My 4L60E is blowing ATF out the breather/vent hose. Fluid level is good and the trans didn't even hit 160 degrees according to the new gauge i put in ( sender is in the pan). It only seems to do it when i really get into the gas. Under normal acceleration it shifts fine and no fluid comes out. Any ideas?

Oh, i did have to swap the output shaft for one that matches my t-case. Maybe i re-installed something wrong that is causing to much pressure? Thanks.

 

Normally only a couple of things will cause this. The obvious is what you already stated heat. The other is excessive fluid pressure that is dumping into the case when it should not. Causes could be a gasket that is cut or blew out, folded over gasket, pump that is not true and is blowing off pressure under high line pressure and so on. When you swapped out the shaft did you remove the valve body? Did you use new gaskets on the pump and valve body? Might want to retrace your steps to see if you missed something. Vince

 

Thanks for replying. The trans had 3 miles on it when i swapped the output shaft, it was out of a damaged 2006 Envoy. I did remove the valve body and reused the original gaskets. Not sure if it's related but i am still having some tuning issues, meaning that it will hit the rev limiter under WOT attempts.

 

Are you running a stall converter? That could have something to do with hitting the rev limiter. That might be tuning related. However we still have the vent issue. Maybe if you fix the vent problem the other problem might be corrected depending on what you find.

 

All stock , no mods at all to the trans. The mph and RPM shift points were lowered and it helped a little. I noticed that it still revs up a lot before shifting under heavy acceleration and it sometimes hits the rev limiter. It shifts fine under normal driving.
I am running low gears ( 4.88's ) with 36" tires so maybe that is affecting the shifts

I have the breather emptying into a bottle in the cab so i can contain the mess. I noticed that it seems to pour out right after heavy acceleration. It just kinda drains out of the breather tube, it doesn't spray out. If i drive it in " D " and stomp on the gas it will drain out once it has shifted into 3rd and then stop. I doesn't come out continously. Thanks for the help.

 

Make sure that in your tune that the proper rear end ratio has been entered and also the tire height. This very important and have seen many problems cause by misinformation. I did not mention this before but make sure that the trans is not overfilled this will cause oil to be pushed out of the vent as well. Vince

 

Tire size and ratio was entered properly and double checked.
I took the pan off to put the temp sensor in. I was driving it around to warm it up so that i could check the fluid. That is when i saw the fluid coming out the breather. It was almost a quart low but it wasn't overheating or slipping.