GMC Yukon Transmission Question

[magqw7]

My wife has a 2017 Yukon with 126,000 miles. Had the transmission flushed(without me knowing) and approx 150 miles later we have issues. I got in it, started it, it runs fine and cycles through the gears for approx 30 seconds and then its like it is shifted into neutral. Shut it off for about a minute and the same thing happens. Took it back to the shop that did the flush and they say they flushed it again and even dropped the pan and replaced the fluid and still have the same problems. I limped it to another shop and they are saying it needs a new tranny. No codes were ever thrown and it was fine before the flush. Is there any way a valve or sensor could have gotten clogged or maybe just the torque converter? The other transmission shop is 3-4 weeks out to take a look at it. Any ideas?

[june-bug]

I don't know the answer to your question but I have owned three GMC's in the past. Two of them didn't make it to 100,000 miles before the transmission went out and the third one was about where your miles are now. Needless to say I'm not a fan of GMC transmissions.

[fynns]

Yea, agree. You get 100k out of the trans, your doing better than most. Mine was built with 96k roughly on it. 6 and 8 speed transmissions are known for issues. Flushing didnt do anything if I had to guess, coincidence is a bitch sometimes.

[1BADAIR]

6l80? Flushing is the worst thing that could be done. Change fluid every 40k. If you plan on keeping it a long time have them put a different convertor in other than stock.

[Riccochet]

Sounds like a valve body issue. You're getting pressure from the pump, or it wouldn't go in to gear at all. If the clutches were shot it would just slip no matter what. I'd bet one of the regulator valves is collapsed. Sonnax makes a good valve body rebuild kit for like $200.

[Kanuck1958]

What transmission?
Are you saying when you shift into drive it goes to neutral after about 30 seconds? Does it do the same thing in reverse?Are you able to get it to upshift before it goes to neutral?

[magqw7]

What transmission?
Are you saying when you shift into drive it goes to neutral after about 30 seconds? Does it do the same thing in reverse?Are you able to get it to upshift before it goes to neutral?

8 speed. Yes. Yes, same in reverse. Yes, it will upshift before it goes to neutral - this is the only thing that puzzles me and I have some hope the tranny isnt shot

[Dstacks7]

Clutches are gone. Common issue with 8 speeds. Sorry but that's my personal bet

[CJ1]

Once you knock all the crap loose in there with a flush and new fluid loaded with detergents it's normally game over. AND it normally happens within a few hundred miles of the flush. Rebuild time. CJ

[Wedgestank]

I don't know the answer to your question but I have owned three GMC's in the past. Two of them didn't make it to 100,000 miles before the transmission went out and the third one was about where your miles are now. Needless to say I'm not a fan of GMC transmissions.

amen to this. Great trucks. Shitty transmissions. Never buy another.

[santee bass]

My 2003 Tahoe,250,000 miles & still has original transmission
(never touched) & the front end has never been checked.

[John Jackson]

Once you knock all the crap loose in there with a flush and new fluid loaded with detergents it's normally game over. AND it normally happens within a few hundred miles of the flush. Rebuild time. CJ

+1
All the clutch plate friction material wears and is carried in the fluid. These clutch particles help the clutch plates grip in a transmission with a lot of wear or miles. Once you flush and install new clean fluid, with nothing to help as friction material, the plates slip and finish burning up. I would never change transmission fluid in an automatic tranny.

[jbsoonerfan]

My wife has a 2017 Tahoe and it started doing the same thing at 54,000 miles. Took it in and they said it needed to be flushed, they flushed it and about 200 miles later it got 10 times worse. Took it back and they reprogrammed it and it has been fine ever since. My wife's best friend has a 2019 Suburban and she took it in just to get the transmission flushed at 39,000 miles because the dealer "recommended" it be done at 40,000. A week after she got it back it started slipping. She called them and they told her it was normal to do that for a while. I told her it was absolutely not normal and she should take it back and demand they look at it again. Sure enough, a reprogram and it has been fine ever since.

[jml]

My wife has a 2017 Tahoe and it started doing the same thing at 54,000 miles. Took it in and they said it needed to be flushed, they flushed it and about 200 miles later it got 10 times worse. Took it back and they reprogrammed it and it has been fine ever since. My wife's best friend has a 2019 Suburban and she took it in just to get the transmission flushed at 39,000 miles because the dealer "recommended" it be done at 40,000. A week after she got it back it started slipping. She called them and they told her it was normal to do that for a while. I told her it was absolutely not normal and she should take it back and demand they look at it again. Sure enough, a reprogram and it has been fine ever since.

My Avalance and my wifes Escalade both went out at 125,000 miles.

[jbsoonerfan]

My Avalance and my wifes Escalade both went out at 125,000 miles.

My wife's 2010 went out at 160,000

[billnorman1]

My 2003 Tahoe,250,000 miles & still has original transmission
(never touched) & the front end has never been checked.

My 2007 Silverado bought new is a P.O.S. Yesterday I fixed the A/C which never worked since it was new, it had the evaporator clogged externally with some kind of black fuzzy shit. I sprayed it out with Isopropyl Alcohol and high pressure air. All that aside, my trashmission has never been touched and I never will (knock on wood) with 240,000 miles. Maybe it's because the truck loses weight every day as the tin worm eats it.

[Kanuck1958]

A transmission service fast learn may work here but a scan tool is required to do that. Next best guess is the 12345R boost valve is stuck (debris) allowing the 12345R fluid to bleed off into the exhaust backfill circuit or the knockdown circuit. Bottom line is you need a qualified tech to look at it. No easy fix here.