What about the rubber biscuits in the cross-member that the differential mounts on?

 

Are you talkin' about where the carrier (cover)assembly mountson either side ofthe frame, or the front support at the frame cross member?
These are the only points where the dif mounts. Any movement at these points may (might) cause rubbing, but at least one of the carrier and the front support would have to be bad.Since both axle shafts are rubbing, I would suspect that all three mount bushings are bad.If I'm wrong on this, please correct me, but this is how I see it.

 

The one on each end of the cross-member. I agree that if the trailing arms are OK, then it is probably the rubber mounts.

 

The rubber bushings on top of the crossmember look like they are in pretty bad shape. Do those come with the body mount bushing kit? I ordered a energy suspension kit from summit. I have not received it yet, so not really sure what to expect. It was only $60 bucks shipped.

 

None of the suspension kits that I was looking at have the rear cross member biscuits, I ordered them separately, I think they were $60 each, I think they are suspect given the description of your problem.

 

The trailing arms are not connected to the dif in any way, other than the axle shafts and strut arms. I do not believe that the body kit includes the dif bisquicks. You may as well change the dif mounting bushings that attach to the side frame rails too. I'm guessin' that these will be in your kit from summit.

 

The '63-'79 rear suspension was the first design IRS, GM changed the layout for '80-'82. In the case of the '77 the problem has to be either the body or the differential has changed position. The diff. is bolted solid to the cross member which is then hung from the frame with the rubber biscuits.

 

[sm=exactly.gif]That's what I was tryin' to say. Thanks buckshot.