shifting noise.

[Red73BB]

Whenever I shift from drive to reverse, it make a loud thump and the rear end squats. This happens after I've driven it and the motor/transmission is warm to hot. When I first start up It doesn't do this so I don't think it's the u-joints. My friends '68 does the make the same sound when shifting to reverse. Is this normal? :confused
Gary

 

[69MyWay]

Gary,

I don't know how normal it is, but it is pretty common to hear thunks and clunks in the rear of these cars.

Your sound can be coming from the front mount on the diff. They wear out and cause enough play to allow the diff to move up and down when put under a load. This is easy to see when shifting from forward to reverse.

It is fairly easy to replace.

U-joints may also clunk. Often, a bad u-joint will also cause a vibration at certain speeds.

If there are no other problems such as vibrations and squeaking noises, I would guess the diff mount is the problem.

Chris

 

[Eric]

I agree w/ Chris about the diff being the source of the offensive noise. As for the squat, mine does it too and I just write it off as torque. If you're still worried about the u-joints, lift it up and grab the shaft(s) and try to move it/them. There shouldn't be any play.

Another obscure thing that could cause a thump in the rear can be a loose battery. I only know this because mine used to have an awful loud and hard thump when I started backing up or turned hard. The battery was slamming against the compartment:eek and I didn't figure it out until I had to jump the thing off. This was after I had checked everything conceivable under the car.

Also, remember you are physically sitting a lot closer to the differential so you're going to feel and hear it more than you would in any other car.

 

[Doug78]

... physically sitting a lot closer to the differential...

Understatement of the year!!

Your toes are next to the flywheel the rear diff practically supports the seatbacks ... but I agree with the battery making thuds I found that mine was only being held in by gravity and we all know how ellusive THAT can be.