Low & reverse are slipping

It's official. I damaged the 4L60E I built. I've built up the truck so much between the transmission and the 6.0L but NEVER got on it. I finally decided it was time to see what she'd do so I got on it from a stand still, still didn't floor it but heck is the truck FAST.

1st gear (via D on column) and reverse surge... It feels like the clutch pack isn't fully locking up. 2nd, 3rd, 4th, TCC lockup all operated as expected. Neutral works fine too. I didn't test selecting 1st on the shift (should have). I've removed the pan now.

No material in filter (I cut it open).
No debris in pan
Magnet had a little gewie slime on it.
Fluid was changed a few thousand miles ago.

Backstory: Truck felt like it had no power backing out of parking space. 1st gear felt same on my drive home Saturday (a few days ago after I had mashed on the gas to see what the truck had in it). I limped home and checked the fluid which was low, almost none on the stick when I checked it from a cold idle the next morning. I also found a leak in the fittings for the thermal bypass I installed. I topped the fluid off and drove it about a mile, it drove perfectly fine in 1st gear and reverse. The symptom was gone. I went to drive it today, made it about 3 miles everything was perfect then the symptom came back. I parked it and checked the ATF level. I have a hell of a time reading that thing. It seemed to be fine. I limped it back home 2, 3, 4th seemed to have no issue and held well. I parked on flat ground in front of my house and checked the fluid again. I tried reverse (at idle) and could hear a chattering so I added more fluid. It backed up the driveway like there was no problem (I have a steep driveway). I kept checking the stick and thought I'd try reverse again, but was doing it again on flat ground in my garage. Fluid smells normal but I definitely smelt something driving it when it acted the second time.

I know enough to be dangerous here... I did build the transmission but have only built one. I worked like a dream until I railed on it with low ATF.

Baffled...

Looks brown in camera ~ but in life it is pink.


Fluid looks like new


There was some geew on the magnet

Boost Valve checked and moves freely in bore (not stuck). removed pressure regulator valve in pump as well and seems fine.

Trying to come up with additional things to check. Don't really want to drop the case if I don't have to.

@NickTransmissions ?

@NickTransmissions I dropped you a comment on one of your videos. One of the guys who helped me build the trans (not Dana) is assisting me with diagnosing it. You helped me on a harsh 1-2 shift I've never been able to clear up (more below).

I'm currently investigating with service pan off. I think my next step is to remove the valve body. I am wondering if there's a port under there where I can pressurize the low reverse clutch pack piston with shop air? I'd like to see if it holds pressure.




Backstory: Dana had drilled my separator plate, however, I never used his shift kit he supplied from TransGo. I switched to Sonnax accumulators as well (he supplied pinned accumulators). Long story short, I kept the separator plate he drilled for the shift kit. Never could smooth out 1-2 shift. You mentioned drilling those smaller on a new separator plate. I never got around to that.

Engine is a built LQ9 & These are the transmission parts I used in build


Checking a few more things. The engine and trans have a tune on them. Apparently turning on the shift light function for manual transmission will burn up. The shift light is OFF in my tune.

@Matthew Jeschke - I'm thinking you may have somewhat stressed the forward and low reverse/reverse input clutch packs when you got on it heavy when it was low on fluid, assuming that occurred recently and the surging (slipping, delayed engagements?) was not happening until then. Your fluid looks dark but you mentioned that was due to the lighting.

Re the item you are pointing to in the picture of his instructions - that is the EPC screen. I'll be honest - while all the Transgo shift kits have a 'fix' for that issue, I hardly ever see it and not convinced it's really a problem that it's made out to be in the Transgo literature. Dana worked primarily with Transgo and a couple of former GM Powertrain engineers to develop his kits and they work great. But this particular 'fix' was carried over into his kits, probably unnecessarily. I do often see that wire spacer at the bottom of the pan in many of these transmissions that come in w/the Transgo kits installed.

Once you remove the valve body, refer to my video on doing a case air check - it will show you where to apply air for all of your clutch packs. This video shows me doing it without the air test plate so all you need is an air source and nozzle:

Excellent thanks nick! Yeah I'm certain I stressed the lo-reverse pack. I'm hoping I can resolve this w/o opening the case... If I open the case I'm changing that clutch pack even if it's still w/in spec. I may keep the rest of the clutches... bit undecided. I need to find a supplier to get the parts. RockAuto is no longer where I live. I'd purchased misc trans parts last time from them.

I should elaborate, Dana was a super nice guy. But the shift kit parts made me nervous (they looked cheap and like they might break under use). I threw them away and had somebody else help me who knew how to tune so I wouldn't need a shift kit. We switched to Sonnax parts where feasible.

The one thing I regret having done was I kept the separator plate Dana drilled for the shift kit setup he sold me.

NOTE: Pressure manifold looks good.

Teardown notes...

Didn't take photo but pressure switch visually is in good order. No torn seals.


Visual inspection of valve body. All check balls where they are supposed to be.
Removed two solenoids and there was nothing in filter screens.


Separator plate came off as well. No burnt gaskets. Filter screens are clean.
Can see some evidence of clutch material around accumulator area of separator plate.


Nothing abnormal seen on case side.