I have a 1999 dodge ram 2500 cummin diesel automatic. I have had my fair share of problems as i use this heavily as a work truck, Im on my forth front end and after hours of tinkering squared away all my ground wires so that my tranny will shift into overdrive as it should. My speedometer used to work fine but then it started to only read at 35 and over, then 45 and over, and just recently not at all. Im guessing that this is the sensor but i was curious to see if anyone else has had this trouble and how much the new sensor is, if that is what it is, and if its on the tranny or the rear diff. Any help would be appreciated. Thank you

 

What did you do to fix your erratic tranny?

 

I cleaned up all the grounds, especiall the battery terminals. There is a black wire coming out of a cluster by the firewall behind the abs on the driver side(ill take a picture later) that had become disconnected and was the problem. But i have learned that if my terminals get messed up my tranny will start getting erratic again. I clean up to posts really well and and make sure i have good clean surface contact.

 

The reason that I asked is that I have recently cleaned my terminals to where they look like shiny nickles, and I still have erratic shifting. I was told that the ground wires corrode under the jacket and that I have to remove some of the wire and replace the terminal ends. That's next on my list of things to do.

 

there is a speed/ABS sensor on top of the rear diff that might/might not have something to do with your problem. there is also a speed sensor on your transmission output (or t-case on 4wd) that is part of the process.

i've also got speedo problems, but mine refuses to work at any speed in hot weather, after the truck sits in the parking lot and the dash gets good and hot. i changed the cluster a couple of years ago and that seemed to fix it for awhile, but this summer it started doing it again. i recently changed speed sensor on t-case, no help. when mine stops working, it usually won't work again until the next morning, after everything is cool. i'm baffled.

 

Check every ground wire you can find. The diesel models seem to be extra sensitive to ground wires. Ive rebuilt a few and the owner of the truck puts the trans in and has problems with shifting. Come to find out the knocked a ground wire loose or disturbed on and it wasnt getting good contact. Tighten them up or clean them up and the trans works just fine.

 

i was so happy the morning i re did my ground wires and the tranny started working normally again, 2 different trans specialist could not find the answer to my problems and to find it being something as simple as a wire made my day.

 

hey, thejon2524 can you please post that picture of the black wire behind the abs that you were talking about? my 99 cummins has no overdrive. a trans specialist scanned it and it came up with a short or broken wire somewhere. i cant seem to find this black wire you are talking about so if you could post a pic of it or give a great location decription i would appreciate it.

 

His post is from 2008.

Dave

 

I've had the erratic shifting (usually between 40 & 50 mph) issue for a couple of years. When I described the problem to a mechanic friend of mine, he instantly knew the problem: a bad diode in the alternator. We replaced the alternator and the problem went away -- for about 1 year.
Alternator tested good. After doing some research online, I read that having a bad ground to the alternator could cause it, so I cleaned up the ground connection to the body and that seemed to fix it -- for about 1 year. I replaced the ground wire with a heavier gauge wire and that fixed it -- for about 6 months. More research indicated that connecting an accelerator pedal position sensor noise isolator ( $9.99 - see instructions for installing it) would take care of the problem. That seems to have fixed it and is still working 1.5 years later.