Any 6L80/6L90 experts out there?

[87Skier]

Were the 3-5 Reverse clutches and the 2-6 housing snap ring the only ones that require a specific orientation for the snap ring?

I'll replace the torque converter instead of having it inspected.

I put it back together. The valve body separator seemed to be in decent shape. All the checkballs looked good. I replaced them with Sonnax torlon checkballs. The only issue I had was that the rear case plugs included with the seal kit do not fit. They are physically much larger than the holes in the case. Can you tell me if these look right?

[clinebarger]

I remember 2 of the clutch packs you had too index the snap rings.

Those plugs look to be correct, Let me do some digging & I'll get back to you.

[clinebarger]

I called my local dealer.....Didn't get anywhere, I don't have a 2wd 6L90E to test fit 4wd plugs in, Can you give me the hole sizes in the case?

[87Skier]

The case was measured close to 15/32" or 12 mm.

The case plugs are about 16.5 mm or slightly larger than 5/8".

I attached a picture of the case plug area. A high resolution image is at the link:
https://1drv.ms/i/s!AqJisnJDkgyPiYlbZviScO7p1I6hGA

[87Skier]

Clinebarger, did you find out anything about the case plugs?

[clinebarger]

Originally Posted by 87Skier

Clinebarger, did you find out anything about the case plugs?

I did, Sorry I forgot.....Real busy at work. All the plugs I have saved measure the same as yours.....I guess GM drills the cases different between 2 & 4wd??


700R4 MTV-Up & MTV-Down valve bore plugs measure 12.49 MM, With some red loctite or retaining compound......They will knock in & seal good in a 12 MM hole.

The MTV Up & Down valves are located opposite of the TV Plunger, Post 124 in the 700R4 build thread sticky shows where they are.

There may be something more accessible to you..... But I couldn't find anything.

[87Skier]

No worries, I haven't had a lot of time to work on it.

I ordered a new set of calipers (been on to do list for a while), so I'll get a more accurate measurement before trying this out. I'll update when I get the measurements and parts to see if it will work.

[87Skier]

I'm having trouble locating the MTV plugs as a separate component. Would the generic Dorman 555-005 work? Looks like the larger end is 13.5 mm and tapers down to 11.75 mm.

This dorman part is the closest I can find to the 12.5 mm valve body plug for the MTV.

Would drilling and tapping for a NPT plug be a good idea? Looks like it falls between a 1/4" and 3/8".

[87Skier]

Thought I would update in case anyone is looking at this later on.

I got a set of calipers and the rear case holes measured out at 0.49". I ended up going with the Dorman 555-005 plugs, which have a small end of 0.464" and a larger end of 0.536". I used some sealant and drove the plugs in. Didn't have any issues.

[GM man]

87Skier,

Just fyi about the 6L80. Just had to replace the one in my wife's Yukon. It had 150K on it and my transmission guy (who knows more about trannys than any 10 people I know combined) told me that he was surprised it lasted that long. He usually sees them with about 120K and some as low as 100K. He told me that there is a design flaw in them having to do with the torque converter. Anyway, I'm doing a LS swap in my Jimmy right now and he insisted that I go with the 4L60 over the 6L80. My only experience with this is my wife's vehicle, but just wanted you to know since you're working on yours right now.

[87Skier]

I'm not too concerned about the transmission failing at 100k. I don't know how closely you read this thread, and totally understand not reading it, but we have tried to address most of the issues.

It seems the the biggest failure points for the transmission are:
Cracked pistons
Valve body issues
Torque converter problems

The pistons were redesigned at some point, and early ones tended to crack and burn up frictions. This was a problem in the 700R4/4L60 which also had to be taken care of in the late 1990's.

Valve body issues seem mostly tied to the check balls. I've heard steel check balls were used for a while, but mine had plastic. Even then, the plastic ones in mine with 56k miles, didn't look completely spherical. I replaced the separator plate and gasket and used torlon check balls. There have been all sorts of incidents involving check balls sticking and locking out drive, or burning up clutches.

Lastly, the torque converter as you mentioned. I don't think its a specific flaw inside the torque converter but rather a flaw with the transmission control. GM, probably for comfort reasons, decided to engage the torque converter clutch through PWM. This makes it more comfortable for the driver and makes everything seem very smooth. But considering that the torque converter lock-up is available in 2nd through 6th, that is a lot of wear on your converter. That is probably why my pan is full of friction material. This is probably why yours failed, and my will be programmed to either apply or don't. No gray area.


If it does fail, rebuilding it is actually fairly simple. I would say it is easier than rebuilding a 4L60, but it does require calibrating the clutch packs in the computer, which may not be easily achieved by your typical shade tree mechanic like myself.

But I agree, these have their issues. 4L60's have their issues too. I just know whatever I use, I'll be tearing back into at some point in the future to fix it.

[GM man]

Well the specific issue that he was telling me was the number 1 cause of the failures in those 6 speed trans is the clutch lining on the torque converter. When that fails it causes the adaptor plate (I think) to start eating into the aluminum trans case which sends pieces of aluminum through your pump which in turn causes the tranny to crater. That clutch lining (that looks like sandpaper) is fastened to the torque converter with an adhesive that sucks and is the culprit behind the whole thing. He's told me that Raybestos and another company makes a lining that doesn't use that adhesive that sucks but he hasn't been able to get a hold of any of them. I'm no expert and not at all telling you what to do, I'm just trying to let you know what happened to mine and what my transmission guy, who is an expert by anybody's standards, told me about. I wished I would have known this before mine crapped the bed. I hope yours works out, good luck!

[87Skier]

I understand completely. That's one of the reasons I was alarmed when I looked in the pan. If you look back through the posts, you will see my pan had a lot of friction material, which came from the converter.

I talked to someone about their rebuilt converters and they mentioned using a high carbon kevlar clutch. Should give a longer life, so I'm planning on going with this.

[87Skier]

Just wanted to post an update on this...

I started my swap in June and got to drive it today. Still a lot left to do, but the transmission worked pretty good. I think I need to run the relearn procedure as there is some slight flares and delays in shifting, but I did tear it down completely, and it hasn't been ran in a while.

In the short drive I took (about 15 minutes, 8 miles) it was already starting to shift better. It didn't slip or clunk, gear shifts are smooth, engagement is smooth (was a bit delayed until fluid was up to capacity). It hasn't leaked any fluid out, and it stayed sealed while I hoisted the engine and transmission in the truck at a 60 degree angle.

Thanks again to clinebarger!