The title pretty well describes it. Noticed a few months back my speedo bouncing a little. It's grown progressively more pronounced along with my level of concern. To be clear I'm not referring to the tack or cps issues. Anyone know what could be causing this? With a magnetic pickup in the diff and an electronic cluster I don't have a clue where to start......and I don't want to start along side the road after something's died and I'm stranded. Thanks in advance!

 

Maybe a bad or dirty speed sensor?

 

Sounds like a good start. Assuming the speed sensor is the pickup in the diff I need to do some cleaning and change the fluid?

 

just pull the VSS out of the rearend and wipe it off with a clean rag

 

Have you looked closely at the wiring to the VSS yet? .

 

VSS would be? Something to do with the speed sensor? Getting the impression this is a sign I've neglected the proper cleaning and feeding of a Sterling Axle.

 

Speed sensor on the axle .....

 

*cough* PSOM *cough*

 

Could be but start with the easy stuff! Pull the VSS and clean any rust off the mounting. Wipe the sensor off and look close at the connector/wiring.

 

Rust on the mounting surface is a very good call.....

 

Here's the dumb ? but what will the rust do does the VSS make a ground on the rearend?

 

It increases the gap between the VSS & the tone ring ....

It keeps getting worse over time ....

 

Thanks for the info

 

I've had one wire in the harness up near the frame above the axle broke or pinched on my 96' powerstroker... also I've had a bad speedo with only 178,000 on it that was bouncing and causing shifting issues...

 

Pull the speed sensor on the rear axle and clean it. But while it's out.....here's the kicker. Have the rear end up on jack stands and have someone slowly spin the wheels while you look at the tone ring with a flashlight. Make sure there are no teeth missing or chunks gone. If there is.....there's only on thing that causes that and that's broken differential parts. So if the tone ring is okay, reinstall the clean sensor and breath a sigh of relief. Then start looking up the line if the speedo still jumps.