15 8 speeds does yours clunk?

Stoddard · May 5, 2015

I have a 15 6.2 8 speed built in December and now have just over 8,500 miles on it. I complained to the dealer right away about this thing shifting weird and having harsh downshifts in under 1500 miles. Now in the last 3000 miles its developed a nice drive line clunk between shifts in town and per the tsb I'll attach does the exact same clunk repeatably. I just took it in again and they said they couldn't find anything. I took the service manager for a ride. 0-40-0 3 times in a row and he played the game oh i can't hear it and reminded me I have larger tires on (305 55 r20) and "it throws the calibrations off so bad". These tires are barely 1" taller than stock. My gf's '06 half ton has over 210,000 miles and doesn't make noise like this. He did say bring it in till its worse but I'm sick of waiting. Its a new truck.

If you drive from 0-40 nice and the brake to a stop, take off again it pops.

Does anyone else have this noise?

#PI1450: Snap, Pop, Click, Tick or Clunk Noise on a Launch - (Mar 27, 2015)

Subject: Snap, Pop, Click, Tick or Clunk Noise on a Launch

Models: 2015 Cadillac Escalade, Escalade ESV

2015 Chevrolet Silverado

2015 GMC Sierra, Yukon, Yukon XL

Equipped with 8L90 Automatic Transmission (RPO M5U)

Built Prior to December 1, 2014

Attention: This PI also applies to any of the above models that may be Export vehicles.

Condition/Concern

Some customers may comment on a snap, pop, click, tick or clunk noise, typically on a launch after a stop.

This condition may be caused by clearance between C1 and C2 clutch reaction plates (steels) and the case.

Recommendation/Instructions

This procedure will load the plates in one direction and then the other direction to maximize the motion of the plates. The impact of the plates on the case is what results in snap or the clunk noise. The C1 and C2 clutch reaction plates (steels) were revised in transmissions built November 5, 2014 or later to prevent this noise condition.

Procedure to test for snap or clunk:

Warm the transmission to at least 40°C (104°F) sump temperature.

Place the transfer case in 2WD.

Drive the vehicle in Drive, up to about 64 km/h (40 mph).

Release throttle and bring the vehicle to a stop.

Launch the vehicle and listen for a snap or clunk.

Repeat several times to confirm the snap or clunk noise.

If this test confirms the noise, the transmission should be replaced. Refer to the latest version of PIP5200 and contact PQC for a replacement transmission.

Important: If the transmission is replaced, the transmission solenoid characterization reprogramming must be performed using the TIS2Web Service Programming System (SPS). Refer to Solenoid Valve Characterization Reprogramming in eSI. The Transmission Service Fast Learn Procedure must also be completed. If these procedures are not completed, shift quality may be less than optimal.

TJay74 · May 5, 2015

I will say this, 1" will throw the calibration off and can cause the issues. Everything in the calibration is based on tire height, speed and rpms. Change one of those variables and it will cause all sorts of issues.

You cant compare a 2006 with a 4L65E transmission with a 6L80E/8L80E transmission, they are two entirely different animals. The old 4 speeds transmission don't use nearly as much logic in shift control as the new transmissions do.

One of the main reason when I replaced my tires I stock with stock size, I have been into the stock calibration and there are page after page of calibration tables that all rely on and reference each other to make the shifts happen in the new 6/8 speed transmission.

Sierra Matt · May 5, 2015

Subscribed

bboyce536 · May 6, 2015

Yes and no. 3/15 build date. Clunked going into gear but has yet to on the 0-40-0 test. 180 miles on it.

CounterMeasure · May 6, 2015

If he thinks its the tires, then he should be willing to hook up a Tech2, and hit the 3 or 4 buttons that put it back into Fast Learn, and let you drive it around to recalibrate to the new tire size. If it still does it, then he's out of excuses.

evilhunter101 · May 6, 2015

I have a clunk but I've only noticed it at highway speeds when letting it coast and then giving it gas to get back up to speed or to maintain whatever speed I coasted to. I will try the 0-40-0 thing tomorrow if I get a chance and report back.

