4l60E Issues of the line, doesnt feel like shudder.

[Jpodesto]

Hi, I had my 1996 GMC C1500 Sierras transmission rebuilt for the third time, it works OK, but off the line the rpms start to climb and then all the sudden it grabs at about 1400 RPM(1st gear). It seems like its getting to the stall and the TC is grabbing. It feels good from 1-2 and 2-3 and 3-OD. It doesn’t seem like its slipping, there’s no shudder it just grabs at about 1400 RPM. The truck originally had 2-3 band failure. I assumed it may be the TC but no luck; (I replaced the torque converter today with another rebuilt one). I haven’t had a lot of drive time yet, so no codes yet. It actually drives pretty well except for the issue of the line. My rebuilder is pretty unhelpful, he just states I have an electrical problem, but doesn’t know what. I pulled the transmission out and had him rebuild it twice now 1st time was a total failure and the second one was having this issue and an overdrive issue (now fixed). Before my last rebuild it pulled a code p1870, but it was very rare and only happened twice in 3-4 thousand miles.

It has the Transgo shift kit in it as well as a corvette servo. I also replaced all the electronics(except the one on the outside of the trans that attaches to the shift cable) as well as the wiring harness. I also did the computer update from GM (AC12167310).

I just need to work out this 1st gear grab issue. I’m getting really frustrated with this. Does anybody have any ideas????
Please note, although no boardcode and smiley buttons are shown, they are still useable

[maxwedge]

Welcome to AF. So it reachs 1400 before it moves? Like the conv had a high stall speed or is the trans slipping in 1st then catches at 1400, from here this is tough just to feel/understand which this is.

[Jpodesto]

Thanks for the welcome!!

It will move. If you let of the brake and let it idle it will move forward like a normal operating trans would.

It has a stock stall converter in it.

I guess it could be slipping, but it has new bands. And it doesnt feel like any other vehicle ive had that had worn out bands. There always pretty smooth and then start to shudder into gear smoothly.

If you put one foot on the brake lightly and one on the throttle and slowly start to push the throttle it will hold it until it gets to 13-1400 RPM and then it grabs and goes. It doesnt ease into it either, it grabs pretty hard. Im not sure if the lock up is working incorrectly or what.

I changed my TPS and swapped my VSS from another working trans without any luck.

Im a very abled mechanic but im not famaliar with the inner workings of a transmission.

[maxwedge]

What you describe sounds like internal pressure loss in low gear, not an electrical issue, or convertor, assuming it is a stocker. Get this back to your trans guy and let him feel this, I'd like to hear what he says.

[Jpodesto]

Unfortunatly, he is of no help, I brought the truck to him last time and he wouldnt even road test it with me. He did how ever offer to rebuild it again which he did. But thats where i am know. My warranty is also up too, which was a year this month. And he has had it apart 3 times know, and the last time he stated he found nothing wrong with it (although overdrive now works better). One thing that strikes me as odd is every time he rebuilds it he states that it is too dirty, and tells me to clean out my cooler lines. I have cleaned the lines every time before I reinstall the trans. I run a flush both directions and it has a new radiator as well. Im not sure where this "dirt" is coming from that he tells me is in there. I clean the lines really well and there is usually no dirt that comes out(I run the flush into a clear water bottle).

This was the first and last time I will ever go to him. Ill try some local shops. I might just try to rebuild it myself next time after this one quits completely, whats the worst that can happen, it wont work, lol.

Are there any thing I can check and or change that are possible fixes for pressure loss? EPC, boost valve etc...
Also its sluggish into reverse, I just noticed that today 4-1-2011