Who likes their 8 Speed?

jimmyboy8301 · May 4, 2017

It seems to me after 8,000 miles the truck definitely shifts better under load, such as heavy acceleration as opposed to old man driving.

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mookdoc6 · May 4, 2017

It seems to me after 8,000 miles the truck definitely shifts better under load, such as heavy acceleration as opposed to old man driving.

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Ever since the 6spd adaptive trans hit 2008 or so. The 2200+ rpm shifts is where they seem to shift smooth? The old man driving is out which is all I know and this 8L90 likes higher RPM's no doubt......Just trying to figure out why it shifts like ass until I hit 140+ temps........GM says it running like a Sierra sir no problems? Huh

Edited May 4, 2017 by mookdoc6

jimmyboy8301 · May 4, 2017

Ever since the 6spd adaptive trans hit 2008 or so. The 2200+ rpm shifts is where they seem to shift smooth? The old man driving is out which is all I know and this 8L90 likes higher RPM's no doubt......Just trying to figure out why it shifts like ass until I hit 140+ temps........GM says it running like a Sierra sir no problems? Huh

you need lower rpms to achieve the exceptional mpgs these trucks are capable of, but higher rpms for a smooth ride lol

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silver sled 16 · May 5, 2017

Hello all just an overdue update. For those who don't remember me or my story had an 2016 sierra with 6.2 8 speed with a ton of trans issues. I was granted trade in assistance from gm. I ordered a 2017 sierra with 6.2 and 8 speed to replace current one. Took couple months to build and was damaged during transport to dealer. I took that as the final sign and decided to go with the 2500hd. I placed another order for a 2017 Denali HD Duramax. I took delivery this past Sunday and it is amazing. I do miss my cadillac ride of the 1500 and the corvette engine but nothing compares to a diesel. It is significantly more heavy duty than my 2008 duramax and more refined. I did cough up another 10 grand but the difference in resale/trade in value makes up for it. At least that's what I'm telling myself and wife. Ha. I wish I could have both trucks. They both are sweet and have thier place. Guess I'll try another 1500 series truck in 10 years or so. Gm makes it hard to hang on to these trucks when they keep making them more beautiful and capable every year

Edited May 5, 2017 by silver sled 16

mookdoc6 · May 5, 2017

Hello all just an overdue update. For those who don't remember me or my story had an 2016 sierra with 6.2 8 speed with a ton of trans issues. I was granted trade in assistance from gm. I ordered a 2017 sierra with 6.2 and 8 speed to replace current one. Took couple months to build and was damaged during transport to dealer. I took that as the final sign and decided to go with the 2500hd. I placed another order for a 2017 Denali HD Duramax. I took delivery this past Sunday and it is amazing. I do miss my cadillac ride of the 1500 and the corvette engine but nothing compares to a diesel. It is significantly more heavy duty than my 2008 duramax and more refined. I did cough up another 10 grand but the difference in resale/trade in value makes up for it. At least that's what I'm telling myself and wife. Ha. I wish I could have both trucks. They both are sweet and have thier place. Guess I'll try another 1500 series truck in 10 years or so. Gm makes it hard to hang on to these trucks when they keep making them more beautiful and capable every year

So did it come with the L5P Duramax 2.0? Dang.........is all I have to say if so!

silver sled 16 · May 5, 2017

Yes new oil burner. Not sure what you mean 2.0.....

Dnt · May 6, 2017

You might just need to tweak the trans settings a bit to get what you want?...........

https://www.youtube.com/watch?v=oPSXTcMtO0k

mookdoc6 · May 6, 2017

Yes new oil burner. Not sure what you mean 2.0.....

The latest Duramax is a "Clean Sheet" design.....AKA: Duramax 2.0 the LB7 had tweeks no doubt over it's run but this baby is all NEW!

DirtyDave · May 6, 2017

My 8 speed was very clunky when I first got it. My 6 speed in '14 would clunk occasionally on 2-1 downshifts, but not bad and not often. The 8 speed was extremely harsh and clunked and banged a lot. The dealer did a reprogram for me early on and that seemed to smooth it out a lot. I still get an occasional slam bang with 1-2 or 2-1. Always under light or no throttle. At WOT it is super smooth. Honestly, I'd rather have the 6 speed back.

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silver sled 16 · May 6, 2017

I have to say L5P is asleep and thirsty out of the showroom but so was my LMM.The more I drive it the better it gets. At 300 miles now and getting 14 mpg aroung town average. Haven't pushed it yet at all.

Edited May 6, 2017 by silver sled 16

Tjheems · May 12, 2017

Just read this entire thread from start to finish...what a whirlwind of emotions!

So I bought one of these 2015 GMC Sierra Denali 6.2/8 that was previously a buyback from GM....I talked to the dealer that bought it back (it was in maryland) and they claimed the P/O was making the truck do it...and they kept referring to driveline lash. I drove the truck and didn't see any problems or anything during the test drive...I ended up buying it. only 17k on it, and got an extended warranty.

I've def. had the random harsh clunk about 1-2 times per tank, and a tougher shift in the early morning after it sat all night. It will give a hard downshift a few times on every drive and the hard shifts are only more apparent if I go into M-mode on the shifter. I also get this weird oil temperature fluctuation that shoots up and down and up and down for a little bit during driving (not all the time...still building the situation on that one...but I do have it on film). I've been trying to catch the clunks on film too, just so I have some..."see I told you it does it" when I go to the dealer.

