I have an annoying buzz in the rear end. I have changed all the U joints, using AC delco made in the USA joints, changed all of the rubber suspension components, greased the half shafts, dissasembled the rear hubs and greased the bearings and everything else I can think of. At 65 or so, I get a buzz that shakes the mirrors, shakes my butt in the seat, etc This is high freq. I got under the rear of the car today and put a dial indicator on the half shafts and found that there was .006 on both at the differential end, and almost nothing at the hub end. then I happened to deflect the center of the shaft with the indicator on it, the damn thing bends in the middle about .0010. This car only has 54,000 on it and I can't imaging these shafts being worn completely out..

Anybody got any clue about how much flex in these shafts is o.k. Is this why follks want to go with CV joints, etc. BTW, I am running a stock R-180, with a 350 chev and a T-5. I also noticed that the passenger side yolk at the differential has some play too...Car is nice and smooth up to 65.

Could it be a bad wheel bearing, or wheel out of balance. Lump in a tyre.?

new tires, balanced twice, wheel bearings are original, but were disassembled, cleaned, regreased, smooth as silk. even the seals were still good.

What is the condition of your transmission and diff mounts?

Probably a pinion angle issue. This happens a lot with V8 swaps. Over at www.hybridz.org there are instructions on making your own laser measuring tools and getting the angles right.

A simpler fix would be tire balance. I know you said you had it done twice, but if you have nice rims or a dumb mechanic they might only put the weights on the inside. That is a static balance and it's not the same as a dynamic balance with weights on both sides.

I've read that thread, and will check the pinion angle. Since I replaced all of the suspension rubber, with new stock rubber I need to have the front and rear aligned anyway, I'll have all 4 balanced again,, with special attention paid. And yes, it does have nice 15 inch billet centerlines on it.

It was the pinion angle. I used the lasers on it and it was out 7/8ths of a inch. All I had to do was rotate the nose of the diff down by modifying the Ron Tyler mount a little. Smooth as silk up to 100 now. Thanks for the suggestion, feel good about yourself for the rest of the day!!

Glad to help!