So I'm playing around with an early model 4L80E build atm and came across an air check diagram that I had saved in my files where it appears someone mislabeled the "forward clutch" apply port. That is actually the regulated apply port. Tried locating the source of the image again but couldn't find it. I added the question marks and "drive" and "line" holes.



So here I am shooing air in that port wondering why the hell the forwards aren't applying lol.
As it was explained to me, shooting some compressed air into the DRIVE hole (not the one incorrectly labeled forward clutch above) actuates the forward clutches.
Referring to the tech guide, I followed the path labeled "drive" and saw that it leads to the forward clutch. I was wondering if I had blown a seal or something. Forward was originally checked on the bench using hole on the input shaft while blocking the other hole.
I see also that the "regulated apply" circuit goes to the TCC valve in the pump.
I see also that "Line" hole in the case goes to the PR valve circuit. I know vacuum testing the PR valve on the pump is the way to check for leaks but can one shoot air through the "line" feed hole in the pump and stroke the PR valve and listen for leaks? Vacuum test was good.









So to stroke the TCC valve, it looks like one must apply air to the hole circled in white, while blocking the hole circled in red. That's what I did and heard it move. When I went to vacuum test that circuit in the pump, I didn't get any vacuum reading until stroking the valve, which isn't mentioned in the sonnax vac test instructions.



I was also trying to check the Overrun Clutch for leaks in the case and wasn't getting anything, so I stacked overrun on the pump and saw that I wasn't using enough air. Needed at least 75 psi. Maybe my air gauge is messed up but that seems high.
Also came across this vid of hooking regulated air directly to the pressure port while blocking the oil filter inlet and listening for leaks while shifting through the gears. Sounds like something to just do after assembly as a double check for any leaks.


I think I got it all sorted out. The digital version of the Hydramatic tech guide is nice. I managed to get my hands on a hard copy as well.

 

hey Dino, on that TCC apply/enable valve pull the valve and make sure the last builder didnt 180* it by mistake. I have seen that before. The long shank end is the sprung end, the short end goes in first.

and yea IME it takes a fair bit of air to move the overrun piston. I always slop the sealing areas really good with assembly lube and that helps with air testing the assembled unit.

 

This one I got lucky and it was an untouched core. I did verify the TCC enable valve was in the correct orientation. I think I was telling you that one of the bores in the pump that a coiled pin 8661838 goes through got so worn the pin was just dropping right through the bore whenever the valve was stroked and no longer putting pressure against the end plug lol. Had to replace it with an oversized roll pin. It's for reasons like this that I disassemble everything in the pump and check it using those Sonnax O-ringed end plugs that you suggested awhile back.