15 8 speeds does yours clunk?

Higgs Boson · May 6, 2015

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.

Pressures, not shift points. Tire size and gearing is part of the tune. Fast Learn is not available (don't know why) in all the 8-speed TCMs so it can take a really long time to perform the Learn process, on the ones with Fast Learn then it's like the old ones

f8l vnm · May 6, 2015

I have the same Clunk on my 2014 6.2 Sierra .

It only happens in low speed driving 10-30 mph and as soon as I take my foot of the gas , there is a loud clunk.

Seems like worse when cold.

Dealer says its normal and its learning ....lol , good ole GM

Fishbait · May 6, 2015

I also have a noise when I take off from a stop. It's not necessarily a hard clunk it sounds more like something is loose in the front end.I will stop by the dealer next week to get it checked out.

BluByU14 · May 6, 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.

This is exactly what my 2015 Sierra did. Mine was built in December of 2014. Pleaded my case to the dealer and GM....even took the service manager for a ride and produced the "clunk" for them. They swore up and down it was normal. Had it to them 4 times in 3 months for this problem that continued to get worse. Drove me absolutely nuts. Traded the Sierra for a Ram to end all the bullshit GM was trying to pass over on me. This issue was just one of many problems I experienced with that truck in just 3 months of ownership. Sounds like the newer built units (January 2015 and on) dont have these issues.

440hsp · May 6, 2015

I hope not because mine is sceduled to be built may 18th.

jrsmall0221 · May 7, 2015

Don't know if it's the same issue or not but my 14 6 speed clunks at slow speed. Usually when I let off the accelerator. It's not regular enough for me to replicate so I haven't taken it in. About 25k on the truck. It has done it from day one. Never gotten worse though.

Sent from my iPhone using Tapatalk

Jordan18 · May 10, 2015

No audible clunk at any speed. New 6.2L with max towing. Very good throttle response which surprised me. Alot more responsive than a friends 14 5.3L.

n i c k · May 10, 2015

My '15 max tow has clunked a few times. There are 3 speed humps in my neighborhood, as I approach each one the transmission downshifts faster than it should I get crazy engine braking. After I go over the speed humps, the transmission can't decide what gear it wants to be in and the truck will start jerking. There has been some very loud clunks as of lately. I picked mine up 3 weeks ago and it has 1500 miles on it now.

With that being said, this weekend I finally got to drive the truck on some long hill climbs. 6% grades for about 5-10 miles at a time. The truck held 85 on cruise control with no problem. I couldn't even feel the down shifts when it needed to. The truck easily jumped to 95mph whenever I needed it to on the climbs. If the low speed transmission problems can get fixed as well as the sluggish throttle response, I'll no longer regret buying this truck.

mkeddie · May 10, 2015

Subscribing........I had similar clunk that threw a code and locked the transmission from shifting....auto or manual....glad I had a scanner with me was in a rush cleared codes started it back up been fine for 1k miles.....don't know what the code was

CounterMeasure · May 11, 2015

My '15 max tow has clunked a few times. There are 3 speed humps in my neighborhood, as I approach each one the transmission downshifts faster than it should I get crazy engine braking. After I go over the speed humps, the transmission can't decide what gear it wants to be in and the truck will start jerking. There has been some very loud clunks as of lately. I picked mine up 3 weeks ago and it has 1500 miles on it now.

With that being said, this weekend I finally got to drive the truck on some long hill climbs. 6% grades for about 5-10 miles at a time. The truck held 85 on cruise control with no problem. I couldn't even feel the down shifts when it needed to. The truck easily jumped to 95mph whenever I needed it to on the climbs. If the low speed transmission problems can get fixed as well as the sluggish throttle response, I'll no longer regret buying this truck.

Although I am not sure where I'd ever need to be doing 95mph on a hill climb, I totally agree about the low speed problems. There's a very specific spot in my neighborhood that has a slight incline that consistently shows the transmission is confused. Doing 20mph, hitting that incline, the transmission will suddenly upshift then immediately decide that wasn't right and literally bang back up to the gear it was in. All while staying in V4. The transmission hardware and software engineers should be forced to do city and residential driving in the truck for weeks on end as punishment for their terrible design decisions about how to make the transmission behave.

And god help you if the transmission is cold...

Higgs Boson · May 11, 2015

I was in parking lot yesterday and going 5 mph. I let off gas to let a car pull out in front of me, as I eased back on throttle it clunked so hard I thought it broke! This was not a normal driveline slack clunk.

To note, I have under 200 miles on the truck, picked it up Thurs (or Fri?).... I had it run through the shop to upload any updates of transmission TSBs or recalls, etc.

I know they have the newest stuff in there because when I test drove it, I pulled the tune and it read out fine. When I bought it and brought it home there is a new tune that is not yet defined, had to send it off to get decoded!

So now I have to drive a stock truck. Ugh.

CptMcSaug · May 11, 2015

Just for some thought, one guy swore he had transmission clunk and it ended up being in the rear or something. Everyone goes straight to the transmission

Post 584 http://www.gm-trucks.com/forums/topic/164949-anyone-with-a-2015-62l-with-the-8-speed-auto/?p=1616330

Higgs Boson · May 13, 2015

So I was looking at the torque converter tables in the truck A8 last night and they are retarded. I copied and pasted the Vette A8 tables into the truck and have had smooth non-clunky shifting up and down for the whole morning.

I think a lot of the clunk we feel is the torque converter clutch locking or unlocking at the wrong time vs the actual shift.

Another issue is the A8 is a 4.56 first gear and there is a huge gap to second....Smoothing that out in an up or downshift can't be easy, especially under varying throttle conditions,

As I get more access to more tables in the A8, hopefully I can look into it further. As for now, get the Vette TCC lock and release table into your truck. You will love it.

blwright · May 14, 2015

Something new is happening to my truck. After parking and turning off the engine, about 5 or so seconds later the truck lurches forward ever so slightly. Anybody getting this?!