VDO Speedo Calibration Issue

[Lawler]

I have been messin around with my VDO gauge for 2 weeks now and just can't get it right. This is what I have:

1. Tremec TKO 600
2. 3:73 rear
3. Three wire hall effect sensor

I have run the auto-calibration many times and I get a different pulse number each time. Not just a few pulses off each time, but a major variance in the data with each mile run (slowly no more than 20 mph). The gauge seems to be all over the place. Will hold steady for a while then bom 120mph! mopst of the time it wont get over 40 mph. Pulse numbers vary from 4500 to 16550. They fall all over the place between these hi and low data points.

I installed the 1N4005 diode inline with the red signal wire today and basically got the same responce from the speedo. The speedo is wired to a three wire hall effect sensor. The pulse auto-calibration number was 5550. At first it seemed to be right but when I got on a good road it would max out at 60 when I know better ( the scenery was stretching a bit)

Any assistance would be greatly appreciated.

Kinton

[hog]

Lawler
Is the sending unit seated in the transmission good? It sounds as if something is loose with the pulses jumping around. I have VDO gauges and used a Ford E9TZ9E731A sender which worked fine.
Hog

[Lawler]

Hog,

Thanks for the PN. Yes, it is seated well. However, I will double double check it.

Kinton

[Barnsnake]

There are multiple ways to calibrate those speedometers. I tried the "drive a mile" method, but it exited calibration mode before the end of the mile every time. I finally created a speed versus RPM chart for 4th and 5th gear (after carefully measuring my tire circumference), then used the "manually adjust speed" method while driving at a fixed RPM. It has been rock-solid ever since.

[Ron61]

Lawler,

I had VDO gages on my car and the only problem I ever had was much like what you describe. I traced it to a loose connector on the sending lead from the speedometer Hall Effect drive. I used the drive a mile method several times and then had the CHP radar check me and it and the tach were right on every time. When diving a mile, just set it on Automatic, drive at any normal speed, don't spin the tires and when you reach your mile marker stop. Do exactly as the papers say and it doesn't make any difference what gears or tires you have, it should be correct. As I stated I did mine several times over the 16 years I owned the car and never had any problem after I found that loose connector. I just got three new wires and ran them from the speedometer to the sensor and that fixed that. If that doesn't cure it, you could have a bad Hall Effect Sensor, but I have never seen one go bad. Or the speedometer head itself could be bad which would be the more likely. But first make sure that you have your sensor and other leads good and that none of them are shorting anywhere. I also saw that cause what you describe on another car.

Edit: In thr full Auto mode which is what I used the needle will not read until you have driven the mile, stopped and pushed the button. It will automatically calibrate the speedometer, sweep the hand across the face to the highest speed and it is ready. I once ran just over a mile to see what it would do, and I always zero my tripometer before calibrating it, and it just added .2 miles to shown that I had driven that far past the mile marker I used. The speed that you drive in or gear you use makes no difference as long as you don't spin the wheels. I never tried the counting the pulse method as it was easier to let the chip do the calculations.

Ron

[WildBill3]

good info guys my son has been having the same thing going on in his truck with VDO's seems pretty comon!WB3

[Lawler]

Thanks for the tips. I'll trace out everything. I do have the speedo cable bundled with all of the other wires that run to the dash and I terminate the speedo cable into a main connector that runs to the dash. From to connector to the instrument (speedo), the cable is not shielded. This is probably contributing to the problem.

Thanks again,

Kinton