]

If the speedometer is working, it's definitely gear failure, regardless of mileage.

[dwcains]

There's really no relation between the two systems that would cause that, and the gears fail based on age more than use. The plastic just deteriorates and crumbles into pieces. At least there isn't any duplication of labor to replace the gears, and it's not too bad of a job.

[DaddyBear]

Thanks for the feedback gents. Apparently the odometer system is separate from speedometer as I came across the following articles which indicates 2 connectors specifically for odometer. Now if there are wires that end up to the back of the instrument cluster for the odometer only, then were do they originate from? Is there a sending unit in transmission or the wheels specifically for odometer?

viewtopic.php?f=2&t=25902&p=184878&hili ... er#p184554


(On page 10)
http://www.odometergears.com/documentat ... cement.pdf

[Brucey]

on >5/82 builds there is a single sender unit (in the diff) sending to the cluster that provides the signal for the speedometer (which is electronic) and the odometer (also electronically driven). The signal is processed differently for each instrument. The speedometer signal ends up being a current vs speed which deflects the speedo needle (the speedo is effectively an analogue current meter).

The odometer system is simply driven by a stepper motor. The two odometers are driven from a single gear train which is 'split' in thevery final stage to drive both odometers. I think it is as simple as one pulse from the sender unit in the diff = one pulse in the stepper motor. There are thousands of pulses per mile. The electronics that process the signal and drive the motor are very reliable, but the gear train connected to the stepper motor is not. The gear train sees a varying (pulsed) torque with every step of the stepper motor, and the very first gears (that see the worst load) are the ones that fail most often. The smallest gear (which is a push-fit on the motor shaft) tends to split or lose some teeth and the mating gear tends to lose teeth as well.

If your speedo works and your odometer does not, the very first thing to check is that the gear train is intact. 95+ times out of 100 it won't be and you will need new gears. If the gears are (miraculously) OK then the next thing to check is that the odometer drive board is making good contact with the rest of the speedometer board.

If the speedo electronics are faulty, it is easy enough to change them for good used items, since the speedo is a separate module and even faulty modules are usually electrically sound (because they almost invariably have faulty gear trains.... )

hth

cheers

[dwcains]

+1, as usual when Brucey chimes in. I've had the OBC disconnected in my car for a while because the console is out, but the speedo/odo are still operating properly. Perhaps the mechanic hit the trip reset, which often breaks the old, fragile gears?

[DaddyBear]

Brucey, thank you for yet another informative analysis. I'll definitely get the cluster checked for worn gears... Also thanks to Dean and Ken...