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E30 Speedometer Repairs - Failure Modes

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  • cory58
    replied
    I also get much satisfaction from figuring things out, but it was really easy to send my cluster to Bavarian Restoration. bavrest.com

    Leave a comment:


  • dj_Roo
    replied
    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.

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  • nando
    replied
    Originally posted by jlevie View Post
    The speed signal from the differential goes to the cluster, then to the OBC and cruise control.
    and DME.

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

    Leave a comment:


  • ThisGuy310
    replied
    Originally posted by 03IRM3 View Post
    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?

    Leave a comment:


  • mlytle64
    replied
    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!

    Leave a comment:


  • mops
    replied
    Originally posted by Helion42 View Post

    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.

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  • JakeP
    replied
    Originally posted by Helion42 View Post
    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.

    Leave a comment:


  • Helion42
    replied
    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.

    Leave a comment:


  • mops
    replied
    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.

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  • 328ijunkie
    replied
    Great thread!

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  • mops
    replied
    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.

    Leave a comment:


  • mops
    replied
    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 :)

    Leave a comment:


  • Kilawin
    replied
    So a M3 cluster into a 318is is a direct swap or does the code plug still need to swaped out.

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  • 03IRM3
    replied
    Okay - I attached the image of the MotoMeter unit. The arrow is pointing to the potentiometer used to adjust the calibration of the speedometer. This does not change the odometer reading itself - just the needle position in relation to input frequency generated by the speed sensor.

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

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

    To adjust, connect a power supply to ground (31) and the +12V input (+) to power up the unit. Connect a signal generator to the signal input (31b) with a square wave of about +10V. The frequency in Hz to input is based on the constant K divided by 3600 times speed in MPH:

    Hz = (K / 3600) * MPH

    So in my case, I would input a value of (7784 / 3600) * MPH to check the indicated speed. I played around with trying to input a frequency in 10 MPH increments and adjust but found this to be fairly difficult. So I ended up setting the input frequency to 140 MPH, adjust the pot, and then check the indicated speed across the sweep. This provided a much closer overall difference between the indicated speed and what the actual speed should be.

    It may be because of the circuit design itself does not provide an exact linear change with input to the IC the pot is connected across opposed to the value of resistance it sees. Plus they are using a somewhat high resistance that makes it difficult to adjust with a pot. Just remember after making the adjustment, turn the pot back the opposite direction just a touch and let the circuit settle for a few seconds before making another change.

    Anyway, that should help. I don't know that all the MotoMeter units are set up in this manner, mine was which made my work easy.
    Attached Files

    Leave a comment:

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