When cool, there are no problems and all shifts occur normally.

When hot, my transmission shifts fine 1-2, and sometimes hesitates going 2-3 (it'll eventually shift though as I go faster). The odd thing is after it has shifted to 3, and I've cruised for a while, sometimes the engine suddenly revs up like its not connected anymore, almost like I've shifted into neutral with a light connection still. If I give it gas I will still provide a little power, but I'm maxing out the engine. When I let off the gas, the rpms drop to idle just like it would do if I were in neutral and coasting. If I shift it manually to 2, it downshifts and engine braking occurs. If I shift back into 3, it will go back to 3rd for a while then the problem will come back eventually. The only consistency seems to be temperature, and there doesn't seem to be slipping in 3 other than when this occurs. It's definitely an on-off kind of thing; either its slipping or it isn't.

I replaced the vacuum modulator with an adjustable one hoping that would fix things. I went for a test drive immediately and found the car ran and shifted much better and where I wanted it after I adjusted the modulator for lower vacuum...However the other day after driving longer (letting it get hot) the problem reared it's ugly head.

Any ideas?? I've read up a lot and cant seem to figure it out!

Oh, mileage=111k...I want to upgrade to 200r4 but I'd like to graduate college and get settled with my own garage first. "Replace it" is the obvious answer but if there's something else that will hold me over for a while I'd like to try that.

 

Forgot to mention that the detent cable functions correctly when tranny is cold.

 

Take it off the radiator and put it on it's own cooler, not in line with the radiator, for now. They don't cost much.

 

Check your tranny oil level when it is warmed up and the engine is running. It sounds like you have low oil level.

 

It may be the fluid level is actually too high? I've read that an overfilled transmission can churn air into the fluid and cause the transmission to slip. Might explain why it runs better cold and slips hot.

I find it hard to see the true fluid level on the stick, but I see that it reads a lot higher with the engine shut off than when running, and reads higher when running and warm than when first started.

 

Unless you're one of those NCRS guys (), install a finned pan for about $130 from Summit. I did for my Turbo 400 and it added 2 additional quart capacity and theoritally helped with lowering the temperature. And yes, you DON'T want to overfill an auto transmission.

 

If your filter is not clogging, it may be the oil sealing rings on the pump stator. An overhaul would be in order. The thicker (cooler) fluid may be adequate to supply pressure until the viscosity lowers when hot. I would double check the vacuum supply to the modulator, remove any restrictor located up at the intake and check both rubber hoses. A loss of vacuum will also cause it to fall out of 3rd gear. A trans. shop can check your line pressures but you may not make it out of there with your wallet attached. Dropping the pan would allow you to inspect the contents for metal residue or clutch material. Even badly worn pump gears could cause your problem.

 

I double checked the fluid level today when hot and it was a bit high, but I drained some and still have the same problem. If I shift into neutral and then back into 3, it shifts to 3rd and acts normal for a little while until the problem starts again.

I bought a filter today to replace it, but the pan seems to be stuck like glue, so I can't get inside to pull the old one to inspect...I've seen pipefitters use brass wedges as to not marr the mating surfaces, but where can I buy something like that? Lowes? I'm just a little skeptical of using a hard tool steel screwdriver as the shop manual suggests!

 

back off about two threads on four "corner" bolts of pan to keep pan off floor and out of your face. remove other bolts. you could use wood wedges poss. wood clothes pins sharpened to a fine edge. when pan comes loose fluid will come at same time. fully remove bolts from back corners, pan will droop but not fall,slowly loosen front corner bolts with large catch pan under tranny pan and remainder of fluid will drain as you loosen bolts. Sometimes a plugged filter will cause a loud whine from trans.. Check pan for debris and repost results. Clutch plates may be burned causing problem. Good luck, mds...

 

def agree. time to take of the pan. look whats in there. put new filter on and get one of the deep pans with a drain plug.

 

On level ground, in neutral, just jack the front up and use jack stands for safety, starting from the rear of the pan, remove all bolts working your way around to the front center two, barely loosen those and stick a screw driver/putty knife at one back corner of the pan and pry gently. The weight of the fluid and your prying should cause the pan to release. Ideally, a large catch pan is needed to keep the fluid off the floor. If one corner doesn't work, go to the other corner or back and forth. The pan can be easily straightened in the unlikely event that you bend it. When you get to the point of putting pan back on, straighten the rails and flatten around bolt holes, use a cork gasket dry (no sealer) and don't over-tighten pan bolts.

 

The nature of the problem has lead me to believe that the detent valve is sticking, causing it to hunt between 2nd and 3rd, as the GM manual troubleshooting states. I removed the detent cable from the throttle, but the problem still comes and goes, although it seems less often than before. When the problem starts, I've just been shifting into neutral for only a second and back into 3...it quickly shifts into a solid 3rd gear again, which consistently works. I cannot tell enough from the limited information given in the GM manual as to why this would fix a sticking detent valve, anyone seem to understand this? The detent cable still springs, so I assume the valve must be springing back into place as well. I guess it could be leaking?

The problem definitely correlates with cruising when I am barely touching the gas or letting off of it because the car in front of me is slowing down, so I presume that the fluid is heating up from the slight engine braking; however, the fluid temp cannot be the main cause as my trick that fixes it won't change the fluid temp.

Detent stick/leak seem probable??

 

My truck has the same problem could you tell me what you did to fix the problem

 

Nobody has added to this thread in a while so, I thought I would add a similar question to restart the conversation.

My TH350 begins to slip at when starting from a stop if it is really hot. No cooler, do you think that would fix it ? its like a clutch is depressed. I have to make sure i put t in neutral at lights.

 

I've had this before...

If the intermediate clutch slips allowing the direct drum to backdrive, the rpm goes up. Putting the shifter into manual second applies the intermediate band and stops the backwards rotating drum and briefly stabilizes the trans; when the shifter is returned to drive, the trans may stay in 3rd, but when the intermediate clutch starts to slip again, it's the same problem all over again.

Bottom line, pull the pan - you'll find debris and clutch grit, maybe even some metallic pieces. Unfortunately, it's time for a rebuild.

 

so did you find out what was wrong with your trans as I am having the same problem , I have put a bigger cooler rebuilt the trans changed the converter and to top it off the converter is pushing on the flex plate wen I rev up the motor making sparks from the starter drive

 

Guys - this was 6 years ago. The OP probably sold the car by now. Start a new thread to get the info you need.