Strange clunk

[AirSpeed]

I recently noticed a clunking sound coming from the front drivers side of my 72 GMC 4X4, it's a sharp sounding clunk, not dull, it sounds like a hard piece of steel hitting the frame, I can hear it when I'm going slow and hit a small bump or uneven road. I can feel it in the floorboard with my feet. I spent more than an hour under the truck tightening everything up. Nothing was loose, the tie rods ends are all good, I can't find anything that could make this sound. I jacked up the axle and tried to recreate the sound with no luck, then I jacked up the frame and tried moving everything around that way and can't find anything! The truck drives nice and smooth, there is no vibrations, everything seems fine! I opened the hood and checked out everything under there, everything is tight!
What could I possibly be overlooking? This is driving me nuts! Thanks for any suggestions!
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[Sammy]

I think your in the right area where you are looking. Jack the wheel off the ground and check the upper and lower ball joint for excess movement using a tire arm under the wheel for play. Since it is noticable when you hit a bump check the springs for a cracked coil and proper seating, spring pockets next. If you still haven't found it start checking the frame mount around the power steering box (they crack usually 4Wd), pitman arm, nut and that area. Something made that noise keep looking. Good Luck.

[dave2953]

I had the same issue with my truck and it ended up finding the nuts loose that hold the upper control arm to the frame (where the shims are) Not sure if this is the culprit but figured it was worth a look.

[AirSpeed]

Thanks for the suggestions. Yesterday I made a little remote Video camera, attached some magnets to it and connected it to the monitor on my stereo, I mounted it in a bunch of different areas hoping to see something moving around causing the sound, I aimed the camera at more than 20 different areas under the hood, around all the steering components, everywhere I could think of, the video is very clear so I thought I would find the clunk in no time, I still can't find the damn clunking sound! It's driving me insane! I was kinda neat to watch everything working though!
Everything is tight, this has been a nightmare, I have never had this much trouble identifying a sound coming from under a vehicle, guess I'm going to have to give in a take it to a shop! I can't understand where the damn sound is coming from! I tried to talk my wife into hanging under the truck and listen to where the sound is coming from while I drive around but no deal! she thinks it's dangerous! Silly girls!
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[vectorit]

Have you verified that the motor mounts are good, or the T-case frame mount on the passenger side of the frame?

What about the leaf spring shackles, and the bushings in the frame for them?
I have also had broken leafs that would make a solid clunk, so solid I felt it in the seat and in the steering wheel.

Have you verified that your hubs aren't sloppy? you can check by grabbing hold of the top half of the tire, then push/pull on the tire to see if you get slop or a clunk in the hub.

[1972RedNeck]

Originally Posted by dave2953

I had the same issue with my truck and it ended up finding the nuts loose that hold the upper control arm to the frame (where the shims are) Not sure if this is the culprit but figured it was worth a look.

I don't think stiff axle 4X4's have control arms.

Have you ever swapped motors? Is the pumpkin hitting the oil pan? Ball joints would be my thought.

[leddzepp]

check your front driveshaft
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[NGN]

Maybe upper or lower shock mounts.

[AirSpeed]

Thanks for all the replies! I took a wrench to every single nut and bolt under the truck, everything is tight. I checked the the entire front axel, leaf spring bushings, the front drive shaft is off, I took it off a few months ago to rebuild it. I checked the shock mounts, t case mounts, motor mounts, I cant find anything! It's the strangest thing! I did have the transmission rebuilt a month ago, I can't find anything lose on the bellhousing or anything they would have touched pulling it out or replacing it.
I feel it under my left foot on the floor, right near the the rear leafspring mount, the bushing is flat on the top so I aimed the camera at it and took it for a drive, it didn't move at all. I guess I'm going to have to start changing bushings, tie rod ends and every other part until it goes away! It really is bizzaro! Thanks again for the suggestions and any others that may come up! Aaron.
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[ChevLoRay]

I once bought a '76 Blazer 4WD. There was a stack of tickets in the glove box, all of which were about trying to resolve a clunk when starting or stopping. One of the fixes was to install a part-time kit in the NP203 transfer case. Another was to replace the torque convertor bolts (when replacing the starter drive, I found 2 of those bolts in the nose of the starter). Anyhow, the problem was the combination of 12-inch wide wheels, with 1200-15 Swamp Thing tires on them, and ultimately was fixed by lubricating the slip yoke on the front driveshaft. I also replaced the wheels with a set of 8-inch wide wheels and then put a set of 31-11.50 Wrangler radials.

All because of a lack of lubrication.......