4L80E Hard Shift Problems

[Billy_the_Kid]

I have a '00 Chevy 3/4t 4wd 6.0l and lately it has been doing an occasional hard shift from 3rd to OD just as you let off the gas it slams in to OD. This has been happening on and off for about 6 months now. Then last weekend it started happening every time it went from 3rd to OD. Then on Monday it got real bad, on every shift from 1st to 2nd to 3rd to OD, and eventually it wouldn't go into OD or into TC lockup. All upshifts were slamming REALLY hard, felt like we were getting rear ended. Tranny temp was normal around 170 or so. We parked it at a friends house and let it sit for a couple hours, it cooled off and when we drove it home there were no problems at all. WTF????

The GM dealer service tech guy said there was only one code for a delayed TC slip of more than 20% but that was like 15k miles ago. Otherwise no tranny codes came up, and they cold not repeat the hard shifts that we had experienced the day before. He said there is a known problem with the 4L60E trannies in the 1/2t trucks that is identical to what I'm describing, and it requires changing the entire valve body... at a cost of around $900!! I've also read that it could be a speed sensor, line pressure regulator or TPS.

Has anyone seen this problem before? Thanks for the help.

[picone]

Same exact thing on my super duty, except it all happened between barstow and laughlin. I thought for sure I was going to drop $3k that weekend getting a new tranny, but no, the guys at the dealer were pro's, and they figured out it was the speed sensor (VSS). $90 in Laughlin and I was back on the road.

The 4L60E won't change gears at all if the VSS isn't sending any signal. Yours sounds like it is on it's way out, and has been for 6 months. Try a different chevy dealer or just go buy one, they're only like $35 and take 5 minutes to install.

Good Luck.

[matt_helton]

sounds like a TCC problem. are you sure there is no codes??? there sure should be from what your describing. id have the dealer double check for hard codes.

and the 4L80E has two speed sensors, an IN and an OUT. usually with a speed sensor problem it will go into "safe mode" which is only first gear.

intermittent problems are a pain to diagnose but id still check again for hard codes with a GM TECH 2 before i did anything else.

[FABRICATOR]

I would double check for codes. You need to be careful because the pump in the 4L80E is variable displacement and variable pressure. It can literally blow the servo cavity out the side of the case. One thing included in a shift kit (http://www.txchange.com/sk.htm) is a pop-off valve installed on the valve body in the servo circuit to prevent this. It could be the pressure control solonoid, but these parts are too expensive to be guessing. I doubt you need a new valve body. A good trans shop should be able to help you without ripping you off.

[FullsizeFun]

My dads 96 dually had the exact same problem. It was the TPS sticking wide open. this is caused by hauling a** and using the Kick-down alot. (me and my brothers driving). Nothing will be wrong with the trans, it is just getting a false signal.

BTW "safe mode" on a 4l80e is 2nd gear.

[matt_helton]

BTW "safe mode" on a 4l80e is 2nd gear


my bad, thats what i meant to say, but didnt think it was a big deal to correct it. 1st, 2nd.......yer still goin slow as hell.