Junkyardjeff

The speedo in my newly purchased 95 is a little erratic so is that the speed sensor on its way out.

Chris_1

iTrader: (1)

Start there. Sometimes cleaning it helps if it has any filings on it. The wiring from the harness over to it is also a usual suspect. If replacing the VSS, that's a good one to use motorcraft for. A damaged tone ring inside the diff can cause a bad signal from the VSS as well.
Rabs module and cruise control can mess with it too I believe.
After that, you usually end up having to do something with the psom.
'94 - up psom's are apparently the better ones - less sensitive to a bad signal from the VSS.

Junkyardjeff

Replaced the VSS with a aftermarket part and no improvement,the truck has a stumble just as its starting to move so I disconnected the VSS and the stumble went away so I am going to pull the cover off the rear end and inspect the tone ring. This truck looks like it could of had the VSS on the trans and has a unused plug on the wiring harness to the trans at that location so if the tone ring is bad can I put a VSS in the trans and eliminate the one in the rear end.

Chris_1

iTrader: (1)

I don't know that for sure, but I wouldn't think so. The VSS is one of the things that everybody says - Motorcraft only. Gotta be a reason I keep seeing that over and over.
The tone ring problem is fairly rare, as I understand it - usually caused by flying bits of metal from crunched up spider gears (or worse).
Could be time to pull the cover and have a good look.
I don't know what it is, because I haven't had to deal with it, but there has to be a test probably involving a voltmeter to test the signal from the VSS and maybe pick up anomalies in the signal. But a really good visual inspection of the tone ring should tell you something. It just uses metal space metal to activate the magnetic pickup in the VSS, like a distributor or an antilock brake sensor. Seems like all the teeth are good, or they're not. Even if one is damaged, you can probably fix it if it doesn't have a piece right gone out of it. Good luck.

Junkyardjeff

Pulled the cover and the ring looks fine so I disconnected the wires for the cluster and no stumble so it looks like the speedo could be messing with the computer,going to pick up a used cluster this weekend.

Chris_1

iTrader: (1)

All you need is the speedo part, so you can pull one out of a non tach cluster - same thing.
95 & 96 are the more desirable ones - redesigned, but you can use any year psom, clusters are more specific.

sdmartin65

The bouncing speedo can be stopped by unplugging the rabs module located behind the glove box. Considering how well the abs works that was my solution.

Junkyardjeff

Just what does that module look like in case the speedo does not fix the problem.

sdmartin65

A black box with a electrical connector, only one back there.

Junkyardjeff

It was a bad speedo,picked up two clusters at the junkyard today and both worked and put the one with the lowest miles in my original cluster. No stumble and stalling and no harsh shifts.