6L80E with upshift noise and gear slippage. Please help!
07-12-2015, 11:33 PM
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6L80E with upshift noise and gear slippage. Please help! Hey folks! I recently picked up a G8 GT with a built 6L80E and a 3200 stall Yank converter. That car is Procharged and put down 705 RWHP a few years back when the original owner had it. I'm the 3rd owner, and when I bought the car from the previous owner back in April everything seemed fine with the transmission. No noises, no slippage, etc.
One day in late may I romped on the throttle and heard a strange, quick noise when the car downshifted into what I believe was 4th gear. Ever since then, I'd often hear a short "squak" (sorry... that's the best way I can describe the sound. Think of a heavy squeak) when the transmission would up-shift into 4th gear while driving gently. I then noticed the sound when up-shifting into 4th gear while driving harder on it too. Here is a video of the sound when up-shifting to 4th while in Sport mode (I put it in Sport mode so you can see in the center LCD what gear the car is currently in):
After another few weeks and a good bit of driving, I noticed the sound start to happen when up-shifting into 6th gear. THEN it started making the noise when up-shifting into 5th gear, too.
Just a few drives later, I started noticing that when holding even 5th gear in Manual mode, the transmission would make the "squak" noise upon receiving throttle. See video below:
I knew there were obviously some issues, but my other two vehicles / money pits are in the process of under-going some repairs as we speak, so I continued to drive the G8 knowing I'm going to need to tear out the transmission sooner than later. During a trip from MD to Pittsburgh over the weekend, going through all of the hills, I noticed the transmission was now slipping in 6th and 5th gears when I tried to give just a touch more throttle to maintain speed while climbing the hills. And now, anytime the transmission up-shifted or down-shifted into 5th, it would make the noise and slip a few seconds before gripping, and then starts slipping again if I maintained the slightly extra throttle. Here's a video of the same thing happening when trying to maintain speed in Manual mode, 6th gear:
So I plan on enlisting the help of someone familiar with transmissions to help me tear this thing down and get it back together (and upgrading anything that wasn't upgraded already), but it'd be really nice to know what exactly may be wrong based on all of the symptoms I've listed above.
I'm not sure of the details of the transmission build, but the original owner believes it was done back in 2010 or so, so that may indicate what 4/5/6 clutch packs may be in it based on what was available in that time period. The TCM was fine-tuned by a reputable tuner when the car was dyno tuned years back, when the original owner had the car. The 2nd owner, who I bought the car from, claims it was recently street tuned. The person I bought the car from was also not the most honest of people, so take that with a grain of salt. I'm not sure if the TCM tune that the original owner had gotten done has been changed or not with that said, but if did in fact get changed then I wonder if the line pressure on 4/5/6 was addressed properly in the tune... and if that's what possibly caused my issue.
Is there anything specific that anyone can think of that may have lead to all of this? Would line pressure, a bad servo, a bad band, or anything else possibly be the culprit? I'm sure the clutches for 4/5/6 are now shot, but not sure if another component may have possibly led to that scenario, or maybe those clutches have just taken too much of a beating over the years. The car was apparently drag raced a bit from a dig and from a roll when the previous owner who had it built was still driving it... so it's not like this transmission has had a gentle life.
By the way, I've been monitoring the transmission temperature at all times and it has NOT been heating up. The fluid level is also where it should be, but I have not drained any fluid to inspect for metallic flake or any other contamination yet.
Any solid help would be really appreciated. Thanks in advance!
-Andrew
One day in late may I romped on the throttle and heard a strange, quick noise when the car downshifted into what I believe was 4th gear. Ever since then, I'd often hear a short "squak" (sorry... that's the best way I can describe the sound. Think of a heavy squeak) when the transmission would up-shift into 4th gear while driving gently. I then noticed the sound when up-shifting into 4th gear while driving harder on it too. Here is a video of the sound when up-shifting to 4th while in Sport mode (I put it in Sport mode so you can see in the center LCD what gear the car is currently in):
After another few weeks and a good bit of driving, I noticed the sound start to happen when up-shifting into 6th gear. THEN it started making the noise when up-shifting into 5th gear, too.