There was a litany of service records - mostly software updates and then a singular repair that stood out (the dealer said they did it to appease the guy - but he claims it fixed nothing). The customer claim was,

"Customer states hard shift between 30-40 mph. SOP exists road test vehicle - verified concern. Contacted TAC for assistance, Case #8-118239145. Advised tech to replace valve body due to an intermittent internal failure per TAC advised to replace valve body. Filled Fluid to Spec. Performed Valve body MHCV Calibration Relearn. Test Drove Vehicle 18 Miles OK at this time. Old 8L0Y508000291571; NEW - 8L0Y608300471543"

Part numbers used were Valve 4.265Y FP Number 24278901 and they used 8 Qts of 88861037S (DEXVI)

Anyone have any idea what that actually means? I saw no reference to that specific repair in the entire thread. Everything else was related to the Stator repair.

Also, got a little confused on the Transmission Fluid conclusion - so we determined that the recommendation would be a flush and replacement using DEXHP? Is that correct?

Anyways - mine being a buyback has me all concerned to actually see what type of treatment I get at the dealership. They claimed there was nothing wrong with it when they bought it back (could never duplicate a customer concern) and it showed no signs of issue when they sold it to me. They had to give me an extended warranty of 12/mo and 12,000 miles on top of what was left of the factory - and I bought an extended warranty beyond that (which I cancelled through them and actually purchased through USAA).

My truck is a '15 Sierra 1500 Denali with the 6.2/8, built 05/16/2015. Any input on that repair would be great.

Thanks!

Bikemobile · May 12, 2017

Mine is great 98% of the time. Butter smooth, quick upshifts, i love it. Then you are driving through a parking lot at less than 10 mph, brake, gas, turn, CLUNK. I also get a bit of slip accelerating onto the highway first thing in the morning. Like if you rest your foot on the clutch while accelerating. Only with the wheels turned. I wonder if that is some computer torque management kicking in.

Oh well. I bought a 100K bumper to bumper through GM so it's their baby if I ever need it. No software updates to date on the trans. Seems pretty good most of the time. And pulls a trailer like a dream.

The old mercedes derived 5speed auto in my hemi charger clunks like that but at higher speeds, 45+ with brake gas, brake turn gas gas gas! applications. I think it may be the unfortunate marriage of computers, sensors and multiple gears packed into small cases.

My old 3 speed stage 2 turbo 350 with 400 hp 350 chevy in my hotrod clunks too. From first to second with a tire chirp every time above 2500. Thats how we like it though.

Nothing is perfect. But as these trucks get newer and more expensive our expectations grow with them. If I bought a new corvette that clunked like that I would be pissed that my wife vetoed the manual trans and cry in my whiskey glass at night.

Edited May 12, 2017 by Bikemobile

mookdoc6 · May 12, 2017

Mine is great 98% of the time. Butter smooth, quick upshifts, i love it. Then you are driving through a parking lot at less than 10 mph, brake, gas, turn, CLUNK. I also get a bit of slip accelerating onto the highway first thing in the morning. Like if you rest your foot on the clutch while accelerating. Only with the wheels turned. I wonder if that is some computer torque management kicking in.

Oh well. I bought a 100K bumper to bumper through GM so it's their baby if I ever need it. No software updates to date on the trans. Seems pretty good most of the time. And pulls a trailer like a dream.

The old mercedes derived 5speed auto in my hemi charger clunks like that but at higher speeds, 45+ with brake gas, brake turn gas gas gas! applications. I think it may be the unfortunate marriage of computers, sensors and multiple gears packed into small cases.

My old 3 speed stage 2 turbo 350 with 400 hp 350 chevy in my hotrod clunks too. From first to second with a tire chirp every time above 2500. Thats how we like it though.

Nothing is perfect. But as these trucks get newer and more expensive our expectations grow with them. If I bought a new corvette that clunked like that I would be pissed that my wife vetoed the manual trans and cry in my whiskey glass at night.

I have exact same thing almost to a tee! Regarding the 8speed! I have had the fast learn reprogram though......

Snoringbear · May 13, 2017

After towing my 6,000 Lb camper about 500 miles round trip a few weeks ago I was getting the clunk and hard low speed shift every now and then. So, took it in to the dealer who ran diags and reprogrammed the tranny. He said that towing the camper changed the adaptive learn program. So, anyway, long story short its shifting ok now. The customer rep also stated that he didn't expect an improvement with the ten speed tranny. Personally, I would like to see a 1st gear lock-out feature for no-load driving, would smooth out starts and stops for sure. With the 6.2L which has 420hp and 460ft lbs of torque there's no need to take off in granny gear.

Bigmac · May 13, 2017

Different scenario in my 2017 6.2 8 speed. Acquired the torque converter shake as noted in many tsb's. Replaced converter and did flushes. Actually worse and is very bad pulling trailer. Only occurs 2-3 gear at 1500 - 2500 rpm's

Tech line involved and dlr has sent picco readings to them but problem still unresolved. I waited till mid year to get this as I thought all trans problems would be worked out. Shifts great but. Still has vibration. Waiting for next steps from field engineer. I was advised they are having trans fluid problems. Might be bs - who knows.