A way out there idea. Were the trunions welded in perfect phase in the drive shaft tube? I think it could easily be something to do with the drive shaft.

RIP

As promised, update on where we are at with this fun issue:

Picked up a new to us American at the end of the racing season, put our motor and trans in it but unfortunately didn't have time to get it out.

Took everything off the "broken" car and just yesterday blasted off the powdercoating down to the bare chassis hoping to find a crack or break. Did not find anything. Weighing our options at this point..

quote:

Originally posted by SC4400:
A way out there idea. Were the trunions welded in perfect phase in the drive shaft tube? I think it could easily be something to do with the drive shaft.

RIP

Hopefully already covered...Very possible it could be universal binding under acceleration and deccel.. in 1978 new crew cab had a vibration the dealer could not find. Years later I figured out not only did they miss the mid shaft timing but also rear shaft was not in phase when welded. Just a couple of years ago, lowered wife’s Silverado and picked up a bad vibration.. yep universal bind. Bought 7deg shims and fixed it...

Brake Rotor ??? Maybe cracked. It’s no fun chasing issues —- spending money with no results.

Take small bottle jack and try jacking up between frame rails next to each upright to see if something moves found an upright cracked in my old car that way

Have you got weight in the nose ?, check the toe-in? ,some dragsters like nose weight . And toe'd neutral or out will wonder and shake like crazy

This may have already been suggested in the earlier replies which I didn’t read all of them, but have you checked the threads on the 4 link heim joints to see if you may have pulled the thread loose. I read about a very similar problem that happened to well known super stock racer and the only way he found it was using a go pro at the rear end. You could see the 4 link bar expanding and retracting under load but otherwise it was oblivious to the eye. Just a thought