I'm in a real tough spot now. I have a 95 F-150 with mazda tranny and 8.8 inch rear. My speedometer needle started flickering and bouncing..making the truck run ##### and want to stall on me at like 2-3 mph when i was starting out. So i unplugged the ABS sensor from the rear end and the speedo doesnt work but it runs fine. I replaced the ABS sensor in the rear end and that didnt fix the problem, needle still bounces alot and wants to stall on me. I believe there is another sensor on the top of the tranny on the drivers side...i unplugged that but it didnt change anything with the speedo. Does anyone know where i should look or what to do next. I'm thinking that it might be a problem inside the rear differencial. Thanks

 

I'm unsure but is our rig's speedometer controlled by electical or cable? If it is cable you probably have a broked cable......

Just a thought

 

If you replaced the sensor on top of your rear end, and it didn't fix it then the part in the diff that the sensor uses may be dirty on need replacing. I can't remember what it is called. I want to say is a hall effect pick up. Thats probably what it is.

 

I am 99% sure its electrical...its a 95 and theres no cable anywhere so i'm sure its electrical. I do need to change my differencial fluid, should i try that and go from there?

 

Theres a ring in your rear diff that is bolted between the carrier and the ring gear. The speed sensor picks up off of this. Check it for any bent teeth, only a 1/16 of an inch off will throw it off. Well you have it apart, check the clutch plates if you have a Trac-lok installed, they have a habit of breaking the tabs off. Your truck is electrical, no speedometer cable.

Ryan

 

I had the same problem but my speedo would jump between 60 and 110 kilometers per hour It ended up being a blown diff (when I took it out it broke into 6 pieces and I have them to prove it!) so spend a couple bucks on oil and take a look in the rear diff!!!

 

The problem could be with the instrument cluster. On your truck, the cluster (also known as a PSOM Programmable Speedometer Odometer Module) receives the signal from the rear axle speed sensor. The PSOM then creates a new signal called VSS, which it sends out to the PCM (Powertrain Control Module). Sometimes the PSOM starts to screw up the VSS output.

When the PSOM receives the slow speed signal from the rear axle, instead of sending out a 1-2 mph signal to PCM, it sends out a very high speed signal (usually well over 100 mph). The PCM thinks that the speed limiter is being reached, and shuts off fuel injectors, causing a stall or stumble. It usually occurs right after shifting into gear with very little movement of the vehicle. You would have to take it to the dealer to verify that this is occurring, or if you had a scan tool you could monitor VSS in PCM, and see if it is spiking high. If this is the case, the PSOM (cluster) will have to be replaced. The new cluster should be of an updated design to prevent this from occurring again.

It is always a good idea, as the others have recommended, to verify that the rear axle speed sensor and tone ring teeth are good, and the best way to know for sure is to remove diff cover. Even seemingly slight damage to the teeth can cause problems.

Hope this helps,
Brian

 

Thank you very much, i will start with the differencal.

 

Check the wiring to the abs sensor.I had dual exhaust put on my 95 f150 and when i loaded the bed with junk the wires burnt in half on the ehaust pipe. the plastic sleeve on the wires did not burn all the way thru but it still burnt the wires in half.

 

Well i had my computer scanned and the code came up saying that..when i'm going between 2-3mph and the engine wants to die, the speedo is telling my computer that i'm going between 130-180mph which is tripping the speed limiter. So Brian, does that mean that it could be the cluster and the speedo needs to be replaced??

 

I'm having the exact same problem with my truck (1995 F150 w4.9&5spd). After reading the info on this thread, I unplugged the speed sensor and the problem went away. Thanks for the help Brian (babarche)

I took it to the dealer and the problem is in the speedometer module. They told me $451 for the part. Is there a way to disconnect the speed limiter and leave the speedometer functional. I don't want to spend the money for the new module. Any help would be appreciated.

Tom

 

451 sounds alil high, i'm getting a whole cluster from ford, brand new at 350. If you unplug the ABS speed sensor at the top of the rear differential then it will stop the problem, but your speedometer will not work at all, and it won't record ur mileage.

 

 

i have a 1992 f150 4x4 i have replaced my speed sensor and it didnt fix my problem my speedo dont work and my odometer wont record my truck shifts very hard from 1 to 2 gear

 

First off you need to start a new thread, this one is 10 years old.
You have no output from the PSOM to the Computer or the speedometer/odometer.
Is you your yellow RABS lamp in the cluster on or flashing also?
If not you may have a bad PSOM.
If so you may have a bad PSOM, RABS moudle, wiring/plugs or rear end tone ring gap.