2014 Sierra driveline clunk

zert100 · September 17, 2015

So I've been dealing with this clunk on my '14 6.2 Sierra crew s/b. It is most noticeable when letting of the gas in second gear, but is also noticeable in higher gears to a lesser degree. It will clunk every time I let off the gas in second gear. The driveline will absolutely not clunk in first gear. The first time I took it in to the dealer the service manager rode with me and agreed that the clunk didn't seem normal and suspected the rear axle or driveshaft was the culprit. I was pleased that he appeared willing to dig into the problem and was hopeful for a resolution. Later that day I returned to pick up the truck and was told that they performed the TSB relating to torqueing the shackles and U bolts. I didn't expect that to fix the problem and it certainly didn't. I brought the truck back shortly after and they checked for any TCM updates to no avail and opened a case number with GM. After that they handed me the TSB stating that clunking is normal. Yesterday I went in for an oil change and told them I'm still not satisfied with the low speed clunky driveline of this truck and asked to drive one of their loaners to compare the low speed driving characteristics. The truck I drove had no noticeable clunking at all. This test drive only reinforced my belief that something in not right with mine. Of the 5 late model full size GM 4x4 vehicles I've owned none of them clunked like this 2014. An occasional clunk is to be expected especially in a 4WD and I could live with that, but this thing clunks all the time! This does not seem appropriate for what is otherwise a very nice driving and expensive vehicle. I am totally frustrated with how my dealer and or GM is handling this case. Has anyone had any luck getting this type of issue fixed? Any insight is appreciated.

Edited September 17, 2015 by zert100

davidegl · November 13, 2015

Same problem on my 2015 Denali. Dealer has looked at it three times and service advisor has heard the loud "clunks". The dealer says it won't affect longevity and at 22m miles I can't refute that. Even if it doesn't affect longevity, it will definitely have a detrimental effect on resale. I emailed GM corporate and received three phone calls from a lady who was asking about my progress. I told her there was none. You may know by now that GM has issued a TSB telling dealers not to fix the problem and they will not be reimbursed if they do. I'm currently looking for a quality driveline service facility in the midwest hoping I can get it fixed. I have had five GM trucks and really only two without significant issues. Those who are thinking I should have learned my lesson before now have a valid point. Never again is all I can say.

mrbadwrench · November 14, 2015

The clunk is take-up of driveline slack in the differential and transmission output shaft. The amount of slack will vary from unit to unit. As the unit ages, the clunk will slowly become worse, however it is not a safety or driveability concern.

A variety of different vehicles will have this clunk. For example, both my Toyota Tacoma and my Ford E-350 work van have some type of clunk when you let off the gas.

The clunk can be compounded by axle wrap on certain vehicles, however the GM 1500 trucks do not themselves suffer from axle wrap.

The re-torque of the axle u-bolts is designed to confirm that axle wrap is not present.

Other than checking the u-bolts, the reason GM will not "fix" the problem is because technically there is nothing wrong. Driveline slack is a normal characteristic of a vehicle with a solid axle, divorced transmission and long driveshaft.

Driveline clunk can be improved with an aluminum driveshaft. Reducing the rotational mass of the driveshaft will help reduce the shock force.

Installation of a u-joint dampener will also help.

davidegl · November 15, 2015

Your idea of "normal" is based on your experiences as is mine. I'm guessing, without any way of knowing, that the clunk you experience in the two vehicles you mentioned are not comparable to the issue in my truck. The three other GM trucks I had with significant issues didn't have this specific problem. The 2008 Tundra with 90,000 miles I traded in on this Denali didn't have any "clunk" at all. A loaner truck from the dealer that I drove for two days didn't have this issue. A friend of mine with a 2002 GM half-ton and over 270,000 miles has zero "clunk".

I'm quite sure you would agree it as a serious quality defect if you experienced the same degree of issue. Anyway, to each his own. When I buy a $60m vehicle, regardless of who the manufacturer is, I expect it to be a quality product. This truck is the antithesis of a "quality product."

Tattooo · November 15, 2015

My 14 clunked from day one unil the recall ironed most of it out....