Just a few drives later, I started noticing that when holding even 5th gear in Manual mode, the transmission would make the "squak" noise upon receiving throttle. See video below:
I knew there were obviously some issues, but my other two vehicles / money pits are in the process of under-going some repairs as we speak, so I continued to drive the G8 knowing I'm going to need to tear out the transmission sooner than later. During a trip from MD to Pittsburgh over the weekend, going through all of the hills, I noticed the transmission was now slipping in 6th and 5th gears when I tried to give just a touch more throttle to maintain speed while climbing the hills. And now, anytime the transmission up-shifted or down-shifted into 5th, it would make the noise and slip a few seconds before gripping, and then starts slipping again if I maintained the slightly extra throttle. Here's a video of the same thing happening when trying to maintain speed in Manual mode, 6th gear:
So I plan on enlisting the help of someone familiar with transmissions to help me tear this thing down and get it back together (and upgrading anything that wasn't upgraded already), but it'd be really nice to know what exactly may be wrong based on all of the symptoms I've listed above.
I'm not sure of the details of the transmission build, but the original owner believes it was done back in 2010 or so, so that may indicate what 4/5/6 clutch packs may be in it based on what was available in that time period. The TCM was fine-tuned by a reputable tuner when the car was dyno tuned years back, when the original owner had the car. The 2nd owner, who I bought the car from, claims it was recently street tuned. The person I bought the car from was also not the most honest of people, so take that with a grain of salt. I'm not sure if the TCM tune that the original owner had gotten done has been changed or not with that said, but if did in fact get changed then I wonder if the line pressure on 4/5/6 was addressed properly in the tune... and if that's what possibly caused my issue.
Is there anything specific that anyone can think of that may have lead to all of this? Would line pressure, a bad servo, a bad band, or anything else possibly be the culprit? I'm sure the clutches for 4/5/6 are now shot, but not sure if another component may have possibly led to that scenario, or maybe those clutches have just taken too much of a beating over the years. The car was apparently drag raced a bit from a dig and from a roll when the previous owner who had it built was still driving it... so it's not like this transmission has had a gentle life.
By the way, I've been monitoring the transmission temperature at all times and it has NOT been heating up. The fluid level is also where it should be, but I have not drained any fluid to inspect for metallic flake or any other contamination yet.
Any solid help would be really appreciated. Thanks in advance!
-Andrew
Last edited by MEAN GTO; 07-15-2015 at 07:02 AM.
07-09-2021, 07:06 AM
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Did you ever figure out what it was that was causing this issue? I’ve got a 2012 yukon that is pretty much doing the exact same thing as you described and your video shows except mine only does it when shifting into 5th.. When lightly accelerating and it shifts into 5th it makes that horrible loud squeal and it almost seems like it’s locking up. what i mean by that is when it shifts into 5th and starts to squeal its like the front brakes are aggressively pushed for a brief second and then released. if i try to remotely touch the accelerator pedal while it’s in 5th it just starts to squeal and slip.
I just drive it in manual mode and keep it set to 4th so it don’t shift to 5th. When i have to get on the interstate i run it up to 4th and let completely off the gas and and switch the manual mode to 6th so it completely skips 5th.. It works fine, but i really want to know what is causing this.
Side note previous owner told me trans was just rebuilt a couple thousand miles before i bought it. Obviously a lie but i guess could be true with whoever rebuilt it not doing something right.
I just drive it in manual mode and keep it set to 4th so it don’t shift to 5th. When i have to get on the interstate i run it up to 4th and let completely off the gas and and switch the manual mode to 6th so it completely skips 5th.. It works fine, but i really want to know what is causing this.
Side note previous owner told me trans was just rebuilt a couple thousand miles before i bought it. Obviously a lie but i guess could be true with whoever rebuilt it not doing something right.
