Ok...I have searched every thread on clutch chatter. Have a bad problem. Here's the set-up...ran an original 216 with T5, 3" blocks, original leaf springs, junk yard drive shaft, Chevy 10 bolt, original clutch and flywheel in a '48 Chevy truck for a year...no probs!!! Changed in Dec to a 283, new flywheel, new pressure plate, same disc, new TO bearing and arm, same linkage, same T5, new mounts...and I have chatter. Checked...pinion angle...adjusted today...no change, checked clutch and flywheel...no obvious prob...checked all bolts...new trans mount...changed engine mounts...no change! Replacement T5! Had second pair of eyes today...nothing obvious! Have NOT changed clutch spring, or pulled new flywheel off to have surfaced! Have NOT installed anti-chatter rods on trans! Really bad chatter in reverse..mild in 1st! Goes away if I can get to the point of letting the clutch out all the way.! By the way...have an oil leak near the back of the manifold...runs down the bellhousing. But after removing the trans and clutch...no oil on inside of bellhousing. Clutch was dry!! Today, we replaced the rear trans mount, made sure everything was tight, adjusted the pinion angle some.