Clunk/thud while accelerating/slowing down

[zert100]

I did speak with someone at a local driveline shop. Unfortunately he didn't have any silver bullet ideas as to what could be causing the noise. He did say that the slip yoke problem is mostly a thing of the past because GM went to a Borg Warner transfer case in '08 and they haven't seen issues with the yoke on the new trucks. He did say that I could check with a shop down the street that has a "chassis ear" to try and isolate the noise. I am at a loss as to what the culprit is. It is hard to believe in the age of social media that someone hasn't figured out how to fix this seemingly common issue. there has to be thousands of trucks out there with this problem. The only thing the dealer did was re torque the shackles per a TSB and show me the other TSB that states clunking is a normal characteristic. I could, and have, lived with a little clunking now and then in my past trucks, but this thing clunks loudly and consistently ALL of the time!!!

[nadrojcote]

Any down side to running the shackles / leaf spring clamps if there is no drive line issues?

stiffens the ride a bit, some prefer it, some don't.

[stevev]

on our factory setup, is the very bottom leaf the overload spring? Because I did a google search and some other forums were talking about these leaf clamps to reduce axle wrap, but they said don't clamp around the overload spring because it would ride too stiff. They said clamp the leafs above the overload spring.

[Jordan18]

I wonder if this actually happens with max tow-optioned trucks, as the leafs are beefier/stiffer from factory than normal (I don't recall if there are extra leafs over non-max tow trucks).

 

Looks like all of you guys have 14' non-NHT

 

I did speak with someone at a local driveline shop. Unfortunately he didn't have any silver bullet ideas as to what could be causing the noise. He did say that the slip yoke problem is mostly a thing of the past because GM went to a Borg Warner transfer case in '08 and they haven't seen issues with the yoke on the new trucks. He did say that I could check with a shop down the street that has a "chassis ear" to try and isolate the noise. I am at a loss as to what the culprit is. It is hard to believe in the age of social media that someone hasn't figured out how to fix this seemingly common issue. there has to be thousands of trucks out there with this problem. The only thing the dealer did was re torque the shackles per a TSB and show me the other TSB that states clunking is a normal characteristic. I could, and have, lived with a little clunking now and then in my past trucks, but this thing clunks loudly and consistently ALL of the time!!!

 

PS

 

I just seen zert's post and he has a max tow but it's a 14'. With the 15's and the 8 speed, it has always been considered the culprit for clunking and not the leafs.

 

I have not heard any noises like this yet but I would include this thread as place to start.

[bdbake01]

So I decided to give the clamping a trial run. For ~$30, seemed like a worthy experience.

 

I first checked the axle strap nuts, and I gotta say, they were laughably loose. Like, seriously. A couple seemed almost hand tight. On the driver's side I set my wrench to 50 ft/lb, ALL 4 TURNED. Wow. I got almost 2 full rounds on the driver's side, all 4 nuts, before I hit 78. Passenger's side, I set the wrench at 35 ftl/lbs and 2 of the four still turned!!! I'm guessing my nuts left the factory between 30 and 40ish ft/lbs. (please insert joke as you wish) Kinda surprised the axle hadn't rotated in the cup.

 

First, tighten the strap nuts. I'd recommend you do the same, free fix and can't hurt.

 

Next, I added two sets of clamps, both fore and aft of the axle. This brought the "overload" spring (which, it isn't actually what I would call an overload) into contact with the second leaf. This actually compressed the springs into a liiiitle bit of a W shape since the leafs have a tiny spacer in between them, but I did not put one in where my new clamps are. Other than the possibility for a bit of noise (maybe when cold out?) I don't see it causing a big problem. Torqued the nuts to 78 as well, which did deform the plates a bit. Superior Automotive pieces from Advance Auto.

 

Took her out for a ~50 mi spin on familiar roads. Like others have said, the rear is a bit stiffer. Definitely a bit more excitable on breaks in pavement. We all know the shocks aren't overly stiff, and that's even more evident now. Left to this setup, I think I'd prefer stiffer shocks out back to match the now higher spring rate. This isn't a huge deal, and honestly I only noticed because I was really looking for it and I'm familiar with the ride. Wife didn't notice anything.