My 16 with the 8 speed is quiet & smooth as glass....no clunk

zert100 · November 16, 2015

The clunk is take-up of driveline slack in the differential and transmission output shaft. The amount of slack will vary from unit to unit. As the unit ages, the clunk will slowly become worse, however it is not a safety or driveability concern.

A variety of different vehicles will have this clunk. For example, both my Toyota Tacoma and my Ford E-350 work van have some type of clunk when you let off the gas.

The clunk can be compounded by axle wrap on certain vehicles, however the GM 1500 trucks do not themselves suffer from axle wrap.

The re-torque of the axle u-bolts is designed to confirm that axle wrap is not present.

Other than checking the u-bolts, the reason GM will not "fix" the problem is because technically there is nothing wrong. Driveline slack is a normal characteristic of a vehicle with a solid axle, divorced transmission and long driveshaft.

Driveline clunk can be improved with an aluminum driveshaft. Reducing the rotational mass of the driveshaft will help reduce the shock force.

Installation of a u-joint dampener will also.

mrbadwrench,

You appear to be very knowledgeable and make some good points. My biggest issue with this characteristic is that it appears that only certain vehicles exhibit this clunk. It seems to be a quality control issue that GM should be able to get their hands around.

Like I stated in the original post, I do understand that a certain amount of driveline "slop" is to be expected and frankly is needed for everything to mesh together. But for GM to say that any amount of clunking is normal does not seem like an appropriate way to deal with all of these cases.

I feel that a lot of the slop in my truck stems from the trans. I find it odd that I have absolutely no clunk in 1st gear. Do you have any idea why that may be? Also, what is a U bolt dampener. I didn't find anything with a quick google search.

Thanks.

Edited November 16, 2015 by zert100

fondupot · November 16, 2015

Trucks will vary depending on manufacturing tolerances. Which is why some experience a clunk worse than others, and why some dont even have the clunk.

If the current Gen 6 speeds are the same as the previous 4 speeds, you can remove the driveshaft from the back of the transmission/transfercase (make sure you engage your parking brake) and grease up the driveshaft yoke with axle grease. This will help the yoke move more freely.

Or you could try this....I remember reading about it back when I had my 2002. Never got around to doing it though.

Edited November 16, 2015 by fondupot

zert100 · November 16, 2015

Same problem on my 2015 Denali. Dealer has looked at it three times and service advisor has heard the loud "clunks". The dealer says it won't affect longevity and at 22m miles I can't refute that. Even if it doesn't affect longevity, it will definitely have a detrimental effect on resale. I emailed GM corporate and received three phone calls from a lady who was asking about my progress. I told her there was none. You may know by now that GM has issued a TSB telling dealers not to fix the problem and they will not be reimbursed if they do. I'm currently looking for a quality driveline service facility in the midwest hoping I can get it fixed. I have had five GM trucks and really only two without significant issues. Those who are thinking I should have learned my lesson before now have a valid point. Never again is all I can say.

Does yours only clunk on deceleration as well? I sent you a PM also

GMCguy78 · November 16, 2015

Same problem on my 2015 Denali. Dealer has looked at it three times and service advisor has heard the loud "clunks". The dealer says it won't affect longevity and at 22m miles I can't refute that. Even if it doesn't affect longevity, it will definitely have a detrimental effect on resale. I emailed GM corporate and received three phone calls from a lady who was asking about my progress. I told her there was none. You may know by now that GM has issued a TSB telling dealers not to fix the problem and they will not be reimbursed if they do. I'm currently looking for a quality driveline service facility in the midwest hoping I can get it fixed. I have had five GM trucks and really only two without significant issues. Those who are thinking I should have learned my lesson before now have a valid point. Never again is all I can say.

My 15' Denali has a clunk also, it seems to happen more in the lower gears and doesn't happen all the time, I just wrote it off as being a GM vehicle because every GM vehicle I have owned had some sort of clunk when driving and I have never had any problems.

Can you please keep me posted or your findings?

