Just fixed my son's speedo, od problem. replaced the VSS and is working fine.

 

I had the same problem with my 1992 D350 Dually. The Odometer had 112,234 miles on it. I pulled the instrument cluster and took it to Zepco Speedometer Repair in Dallas. They had it repaired the same day. The Tech told me it was a common problem with these speedometers. Cost me $115.00 and saved a lot of hassel.

 

So, now I've replace the VSS and all was well for a couple days until I started out on a 4 hour trip to NC. Suddenly the O/D wants to shift out unless I'm 65mph or faster. Odo. and speedo are fine. I can cycle it back using the accelerator, but it's very frustrating and I'm sure not good for the trans.

I'm out of town with limited tools (volunteering at the US Amateur) and I'm wondering if I need to tighten the VSS up more. I tightened it down considerably when I installed it, but it will still "clock" around. I'm afraid of splitting the nut that you tighten it down with.

Any suggestions? Am I barking up the right tree? The VSS was $97.50 from the local dealer. Amazing how much these sensors run.

Thanks,

Tripp

 

You should not be able to move the sensor if the nut is tight enough.

However - if the speedo is not erratic during the OD trouble, then the VSS is not causing the problem. It sounds like TPS trouble since you can make it work by playing with the pedal.

 

Sounds like dealer triple netted you on part. Retail was less than $35.00 last time I purchased one.
Just on a fluke, add a extra pint of ATF+4 and see it that affects. It will not hurt anything if doesn't help.
Try going through any ground connections you can find and the battery terminals also.
The inhibits for OD include vehcile speed, temperature, throttle position, governor pressure, OD off switch, and manifold vacauum.

 

1st gens don't look at governor pressure and they don't even have a MAP sensor.