Transmission was rebuilt by a local guy but by the time we got it in the car the builder died in a house fire. We need some help!!! This is a complete new build. Engine, Transmission, wiring is all new/rebuilt. We have no way of knowing what works because there is obviously no history.
The problem we are having is no reverse. Everyone said check the reverse pin. We did and it was in the short end of spec. We put in a longer pin and are setting around .090 now. Still no difference. At cold it shifts mushy into reverse and wont hardly move the car. After a few minutes you can't even feel it shift. All forwards seem to work fine. Unplugging the harness you still have to run the engine up to 900-1000 rpm range before it shifts into reverse. Its a nice solid shift at that point. If i hold the brakes and lay into the accelerator the rear wheels start to spin.
Pressures are as follows:
plugged in @ Idle Park 70 psi REV 70 psi. Increasing Rpm only adds 10 psi to both
Unplugged idle Park 130 psi Rev 100psi.
with Rpm Park 190psi. REV 280psi
why do i lose pressure when plugged in? I thought Rev was all hydraulic? And when my neighbor who worked for gm garage comes over and plugs in his laptop it says the transmission is in park regardless of what gear you're actually in? But again it does shift into all forward gears. Oil is level at bottom of case. Valve body is from Sonax. All solenoids show resistance as well as the speed sensors.

 

The band could be broken. You say forward gears seem to be there, are you SURE third gear is? If you have third then you know the direct clutches are working, half of the problem is eliminated. Pressure should max in reverse, could be looking at a problem there too. What year is this unit? There are several style of EPC solenoids and valvebodies/cases. Do you cooler flow?

 

I have reverse with the transmission Unplugged. Im Not sure how i could have any reverse with a broken band? Im guessing the unit is around a 2000 model. It has the later return line towards the back of the transmission. I was thinking the valve body changed in 05 but im not sure. I guess the numbers on the side give the year of manufacture and i could call sonax and make sure the valve body they sent is compatible. I put a pressure guage on my pickup truck and it shifts into reverse at idle with 60psi. If i hold the brakes it loads the engine and thr pressure goes way up. I stopped at a little over 200 psi but im sure there was more there. This rebuilt transmission never builds over 80psi plugged in.

 

Presure with harness plugged in low at all throttles and high with unplugged tells you regulation is working and you have a bad PCS Also presure is still controled in rev by the PCS just with a BOOST . So I think you are dealing with 2 separate issues a bad PCS being one of them.
REV since you have checked the REV SERVO and the pin travel I would take that off the table also.
VB any model except the very very early sould be compatable . VERY EARLY meaning pre 95 which requires a long tube front to back.
Since you have all fwd gears 1-2-3-4 though I imagine a bit slippy with no line rise we can assum the direct clutch as far as the 3rd gear side is in tact.
Personaly I would 1 replace the PCS AKA EPC and while in pull VB and air check with your head towards bell the Hole right of the center support bolt.
Should make a distint bump and should not leak But if i am remebering my charts right some air may come out the hole on the hole other side of the center bolt. Then air check from the hole other side and no air should come out the right side (The way the internal seals are set up in the drum assuming not "dual fed" the center seal in drum acts as a one way valve of sorts alowing both chambers to be used for rev but only one chamber for 3rd . Now if when air applied to either side comes out other then its been modded for "DUAL FEED" but the REV side not propery blocked. This would cause a in 3rd gear though via the rev circuit but should not affect reverse in the other direction.
Also its possible he could have intended to do dual feed but forgot to remove the center seal in drum and or the ring on cenetr support but did block the rev feed hole in case . But with this it would it sems just cause a weaker reverse only using the direct clutch section of the drum.
My best guesses are .
1-DAMAGED OUTTER SEAL ON DIRECT CLUTCH PISTON
2-Broken aluminum direct clutch piston
3-Missing or damaged/stuck check ***** at position 7 or 11
4-Missing ORING at TFP switch
^THIS ALL FOR REV^

BAD PCS aka EPC for presure rise issues .

 

Dual feed id say. I pressured everything i could except a couple places along the front edge that i couldn't get to when i had the valve body off. Everything made a thud sound and i never heard air pouring out anywhere.