Strange thunk from driver's floor?

[MattHarrell]

I've got this strange, meaty thunk that comes from the driver's floor when I go over bumps. It doesn't have to be a big bump - sometimes a dip in the road will do it. It also doesn't always happen. This appeared some time (a month?) after I switched from 29" to 31" tires but I don't know if that has anything to do with it. I can feel it in the driver's floor (pretty good through the accelerator pedal) but I don't think it's nearly that obvious to the passenger. Here's what I've done to try to find it

1. retighten all front and rear suspension bolts to specs
2. pull up and down on all underside parts
3. switch shocks to rancho 5000s (I was just waiting for an excuse to do this)
4. check radius arm bushings
5. check drivetrain u-bolts for excess play
6. check engine bay for anything that might shift around

and I also brought it in to a local NTB for an alignment and they checked the radius arm bushings, bearings, brake pads (for excess play), and engine mounts.

It doesn't seem to affect driveability and actually seems to lessen up when at highway speeds. I'm mostly worried since I don't want something to just fall off the truck. Anyone have any other ideas I should look for?

 

[hvac man]

Hey matt, I think it is the rad arm bushings. Even when they show no signs of wear, the added stress of the larger tires can make the factory rubber ones compress too much. I would suggest going with some poly bushings or just learning to live with it. All of these front ends do this to a certain extent. The poly bushings are just a little bit stronger and tend to give less play.

 

[unclemeat]

My 91 Sport had a factory recall for a front end problem. It sounds similar to your problem. I do not remember all the details, it was at least 8-years ago. You may want to research recalls, if your other actions do not provide a solution.