transmissions with issues non PT related

[gearheads78]

I have a 2000 OBS GMC truck with 5.7 and 4L80e. Currently has 180K miles. For the last 3 years or so it has had an intermentent problem. I will be going along sometimes towing and somtimes not overdrive will go away. It does not slip or anything its just like I only have 3 gears. Once I slow down or stop it will bang into each gear like it has a shift kit in an old hot rod. I have never done anything about it since I rarely drive the truck any more and it's not left me stranded. If I turn it off even for a minute something resets the problem is gone. Some times it comes back 30 min later and sometimes it won't do it again for a week.

A few weeks ago I bought a 99 Olds Silouette van for my wife. It has 95K on it. Well about a week after we got it she calls me and says its shifting funny. She stopped at the store for a few and came back out and it was fine. She drove several days and it did it again. I have driven it and it was always fine. Finally it did it to me. It hard shifts just like my GMC and resets when you turn off the key. So what the hell did she park too close to the truck and it gave her car a transmission virus. LOL I can keep dealing with mine be hers will have to be fixed. Any educated ideas out there. Internal transmission stuff is my weakest car guy credentials.

[BA.]

If no one chimes in here, the guys at this forum can most likely help: http://www.fullsizechevy.com/forums/

[MarkB]

You need to get both vehicles on a scanner. The Van will most likely be a code 1870, which is fixed by installing an updated EPC (Electronic Pressure Control Solenoid). As for the truck it could be several silly items, they have multiple issues with sensors & solenoids, just look at your memory codes and it should have store one, once you have the code let me know and I can point you in the right direction.

[gearheads78]

Thanks I will borrow a snap on scanner from work and check it out.

[gearheads78]

OK here is an update.
Van P1811
GMC P0741 and p1870

[MarkB]

The 1811 on the van is for the EPC Solenoid, extremely common. Just have them service the transmission as long as there is not too much debris you have caught it in time and you can just install the updated EPC Solenoid. (I didn't mean to say 1870 in my earlier post, I was thinking of the truck at that time).

As for the GMC the 1870 is for the TCC slip as well as the 0741. Usually it is too late when you have the 0741 set as well as the 1870. This is usually a converter and pump that is needed to cure this issue. Let me know if you need additional information. You could pull the pan and check for debris, if the pan is clean you can look at the pwm (TCC solenoid) and ensure that there is not a crack in the solenoid around the o-ring area, this isn't too common but I have seen it. I see the converter being the issue most of the time, but I would recommend if pulling the transmission to check the pump and bushings in the pump for wear.

[gearheads78]

Going to put the PCS in the van this weekend. What a pain to go through to get the side cover off.

[GetMore]

On a related note, I have another question for you, Mark.
I've got a 2001 Silverado 2500HD 6.0/4L80E, and I noticed that sometimes, on the highway, the rpms were just a little higher than they should be. Maybe 100-200 rpm. If I let off the gas slightly the rpms would come down to where they were supposed to be.
Sometimes this would not occur.
The torque converter is locked up in both situations. If I touch the brakes to unlock the converter the rpm goes up even more.

I wouldn't worry, except I have seen the transmission temperatures go up to 200 degrees while driving on the highway, even in 70 degree weather. That seems awfully high, especially since it has the aux cooler.

I had checked it, and there are no codes.

[my72vette454]

I have a 4l80e behind a 6.5 diesel four wheel drive pickup and it does the same things that yours does. I had it scanned and while I dont remember the codes, the main problem with mine is the converter wont lock up anymore which makes the trans run hotter and thats when mine acts up. Mine will just drop out of overdrive and after ten miles then it will go back into overdrive. Or sometimes when I come to a stop, it will stay in second and refuse to upshift or downshift unless I shut the pickup off and restart it again. It seems to create enough heat that it makes the engine run hotter also. I can no longer pull a trailer with it as that makes it worse. I cant decide what to do with the pickup, a 1994 chevy diesel with 270,000 miles and the motor and injection pump are both on the way out too. Hmmm, maybe a spare trans for the vette, Huh Mark?

[MarkB]

With your tach showing 200 RPM higher then normal, would point towards your converter slipping. Even though you feel it unlock when you tap the brake, doesn't mean that it is fully locking up. If you put the truck on a snap on scanner you can watch TCC slip %, it should be 0 or a negitive when fully locked up, it can allow up to a 240 RPM slip when going up an incline before setting a code, but if you are seeing a positive number while the converter is locked up on flat ground then your converter is slipping. This is very common on these trucks. Many updates have been made on the converter and the lock-up piston due to this issue.