To All With Gm Step Bars On Their Gmt900's

VMax2007 · April 4, 2008

I and my dealer spent all winter (3 different attempts) trying to find my "Mystery Clunk" in my truck. I went back and forth thinking it was suspension/shocks to thinking it was something loose in the engine bay. What made it even more strange was it was temperature dependant. It would only do it when it was below 30 degrees F or so and got noticeably worse when it was below 10 degrees F. It did it mostly over bumps, but also during deceleration too sometimes. On cold mornings, I would drive out of my warm (insulated) garage and it would be silent, but after driving several miles in the cold, it would start doing it. Very strange!!!

On Tuesday, I brought it back to the dealer for it's semi-annual Auto Butler treatment and since it had snowed 6 inches here on MOnday, the roads were a little rough and it was about 25 degrees Tuesday morning, so I asked them to try to find it once again. They happily obliged. This time they mounted wireless mics on the shock towers and in a few other places to try and find it. They quickly ruled out the shocks and any other suspension component. Then they put it back on the rack and found this and sure enough, there is a TSB for it. I was skeptical as hell and had zero confidence this was the cause since it would seem to me that this would cause a steel-on-steel squeek/creak, not a "clunk". I am happy to report I was wrong. My truck is now silent, even on the cold mornings we had this week and on the one specific off-ramp where it did it the worst.

If you have the GM Accessories Step Assist bars ("Nerf bars"), read this:

Service Information

Document ID: 2072529

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#08-08-61-003: Modification Procedure for Assist Step Bracket Installation Due to Underbody Interference - (Feb 26, 2008)

Subject: Modification Procedure for Assist Step Bracket Installation Due to Underbody Interference

Models:

2007-2008 Chevrolet Silverado

2007-2008 GMC Sierra

Modification to the right hand second assist step bracket may be necessary for installation due to interference to the underbody.

Modify assist step bracket to create additional clearance between the assist step bracket and the cross-sill bracket. Modify the bracket following the dimensions in the illustration above.

Follow the manufacturer’s specifications for repainting. For the proper refinish materials, refer to the 2008 GMWI5406 GM Globally Approved Refinish Materials information. The refinish materials information is now online at the GMGOODWRENCH WEB SITE*. Printed books have been discontinued. To access the site, follow these steps:

• Go to www.gmgoodwrench.com.

• Click on For Body Shops & Services link at the bottom of the page.

• Click on GM Technical Repair Information

• Click on Paint Shop tab.

• Select the applicable downloadable link of the GM Approved Refinish Materials Guide.

• *In Canada, the 2008 GM Approved Refinish Materials information is also available on the GM infoNET under the Service and Body tab.

Warranty Information

For vehicles repaired under warranty, use:

Labor Operation

Description

Labor Time

B9847*

Step, Assist Bracket Modify-Right

0.5 hr

*This labor operation number is for bulletin use only. This number will not be published in the Labor Time Guide.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information.

WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION

Griffin86 · April 4, 2008

Thanks for the heads up!

GeoHawk · April 4, 2008

Thanks Jeff. I haven't heard anything from my steps over the winter, but I'll know where to look if it pops up.

tobias · January 6, 2009

Maybe it's CSK?

Darkanion · January 6, 2009

I bet there's a TSB for it somewhere.. They're just hiding it from you, because they don't want to do the work!

tobias · January 6, 2009

I bet there's a TSB for it somewhere.. They're just hiding it from you, because they don't want to do the work!

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Darkanion · January 6, 2009

You'd think GM would've fixed this by now and issued a recall and replaced them all, already! This is such a big deal for their customers!!

alaska511 · January 6, 2009

Glad you finally got it resolved, Jeff.

I am sure this was my issue with the cold weather as well.

VMax2007 · January 6, 2009

Glad you finally got it resolved, Jeff.

I am sure this was my issue with the cold weather as well.

Yeah....I wish!

MS3DALE · January 6, 2009

Maybe it's CSK?

