E30 Speedometer Repairs - Failure Modes

[Carmeyer]

Good news, my odometer is working now. It must have just been the small bits of plastic on the gears, as I mentioned in my earlier post.

[Carmeyer]

I'm in the midst of trying to fix my motometer odometer. So far I replaced the gears and the odometer started working but I noticed the backlight for the speedometer and fuel gauge was out. So out came the gauge cluster again. Luckily it was just a bad bulb but I broke the A tabs off the cluster when I was reinstalling it.

At this point I have repaired the A tabs and reinstalled the cluster. But on my test drive the odometer worked for less than a mile. So I pulled the cluster back out. The gears were all aligned and the small drive gear is turning the other gears and the odometer is advancing. However, I noticed some binding in the gears and I found a few small bits of plastic on the gears. I am 99% sure the bits are from the holes I drilled when installing the A tab repair kit. The repair kit was from German Iron and the repair tabs are attached to the housing with screws. Fit and finish of the repair tabs is very nice, btw. I blew the bits of plastic off the gears and everything is turning smooth now. I have not reinstalled the cluster in my car yet because it's getting late. I will report back after I get it back together. I sure hope I found the cause.

[cory58]

I also get much satisfaction from figuring things out, but it was really easy to send my cluster to Bavarian Restoration. bavrest.com

[dj_Roo]

Capacitor failure. It is a common issue that occurs on the VDO speedometer. On the board of the speedometer head lives a 220uF electrolytic capacitor.

I just replaced the bad gears in my VDO unit and still no odometer movement. I did see the discoloration on the pcb that 03IRM3 mentioned so I wanted to try changing the capacitor. Does anyone know what type of cap I need? I'm handy with a soldering iron but don't know crap about the differences in components.

[nando]

The speed signal from the differential goes to the cluster, then to the OBC and cruise control.

and DME.

[jlevie]

The speed signal from the differential goes to the cluster, then to the OBC and cruise control.

[ThisGuy310]

There are four contacts on the opposite end of the board as follows:

+ - Power (+12V)
A - Signal output
31b - Signal input
31 - Ground

Is it possible to run the motometer speedometer with only the
+ - Power (+12V)
31b - Signal input
31 - Ground
wired correctly? Will the gauge function with only those three connected?
I am trying to ask what is the A signal output for? Where does that wire connect to? What is the output of the speedo used for?

[mlytle64]

in 03irm3's description of calibrating a motometer speedo, does anyone know which way to turn the pot to decrease what the speedo reads? any idea as to the sensitivity? (i.e. 1/4 turn equals 10mph)

noticed that my newly acquired eta speedo reads 10% high accross the range.

thanks!

[mops]

Is there an easy way to fix this or do I need to know the stuff that 03IRM3 was explaining? I don't think I can easily get ahold of a signal generator.

I was able to successfully trigger e30 speedo by "PC signal generator", i.e. you put the cable into "speaker out" on your computer then you play sinne or square wave. There are programs that will allow you to generate different waveforms from your PC.

[JakeP]

Is there an easy way to fix this or do I need to know the stuff that 03IRM3 was explaining? I don't think I can easily get ahold of a signal generator.

Since you know how to take the speedo apart now... Drive down the road with a gps and check the difference. If there is a difference, turn the pot a little bit in one direction. check again. If the difference increases, turn it the other way. adjust till you're close enough for your liking.

OR

Borrow a signal generator.

[Helion42]

potentiometer?

Hey I was recently replacing an odometer gear on my girlfriend's E30, and saw this little adjustment on the speedo, and of course my curiosity was all like "hey it moves!". I thought I put it back in the right spot, but now the speedo reads funny... I haven't had a chance to test for accuracy, all I know is that when you get rolling the speedo doesn't move much and then moves what feels like very slowly compared to how it's supposed to.

Is there an easy way to fix this or do I need to know the stuff that 03IRM3 was explaining? I don't think I can easily get ahold of a signal generator.

[mops]

I managed to repair the VDO unit by replacing gears with the set found in jaycar electronics as per the guide on e30tech.

I was unable to find replacement gear for the motometer unit - particularly the uncommon 44x17 gear... I would prefer to use motometer unit because a) it is in metric units, which is my preference and b) because it is possible to calibrate it via the trimpot provided.

[328ijunkie]

Great thread!

[mops]

Ok, i have pulled apart both instrument clusters last evening. one is vdo other one motometer.

on the vdo there's 1 tooth missing from the 12 tooth drive gear (the smallest one). I was able to bench test it and speedo and odo is working fine - all though odo stopped working in the car. Perhaps the fact i took it apart and put it back together have fixed it.

the motometer one.... the small 12 tooth cog is complelty stripped of it's teeth. also the gear that drives it (bigger one) is also missing few teeth, so it will also have to be replaced.

I'll go to jaycar today and see if the have those replacement cogs.

[mops]

Fantastic writeup.

My odometer stopped working recently. I did a quick search and found lots of threads about damaged gear inside the speed.
So i thought easiest fix would be to go and buy another instrument cluster, which i did and.... odo also doesnt work. I took the original dash apart and i see 1 tooth missing of the infamous odo drive gear, but if i manually spin the shaft is still keeps turning the other gears therefore issue must be electrical...

I'll have to do more investigating... and take apart the 'new' instrument cluster and see what's broken there....

I'll report my findings :)