Thumping noise in floor when coming to a stop

[combatmech]

Howdy all,
Over the past month or so, i have noticed a "thump" under my left foot when I apply the brakes or after I let off the go pedal. It's has become more frequent over the past few days At first I thought it was my high-tech anti-theft device moving around the floor.
Checked brake fluid, it's good. All brake components are secure and do not show signs of leakage.
Looking through the -20, #47 in the suspension T/S tree, "excessive noise during operation" is the closest thing to what the truck is doing. All other systems are working as advertised.
Looked at all the items on the checklist and suspect two things. The drivers side shock, upper mount rubber ( on the shock itself ) is dry-rotted like crazy. I also suspect the body mount that is right under the drivers floor. I took a look at the sheet metal and didnt find anything noteworthy.
Just wanted to see if I have over looked anything, any second opinions or if anyone else has encountered this.
Thanks in advance

 

[doghead]

Inspect your motor mounts and transfercase mount.

 

[combatmech]

Wilco... Thanks Doghead!! My last truck did it REAL bad during acceleration. The thump is more felt than heard and seems to be isolated in that one spot. I do have a 4" X 5" hole in the floor on the most outboard side and forward of the door frame on the drivers side ( where water collects from leaky floor vents ) That part of the sheet metal goes right where the body mount is....I'll look around more though

 

[Woodsman]

Inspect your motor mounts and transfer case mount.

That would be my guess also. It's certainly what it sounds like. If you check it out and confirm it's the mounts I wonder how much better the urethane mounts would be? That might be the direction I would go with.

 

[combatmech]

Looked at the engine mounts, X-fer case mounts transmission mounts and didnt really notice anything odd. It still does it, just not as bad. At some point when I'm not so busy, I'll look into it more. I have a long list of things to do. Shocks, oil change, tire rotation......

 

[cucv1833]

Looked at the engine mounts, X-fer case mounts transmission mounts and didnt really notice anything odd. It still does it, just not as bad. At some point when I'm not so busy, I'll look into it more. I have a long list of things to do. Shocks, oil change, tire rotation......

Keep us posted mines doing the same thing i looked over it slightly and didnt see anything out the ordinary. Mine just started to thump under the driver side floor pan when i slow down to 15 mph or less. It doesnt do it always only 25% of the time. I will check my mounts real good when i get time.

 

[67_C-30]

Mine does it on acceleration, and I have pretty much isolated it to the transfer case linkages. I feel it in 4X4 shifter if I put my hand on when I acelerate from a stop. I don't know exactly what is causing the thumping or what is making contact, but I'm pretty sure that's where its coming from.

 

[Cucvnut]

if you don't fix motor mounts they can crack your fly wheel from stress

 

[Woodsman]

There is another thread running now with a similar problem description. Both seem to be related as to the symptoms.

 

[overkill375]

this problem can often be the upper, rear spring bushings on the front springs. This is the bushing that goes thru the frame and is often neglected.

 

[superburban]

Really bad ball joints on the front axle will cause a clunk noise consistant with what you describe.

 

[camogriz]

I agree with overkill that you should check the rear mount of the left front spring. The bushings in there seem to wear out pretty readily. Check the spring bushing and it's mount. The mount moves with the motion and suspension travel of the vehicle, which is what you seem to have described.

 

[combatmech]

I drove the truck all day... and it's pretty much stopped. ( for now ) I'm sure it'll be back. I'll check the springs as time permits. Thanks for all the inputs guys!!!

 

[combatmech]

Update.... Changed all four shocks about a week ago, found that the drivers side rear upper shock bolt had been working it's way loose. Good thing the back shocks came with new upper bolts!! No more thumping noise!!