Reverendbiker · January 6, 2009

Interesting. I installed a set of Westin bars on my truck and had exactly the same problem. Since I didn't experience the noise before installing the bars I was pretty sure where to find the problem, but it would have been a real head-scratcher if the bars had been on the truck at delivery. To tell the truth, the nerf bars wouldn't have been the first place I would have looked for what sounded like a driveline "clunk." I slid under the truck, made a small adjustment at the forward mounting point, and the problem was solved. Glad you got it resolved; mystery noises can drive ya crazy.

VMax2007 · January 6, 2009

Interesting. I installed a set of Westin bars on my truck and had exactly the same problem. Since I didn't experience the noise before installing the bars I was pretty sure where to find the problem, but it would have been a real head-scratcher if the bars had been on the truck at delivery. To tell the truth, the nerf bars wouldn't have been the first place I would have looked for what sounded like a driveline "clunk." I slid under the truck, made a small adjustment at the forward mounting point, and the problem was solved. Glad you got it resolved; mystery noises can drive ya crazy.

I didn't. This is an old thread. Still chasing it, and I am out of clues.

Huntervh · January 6, 2009

I know this is an old thread, and since you have not found the culprit maybe this will help.

Remember before Christmas when we had the extreme cold weather(-10 -20F) My truck started clunking while sitting on highway 55 in Plymouth, hit the gas - clunk, hit the brake - clunk.

Drove it straight to Walser in Bloomington, they had it sitting in the shop for a few hours before the mechanic had a chance to look at it. Of course he could not replicate. Went and picked it up - no clunking! Get half way home, sitting in rush hour traffic, hit the gas - clunk, hit the brake - clunk.

Went back to Walser the next morning, clunking all the way. Asked the service manager to go for a ride along, car sat in the shop for 15-20 minutes, took it out and NO FREAKING CLUNK! Drove around for about 10 minutes and it started up. Service Manager started to hear it, took it back to the shop, the Manager jumped on the back bumper and CLUNK. Come to find out it is the leaf springs expanding and constricting in the cold weather. Aside from not driving the truck in -10F temps, I am not sure what can be done.

alaska511 · January 6, 2009

Glad you finally got it resolved, Jeff.

I am sure this was my issue with the cold weather as well.

Yeah....I wish!

SHIT! I got burned by the old thread monster, sorry Jeff!

VMax2007 · January 6, 2009

I know this is an old thread, and since you have not found the culprit maybe this will help.

Remember before Christmas when we had the extreme cold weather(-10 -20F) My truck started clunking while sitting on highway 55 in Plymouth, hit the gas - clunk, hit the brake - clunk.

Drove it straight to Walser in Bloomington, they had it sitting in the shop for a few hours before the mechanic had a chance to look at it. Of course he could not replicate. Went and picked it up - no clunking! Get half way home, sitting in rush hour traffic, hit the gas - clunk, hit the brake - clunk.

Went back to Walser the next morning, clunking all the way. Asked the service manager to go for a ride along, car sat in the shop for 15-20 minutes, took it out and NO FREAKING CLUNK! Drove around for about 10 minutes and it started up. Service Manager started to hear it, took it back to the shop, the Manager jumped on the back bumper and CLUNK. Come to find out it is the leaf springs expanding and constricting in the cold weather. Aside from not driving the truck in -10F temps, I am not sure what can be done.

Thanks, but it is definitely NOT coming from the rear of the truck. It is coming from either the front clip area or most likely in the engine compartment. It is weird, because it happens mostly over bumps, but it is not necessarily timed to the frequency of the bumps, it is more of a resonance type of clunk. Sometimes you can hear it while decelerating on off ramps with or without braking (it's NOT the brakes) and hitting small ruts or bumps. It begins at about 20 degs F and gets worse the colder it is. It is really bad when below 5 degrees or so. the best way for me to describe the sound would be if you put a golf ball in a small wooden box and shook it. I am guessing it is some type of plastic component hitting the frame/chassis someplace. It does not sound like metal on metal.