 

One thing I DID notice, which I wasn't expecting, is the front end seems to float around a lot more now. I'm taking a long trip today, I'll watch it more, but it definitely seemed to float around more than I recall. Very odd. Again, stiffer shocks would help this.

 

As for behavior, my tranny has always seemed to shift fine. I can put it into virtually any gear I want at any time just using the skinny pedal. Maybe it's my comfort with GM vehicles, but it just worked for me. I like being able to put the tranny where I want just using the gas, and that's always worked well here. On occasion I have noticed it hunting around or shifting up/down a biiit too soon, but it was ALWAYS during odd periods. I was doing something that the computer couldn't possibly have predicted, odd pavement, etc. None of that has changed, and it may shift a bit smoother. No doubt, the tranny seems to be bolted to the rear much more firmly now. But not harsh at all. Probably a lot less harsh actually.

 

There are two spots in this trip that I can normally make the clunk/slap noise, and I wasn't able to do that yesterday. Has it fixed the clunk? Well...not enough evidence yet, time will tell. But I couldn't make it do it.

 

Ultimately, jury is out. I like the planted feel in the back, smoothness is nice, I'll update after more miles.

 

Oh, and the rear dropped about 1/4" after clamping. Yes, I measured.

[sugarjohnson]

Nice write up....

[Sooperdave]

I showed this to fondupot before, but I dont think I posted it. This is a good video to demonstrate whats causing the clunk, it shows the yoke popping in and out with axle wrap. It is an extreme case, but perfect for giving an idea of whats going on.

 

Crap!! That is something nasty! This thread has me thinking of adding the clamps. Are the springs for 14's with Max Tow actually different from rest? I was under the assumption it was a stiffer spring?

[JimmyVal]

So I decided to give the clamping a trial run. For ~$30, seemed like a worthy experience.

 

I first checked the axle strap nuts, and I gotta say, they were laughably loose. Like, seriously. A couple seemed almost hand tight. On the driver's side I set my wrench to 50 ft/lb, ALL 4 TURNED. Wow. I got almost 2 full rounds on the driver's side, all 4 nuts, before I hit 78. Passenger's side, I set the wrench at 35 ftl/lbs and 2 of the four still turned!!! I'm guessing my nuts left the factory between 30 and 40ish ft/lbs. (please insert joke as you wish) Kinda surprised the axle hadn't rotated in the cup.

 

First, tighten the strap nuts. I'd recommend you do the same, free fix and can't hurt.

 

Next, I added two sets of clamps, both fore and aft of the axle. This brought the "overload" spring (which, it isn't actually what I would call an overload) into contact with the second leaf. This actually compressed the springs into a liiiitle bit of a W shape since the leafs have a tiny spacer in between them, but I did not put one in where my new clamps are. Other than the possibility for a bit of noise (maybe when cold out?) I don't see it causing a big problem. Torqued the nuts to 78 as well, which did deform the plates a bit. Superior Automotive pieces from Advance Auto.

 

Took her out for a ~50 mi spin on familiar roads. Like others have said, the rear is a bit stiffer. Definitely a bit more excitable on breaks in pavement. We all know the shocks aren't overly stiff, and that's even more evident now. Left to this setup, I think I'd prefer stiffer shocks out back to match the now higher spring rate. This isn't a huge deal, and honestly I only noticed because I was really looking for it and I'm familiar with the ride. Wife didn't notice anything.

 

One thing I DID notice, which I wasn't expecting, is the front end seems to float around a lot more now. I'm taking a long trip today, I'll watch it more, but it definitely seemed to float around more than I recall. Very odd. Again, stiffer shocks would help this.

 

As for behavior, my tranny has always seemed to shift fine. I can put it into virtually any gear I want at any time just using the skinny pedal. Maybe it's my comfort with GM vehicles, but it just worked for me. I like being able to put the tranny where I want just using the gas, and that's always worked well here. On occasion I have noticed it hunting around or shifting up/down a biiit too soon, but it was ALWAYS during odd periods. I was doing something that the computer couldn't possibly have predicted, odd pavement, etc. None of that has changed, and it may shift a bit smoother. No doubt, the tranny seems to be bolted to the rear much more firmly now. But not harsh at all. Probably a lot less harsh actually.

