The issue I'm having is that the speedometer stays at zero till I reach about 40 mph (Guess based on rpm), and then it reads about 20 mph below the actual speed. The odometer shows movement although the speedometer shows 0
So far, I cleaned the contact-points on the 2 plugs in the back of the speedometer housing. That did not solve the problem.
Has anyone had this or similar problem?

 

Try the earth/ground connections and the big multiplugs.

Does your ABS work normally?

 

I just responded to your post on the other speedometer thread.

 

Thanks for your quick response.


I have already sanded all the contact points on those 2 big plugs on the back of the speedometer housing, using 600 emery paper.


No change.


I have not seen a specific ground cable, possibly the ground is at some points on either of those 2 big plugs.


About the ABS, it seems that a new pressure ball container will be necessary.

 

If your odometer reads the correct miles for the distance traveled then the speed interface and all connectors ore ok. You will need to pull the instrument cluster and check for a binding needle, move it by hand very gently, you should be able to move it with very light pressure.

 

Thanks for this advice, Will report back when done.

 

I noticed that when the car slows down, the speedometer needle goes to zero, and does so very smoothly.

 

I thought I would answer this question in your thread to keep 1 thread on your issue.

If the interface unit is outputting pulses then it is working, it is impossible for it to output a different number of pulses. It uses a digital counter so the output is directly proportional to the number of input pulses. It is possible for the diff VR or cable to be faulty causing the number input pulses to be incorrect.

Did you reset the TC while driving if you reset while stopped then the TC will average 0mph to 70mph which can significantly effect the average, the average of 0 and 70 is 35.................. not saying this is the reason but just be aware.

Best way to check speed is to drive car over a known distance and check the miles traveled on the odometer. If you mark out a mile on a deserted road reset the odometer and drive the car over that mile at ANY speed the odometer should read 1mile. Or you could get a friend in another car with good speedo both of you reset the odometer and drive a few miles and compare the readings. If the odometer reading is within 5% then the speed interface is working correctly and the problem is in the speedo needle drive mechansim. This is the way I would approach this problem.