CounterMeasure · May 6, 2015

I have a clunk but I've only noticed it at highway speeds when letting it coast and then giving it gas to get back up to speed or to maintain whatever speed I coasted to. I will try the 0-40-0 thing tomorrow if I get a chance and report back.

What you are describing is a clunk from the amount of gear lash in the driveline. GM has a TSB that explains "this is normal". Surprise, surprise.

My original transmission was replaced based on info in this PI before it was made public to dealers, which turns out, wasn't the source of the main noise after all. My *replacement* transmission makes two noises that I am getting used to:

-Whine from straight cut gears in 1-3.

-A click when shifting 5 to 6 at 35mph.

The second noise was also in the original transmission, so I guess its normal. The first is a characteristic of improvements the made in a newer revision of the transmission.

evilhunter101 · May 6, 2015

What you are describing is a clunk from the amount of gear lash in the driveline. GM has a TSB that explains "this is normal". Surprise, surprise.

This makes absolutely no sense to me since my transmission hadn't clunked at all until about 7400 miles. Not saying you're wrong or anything, just that GM's TSB response is inadequate at best.

I also have that gear whine. So weird. But honestly, I kinda like it. It's like its powering down. Dumb, I know but I can definitely live with that whine.

I *hate* the clunk. Makes the truck feel cheap, and it was anything but cheap.

CounterMeasure · May 6, 2015

This makes absolutely no sense to me since my transmission hadn't clunked at all until about 7400 miles. Not saying you're wrong or anything, just that GM's TSB response is inadequate at best.

I also have that gear whine. So weird. But honestly, I kinda like it. It's like its powering down. Dumb, I know but I can definitely live with that whine.

I *hate* the clunk. Makes the truck feel cheap, and it was anything but cheap.

If you didn't have it before, then perhaps you have a bad u-joint? When mine makes the same bang-clunk when getting back on the gas, its the same feeling I've had when a u-joint wears out.

I am not a fan of the switch from helical to straight gears. Besides the noise, what that tells me is GM engineers didn't believe the transmission design could handle the axial loads the helical gears made, possibly in towing scenarios, which doesn't happen when the same transmission is in the Corvette or Camaro. So, instead of beefing up the bearings and case to handle the axial loads, they just switched to straight cut gears to relieve the load. I consider that the cheap way out.

TJay74 · May 6, 2015

If he thinks its the tires, then he should be willing to hook up a Tech2, and hit the 3 or 4 buttons that put it back into Fast Learn, and let you drive it around to recalibrate to the new tire size. If it still does it, then he's out of excuses.

There is no such process in the Tech II to do this, the fast learn is for the adaptive shift properties and does nothing for the tire size as it is hard coded into the computer and cant be changed by the dealer.

evilhunter101 · May 6, 2015

If you didn't have it before, then perhaps you have a bad u-joint? When mine makes the same bang-clunk when getting back on the gas, its the same feeling I've had when a u-joint wears out.

I am not a fan of the switch from helical to straight gears. Besides the noise, what that tells me is GM engineers didn't believe the transmission design could handle the axial loads the helical gears made, possibly in towing scenarios, which doesn't happen when the same transmission is in the Corvette or Camaro. So, instead of beefing up the bearings and case to handle the axial loads, they just switched to straight cut gears to relieve the load. I consider that the cheap way out.

It just started acting up last Thursday I believe, so haven't been able to troubleshoot yet. I've never had to deal with a bad u-joint so didn't know what that felt like and I'll definitely check for that, thanks.

While that is the cheap way out, it is also a nearly guaranteed fix. Anything else without proper time for testing might have had reliability issues in the long term and at worst, could've left a lot of people with major repair bills after warranty ended, especially with the switch to 30k warranties. Of course, now we'll never know.

CounterMeasure · May 6, 2015

There is no such process in the Tech II to do this, the fast learn is for the adaptive shift properties and does nothing for the tire size as it is hard coded into the computer and cant be changed by the dealer.

I might be misunderstanding what Fast Learn does then. My understanding is it clears the shift tables so that they can be rebuilt based on real-world driving with the vehicle under its normal operating conditions. This would include a change in tire size.