Laust Pedersen

I have had a non-functional odometer for years now. First some sticker fell down and blocked the view of the odometer (1st picture) and a few months later both the odometer and the trip odometer stopped working. However the speedometer has been and is working just fine.




I understand that a common problem is a broken plastic gear wheel for the odometer. So instead of looking for parts and attempt a repair, it seemed to be a better solution to remove the instrument cluster from my 1987 (white) parts 951, clean it up, restore the light guides and install it in my non-S 1988 (black) daily driver.

See 2nd picture for the light guide repair. I used aluminum foil as a reflector for the light guides and the 3 bulb cavities.




The good news is that the “new” increment cluster looks good, the instrument lights are much better than before and almost all of the instruments work well (including the trip reset)

The bad news is:
1. The odometer and trip odometer still do not work
2. The warning light “ ! ” is now constantly on (no message light on what the problem may be)
3. The instrument clusters were very difficult* to get in and out of the dashboard.

* I followed Clark’s Garage procedure, but did not remove the airbag-steering wheel, since the rectangular plate in front would be (and certainly was) the point of interference. I did manage to get it out and in by making and inserting a wedge-shaped piece of wood to (vertically) open up the gap in the dashboard for the instrument cluster. The only angling I did of the instrument cluster was ~15 degree rotation on a vertical axis, so I could wiggle it out to the right of the steering wheel … after the 4 screws and 3 electrical connectors were removed.

So my question obviously is: How do I correct the “bad news”?

Does the instrument cluster have separate pulsed inputs for the speedometer and odometer(s)? And if so, which wires?
One input seems unlikely, since I know that the substituted odometer should have worked.

The 3rd picture shows the backside of the (substituted) instrument cluster and the two showed subtle differences between the flex circuits.




Laust

PS The writing on the small sticker that fell on top of the odometer said “6411 pulses / mile”.

Tom M'Guinn

Well, there is only one sensor in the tranny -- so only the one signal -- 8 pulses per one full tire rotation. 6411 pulses per mile sounds about right. Read all about it in the speedo calibration article in the link below this post. The simplest (and probably most likely) problem is that the odometer on the new cluster is broken too. You can bench test it by sending an artificial signal from the arduino if you're up for making a tester. In the video below, I'm bench testing with one pulse fed directly to the speedo and you can see the odometer also moving. If your odometer does work, but just not when installed in the car, then the only thing I can think is that the reset switch may be bad -- sending a shorting signal constantly and preventing the odo from working. Seems like a long shot though...

Laust Pedersen

That’s what I thought, that both speedometer and odometer were driven by the same pulse through a single wire.

The new odometer worked fine when its car died many years ago and the trip odometer was at about 330 miles, which I reset just before the test drive.

I wanted to see if there was any physical damage to the gears in the original instrument and dove a bit deeper into it. Sure enough, the typical gear wheel had the inner teeth torn off and just mild touching resulted in the carnage seen in the picture. So I can easily imagine that just the resetting process could shake off a few teeth in the “new” odometer.

Anyway, I will purchase and install a new gearwheel, mix and match the best components of the two instrument clusters, install the result and write back about the results.

Laust

Tom M'Guinn

Looks like your well on the road to recovery. Those gears are like pressed powder when they get old. What we need is someone to recreate the gear in brass and sell them to the rest of us.

mikeyoman

anybody got a 3D printer handy

VWaddict

I've used the Rennbay odometer gear with good results, when the original ear turned into Neufchatel cheese.

gregeast

I went through 2 or 3 gear replacements without long term success. I determined that the shaft that carries the brown gear had enough up and down slop in it to allow the gear to lose contact with the worm gear. I wrapped the wire from a bread wrapper tie around the shaft to create a spacer, been working fine for 6+ years now.