Hello. This is not the first 4l80e i have overhauled but i need a little help. Transmission was just tired. No major issues on tear down. My question is after complete assembly and the transmission sitting on the bench should the input shaft spin feely in both directions. feels disconnected from rest of drive train. took completely apart and reassembled but before i put the valve body on i air checked the fourth clutch and doing so stops the input shaft from spinning freely. On assembly on do not soak the frictions but lube all other moving parts. Clearances are fine on clutch packs and input and output shaft. I have another 4l80e on the bench still together but lost reverse (plow truck) with an input shaft that takes some effort to spin and will spin when spinning the output shaft. That is also not the case with the one i just overhauled. Am i just chasing a ghost or am i missing something? Any help would be appreciated. i'm kinda at my wits end ,thanks.

 

I used to just throw my clutches in dry. There is a different feel to the input shaft turning from the clutches being dry or wet. I don't have a 4L80E in any shape to check against but the input one-way clutch should be holding the drum one way and overrunning the other. The dry frictions have very little resistance in holding them from turning. The wet frictions create a lot more resistance to that turning effort.
I remember going to work for a shop that thought it was a waste of time to soak frictions. I also remember how it was quite the adjustment on how it felt.
I soak all my frictions. 1st because it gets all the air out before installing them. 2nd all the loose fiber doesn't end up in the filter. 3rd I like the way they air check and feel wet over dry. That's just me, yes it is a little messy and I'm OK with that.

 

Thanks for the reply. I have always installed the frictions dry because i got a better feel when checking clearances with a feeler guage (old school?). Maybe i should just soak them after that. Anyway getting back to the input shaft it spins either way like a top. as for one way clutches holding i checked proper rotation and holding on the bench before installing in the case. on a 4l80e it would be pretty hard to screw those up. I hope somebody out there has a 4l80e just rebuilt on the bench for a comparison. thanks again.

 

I don’t have one on a bench to check but out of curiosity what’s the output shaft doing? Not sure what your bench setup is but once you get it in the case, I’d also check rotation with the transmission on its side by the output shaft stacked to the cs with the cs bolted in and thick snap ring in place. Grab the output shaft. It will be easier to rotate it counter clockwise than clockwise, but it should rotate in both directions. When fully assembled, it may take 2 hands to rotate the output shaft clockwise. When rotating it counter clockwise, you may hear the spraq squeak which is normal. If something is binding and not rotating clockwise even with 2 hands, you may have a bushing in slightly crooked. Take a rubber mallet and pound on the output shaft in a star shaped pattern to better seat the case bushing if that's the issue. The rest of the bushings if pressed in correctly shouldn't be an issue. The sun gear bushings are finish in place. Use a brake hone or a 1" flex hone and open them up slightly. Only spin the hone a few seconds at a time until the main shaft rotates freely inside the sun gear tube. .0015" clearance if you want to be picky about it but as long as the main shaft isn't binding in the sun gear tube with the new bushings, you are good. Double check that the orientation of all the bearings are correct. You are doing right by making sure it all rotates correctly on the bench before installing it in the case. I check the friction clearance using 2 angled feeler gauges 180 from each other with a steel resting against the pressure plate (so 2 frictions in the stack will be touching each other) as to not damage the friction when checking. Then take the stack apart and assemble correct with the friction going against the pressure plate.

 

Thanks for the reply. The output shaft rotates just as you said, with just the cs installed and completely assembled. The input shaft has no resistance. free wheels in both directions. Tomorow i'm going to take it apart again and tighten up some of the drum clearances. i remember assembling some th400's with almost no clearance in the forward drum since it is always applied except in reverse. i'm hoping if i tighten up forward and direct that will solve my issue. i'll post the results when done. thanks.

 

If you look at the OD section you will find that it is completely independent of the direct/forward drums. Pull the front section and set it up in the pump. Spin it and and see what would cause the issue at hand. Maybe soak only the OD clutches and put it back together. If you are going to tear it down in an upright position. check how it feels before and after your work. The pan & valve body do not have to be removed to check the front section. Do yourself a favor and pull the OD friction out before setting the input set up back in. I tried to install it back with the OD clutches in and dropped a coast clutch and caused it to bind up. There is a little free play in the input shaft to the OD planet/coast clutch and it will allow it to disengage from the OD planet splines.

 

Sorry for the long delay between posts but i finally got this 4l80e rebuild correct. I took it apart for the third time to the center support and rechecked all my clearances. This was a 1995 unit in a 2001 truck. It was a GM rebuilt unit with the wrong output shaft. Also the rebuild kit i had came with bonded pistons where this unit had aluminum pistons. With the bonded pistons installed i was having a hard time getting the clearances i wanted so i went back to the aluminum pistons with no cushion plates. In the end i was able to get six frictions in the direct with 50 to 60 thou of clearance and five frictions in the forward with 30 to 40 thou of clearance. I accomplished this using a combination of 77 and 90 thou steels in both drums, In the forward i had to double up on the first two steels using a 77 and a 90. Intermediated ended having about 70 thou clearance. Input and output shaft clearance came in about 10 thou. Was installed a few weeks ago and shifts great.