overdrive-speedo-problems
 

Hey yall I just bought a 98.5 3500 dually. She runs great. but the speedo does'nt start working until about 25 mph and the od is very radical when it works at all. the rest of the gears work fine and I can feel the lock up and its all very consistant. some times when I feather the throtel, I can feel it shutter, then it goes in and will work for a while, then it goes back and forth. Also, the od off button does not work. ive checked the fusses that I could find to no avail. I have an01 2500 sb that works well so I know what its suppossed to do. I hope its not curtains for the gear box.... could any body help me please?? also I'm a newbe so could some one explain to me how to put my truck descriptions on this thread like yall do??? oh ya one last thing. My a/c heat switch only lets the air flow out the defrost vents. is there a vacume line off or some thing?? any help here would be greatly appreciated

Got enough toys yet? The rear axle speed sensor drives speedo through the ABS module to PCM and speedo. It may be damaged or wiring corroded/damaged (more likely). The OD off buton is a open/ push close switch you can test with V meter. Buy a FSM.
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Look for vacaum leak between pump in front of PS pump and plastic line inside cab.
Welcome aboard.

thanks dozer. Ive managed to replace the vss. and the abs light went out, I fixxed the vacume line now my air goes where i tell it to. but I can't seem to locate the od relay. and by the way thats not all my toys just all the big ones that i can drive on the road. what kind of oil are you running in your fuel tank?

Believe PCM controls the OD solenoid. Sol is on vb inside tranny. It's going to take a FSM to get wiring on tranny. If you could get a dealer to hook up their diagnois tool would be easiest way to diagnois. It's pin out with v meter and understanding of system otherwise.
A long time ago, in a far away place I secured over 1000 gallons of new unidentifible oil. At a very cheeeeep price. I call it WHICH's oil cause don't know if 5/30 - 10/30 - 15/40 - ATF - hydraulic - or which. After careful filtering I mix 20% in summer and 10% in winterf and call the resulting mixture WHICH's BREW. It seems to run fine, a little less noise, a little more smoke, and save $100.00 on round trip pulling trailer from KY to NC and back. Have gone higher but believe 25% is upper limit for me. My other toys include a D8 dozer and large excavator. Have smaller toys also.