rebuilt my 4l80e, was working fine for 40 miles then torque converter lockup wouldn't disengage unless i unplugged the trans harness and drove limp mode in 2nd gear. looked like 12 from pcm engaged erroneously, tried a junkyard pcm after cloned the factory specs to the new pcm and not much changed. dropped the pan to replace the tcc solenoid and i lost forward clutch, had reverse. i suspect filter and intake bushing weren't sealing as they needed separated to remove the tcc solenoid keeper pin. so i've got the pan off and am going to drop the valve body and put in a separator plate i drilled out bigger, then got scared of it being too harsh and bought a new plate and drilled it out conservatively with a little bigger on 3rd for the dual feed. shifts way too soft and while reverse engaged quickly, drive took waayyy too long to engage. i've been trying to find where or how to improve forward clutch engagement time, holding pressure, etc. I am aware it's possible i have a leak in the forward clutch circuit and may need a teardown to fix this. the discussion here: https://bobistheoilguy.com/forums/th...orward.342054/ was very helpful in understanding what potential leak points could be happening. but I am hopeful that is not the problem as i have had low pressure problems with my 4l80e rebuild. I am ditching the sonnax pressure spring, I built the pump with their kit but am replacing their pressure spring with a th400 spring for better pressure off idle, where i am struggling most. when i had a gauge plugged into it i never saw it get above 60psi idle and it need to be closer to 90. hoping filter and new intake bushing will seal and help improve pressure. pump looked fine when disasembled but maybe it was worn past it's ability to build pressure. am gonna try to reassemble and see what pressure gauge says, maybe tune the pcm to trigger the epc bleed off valve less frequently and maintain more pressure. but i wanna improve forward clutch circuit in the valve body and cannot find anywhere explaining how? it takes 3 seconds to engage drive cold and 2 seconds hot. way too long and now it won't even engage drive but maybe halfway while slipping. thanks for your help and time in advance!

 

My advice to you, Before reassembling, perform a "Wet Plate Air Test." Use an air nozzle with a rubber tip and blow air into the forward clutch feed hole in the case (with the VB off). You should hear a solid "thump" of the piston applying. If you hear a loud "hiss" of air, the leak is inside the transmission (seals or rings), and no valve body mod or pump spring will fix it. You will need to pull it back down.

 

Most commonly missed are grooves in the forward drum where the rings on the input shaft ride when it comes to FWD clutch issues with the 4L80E. here because of the small area a little is alot.

 

yeah i'm pretty sure it was the forward drum i delivered to the machine shop with a repair sleeve they bored and pressed in, was cause of original failure of the trans when the bushing gave way on the overdrive planetary gear and allowed the input shaft to drift into the forward clutch drum and bore it out and leak fluid pressure burning 3rd gear clutches up.

i thought i remembered the sonnax pressure spring being long and soft, i pulled the spring out of the pump and it's short and stiff, maybe i put the stock spring back in but i dunno this spring is pretty short. i have a th400 spring i'm gonna put in, much longer. maybe this will fix my pressure problem and hold the forward clutch together. I will try to source a rubber tip blow chuck to apply in my transmission while the valve body is off and listen for forward clutch leaks. thanks for the help guys!

 

That sleeved forward drum is a major red flag. If the machine shop didn't get the bore/finish perfect for the input shaft rings, your forward pressure is bleeding out right there.

 

Line presure should have been first thing checked , However unless insanely low and driven very very very little , Its unlikey the FWD would be first to burn. Upshifting sets INT , DIRECT , OD would take the hit first.
As for raising line with the 80s my go to is simmly add a 4l60e PR valve spring, GETS ME TO ARROUND 240 MAX line every time.
Low line at idle to me would point to BAD or miss calibrated PCS (Unplug the harness at idle if line jumps to 180 up this would be a prime suspect)
But more common would be massive internal leak at rings of FWD clutch , WRONG pump / case combination. Some pumps have an extra lube feed used on some cases, bocked by case in others and in some DUMPPED right into case. This will cause very low idle and lower that normal overall presures. And most common at least from my experience damaged or worn pump and or leakey AFL valve .