Topic: '66 289 C4 rear end/transmission noise

[socalgt]

When the car is cold, there is a "clunk" coming from what sounds like the rear end/driveshaft area.  It only occurs when the downshift occurs from second to first, no other time.  It disappears when the car is warmed up.  I used to think it was the transmission until I isolated the noise to behind me as I drove.  Any thoughts?.....I'll check the u-joints at the rear end and transmission to see if there is any play.  Curious why the noise would only occur until the car is warmed up.

Thanks in advance for any suggestions....

[Hipo giddyup]

 I think the sound you are referring to is wear (slop) in the ring and pinion. I have this same issue with my 66' C4 coupe and have been told it is identified when going into reverse or drive. I would assume it is less noticeable once the gear oil circulates and thins? I am currently looking to rebuild my center this spring since the rear has appr. 200+ original miles on it. No other issues thank fully. 

[socalgt]

I noticed a small amount of play in the ujoints and thought it could be causing the "clunk"....I'll replace them and see if that eliminates the noise.

[J_Speegle]

Since this could be produced by a number of things your either going to have to hunt it down and or go through the process of elimination.

If you really think its behind you (sound can travel and resonate around allot in this older unibody cars) check that the rearend is secure, U joints as you have and see if the clunk can be reproduced by alternating turning the rear wheels and the u joints for a satrt