4L80 issues. Any educated guesses?

Will Carter

Will Carter

Well-Known Member
Joined
Mar 23, 2005
Location
Burlington
I've been fighting this particular transmission for a few rounds now. I'll save the back story and get to the details as of today.

4L80 with CKPerformance full manual valvebody. Brand new build with good parts (don't ask me what exactly, it's been so long I can't remember but they're the same parts that have been holding up in my other transmission).

From Park down to 1st it will not move unless you give it about 3000rpms. It feels like your dragging the brakes. Once it lunges forward it 'frees up' and I can shift through the gears up and down just fine. Starting in 2nd gear is sort of the same way except a little less power input is needed for it to free up. 3rd and 4th are awesome and quick.

Or...I can go from Park down to 1st and wait for about 10-15 seconds and 1st gear will start to pull on its own at idle. So it seems like I can wait this amount of time and let itself free up or I can force it to pick up pressure by giving it throttle.

Also, if I let it free up and get rolling in 1st, shift to 2nd (still at idle or slightly above) and then down shift back into first it will lock itself up solid again until I either power through it or let it sit and free up.

Compression braking on 2nd and 1st doesn't seem right either. 4th and 3rd fall down with rpms. Down in 2nd and the car does start to slow down but it's definitely not because of the compression. It's like it starts to drag on something (like putting on the brakes) in the trans even though the rpm's are already fallen way bellow the current speed. Same with 1st gear as well except if you're not going fast enough it will knock your teeth out on the steering wheel when it catches.

Again, 3rd and 4th seem perfect.


I'm asking here because the trans builder says it's the valve body and the valve body manufacturer says it's the trans builder. Of course, of course...
 
This is in 1st gear. You can hear the amount of power it takes to even get it moving. Had I stayed in the gas about 3 more seconds it would have 'broke free' and rolled on fine. I didn't touch the brakes at any time in this video. That's the trans locking back down on itself at the end. Same thing seams to happen while downshifting at speed.

 
That's exactly what my th350 was doing after the last build before I took it back to the shop that did it.
Diagnosis on mine was a bad front pump, cracked sprag and somehow the gear that is pressed on the governor was upside down...all tis was fixed and wheneve TI get it back together I'll tell you if it's any better.
 
transman731 said:
ron that's not what's wrong with his, and you can't put a 350 governor gear on upside down.
Click to expand...
You would be the expert.
Just sharing my experience.
Maybe I messed up what I as told, somehting about the governor being backward or upside down. Shrug.
good luck will
 
i built his units, and everything internally was in perfect condition, my only question was on the valve body because i have no way of knowing what they do to them. everyone that builds valve bodies does their "own thing" to them and will not release info as to what they do.

i don't know that i'm an expert, a specialist maybe, but being and expert on an automatic may just be an oxymoron.
 
I don't know on the 4l80 if there is anything different internally with a fmvb, but how hard would it be to swap in a different known vb to rule that out. Sure seems like a vb or band related issue.
 
Too much trouble to swap vbs between the known-good trans and this one?
 
transman731 said:
everyone that builds valve bodies does their "own thing" to them and will not release info as to what they do.
Click to expand...
I called the guy Thursday. He told me to get the valve body on the bench, call him back, and he'd go through the test procedure with me over the phone.


Transmission number 1, the original, still has no 2nd gear compression braking after the last rebuild.

Call me or return my PM's or something. Lots of $$$. Still no transmissions that work properly.
 
no second gear braking is normal operation for the trans.

you sent me a pm at 1:39 friday night, i am trying to figure out the solution to the problem(which isn't a malfunction) i have other customers also and i'm not going to piss off 20 customers and drop what i'm doing to try to figure this out. i am researching it Will.
as far as the 2nd trans,if you want it fixed, bring me the car and the trans, i can't figure out what's going on with the trans on the bench. i'm sorry if it sounds like i'm being an asshole but i'm here from 5:00 am until i feel i need to leave (still here at 8:15) and usually on saturdays just let me know what you need me to do. i will keep researching on the no 2nd compression braking.
 
So what's this circled port with the torx pattern in it do? Cause it was almost totally blocked by a piece of the gasket that was covering it. The gasket has torn from the pressure above it.

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afarm9.staticflickr.com_8524_8683659483_c49f42f782.jpg
 
yes that bolt is important, that is not the problem though. that is the 4th clutch bolt, it stops the piston from turning and from the looks of it there are still treads in the piston stopping it from turning.(that bolt is common for breaking and gets replaced every time)
did the vb guys go over it with you, was anything found to be wrong in it ?
 
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