Differential hits tunnel

[Bill H.]

We finally finished our 66 coupe and are working out the bugs.
When accelerating I get a rub at the rear differential / tunnel. I can just make out a slight rub on rear yoke / u joint.
This has been a ground up ,complete restoration. Body was off, no shim indication for body drop.
Did I not put enough shims under body?
the only solution I can think of is to add shims to entire body.
is there another way, like lowering the rear end just a little.?
Not looking forward to adding shims
thanks

[Keith B.]

Re: Differential hits tunnel

How are the rivets holding the bulk head look like My guess is the holes are ob-longed and allowing the body/ floor pan sag

[Wayne W.]

Re: Differential hits tunnel

Make sure the snubber bushing is installed correctly.

[Ray G.]

Re: Differential hits tunnel

Hello;
Another thing to check is your "trim". In the front of each Chevrolet Service Manual are the frame measurements along with the body heights, at the rocker panels, from a level surface.
Hope this helps.
my .02

[Stephen L.]

Re: Differential hits tunnel

The differential on a C2 is bolted solid to the frame cross member. There is no rubber "snubber" on the differential. I assume you are talking about the main driveshaft yoke and not a half shaft. There should be no change in dimension of the clearance between the body (floor) and differential as the differential is bolted to the frame during acceleration UNLESS the frame is possibly "deflecting" at the kickup due to internal rust. The kick up area is notorious for rotting out on these cars. I don't know the clearance dimension in this area but would believe it to be at least an inch.....

[William C.]

Re: Differential hits tunnel

Not really, the front of the differential is controlled by a bracket that is insulated from the frame by some rubber donuts and a centering bolt to match to a bracket on the frame. Lots of areas for trouble, including wear on the holes in the differential case, wear on the holes in the bracket, body sag in the rear compartment from broken bonding in the floorpan and some miscellaneous other items. You should be able to see where the flange is hitting the fiberglass and sort thru the causes from there.

[Barry H.]

Re: Differential hits tunnel

I think Wayne is refering to the front diff to frame mount, which if installed incorrectly can allow the nose to rise upon hard accereration.
Barry Holmes

[Stephen L.]

Re: Differential hits tunnel

This was said to be a fresh body off restoration. I guess I assumed that WORN pieces would have been replaced/repaired. I've included photos of the diff mounted on the frame which shows the front attachment. If that is installed with new parts (and they are installed correctly) then something must be flexing. That is why I suggested the frame kick up problems, which would torque the rear of the frame down pulling the rear body with it.

[John H.]

Re: Differential hits tunnel

This symptom almost always involves worn/incorrect snubber bushings and/or a sagging floor pan at the base of the luggage stop panel. If polyurethane snubber bushings were used instead of the correct OEM rubber with the bonded tubular sleeve and bonded flat washer, that just about guarantees that the rear U-joint will contact the top of the tunnel, as the poly bushings are too thin and don't have either the centering sleeve or the washer.


Snubber2650.jpg

[Ray G.]

Re: Differential hits tunnel

John is correct and makes his point succinctly.