Any ideas as to why I would get a "Thunk" when shifting into reverse only. The transmission is auto and newly reconditioned, the same for the rear end. Shifting into drive, no noise. I was going to change the differential fluid (with additive of course). All responses ARE appreciated.

Aloha,

Bret

Check your U joints while you're down there. Hint: many times just grabbing the shaft to see if you have a bad joint isn't very effective. Put the car on a lift if you can and thoroughly inspect.

Don't forget the axle u-joints. Also look at all drive line and suspension bushings. This could also be caused by too fast of an idle. The system is loaded different in reverse than drive, so you can different effects from loosness or idle.

Ken Styer

Excellent suggestions. I appreciate the feedback.

Bret

Another possibility is the differential. I had all the u-joints replaced in my '73 and still had a thunk when shifting into reverse. Turned out the posi-carrier in the differential was cracked. Replaced the whole unit (wanted to change the ratio anyway) and have never heard the thunk again.

don't forget to check the simple things after putting on new rear cover bolts that hold spring to rear were not tight enouh had clunk tightened bolts it went away

Two more good suggestions to look into. I hope it is something simple like loose bolts or a u-joint. Being the rear end was completely rebuilt, any damage inside should have been identified. ( But, things are often missed.) I will dig into it this weekend and let you know if I find the "gremlin". Thanks again.

Bret