Chassis Question

[Mike H.]

I have a 67 Coupe small block. When loaded with two passengers weighing 500 Lbs. and luggage in the back the pinion drive shaft yoke hits the body tunnel on big bumps. I am contemplating new shocks and rear leaf spring to solve the problem but am not sure that would help. Any opinions or other solutions?
CORDiallyMike

[Patrick H.]

Re: Chassis Question

Hi Mike,

I’d first wonder if the rubber cushion at the front of the differential mount is worn. If so, it would change the angle of the differential and allow it to hit.

The only problem is that per my friends it’s difficult to find a well-fitting cushion in the aftermarket, at least for a C3, and I would suspect it’s the same part on your 67.

Since the rear spring is under the differential, and the differential is hard-mounted to the crossmember, it really should not affect the angle of the differential as the car changes positions. At least, not anything like a worn front cushion would.

Save your money and check it out.

Patrick

[Joe L.]

Re: Chassis Question

I have a 67 Coupe small block. When loaded with two passengers weighing 500 Lbs. and luggage in the back the pinion drive shaft yoke hits the body tunnel on big bumps. I am contemplating new shocks and rear leaf spring to solve the problem but am not sure that would help. Any opinions or other solutions?
CORDiallyMike

Mike------


Something that can cause this condition is the "broken spine" syndrome which can afflict C2 Corvettes. With this condition the fiberglass floor in the vicinity of the driveshaft tunnel cracks and "sags" to one degree or another. The effect is "exaggerated" with a heavy passenger/luggage compartment load.

[Joe L.]

Re: Chassis Question

Hi Mike,

I’d first wonder if the rubber cushion at the front of the differential mount is worn. If so, it would change the angle of the differential and allow it to hit.

The only problem is that per my friends it’s difficult to find a well-fitting cushion in the aftermarket, at least for a C3, and I would suspect it’s the same part on your 67.

Since the rear spring is under the differential, and the differential is hard-mounted to the crossmember, it really should not affect the angle of the differential as the car changes positions. At least, not anything like a worn front cushion would.

Save your money and check it out.

Patrick

Patrick-----


1963-79 differential "snubber" cushions are the same, upper and lower.

[Keith B.]

Re: Chassis Question

To add with what Joe said its the rivets on the luggage stop that the holes get egged out and allow for the body to sag. or your luggage stop has rusted out around the rivets. you would have to remove the carpet on the luggage stop to inspect.. A temporary fix would be to get two hockey pucks and place them between the cross member and floor.

[Peter H.]

Re: Chassis Question

Hey a canadian invention saves the day...peter..canadian guy...

[Tom D.]

Re: Chassis Question

Luggage stop?

[Keith B.]

Re: Chassis Question

The bulk head sheet metal panel behind the seats

[Michael G.]

Re: Chassis Question

Such spacers, with attaching provisions, but unfortunately, without NHL provenance, are available from Silversport.

[Mark M.]

Re: Chassis Question

Mike, Paragon has a great little manual called bulkhead repair manual for 5 bucks. It shows clearly whats involved in this repair. The hockey puck repair is much faster. What an interesting service bulletin that could have been from GM. Large occupant and load support discs from our Canadian parts supplier. I agree to check the rear end front mounts too.

[Darryl D.]

Re: Chassis Question

Is you car noticible sagging in the rear?

If I recall correctly the stated factory load capacity for passengers and luggage is 500 lbs. so not surprised that you are having problems.

This summer I drove my 76K original mile 1965 to Illinois and back. While in Illinois I noticed that the car appeared to be sitting lower in the rear than previously. On the way back to AZ. I had my brother with me and luggage for both of us (over 500 lbs.) and soon started bottoming the car out on some pretty good dips in the road. It got progressively worse. I called ahead to a spring shop in St. Louis and a repair shop and had a new spring built for the car and installed that solved the problem. Mine was scraping on the under car exhaust system.

[Frank D.]

Re: Chassis Question

I have been told that early 63 cars had rubber cushions that served as differential to body mount cushions and prevented contact; although not correct they can be used on later midyears and shouldn't be visible... These aren't shown in the AIM but are in the workshop manual...
Doc Rebuild sells repros of the part as do some other vendors:

https://shop.docrebuild.com/1963CorvetteDifferentialtoBodyMountRubberShim2PieceSetReproOfGM.aspx

[Duke W.]

Re: Chassis Question

Those Doc Rebuild "rubber shims" have nothing to do with the axle mounting scheme. My SWC always had a low frequency exhaust resonance at about 2000 revs, especially with nothing in the cargo area. It was "drumming" of that large flat part of the underbody panel. The rubber cushions were there to both support any load and damp out the drumming. I can't remember how I determined that my car should have had them, but I made facsimiles by gluing together two or three layers of thick, stiff foam rubber matting to get the correct thickness dimension and that solved the problem. The drumming was probably more noticeable on Coupes than Convertibles.

The OP's problem is likely deteriorated front axle mount cushions. Increasing spring force, such as from carrying a large load and applied torque force the nose of the axle up, and if the cushions are deteriorated eventually the U-joint contacts the driveline tunnel.

Pinion seal leaks are fairly common and the axle oil will rapidly deteriorate the cushions.

Duke