Glava2876 · November 16, 2015

So I've been dealing with this clunk on my '14 6.2 Sierra crew s/b. It is most noticeable when letting of the gas in second gear, but is also noticeable in higher gears to a lesser degree. It will clunk every time I let off the gas in second gear. The driveline will absolutely not clunk in first gear. The first time I took it in to the dealer the service manager rode with me and agreed that the clunk didn't seem normal and suspected the rear axle or driveshaft was the culprit. I was pleased that he appeared willing to dig into the problem and was hopeful for a resolution. Later that day I returned to pick up the truck and was told that they performed the TSB relating to torqueing the shackles and U bolts. I didn't expect that to fix the problem and it certainly didn't. I brought the truck back shortly after and they checked for any TCM updates to no avail and opened a case number with GM. After that they handed me the TSB stating that clunking is normal. Yesterday I went in for an oil change and told them I'm still not satisfied with the low speed clunky driveline of this truck and asked to drive one of their loaners to compare the low speed driving characteristics. The truck I drove had no noticeable clunking at all. This test drive only reinforced my belief that something in not right with mine. Of the 5 late model full size GM 4x4 vehicles I've owned none of them clunked like this 2014. An occasional clunk is to be expected especially in a 4WD and I could live with that, but this thing clunks all the time! This does not seem appropriate for what is otherwise a very nice driving and expensive vehicle. I am totally frustrated with how my dealer and or GM is handling this case. Has anyone had any luck getting this type of issue fixed? Any insight is appreciated.

I had the same thing in my 2015 Denali 6.2 A8. Not sure, but you probably have an A6, so it may not be the same, but it was exactly the same downshift 2nd to 1st. -it would slam from 2nd down to 1st pretty much every time I slowed down and it was real loud. It took my dealers service department almost a week, but they fixed it and it is perfect.

The tech at the dealer (Bill Rapp GMC, Tech Casey Jones)was not sending the Denali back until he was satisfied with it -man am I satisfied!

This transmission downshifts smooth as silk through all the gears ... and still goes though the gears like stink when I mash the pedal!

He did the following:

1) UPDATED TCM SOFTWARE, PERFORMED FAST LEARN ADAPTS AND ABBREVIATED COAST ADAPTIVE DOWNSHIFT ROUTINE AND VERIFIED REPAIR.

2) RECALL 15304 PROGRAMMED TRANSFER CASE SHIFT CONTROL MODULE. Prevents 4wd always engages when cold.

3) RECALL 15396 REPLACED TRANS INTERNAL HARNESS WITH INTEGRAL TFT SENSOR. Prevents harsh shift when starting in cold temperatures.

davidegl · November 17, 2015

Does yours only clunk on deceleration as well? I sent you a PM also

It clunks sometimes on deceleration when shifting up if that is understandable. IE You are accelerating and let up on the gas, trans shifts up and clunk happens. Not always and depends on speed...seems to be in the 20-30 mph area mostly.

GMC-AT · November 17, 2015

mine is the exact same as described above. Although.. since the I got the leaf spring clamps.. and the software update to the transfer case ...it's much better.

BenL · March 15, 2020

Has anyone been able to get this clunk figured out? I just bought a 14 Silverado and it clunks when downshifting mostly from 3rd gear down and sometimes it clunks when I let off the accelerator at low speeds.

GmGMCcarguy · July 8, 2020

I just bought a 2017 GMC Sierra 1500 Denali 6.2L Crew Cab Short Box.

I hear the clunking when accelerating and in reverse.

I have a 97 yukon, 245k SMOOTH AS BUTTER in whatever gear I have it. No clunks, clanks, driveline slack (That has to be made up) 42k truck and I am pissed,they told me its "Normal" I left the truck there and I am cancelling my loan, down payment of the check they still haven't cashed and they can keep the truck.

If my 97 runs and drives better than a 2017 Denali I am appalled at GM and their inability to fix the issue they created with a crap design. (Driveline slack, clunking is normal! What kind of vehicle world are we living.)

I know there is a class action lawsuit against GM in california regarding this issue and their 8 speed transmission. Time to get on that train.

Donstar · July 8, 2020

Welcome to this forum. Too bad about your experience with this truck. My '15 rides and drives beautifully. If you end up getting this truck back you will find lots of good advice on this forum.