Engine/Transmission (1994 - 1998) Transmission Trouble Lost Reverse

[JimDavis]

I am having a problem with my 98 12v. Truck is running great just no reverse, it sounds and feels like it is shifting into reverse but just revs as if in neutral. I had it towed home and checked the codes and here is what I got.



P0123 TPS High Voltage (Which I expected been surging in overdrive)

P0401 Insufficent EGR Flow (Also expected since I removed EGR)

P0118 Engine Coolant Temp Circuit High

P0113 Intake Air Temp Circuit High

P1763 Governor Pressure Sensor High



I cleared all codes and took it for a drive and the only code that returned was P0123 TPS high Voltage.



There is also no engine braking in 2nd gear which would indicate a broken band, but when I downshift into 2nd you get a quick rise in RPM then back to as if in neutral.



I am off to drop the pan and see what I find. Any ideas or suggestions would be fantastic.

 

[Joe G.]

There are a few things that can cause no reverse. The direct drive clutches may be bad. That is in the OD unit with the big spring. The big spring may be broken. If the trouble is in that unit then the overrunning clutch will still give you forward gears. The front clutch may have a problem. The rear band may have a problem. I had that happen because of an oil leak that caused the rear clutch to burn up so bad they were welded together.

 

[cerberusiam]

Do you have manual 1st gear? Reverse and 1st are on the same band so if it is that band, linkage, or a jammed servo it will show as no manual 1st gear also.



With having no engine braking I would guess the OD direct section has some issues.

 

[budnate]

sounds like 2 problems, you need to gain control of the Voltage at the TPS and the Orange wire headed to the trans you probably already fried the Gov Press solanoid in the trans, go to the sticky on here there is a whole thread on testing the tps and trans.



peace. B.

 

[JimDavis]

I dropped the pan and no chunks of metal or anything abnormal. The rear band was out of adjustment but I had not noticed any slipping prior to reverse going. To answer some questions yes I have manual first and overdrive seemed to be working correctly. When I cleared the codes and test drove it before dropping the pan none returned except the TPS so I assume the Governor Solenoid is good. I am going to pull the rear band servo and make sure it looks ok, any other things I should check before I put it back together.

 

[cerberusiam]

The OD nomeclature is misleading. There is a set of clutches in the OD unit that are used when OD is not engaged, the OD directs.



If the OD direct spring, clutches, apply piston are non functional you will still have OD and forward gears. There is an over running clutch that will allow OD and all forward gears to work correctly, but, reverse will not work.



It could be something in the VB but usually if all your forward gears work and reverse is gone it is the OD direct unit. Put a gauge on the rear servo test port to verify it is engaging correctly when reverse is selected. If you have good pressure then its likely the OD unit with problems.

 

[JimDavis]

Thanks cerberusiam I am begining to agree with the OD causing the problem.

I do want to check the rear servo thought as it feels somewhat loose in it's bore. I was able to get the snap ring off and wiggle the cover and spring out but cannot remove the servo with the arm in place that engages the band. How to you remove the pin that the lever rides on, so I can remove it. I cannot get it to tap out of the cases and is a real pain in the *** to get to.

 

[cerberusiam]

You have to tear the transmission all the way down from the front. Best thing with the rear servo is put a gauge on it and verify it is working correctly in reverse and manual 1st. If the pressures are not right in those gears its tear down time to fix it right, same if they are good and no reverse.



They can get loose from excessive wear but as long is it is moving there is not much to do about it. When you rebuild get a billet servo with the better seals to solve sealing problems and jamming it in the bore it it gets to loose.