Engine/Transmission (1998.5 - 2002) 1999 Auto Transmission Hunting/Shifting

I have a 2WD 2500 extended cab long box, stock truck with 235,000 on the clock and the transmission just started to act up. I've only had the truck about a year and its been great so far. Now when it gets into top gear it starts unlocking the torque converter and locking it back up. The RPM's keep changing about 300 or so up and back down. This is most common when on flat ground and during periods where the throttle is only maintaining speed. It will however do it under light acceleration going uphill if its light throttle and the hill isn't too steep. Sometimes at slower speeds its even changed gears down and then back up to where it was. Any suggestions would be much appreciated. Thanks.

TGrost
1999 2500 Quad Cab Long Box
2WD 235K Stock truck

 

There are many solutions that may or may not work. I've tried them all over eight years or so and two years ago I came across the solution that has worked for me and never come back. There is a black w/brown tracer wire that runs within the wire bundle over the top of the alternator to the passenger side battery. That wire needs to be separated out of the bundle as far back to the drivers side as you can go and rerouted on top of the radiator or other location. The wire picks up interference from the alt causing the transmission to misbehave. No need for filters, aluminum foil, etc. It's always wise to make sure all negative grounds are well maintained (there is a hidden one under one of the battery trays). But the fix that's worked for me for over two years is separating that black ground wire away from the alternator as much as possible. Good luck.

EDIT: It might be a black with white tracer wire in that bundle. Mine might have be dirty enough to look brown but it's the big ground wire going to at grey plastic connection to the passenger battery. People have rerouted it along the firewall but I just did it from about mid engine to the top of the radiator and then as far away from the alternator as possible to the pass battery.

 

Thanks, I'll have to try the ground wire fix!

 

Tgrost,
FWIW, the trans hunting for the right gear, at light throttle, 40-55mph, with my truck, has ALWAYS been a bad ground. Sometimes it is as simple as cleaning the passenger side battery ground terminal. Other times it has been a case of cleaning all grounds. I've heard about many fixes, but this always works for me.
I bought my 98.5 new in 99 and for the last 321,000 miles, if the trans issue re-appears, I clean grounds. They are always somewhat crudded up.

YMMV

KenR955

 

I was plagued with this TC lock issue for several years and nothing seemed to solve the problem until I used the Suncoast re-wire method. FWIW, don't ignore your alternator, it's a known contributor to this issue

 

Lot of people overlook the vehicle speed sensor also. The grounds always seem to be the problem though. It seems that a combonation of all the fixes is the fix.

 

tgrost,


I had the same, very annoying, issue with my 98.5. I did all the fixes listed above, cleaned the grounds, added two noise filters, re-routed the ground wire over the alternator, etc. but the unlocking/locking issue always returned after a short while. Then I replaced the alternator with a new one, not rebuilt but new, from a vendor on ebay. Cost a little over $100. Problem has been fixed for the last 18 months. Also, be sure to re-calibrate your APPS.

 

Another good thing to check is the alternator AC feedback. WWW.mopar1973man.com has a good article on checking that. Youtube also has some videos.