MikeLSXSHAMU

I am having issues with my trans shifting extremely hard on the 1-2 shift after some highway driving for about 15-20 minutes. LS swapped 97 GMC K2500 suburban. trans temps are normal, and it does this no matter if they are 190 degrees or 140 degrees. shift points seem fine. If I turn the truck off then come back a minute later and go drive every thing is fine then. I saw a post on gm-trucks.com about some guy with very similar issues and it turned out to be his TC slipping on the highway causing his trans to command high line pressure until the truck was off. I am leaning towards this since I did the LS swap and now I have much more power than the old 350, I am suspecting I am pushing through that old 97 stock converter. Wondering if anyone else out there has had this issue? Found a few old posts on google about this but it always ends when people say "going to get it looked at tomorrow" and then the post goes dead.

terravast4

iTrader: (25)

by chance did you throw a p1870 code? I had that same issue. it took a while but i lost converter lockup and eventually 1-2 shift wouldn't happen

MikeLSXSHAMU

Not throwing any codes or pending codes at all. was the converter your issue?

terravast4

iTrader: (25)

yes. the converter was bad. I think from there on the trans got hot and caused other problems. I did get the 1870 code randomly and only a few times though

MikeLSXSHAMU

I just did a log, about 40 minutes of driving around. At least 10 minutes on the highway in either direction. I wasn't able to make the trans shift hard on the 1-2. I guess it comes and goes. am I logging the correct TCC slip? its looks very good, under a couple rpm. But percent is 80%?

terravast4

iTrader: (25)

if i cleared the code mine would stop shifting hard but once it tripped the code which could me months later it would act weird till i cleared the code

MikeLSXSHAMU

I am thinking I am at the beginning stages of the TC going out and this is happening once in a while since that log looked pretty good. seems to be whenever this happens I dont have my laptop with me. Pretty sure its the TC causing this since it seems to cause the same this for other people.

terravast4

iTrader: (25)

I think you are right. I ignored mine for about a year then i completely lost lock-up

MikeLSXSHAMU

So I changed the converter in my truck and the day after I lost 4th gear for about 10 minutes then it would come back after the trans warmed up. And no one seems to have an answer for that. Did that for a month. got annoyed, went to the junkyard and picked up a decent 4l80 with 100k on it. put that one in all stock, with stock converter it came with. ran perfect. for about a month untill I am getting the same issue with driving on the highway then the trans acts up again and wants to shift at full line pressure, NO CODES.. . WTF do I do? why am i eating 4l80s?!?!?! is it something in the tune?

hog

Are you sure you are losing 4th gear, or is the TCC not locking up in 4th gear. The TCC wont lock until the trans warms up. This is esp noticeable as the cooler weather comes.
In the Winter, I am on the freeway within 2 minutes of starting the truck, and in the it takes a few minutes then all of a sudden the revs come down as the trans warms up and she locks up. With a higher stall TC this can be perceived as a lost gear because the high stall TC has such a greater rpm drop between lock and unlock whereas the stock TC will only drop about 200rpm.

peace
Hog