I had the 4l60e rebuilt for my cousins 98 TA. After a little over 100 miles it wouldn't go into 3rd or 4th. I drove the car 100 miles and it shifted fine. I gave it back to my cousin and the first time he rips on it, trans wont go 2-3.(no 3rd or 4th) I pulled it out and took it back to the transmission guy. He took it apart and said 3rd and 4th clutches were toast. He ask if there was any nitrous on the car. No nitrous just a small 224/224 cam. What could cause this?

 

The 3-4 clutch is a (THE) weak spot of the 4L60E, but even a stock rebuild should last much longer than 100 miles with that engine. In short, the builder screwed up and should warranty this for you.

There are many threads on this issue, but here is a recent one with my suggestions which are similar to what most performance builders here would suggest:

https://ls1tech.com/forums/automatic...n-problem.html

At a minimum, have the GM 7-clutch kit for a 4L65E installed. It is part #24244615 at the dealer with a list price of $74.

You and/or your builder might find this thread useful too where I list the parts for a 7-friction setup with a tighter clearance:

https://ls1tech.com/forums/automatic...some-info.html

I suspect there was a leak in the 3-4 circuit which immediately caused slippage and failure. Perhaps the 3rd accumulator checkball was overlooked. Again, the builder responsibility to do it right.

Also request the following improvements to be made:
1. Have the Sonnax 4l60E-LB1 boost valve kit installed. (Builder can order that from his distributor.)
2. Have the 3rd feed hole in the separator plate drilled to .093.
Alternatively have him install the Sonnax servo release check valve, drill the
valve as in the instructions and drill the separator plate to .125.

Be sure the line pressure is checked when done and installed. It should hit about 225psi when the throttle is blipped.

I think it is reasonable for the builder to charge you for these upgrades, but not for the overall rebuild.
These are my opinions.
Ted.