GM 6L80e Transmission
 

I have a 2014 GMC Sierra 1500 with the 6L80e 6spd auto transmission. It's at 143000 miles, and I bought it with about 90,000 miles. Fluids and filters are changed regularly.

Started with a torque converter shudder, did some research, seems like a pretty common problem. Dropped it at a local, highly regarded transmission shop on Monday, quotes were $2200 for the torque converter and oil pump, or $4200 for a full rebuild with upgrades depending on what they found.

No surprise, it needs a full rebuild.

Here's the thing, anecdotal internet data aside, Steve told me that they have done anywhere from 3 to 8 of these transmissions PER WEEK for the LAST TWO years! Yep, no less than 3 per week. Even if we err on the low side of average and call it 4 per week instead of 5.5, that is 416 transmissions at one Massachusetts transmission shop over the course of 2 years. He said GM transmission issues outnumber all other manufacturers.

There are three guys in his shop with GM trucks, 2 of them have already rebuilt their transmissions, and one is, as he put it, on borrowed time. We went by another shop last week here in town with two bays, both bays had GM trucks on the lifts.

There are also issues with the GM 8-speed auto and a class action lawsuit for those.

How could GM screw up the design of these so badly?

Especially since the TH400 was, I believe, pretty much bomb-proof.

And I think they've had a few other decent auto trannies (granted, back in the day).

I know a guy who works at the plant that builds the 8 speeds. Even he says to stay away from them.

As for the trannys. They seem to only get so many miles. They're a wear item for sure... but now since standard trans are no longer an option for any new truck. You gotta bite the bullet...


OP. You should buy a turbo 400 with an overdrive and retrograde your new truck.

Tell me more. I am about to buy a used truck. Last Chevy was a 91 suburban with a big overdrive tranny-forget the model. It was essentially a Turbo400 with OD.

GM probably considers it a good design. Lasted past warranty. ;)

$4200 sounds $pendy for a transmission overhaul, but I find myself in inflation shock a lot these days.

Buy new. Sell at 90k miles for minimal loss and get some other sap to rebuild the tranny.

:D Yeah, that...

But, I'm not even sure if that works in this case. My brother-in-law has 75k on his, which is a '15 I think, and has had intermittent torque converter shudder.

There are discussions on HP Tuner about new programming for the 6L80e to increase pressure, and reduce allowable RPM slip. GM also had these set to operate normally at about 190F, which is contributing to the issue. Updates include a new transmission thermostat that keeps it about 50 degrees cooler.

Yeah, it's well past warranty, but a maintained trans should go a lot longer.

I have sticker shock as well, but even at the low end, it was $2200 for a torque converter and trans oil pump. The pump is aluminum, so once the torque converter clutch starts shedding the lining the first damage is scored surfaces on the oil pump.

The extra $2k includes replacing all wear items, new cooler lines, etc. I've seen costs quoted about $1k less in GM truck forums, but those posts are dated pre-covid.

Sonnax has a interesting writeup of what they think the problem is, likely GM redesigned the part to save $0.03, apparently the older part had no problems. My truck has the 6L90 so in the same boat.

I have a 2017 Yukon Denali. (ordered the car) They also suffer from the Chevy shake. Showed up about 50K miles. Dealer changed the tranny fluid, triple flush which helped. They then changed the fluid to their new super duper fluid. Helped I guess. Still shakes.
Here is something else I think related. I can only get about half the life out of a set of tires before we get the shake at about 76 to 83 mph. Doesn't matter the brand of tire. New tires are trued and then balanced on the car. Only way to get a smooth ride. I have replaced the driveshaft. No help.
Dealer and GM either don't know what to do or just won't. Car came with Continentals, then Michelin and now two sets of Bridgestone. Some people say the issue is in the preloading on the axles.

Get you through warranty is what that is called.

Wow, my 2016 Suburban has 140K and I’ve been meaning to service trans. I don’t do any towing but do drive on mountain roads. Maybe I got lucky….

Mechanics love GM, like fat people love cheese .

^^When you say the tires are 'trued' are they actually sipping / shaving the tread to make them round and then balance?

Yes, the tires are trued to the wheel (off the car) and then placed on the car then balanced. Truing does remove some rubber. High spot mostly. There is one place in Phenix City Alabama that specializes in balancing. Other tire shops don't get close and don't care. They balance off the car and get you out the door.
It makes a difference. Side note, since I only get 35 thousand miles on average I have gone to a more soft rubber on the tires. Thinking they will be better in wet conditions. I think the 60 70 thousand mile guarantee on tires is a scam. They only pro rate. Plus any tire good for 70 thousand miles is going to be damn hard.
I did have the factory extended warranty from the jump. Didn't matter on the shake. They either don't care or don't want to fix. Hoping the class action gets some traction.

This is different than what I encountered for the torque converter shudder. That starts to happen at about 1400-2000rpm when at speeds where I am in 5th or 6th gear. Lightly accelerate and it shudders due to the torque converter clutch shuddering.

I had a BMW 535ix wagon that developed a vibration at similar speeds to yours, which turned out to be a bad CV joint on the right front axle. Wouldn't vibrate at any other speed, would happen regardless of load or coasting. Has the dealer checked for defective CV joints?

Knock wood or something. My '14 was fine, right up until it wasn't. Like someone flipped a switch.

Which truck brand do you see the least amount of issues with these days Fred?

I'm not in a position to spend $70k + on a brand new 4WD pickup, so I'll be in the used camp for trucks that are in the 5yr old range.

Two wheel drive.

Im still a GM guy . You just cant beat an ls motor . They all seem to have their own set of problems, which are all similar in the pia and cost factor .