Speedometer Randomly Cuts Out
 

Originally the speedometer and odometer on my 85.2 944 were not working. I traced the cause to a burned resistor on the speedometer's breadboard and found that the odometer gear was bad. I ordered the Armworx speedometer rebuilt kit and a new odometer gear and rebuilt the speedometer. It worked great for about 500 miles and then the speedometer and odometer would randomly not work. They would cut out five or so minutes into my drive and a tap on the dash would sometimes bring them back and sometimes not. Sometimes I would just have to wait and they would come back on their own. Now that the weather is warmer, they do not work at all initially and after a few minutes of driving they will randomly come back after a tap on the dash. Can anyone point me in the right direction on this or has anyone else experienced the same issues and found a cause?

When my 85.5 showed the same symptoms, I found an effective and free fix by unclipping the speedometer sensor from where it attaches to the transmission case (driver's side, in the upper portion about mid-case), and giving the contacts a good cleaning. Has worked well since then.

I appreciate the advice. I'll give that a try today!!

Anyone have a 'scope waveform for the speedo-sensor output?
And how many pulses-per-rev it is?

Thx

The speedometer pulses at 100 Hz for 60 mph. The rest is left as an exercise for the student.