I have a 1995 RV Motor home that is built on an E-350 chassis

I had the transmission replaced last year after some friends borrowed it and it ran after the transmission was out of fluid.

The replacement transmission (overhauled from junk yard) has been working fine and is not using any transmission fluid.

Yesterday, as I was driving it the speedometer started acting very erratic, it was bouncing back and forth between very low speeds and speeds that were close to my actual speed.

It may be a coincidence but I noticed around this same time that when the transmission shifted from a lower gear to a higher gear that I felt a 'bump' in the vehicle - it seemed like when the new gear engaged it was not doing so very smoothly.

Later is seemed as thought he transmission would decide at slow vehicle speeds which gear it should be in and went into a very low gear (high engine rpm) when it should not have.

I pulled over and checked the fluid and all was fine - fluid was pink - nothing unusual.

The next day - when I first started driving it - it did the same thing.

To control the transmission I drove for a while in 2nd gear.

After a while, the speedometer began acting normal and I put the selector back to 'D'.

Things seem to be working correctly now for transmission and speedometer.

I talked to a Ford service guy and he felt the problems were unrelated.

He was unable to look at the vehicle because they are not allowed to work on RVs at his location.

I think the speedometer problem is linked to the transmission problem.

I am going to have an RV place look at it but I am concerned they may not be able to troubleshoot this- especially since currently the speedometer is working. I also am not sure how much transmission troubleshooting experience they have and I may fall victim to their lack of experience in a costly manner.

My speedometer is an analog model so I think that there is a cable that connects to a gear on the differential and the cable translates the rotational speed it measure to the speedometer.

Are these problems linked or are they coincidental?

What should I have the RV folks look at first? I don't want them to give me the expensive problem that fits their bias as to what the problem is. I want to make sure we fix the true cause of the problem and don't just overhaul the transmission because they are not sure what is wrong.
What types of things can I do to narrow down the problem with the transmission? Anything I can do while I am driving it? I don’t really care about the speedometer dial in the instrument cluster but I definitely want to protect the transmission and avoid another costly replacement.

John

 

You do not say what transmission you have. If you have an overdrive button then the problem with the speedo was, more than likely, the cause of the shifting problem. However if you do not have an overdrive trans then the problems are unrelated.
Also while your speedo display is analog it is electronically controlled, so no cable drive.
Not an expert but I think, when you take it to a shop and providing it is the overdrive trans, the first thing I would want done is for them to check for trouble codes (even if no light is on).

 

It's the VSS (vehicle speed sensor) on the rear axle. Buy a Ford one...cheaper and better than the aftermarket ones, or get a used one out of just about any Ford RWD vehicle. I had the same issue on my 92 Bronco.

 

It could be the speedo itself as it seems that the Powertrain Control Module (PCM) gets ITS signal from the speedo which gets ITS signal from the VSS. I changed the VSS on my 1997 F250 Heavy Duty (E4OD)and the problem persists. I've been starting in 2nd a lot until I sort it out but I believe I will change the speedo stuff if I can figure out how to get it out of the dash board! Any ideas? Thanks....