Engine/Transmission (1994 - 1998) Transmission won't stay in OD lock up

[wbuntain]

My 1995 Cummins AT will jump out of OD when I hit a bump. It used to jump out and go back in, but now it seems to stay out of OD. Typically, the engine revs at ~1500 rpm at 65 mph. Now, it is revving at ~1750 at 65 mph. Also, when in cruise control, it will jump out of cruise after hitting certain bumps. Are these problems connected? I just bought this truck from my son's friend. It has 144,000 miles. The fluid level is correct, and bands seem OK.

 

[mfburns]

I think the cruise control issue may be the switch below the brake pedal hitting due to the bumps, causing it to disengage cruise. Try adjusting the switch. There are other threads on this, do a search. That is the first place I would look.



As for the OD that may be more of an electric connector issue, Throttle positioning sensor (TPS), bare wire, dirty connector, etc. I would start by trying to clean the connector going into the TPS on the driver side up by the injector pump. Do a search here on TPS and you will find a lot of threads. ALso check connectors out of the transmission. Engine speed, transmission temp, etc affect the OD lockup and any erratic reading can cause it to pop out.

 

[Extreme1]

I think the cruise control issue may be the switch below the brake pedal hitting due to the bumps, causing it to disengage cruise. Try adjusting the switch. There are other threads on this, do a search. That is the first place I would look.

That's the problem with both the cruise AND the T/C lock up. (It's not dropping out of O/D, just unlocking the T/C)



The fix? Easy! Reach in and push the brake pedal down and hold it. Grab the little plastic plunger that stickes out of the brake light switch and pull it down toward the brake pedal. It will "ratchet" out. Release the prake pedal and it will push the brake light switch button in to the correct depth.



If someone would be following you they would tell you that your brake lights are flashing. I had the same problem on my truck when I bought it. The 8 hour trip home would have been better with cruise.

 

[wbuntain]

T/c

At risk of seeming stupid, what is the T/C?

 

[mfburns]

T/C = Torque converter It has a lock up in over drive. When the lock up unlocks you will see a change in the RPM of about 1-200 RPM higher to maintain the same speed. WHen it locks up you can feel, hear, sense the engine RPM reduce the same amount. This limits slip in the transmission to give better fuel economy.

 

[San Felipe Bob]

Spring

I added an old throttle return spring to my brake pedal to keep it from contacting the brake switch.

It's working great!

I started having T/C unlock issues at certain speeds.

I'm pretty sure it's a dead spot in my TPS.

I have installed a new TPS and will report my findings as soon as I fix the broken rear axle shaft. .



SFB