Rear End "Clunk"?

[C3RVETTE]

Rear End "Clunk"!
When starting cold,I have to wait for my '79 to completely warm up,& the RPM's to drop down to below 1200, or when I try to put it in reverse before then I get a loud -clunk!-sound.I'm not sure if its u-joints,or what?,and would like some suggestions.I've replaced a rubber "doughnut" thats in front of the rear end that helped some.I'm hoping I dont have to tear into the rear end or tranny.When its warmed up & idly normally,its noticeable,but barely

 

[mike weyman]

i'd say drive shaft.

 

[pttsls5]

Check drive shaft and half shafts for any play in the u-joints. They are fairly easy to replace. If there is even the slightest play replace all 6 you will be glad you did if you have ever seen the damage to a fibreglass floor when they let go:cry .

 

[C3RVETTE]

Check drive shaft and half shafts for any play in the u-joints. They are fairly easy to replace. If there is even the slightest play replace all 6 you will be glad you did if you have ever seen the damage to a fibreglass floor when they let go:cry .

Yep,I was thinking of upgrading them to Spicers anyway.

 

[Bob Chadwick]

One other possible problem area is the front differential bushing. When you put it in gear, the differential wants to rotate and this absorbs this. It it is worn out it will clunk when you put it in gear.

 

[brooksman9]

One other possible problem area is the front differential bushing. When you put it in gear, the differential wants to rotate and this absorbs this. It it is worn out it will clunk when you put it in gear.

This was the problem with mine. Also would clunk when let off gas quickly.

 

[76corvette]

My 76 has the same clunk only when its in reverse. I try to back it out slowly and then it doesnt do that. Is it a huge problem i should fix immediately or is it just more of a undesired sound than a problem?

 

[vettenick]

You're not getting off easy on this one. Jack the rear up with horses under the rear frame. If you take the spare tire carrier out you'll have more room. Have someone you trust start the car and move the lever from drive to reverse(with their foot on the brakes) to determine where the noise is coming from. Clunks can be as simple as the u joint to something more involved as excessive backlash in the differential....or worse.

 

[C3RVETTE]

One other possible problem area is the front differential bushing. When you put it in gear, the differential wants to rotate and this absorbs this. It it is worn out it will clunk when you put it in gear.

Thats what I meant I replaced,as stated above.It helped slightly a couple times.