I have a 95 F150 that the speedo is jumping and the motor wants to almost shut off just after it starts moving,I replaced the sensor at the rear end since its the only one it has but no improvement. I unplugged the sensor and it quit wanting to stall right after starting to move so that tells me something in the rear end is making the sensor go crazy or I bought a bad part,Autozone shows two sensors and my transmission has a place for one and is even wired for it but never originally came with the transmission mounted sensor. If the part is bad in the rear end could I mount one in the transmission and leave the one in the rear end unplugged and not worried about ABS.

 

My first thought here is what kind of a sensor is it? If it's a magnetic detector I wonder if metallic debris in the gear oil could be confusing it.

Just a small suggest, but have a look at the gear oil and see if there's any sign of metal in it.

If it's a gear driven sensor - like the transmission one probably is - it could also be a sign of debris in the axle housing. Either way I myself would do at least a check on the oil back there, and possibly a complete drain and fill.

I haven't owned an F-150 so I have no experience with those axles.

I'm GUESSING that the choice of rear axle or transmission mounted speed sensor is an either-or situation. If you have one, you don't want the other one connected - but I could be wrong.

OBSERVATION:
The sensor is new out of the box, disconnected the system seems to behave itself. QED: The problem is in the axle

 

Pulled the cover and everything looked fine including the lube so I put it back togather and put the original sensor back in,then I pulled the instrument cluster and with the speedo disconnected and the speed sensor hooked up it did not act up so I am thinking I have a bad speedo so off to the U pull yard this weekend for another speedo.

 

You know what? Just for kicks maybe you could run by the parts store and compare the rear end speed sensor to a transmission sensor.

If they turn out to be the same it would be amazing, but what if? That could be cool to know.

PS: Shoot some pics if you can.

 

If it turns out the rear end is the problem I am going to buy the sensor that mounts in the transmission since there is a unused plug on the transmission wiring harness in that area and see if that will work,I can care less if the ABS works but would like it to quit stalling and have the cruise control work much smoother and the speedo not bouncing. I need to check that plug to look at the wire colors and if there is a red and a green/black wires then it should work.

 

Keep in mind that the speed sensor works in junction with the transmission, ABS, and cruise control. By hooking it up to the transmission, I can see it still working with the cruise and transmission shift points, but the ABS will not work. Changing the location might cause some other problems.

Question, is the new part a Ford part? I know that some aftermarket parts like the cam sensors for the 7.3's don't work as well as the ones from Ford or International.

 

The new sensor is a aftermarket part and put the original back in and when I grab another speedo I am going to grab another sensor.

 

there may not be a drive gear on your transmission. to mount one there .
Check your wiring and the plug at the sensor you have . I see issues in those often .
Check for past splices and nicks in the wiring .

 

My 08 was having an issue. I replaced the speed sensor on the differential and did not fix it. But, while changing it, I noticed 2 butt connectors. After driving it and noticing it wasn't fixed, I cut the butt connections and one was full of green oxidation. Installed 2 new heat shrink connectors and the issue was solved.

 

Just curious, were the butt connectors factory?

 

No they were not. They were heat shrink connectors I found wrapped in some tape. Whoever used them didn't heat the ends up and shrink them down on the wire. Had they done that, I likely would've never had a problem.

 

I don't know if you found the issue, but would appreciate knowing what you found out. One thing I carry in all my junk is Di-electric grease. I find it is a miracle grease with these computer vehicles.

 

The speedo was bad and it was also causing the stumble just when the truck started moving.

 

My 95 had sensors in both the transmission and axle. It drove me crazy, trying to figure it out, especially since I was stuck in GA with the problem. The A/M sensors was no help. I finally went to a stealership and bought OEM and after flushing the rear, the problem was gone. Both old sensors were tested against the new and both were bad. Never heard of a double failure before. The strange thing is both sensors looked identical. The transmission had a sensor ring in it too.

By the way, the only code that it threw was speed sensor but did not say which one.

 

So far it has been running great,I have not driven it much due to the rear spring mounts were very rusty so they have now been replaced and time to drive it.