What's that loud thud behind driver in lower corner of cab.

[Gregski]

seems like any time I go over some speed bumps a bit faster than I should I hear a loud thud behind me, behind my left elbow, sounds like somebody left a large hammer behind the bench seat (yes I checked, there is no hammer behind the bench seat, lol)

my truck bed is empty, cab is clean, I wiggle the driver side door and don't hear anything loose in there, it sort of seems like it may be under the cab right behind the cab, I honestly don't know I looked under the truck nothing seems lose

any ideas fellers?


1974 GMC 1500 350 manual 2WD

[J Knight]

Fuel tank hitting the bottom of the cab maybe due to a broken or rotted strap.

[Gregski]

Originally Posted by J Knight

Fuel tank hitting the bottom of the cab maybe due to a broken or rotted strap.

Oh, should have mentioned, only have one fuel tank on the opposite side ie the passenger side, good point though, so don't think that's it

[homemade87]

May be the cab body mounts. Those things will make noise if they are wore out. The frame and body will move around a lot. Mine were like power when I replaced them.

[donut]

x2, mine would clunk bad until replaced.

[tucsonjwt]

My guess is loose exhaust/exhaust hanger.

[Robert Crandall]

Mine does it, and I found the problem to be as described in posts #4 and #5. It is on the list to be fixed.

[86c20]

i got something like that found it was some little tool in the cab corner something to check. but my money would be cab mounts.

[homemade87]

If your cab and core support mounts have never been replaced I would suggest replacing them even if this is not the source of your noise. My cab had a miss alignment to the bed. Thought the frame was out of wack . It was the body mounts . It also rides so much better and everything lines up now.

[Rich84]

Check the condition of the rear leafs also..Mine were broken at the eye. It wasn't really noticeable until I unbolted them and they fell out..LOL

[Super_Dave]

I have the exact same sound in my '74 C20 when I go around right hand corners. Thought it was behind the seat too but my cab is empty. Got to thinking it might be cab mounts, loose exhaust hanger, something... but it's only when I turn to the right.

Guess I have an under body experience coming up...

[midnight rambler]

in mine it was a beer bottle

[motornut]

Shock mount?

[Gregski]

not in the location I expected since I found this Sea horse looking pin in front of the driver side door by the top hinge, instead of the back of the door, but we may have our first suspect, it's a pretty heavy piece of metal so maybe this was the thud, I will drive around a bit and report back to you all

[greg64]

Greg, the seahorse is a broken piece of the spring that's part of the door hinge assembly. My body mounts were shot too, in fact the body was sitting on the chassis.

[Your41Plague12]

Mine did the same thing and it was the body mounts and braces. They were rusted out badly, and by the time I swapped cabs, the only thing holding my cab to my frame was my steering and shift linkage.

[Gregski]

Donkey Kong, I guess it wasn't the sea horse (door hinge spring) as the sound is still there, seems like the offending piece slides forward when I brake and slides back when I accelerate

[tucsonjwt]

My 76 had some kind of weight connected to the shoulder harness (I think) which would make that noise. I don't hear that on my 83. Maybe Keith can explain how that works.

[Gregski]

Originally Posted by tucsonjwt

My 76 had some kind of weight connected to the shoulder harness (I think) which would make that noise. I don't hear that on my 83. Maybe Keith can explain how that works.

interesting but I only have the lap belts in this '74