I have a 91 D150 Rwd, with the 5.2. i just got it yeasterday morning, and the speedometer does not work. i found what i think is the sensor by the tranny but i dont think its bad the wires seem pretty solid and the speedo will come on and off while im driving ussually when im on a bumpy road. sometimes it works for 45 seconds some times a full 3 mins, but i dont know how to troubleshoot or fix it... i was wondering if anyone could pass on some information on where to check and what im looking for that could cause this. i dont think the gears are bad because it actully works fine when it does work. also on a side note the ABS and break light are staying on , not sure if that helps any?

 

My 92 also failed at 90000 miles. As it is electronic and if your gear wires are ok I just found another one at the junk yard with 225000 and it works fine. You connector behind the unit could be loose and it is pretty easy to pull out and check.

 

ok ill pull them this afternoon and have a look, thanks. btw it looks like this one started to fail at 125 , the engine has had another 35,000 put on since. so if i get it working how would i correct the millage?

 

You really cant turn it back unless you are skilled in that procedure. If you get a new one you can prep and affidavit as to your actual mileage and have it notarized and send both units to a speedometer repair shop. They will set your odometer. Pretty cheap. Your new one will likely have a lot more miles. You should note however that I believe the odometer is separate from the speed reading. If both your speed and miles are not working the odometer gears and/or wiring at the back of your transmission might have failed also but you wont know till you replace the unit. Pull yours out first so when you go to a junk yard you can do it quickly.