8 speed tranny forgets how to shift

Nuginu · September 20, 2017

Hey guys!

I picked up a 2017 sierra all terrain with a 6.2 and an 8speed tranny recently. I installed fox 2.0 coilovers and the gm borla exhaust on it. I absolutly love the power, i always catch myself racing small cars just to win and tell them "its just a truck".

The only issue i have with the truck is the transmission. On some days, it shift so perfectly that it gets me going. On random occasions, it'll forget how to shift from 1-2 or 2-3 (rarely). Ill punch it, the revs will climb really fast (no wheelspin when it shifts) and when the truck goes to shift into second, itll sit at 6krpm for a few short moments before slipping it's way into second. I find this very weird because i could actually shift into second while doing a breakstand and it does really well (i dont do it often).

My truck only has 6000 kms on it. Also, has anyone noticed that these trucks only have full power in 4th?

It's Tim · September 20, 2017

Sounds like you'll be buying a new transmission soon.

mookdoc6 · September 20, 2017

Sounds like you'll be buying a new transmission soon.

Ha,Ha I like that! Anyway, they EXTREMELY STOUT TRANNY'S the programming SUCKS and they are made for nice load up a hill. They take a seemingly LONG time to shift properly...........

Supreme Pizza · September 20, 2017

Not really sure what to say. If you beat the hell out of your transmission, sooner or later it will give up.

How to destroy your transmission 101:

1) Let the fluid get low

2) Tow extremely heavy loads up steep hills

3) Drag race people on a regular basis

4) Smash the bottom of the transmission driving over large rocks

5) Shift from neutral to 1st gear while the engine is at maximum RPM

6) Pour metal shavings and dirt into the dipstick tube

7) Crush or pinch the transmission cooler tubes

8) Shoot the transmission with a gun

9) Replace the transmission fluid with orange juice

10) Over rev the transmission going down a steep hill with a heavy trailer, in 1st gear, peddle to the metal.

Cant think of much else. Anyone got any ideas?

Nuginu · September 21, 2017

Not really sure what to say. If you beat the hell out of your transmission, sooner or later it will give up.

How to destroy your transmission 101:

1) Let the fluid get low

2) Tow extremely heavy loads up steep hills

3) Drag race people on a regular basis

4) Smash the bottom of the transmission driving over large rocks

5) Shift from neutral to 1st gear while the engine is at maximum RPM

6) Pour metal shavings and dirt into the dipstick tube

7) Crush or pinch the transmission cooler tubes

8) Shoot the transmission with a gun

9) Replace the transmission fluid with orange juice

10) Over rev the transmission going down a steep hill with a heavy trailer, in 1st gear, peddle to the metal.

Cant think of much else. Anyone got any ideas?

This actually made me laugh so much. Made my day. Tranny isent that bad, just has its rough moments. Kinda like stated above, the programming does seem to suck.

Supreme Pizza · September 21, 2017

This actually made me laugh so much. Made my day. Tranny isent that bad, just has its rough moments. Kinda like stated above, the programming does seem to suck.

Good times man, I like your style.

Ya, your trans is probably OK for now, but ease up on breaking the sound barrier. Try to limit your drag racing to hot chicks and douche bags. I would risk a blown transmission on either one, but the rest - meh, let 'em go. You know you can smoke 'em, so there is no need to prove it.

sdeeter19555 · September 21, 2017

The 4spd and 6spd sometimes hang shifts too, not just the 8spd. It's got to be programming or just the right set of sensor inputs that cause it.

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2017SierraSLT · September 21, 2017

The 6L80E's in both my 2013 and 2017 have never exhibited these wierd shifts and abnormal behavior.

sdeeter19555 · September 21, 2017

Our 2008 1500 company truck's 4l60e does and my 2012 2500hd's 6l90e does from time to time...just saying, I've experienced it in both.

I will say my 6l90e seems to have quit, maybe it's a learned attribute of the computer?

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Nuginu · September 21, 2017

Good times man, I like your style.

Ya, your trans is probably OK for now, but ease up on breaking the sound barrier. Try to limit your drag racing to hot chicks and douche bags. I would risk a blown transmission on either one, but the rest - meh, let 'em go. You know you can smoke 'em, so there is no need to prove it.

The sound barrier lol. Seems like manual mode is actually helping the odd shift. I just throw it in m7 to keep it out of 4cyl mode in town. These trucks are all so fast now its unreal. But good point there, i really do enjoy seeing the little civics wonder how on god's earth a crew cab truck walked them. Usually i dont even floor it, just keep it around 3500rpm and it pulls pretty hard for a truck. Think theyll ever put higher performance trannys in their trucks?

The 4spd and 6spd sometimes hang shifts too, not just the 8spd. It's got to be programming or just the right set of sensor inputs that cause it.

Sent from my SAMSUNG-SM-G900A using Tapatalk

Hang shifts, thats the word im looking for. It almost seems like the tcm can't think fast enough.

Our 2008 1500 company truck's 4l60e does and my 2012 2500hd's 6l90e does from time to time...just saying, I've experienced it in both.

I will say my 6l90e seems to have quit, maybe it's a learned attribute of the computer?

Sent from my SAMSUNG-SM-G900A using Tapatalk

It quit? Like as in she exploded, or quit shifting weird.

sdeeter19555 · September 21, 2017

The sound barrier lol. Seems like manual mode is actually helping the odd shift. I just throw it in m7 to keep it out of 4cyl mode in town. These trucks are all so fast now its unreal. But good point there, i really do enjoy seeing the little civics wonder how on god's earth a crew cab truck walked them. Usually i dont even floor it, just keep it around 3500rpm and it pulls pretty hard for a truck. Think theyll ever put higher performance trannys in their trucks?

Hang shifts, thats the word im looking for. It almost seems like the tcm can't think fast enough.It quit? Like as in she exploded, or quit shifting weird.

Mine quit shifting wierd...it hasn't hung a shift in a couple years. I do get a shift flare once in a while (maybe one time every two months), but the hung shifts have stopped.

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6.6LTZ · September 21, 2017

The 4spd and 6spd sometimes hang shifts too, not just the 8spd. It's got to be programming or just the right set of sensor inputs that cause it.

Sent from my SAMSUNG-SM-G900A using Tapatalk

This is true. I had an 18 loaner with the 6spd.

Got plenty of clunks and harsh shifts with only 400 miles on it.

elementaltoad · September 21, 2017

My 6 speed has issues of it's own, mostly lugging and shuddering at lower speed/RPM. It has been great under heavy throttle though, if you want to hot rod, try putting it in manual mode, my 6 speed at least behaves much better there when I want to romp on it a bit.