 

There are two spots in this trip that I can normally make the clunk/slap noise, and I wasn't able to do that yesterday. Has it fixed the clunk? Well...not enough evidence yet, time will tell. But I couldn't make it do it.

 

Ultimately, jury is out. I like the planted feel in the back, smoothness is nice, I'll update after more miles.

 

Oh, and the rear dropped about 1/4" after clamping. Yes, I measured.

I found the exact same thing with the axle strap nuts. I was shocked at how loose they were vs the torque specs quoted here. I set my wrench at 40 ft lbs and 3 out of 4 spun on the passenger side, all 4 on the drivers side. I had to revisit this thread to confirm the spec I thought I read here.

 

I tightened the nuts to spec (78 ft lbs), and took the truck for a 75 mile ride. My issue has been a clunk while downshifting from 3rd to second and then accelerating while the tranny was in the process of downshifting (if that makes sense). I can say the issue in my case is gone. In fact the tranny shifting in general seemed smoother and it got to the point where I stopped thinking about the problem as nothing noticeable was happening. So far, my problem is gone.

 

Thanks to all for bringing this issue to our attention.

[nadrojcote]

I should give an update too. I removed my clamps and tightened my u-bolts a week ago and have noticed a couple times that my truck has made the clunk/thud, but its not nearly as bad as before. I'm going to keep testing and if it bothers me I have the clamps on stand by.

[sugarjohnson]

Well I am trying an entirely new method later this week with a whole new approach. I'll report back and leave it as a surprise.

[iCryWheniGoPoop]

I tightened mine to 78 ft lbs and eliminated most of my noise and like everybody else, mine turned 2 full turns before meeting correct torque specs. Curiosity got to me so I started looking up specs on the actual torque for that size spring bolt and found it to be capable of at least 100ft lbs so I torqued mine to 90 and eliminated all my leaf spring noise. I'm not suggesting this, I'm just telling you what I did. I also found some good reading for you guys if you want to check this out.

http://www.rnhspring.com/Ubolts.html

 

Oh and FYI... Mine was making a lot of noise since I'm putting mine through the wringer testing and tuning.

[zert100]

Well I am trying an entirely new method later this week with a whole new approach. I'll report back and leave it as a surprise.

Looking forward to your results. I hope its different than mine which has been to turn the radio up louder!! Seriously though, the more I drive this thing the more I think this clunking is mostly related to the way this transmission works.

 

How many of you are having the same clunking that I and sugarjohnson have? It is most noticeable in 2nd and 3rd gear when letting of the gas. I don't get much clunking when getting back on the throttle in those gears, mostly just when letting off.

[nadrojcote]

Looking forward to your results. I hope its different than mine which has been to turn the radio up louder!! Seriously though, the more I drive this thing the more I think this clunking is mostly related to the way this transmission works.

 

How many of you are having the same clunking that I and sugarjohnson have? It is most noticeable in 2nd and 3rd gear when letting of the gas. I don't get much clunking when getting back on the throttle in those gears, mostly just when letting off.

sounds to me like it could be your rebound spring slapping against the other springs. Have you tried tightening your u-bolts?

[zert100]

sounds to me like it could be your rebound spring slapping against the other springs. Have you tried tightening your u-bolts?

Yes, I checked them last week. They were nice and tight. I think the dealer checked them as well. Thanks.

[sugarjohnson]

sounds to me like it could be your rebound spring slapping against the other springs. Have you tried tightening your u-bolts?

Yep I have tightened mine u-bolts down x 2 with no change. I also tried the clamps which helped but did not solve it. The description above is spot on. I can replicate it very time. Driving through subdivision 1-3. Accelerate light and then let of gas=clunk. Almost always when letting off never getting back on gas. I had it looked at long ago they said "no problems" imagine that.

 

I have custom tune now and no difference. He even verified that he did not really change shift pressures etc. Its the same with the tune as without. I will say the the truck is much quicker now!