[E30] Speedometer calibration AND subframe bushing update

[mdrainville@xxxxxxxxxxx]

I knew my speedometer was indicating more than the car was really moving (like
any other BMWs). So I decided to check by how much.  I timed a couple of run at
a specific speed on the speedometer vs indicated milestones and did a simple
calculation to find out that the speedo was indication near 11% over!
I find that ennoying to always do the math in my head to know the real speed.

My question is: Is there someone who succeeded to recalibrate the speedo by
installing a 10 turn trim pot at the display (I don't know if it is accessible).
Or a more complicated solution is required like converting the pulse rate from
the sensor to voltage, then reduce that voltage and convert it back to a pulse
rate.
I have the ability to do this mod (I'm in electronics) but my concern is if I
modify the speed signal, will that affect other fuctions like ABS, injection
etc.

Any suggestions?

Michel Drainville
91 318IC (with new subframe bushings, no more clunk=new car!)

PS: For those who answered my last post about sub-frame bushings, Thank You! But
after trying a couple of techniques, I was not able to free the bushing from the
bolt. So I decided to go to the dealer who quoted me 3hrs over the phone to do
the job.  Well, I was very surprised, it took under 2hrs. I was there waiting
for the car and talking with the guy and with his special puller and torch the
job was done quickly (Excactly they charged me 1.76 hrs!) I was very surprised
of the low price of the bill!.   On the 1.76Hr, I spent 0.76Hr in the garage and
1.0Hr  lurking at a MZ3! If only I had the money...

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