Engine/Transmission (1994 - 1998) 98 12v AUTO WONT SHIFT INTO 4TH AFTER REBUILD HELP!!!

[DPadgett]

Ok guys I have one for ya. 98 12v 4wd 180k approx. decided to have the transmission rebuilt/beefed up to handle recent injectors and fuel pump upgrades. My mechanic has 2 12v's and one 24v, all with twin turbos, aftermarket transmissions, etc, he is very competent. He rebuilt transmission, put it back in, and said everything is perfect except it wont shift into 4th. took it back out and examined it, had a dodge cummins technician buddy come out and overlook everything, couldnt find anything, hooked up to check for transmission codes and there werent any, put it back in, still wont shift past 3rd. Before i gave to him to rebuild, this past year it started doing something when it was cold where it would shift into 4th and then jump right back down into 3rd and rev up and then jump into 4th and back into 3rd. really irritating. and also when letting off of accelerator to coast or come down exit ramp it would kick and buck while downshifting. Any ideas? i know my mechanic has done these before but he is stumped and I need my truck back! thanks

 

[kenny61]

Is 4th the overdrive? Is there a tow switch that disables overdrive? Possibly a problem with that switch and or wiring?

 

[LandShark]

A faulty trans temp sensor or bad computer will keep the trans out of OD (4th). You can eliminate the sensor with a 1000k ohm resistor. Could the OD lockout switch be bad? Or have a burned out bulb? You could try disconnecting the OD switch behind the dash.

 

[DPadgett]

Ok I will see if he has tried the trans temp sensor. He swapped the computer from his personal 98 which shifts fine and said mine still wouldnt shift into 4th. Any other ideas?

 

[fest3er]

Ok I will see if he has tried the trans temp sensor. He swapped the computer from his personal 98 which shifts fine and said mine still wouldnt shift into 4th. Any other ideas?

From TFSM:

1. Dash O/D switch in OFF position
   
2. Overdrive circuit fuse open
   
3. O/D switch wire shorted/open/cut
   
4. Distance or coolant sensor malfunction
   
5. TPS malfunction
   
6. Neutral switch to PCM wires shorts/cut
   
7. PCM malfunction
   
8. Overdrive solenoid shorted/open
   
9. Solenoid feed orifice in VB blocked
   
10. Overdrive clutch failed
    
11. Hydraulic pressure low
    
12. Valve body stuck
    
13. O/D piston incorrect spacer
    
14. O/D piston seal failure
    
15. O/D check valve/orifice failed
    

Also check the PCM-to-trans solenoid assembly harness, and the trans relay in the PDC.



My suggestion is to verify the electrical connections and operation first: it's easy and most likely where the error crept in.

 

[SFPADGETT]

Hey Dawson--uncle Steve. Mine did the same thing last week, we pulled and rebuilt it, installed a shift kit and Roy and I installed it Saturday morning. The problem was a blown "O" ring seal (we found a 1-1/2" piece in the pan), which burnt the 4 gear clutch disk's. 1-3 were fine, just lost 4th on way into shop. It was the overdrive piston seal that failed. Also, if you installed a shift kit, verify that all of the correct springs were put in the correct location, all the holes were drilled the correct size, etc. call me if you need to.

 

[DPadgett]

So once again, my uncle was right! just found out tonight from mechanic that it was indeed a rolled o ring that was keeping it from shifting into 4th. Hope this post helps anyone else who comes up on this in the future!

 

[SFPADGETT]

Glad you found it and are back on the road!