Hey everyone. I've got a buddy that has a 1994 3/4 Ram with the cummins 5 spd in it. His speedo in his instrument cluster is out of whack. It will lay over flat on the peg (120 mph?) when he's really doing 45 or 60 mph, something like that. He replaced the sensor on the top of the diff to no avail. Would the one on the tranny be a cause or is that only for the odometer? Could it be it needs recalibrated (maybe it had huge tires on it before he bought it, but it'd have to be monster truck tires or something to be that far off) or is he looking at a bigger issue like the cluster is done for? The speedo is seriously way off and not in the slightest correct from the moment it leaves the zero peg. It's also a 2wd.

 

Speedometer on his is driven by a VSS on the output shaft of the trans/t-case. (depending on 2 or 4 wheel drive.) The VSS is gear driven. If I had to hazard a guess, I would say the VSS itself is having issues, or, there is a short in the wiring somewhere. When he stops, if the speedo goes to zero, I would replace the VSS.

Sensor on rear diff is only for ABS. Didn't start doing anything else until 98 model year.

 

Thanks heyyou. One other thing is his odometer works perfectly...doesn't the odometer read from that sensor also? Maybe that's where the short comes in if he's got one.

 

if the odometer works, but, the speedometer doesn't, that sounds a lot like a cluster problem.

 

That's what my hunch was but thought I'd let the experts weigh in. I'll relay this info to him!