I have built up my forward drum 4 times and it leaks air at the ovrrun hole (air in top hole while holding finger on the middle, low reverse hole). I built it up twice and everything but the overrun held both times. I assumed that I had cut a seal so I got a new kit and replaced them all. Still had the same problem.

I used lip seal protectors, and chased all the seals without forcing them. It would seem that if it was my installing technique some of the others would leak also.

I shook the piston to make sure that the check ball was free and checked the bore for scratches with my fingernail. I used 40 pounds of air for the test.

The low piston engages and hold till I release my finger but the overrun bleeds off.

The overruns will always leak into the forwards on the 4L60 variants. Normal. Run with it.

Thanks for the reply. It's not too often that I hear what I wanted to hear when questioning about a problem.

Thanks for the reply. It's not too often that I hear what I wanted to hear when questioning about a problem.

I hear ya!
I have to be the bearer of bad news all the time, so it's good to give some encouragement at times. :)