Ok, I've been researching this a bit more, and found a thread over on the hotrodders forum where JakeShoe had what sounds like is the same issue with a 4L80E that he built, and he diagnosed his, and found out that the line pressure was too low at idle in the "D-Range"(OD). His had 45-50 psi at idle, so he commanded the PCS to increase pressure a bit by decreasing voltage to it with a scanner and it cured his. So he took the pan back off, and adjusted the screw on the PCS only 3/16 of a turn, and the result was then 60 psi at idle, and it completely cured what sounds like the same issue as we are having, so I am gonna check the pressure and see what it is, and I may also adjust mine until around 60 psi and see if that cures it. The ATSG manual says around 37 psi is sufficient at idle I believe, but several experts say that is NOT enough, and that it needs to be around 60 psi.

 

When this first happened to me on a late model unit years ago, after splitting hairs I found it to be low actuator feed pressure causing the A solenoid to be lazy at scheduling the 1-2 shift valve. A valve body swap fixed this problem for me twice and after that I began to install the early output shaft with the feed hole in all my late units. This allows the output shaft to case bushing to get lubed from the same oil that feeds the rear internal gear to output shaft flange bushing.This lube oil is at a much higher pressure and volume than the actuator feed oil that lubes the case bushing boss via the lube tube that spans the boss and rear of the valve body. I remove the lube tube and plug both in and out holes with cup plugs to increase oil pressure and oil volume to the actuator feed circuit. This improves things a bit.

 

Thanks for the reply Chris, we adjusted the EPC just about 3/16" of a turn, and it now has around 65 psi or a touch above at an idle in D, and that cured the problem we were having above. We also have another problem, and noticed it before as well... when setting still in the driveway idling, with brakes applied, you can have it in the D range, and put it straight up to Reverse, and it stalls the truck sometimes, other times it drags it way down like it's gonna stall, but it has completely died several times doing this. If you go from D, into N for just a couple seconds, and then onto Reverse, it kicks right in and does fine. What would cause this issue? Other than that, it shifts and works great now. Thanks!

 

Just to follow up, it seems as if the stalling issue was do to a dirty MAF and dirty Electronic throttle body, I cleaned both of those, and it hasn't did it again as of yet... its working great now, so far atleast Lol

 

Well... unfortunately, cleaning the MAF and Throttle Body has NOT cured the problem, it does fine going from Park to Reverse, but going from ANY forward gear straight to Reverse will kill the motor, but if you go from any forward gear, to Neutral, just for a couple seconds, and the to Reverse, it works fine. It only does it when shifting to Reverse, no other gears. The problem is also intermittent, it doesn't do it everytime, but it does it frequent. Other than that the transmission kicks in gear, takes off and shifts absolutely beautiful. Does anyone have any ideas of what it could be?

 

Seems like it acts like maybe a valve that gets a bit draggy the warmer it gets. I noticed on the clutch application chart, that the Forward Clutch is applied in low gear in every Range, be it OD, D, manual 2nd or manual Low, but it is not applied in Park, Neutral, or Reverse. When you shift into Reverese, it releases the Forward clutch, and applies the Direct clutch. So, it's pointing to whatever Exhausts the fluid from the Forward clutch, when shifting from 1st gear in any Range, too Reverse, and the reason it doesn't have the problem when shifting into Reverse from Park or Neutral it works completely fine, is because the Forward clutch is not applied in those ranges, so it doesn't have to exhaust fluid before applying the Direct clutch.

 

I doubt it is a forward clutch exhausting problem as the manual valve bore takes care of that. HUGE hole...
This is more likely a pump vulome/efficiency problem. Hydraulic flow is dropping far enough to allow the converter clutch to become monentarilly applied. Install a pressure gauge and watch the needle to see how long it takes for the pressure to recover when moving the shifter. Laggy pressure recovery = low pump volume

 

Thanks for the reply, I have already had a pressure gauge on it, and it has right around 60 psi at idle, an jumps immediately up toward 170 with the brakes and throttle applied, I didn't notice much lag at all going from gear to gear on the gauge, maybe just flickered, but that's it. The pump looked real nice when I inspected it and put it together. Everything works great, as it should, even going from Park or Neutral to Reverse, never a problem. It's only when you are at an idle, in any Range, and go straight to Reverse, but if you stop at neutral for 2 seconds, and then on to Reverse, it works great.

 

I saw your other post too, but what you must remember is the OR clutch, the direct clutch, the low reverse band AND the converter must be filled when Reverse is selected. Going from D to R requires the Forward clutch to vent and the same time the other circuits are being filled. Pump suction, pump efficiency, filter condition, filter seal etc all play into the oil flow. Even if the forward clutch was on when reverse was selected, the engine wouldn't stall, the converter would slip. IE Transbrake function. This is a converter clutch apply in reverse issue

 

UPDATE:: FIXED!!

I just wanted to come back and do a follow up with what fixed our above issue with the stalling in Reverse..... we installed the Sonnax 34200-14K Line to Lube valve, and it completely took care of the problem, and everything works absolutely beautiful now. I will make note of this for every 4l80E I build from now on Lol... Thanks to everyone for all of your help!