2nd Gen Non-Engine/Transmission Thumping under cab

[Mike129]

Hi, all.



My 1998 2500 (12 valve) 4x4 was working fine when, during a long trip towing my race car, it developed a thump under the cab. You can both hear the noise and feel the thump hitting the cab floor under the driver. This thump is evident an very slow speeds when the truck goes over a bump. I looked under the truck for a while but could not find anything that mioght be causing the problem. I then took it to a local shop (not the dealer). They have been looking at it for 3 days without any idea what is causing the "thump. "



This is driving be crazy. Any ideas?



Thanks!

--Mike

 

[pwerwagn]

Mine has a thump when then lower shock mount bolts get loose. I have to tighten them with the impact to make it go away.

hope that helps!

--Jeff

 

[Forrest Nearing]

a bit of a longshot, but I don't know how sensitive your ears and toes are...



my steering shaft has some play in it, and you can hear/feel it thumping at low speeds, especially getting moving as you're letting out the clutch... it's only been doing it for about 40k now. :-laf



Forrest

 

[Mike129]

Mine has a thump when then lower shock mount bolts get loose. I have to tighten them with the impact to make it go away.

hope that helps!

--Jeff

Thanks, Jeff!



Do you mean the front or rear shock mounts? (I sort of cheched the front mounts, but I only checked for looseness with a couple of smallish hand wrenches -- nothing like an impact wrench. )



--Mike

 

[Mike129]

a bit of a longshot, but I don't know how sensitive your ears and toes are...



my steering shaft has some play in it, and you can hear/feel it thumping at low speeds, especially getting moving as you're letting out the clutch... it's only been doing it for about 40k now. :-laf



Forrest

Hi, Forrest.



I have felt this in my steering column as well, but it isn't nearly as hard as the thump under the cab floor, so I think I have something else going on.



Thanks!

--Mike

 

[crabman]

Torque Specs

Mike 129,

Front

Upper nut=30 ft lbs

Lower Bolt=100 ft lbs

Upper shock bracket=55 ft lbs

Rear

Upper bolt=70 ft lbs

Lower bolt=100 ft lbs



crabman

 

[Mike129]

Thanks for the torque specs, crabman. I have the shop manual, but now I won't have to look them up!

 

[Mike129]

Okay, I had the guys at the shop the truck is now at check. It is not the lower shock mounts. In fact, they have had the entire front suspension off and on swaping parts in and out. They don't have a clue.



Man, this is very strange!

 

[Mike129]

Okay, after checking everything they can think of, the shop wants to try replacing the trailing arms off the front diff. They readily admit that this is just a guess on their part, and that they don't see anything obviously wrong with the ones I have, but they don't know what else to do, and it's going to cost a bit of $$ if I let them do it.



Any thoughts on whether this is a reasonable course of action? Can a bad trailing arm mount behave this way? I have to tell them what I want to do in the morning. (Maybe I should post this question under a different topic?)



Thanks for any help!



--Mike