Odometer problems (Audi 100 89)

Hi again,
My odometer suddenly stopped working at 191 k km. It never turned the numbers very smoothly, but always counted accurate enough for my purposes. It suddenly stopped completely. The speedometer still works
fine.
It's the one which gets an electronic signal, not a turning cable.
I tried to do my homework this time round. What I found so far:
- Most people report a failure of speedo and odo together, which is due to bad solder joints.
- Some have odometer problems like me.
- I read somewhere, that a plastic gear might have lost a tooth.
However:
I can take the speedometer unit out, but I cannot take it apart. The main problem is to get the needle off, which is in the way. I cannot see any damage on any gear, when I look at the complete unit.
If anyone can help me to take it apart, I might get there in the end.
Before I forget, I didn't find the pin outs of the speedometer, so I figured them out myself. It has two jumper-like connectors, each with two pins:
Top connector, top pin: positive supply (it says "+15" on the board) Top connector, bottom pin: ground
Bottom connector, top pin: signal in Bottom connector, bottom pin: Some voltage out, which is dependent on speed (Starts at ~10V and decreases with speed to ~7V at 100 km/h).
The signal in just seems to come from a switch which closes to ground and opens while driving.
But I am still stuck with a broken odometer and don't know how to proceed. Any ideas are appreciated.
Thanks,
Christoph
P.S. It is a South African Audi 500, which is equivalent to the US and European Audi100
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Christoph, If you press the reset button on the trip counter _while you are moving_ the plastic gear which the button is connected to may permanently slide away from the connecting gears of the odometer/trip meter. If you search in Audifans you may find the name of the VDO repair facility that can fix the cluster for you - or how some have used a dab of epoxy glue to repair the gear. You'll have to disassemble the cluster to get at it, a great time to replace any burned-out light bulbs in there while-you're-at-it. Cheers!
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Steve Sears
1987 Audi 5kTQ
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Hi Steve,
Thanks for your reply. It seems my main problem is still to take the speedometer itself apart (see below), and there the main problem is to get the needle off.

I have seen that mentioned in a number of places at audifans.com. However, I was under the impression that this applies more to the older speedometers, which are driven by a mechanical cable from the gear box and not by an electronic signal.
It stopped 258km after I last reset the trip counter, no idea whether I did that while standing or moving slowly.

I life in South Africa, I guess I have to find some other way to find the right place.

Again, I thought that applies to the older ones (pre ~1988), which are driven with the mechanical cable. I also have an Audi 500, 1988, which I believe is like the American 5k or European Audi 100 pre-facelift. That one has a more squarish dashboard and the old speedometer with the mechanical cable. There, I did fix it with a bit of glue.

I did already take the instrument cluster out and the speedometer of. I checked all electrical contacts, they seem fine. I have now put the main instrument cluster back but kept the speedometer out, so that I can try fix it (or get it fixed).
Ok, I did get a bit further today. I did the following:
1.) I supplied +13 V and ground to the top two pins (the ones which look like a jumper connection).
2.) I hooked a square wave generator to an oscilloscope and then to the higher one of the bottom two connector and to ground (the lower one of the top two). The square wave was set to go from 0 to 7 V. These were the two values I measured with the Speedometer in the car when I moved it very slowly.
3.) I turned the frequency of the square wave up and down and the speedometer needle moves very nicely, but the odometer still doesn't count. However, the little motor on the board turns. It actually jumps in steps of 1/10 revolution, i.e. it jumps forward 10 times for one full turn. It goes faster with a higher frequency, as expected.
Here is what I measured:
- When the speedometer shows 120 km/h, the frequency of the square wave is 130.5 Hz.
- At this stage, the little motor needs 4.9s for one revolution.
==> 120 km/h is 2 km/min, which is 1km every 30s. ==> The motor does 6.1 revolutions in 30s, I assume it is supposed to do 6 revoltutions per km. I guess there is a 6 to 1 gear ratio from the motor to the lowest dial on the km counter.
However, I don't know how acurate my speedometer displays the speed. I can double-check with a value I found somewhere. Someone stated, that the there are exactly 6644 signals for 1 mile. This would be 6644 / 1.609 = 4129 signals per km.
At 130.5 Hz, I would then be doing 31.64 m/s or 113.9 km/h (well possible that the speedometer shows 120 km/h at that speed). If that is true, I would go 155 m for every revolution of the motor or have 6.45 revolutions per km, which indicates a gear ratio of 13 to 2.
Whichever is true, I can only see that the motor turns and the km number rings don't. I can see one gear close to the motor, which doesn't turn either. It looks as if I could get closer to the problem by taking the board with the motor off. That is srewed on below the black plate, which is under the speedometer needle. It seems all I need to do to get in is to take the speedometer needle off. I tried to pull it quite hard, but I am afraid I might brake something. If anyone can tell me how to get that needle off, I might be able to do the rest myself.
Anyway, maybe the numbers above will help someone else at some stage. If I do manage to take it apart, I will let you know what the problem was.
Thanks for your help,
Christoph
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Christoph, You're really getting technical on this fix.....you wouldn't happen to be an engineer, would you? Regardless of the method for getting the speed signal to the instrument cluster, resetting the trip odometer will still result in a gear failure of the odometer/trip odometer. If the motor turns, but the rings do not, the problem's got to be in the connection between the two. I'm pretty sure that the speedo needle is pressed on to the shaft: Problem with electronic system: http://www.audifans.com/archives/1998/11/msg03712.html Use a screwdriver to remove needle: http://www.audifans.com/archives/1998/11/msg03756.html And hey, to find out about removing the needle - look no further than the land of posting in the subject line:
http://www.audiworld.com/tech/pix/face8.jpg - of course, they're removing the needles to change the colour of the gauge face, not fix anything that's broken. http://www.mnsi.net/~natwhite/Audi/Instrumentcluster.htm - here's your best bet. Cheers! Steve Sears 1987 Audi 5kTQ 1980 Audi 5k 1962 and '64 Auto Union DKW Junior deLuxes (SPAM Blocker NOTE: Remove SHOES to reply)

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