Clunk Under Drivers Floor Pan

botomgun · January 6, 2010

Before you ask, I did use the search feature!

I have a clunk that I feel under the drivers side floor pan that just started when it got really cold out.

Truck: 2003 Silverado 2500HD 4x4 6.0

There was no advanced warning before this started happening. I really only feel it when going from drive to reverse and reverse to drive. It is immediate after I start moving the truck in either direction and then I do not notice it afterwards. I believe that the torsion bar bushing is loose at the crossmember as I can move it around by hand and it makes a similar clunk. It sounds similar to the sound in the cab with the door shut but I am not applying the same amount of force by hand as I the truck does during acceleration. Should I see enough movement in the torsion bars under load to cause this to happen? In other words does the direction of the vehicle make a difference on the direction of force applied to the torsion bar? Maybe replacing the bushing in accordance with #PIT3459A: Torsion Bar Crossmember Bushing Replacement would help?

Searching the forums leads me to believe that it could also be the body mount, but I wouldn't think I could feel that on a level road (not that we have that many of them here). Occasionally when I hit a good patch of bumps, I feel/hear the knocking sound, too. #06-08-61-003D: Underbody Pop or Clunk Type Noise While Turning or Driving on Uneven Road Surfaces (Install Body Mount Insulator) addresses replacement of this bushing. But seeing (hearing?) that the sound is in the same location leads me to believe that this is not the problem..... yet.

Is it possible that the cold weather makes either problem more noticable? Perhaps the bushings shrink a lilttle in the cold and the problem is more pronounced. I do not believe this to be the slip joint problem that Chevy is known for. I had that in my Tahoe and know how that one feels.

Another observation is that I do not seem to feel it when the truck is in 4H. Hopefully this does not turn in to a transfer case problem.

Any advice would be greatly appreciated. I plan to put it on a lift possibly this weekend a poke around to see if anything jumps out as another potential culprit.

Thanks,

Duane

coltbean · January 6, 2010

I had this exact problem. There is a vent under the driver seat that moves air to the rear passengers. I had a bolt that rolled into this vent and it would roll back and forth when I started forward or reversed.

botomgun · January 7, 2010

I had this exact problem. There is a vent under the driver seat that moves air to the rear passengers. I had a bolt that rolled into this vent and it would roll back and forth when I started forward or reversed.

Thanks for the reply, but this is a much heavier clunk than a bolt. After driving it today, I am noticing that it might be more centered under the cab and not just under the drivers seat. Also, contrary to what I stated earlier, I did notice it when in 4H. Hopefully I'll get it up on the lift this weekend and get a better idea of what it might be.

Would still appreciate any assistance and/or guidance that can be provided.

Duane

botomgun · January 10, 2010

Well, I put the truck on the lift today. Poked around for a while and found that the mounting bolts for the transfer case were slightly loose. I guess it was enough to cause the clunk since after tightening the problem is no longer present. Due to the fine roads here in RI, I think I'll check them periodically to ensure they stay tight.