Need explanation please

[Kurt B.]

On a 1968 Corvette rear end, can someone please explain the mechanics or physics of why using a longer bolt from the rear spring to the trailing arm would adjust the ride height. I have heard many say that it does so, but I can't understand why, since the spring is pulling down on the trailing arm via the bolt, why does it matter what length the bolt is? It is stilling exerting the same downward force. My bolts are 6.5 inches long and I have 4 inches of wheel well space showing between the tire and the wheel well. (Gas tank is empty)
Just trying to understand HOW the bolt length would make a difference.
Thank you for educating me,
Kurt #26406

[Joe L.]

Re: Need explanation please

Kurt-----

The bolt length affects the distance from the spring to the trailing arm. This, in turn, affects the final relationship between the trailing arm and the frame. That, in turn, establishes the ride height. That's about as simple as I can explain it.

During the mid-to-late 70s period, the ride height became critically important due to government mandated impact standards (the "5 mph bumper" requirements). During this time, GM used, in PRODUCTION, several different length bolts in order to more precisely set the car's ride height so that the bumper design would achieve the standards. Most of these bolts were never available in SERVICE, though.

[Kurt B.]

Re: Need explanation please

Thanks Joe.
Now I finally understand it.
Kurt

[Carl H.]

Re: Need explanation please

Joe, thanks for the info on ride height that you gave Kurt. My 73 sits 5 inches higher on one side than the other. It has been driving me nuts and I this is the first info that I have heard that might solve the problem. Was one of my bolts likely changed somewhere along the way? Is it adjustable? Thanks in advance.

[Joe L.]

Re: Need explanation please

Carl-----

5" is a lot. It's more than I would have expected unless the bolts are of grossly different lengths. In any event, your bolts should be very close to 6-1/4" from the base of the head to the bottom of the thread. There ahould be very close to 3/4" of thread at the bottom of the bolt which is included in the overall length of 6-1/4". For all practical purposes, the factory bolts are non-adjustable. It may be possible to install the nut a few threads down and still install the cotter pin. However, the assembly is supposed to have the nut threaded on as far as it will go and, then, the cotter pin installed.

1973 models did not originally use different length bolts in PRODUCTION to adjust ride height. That practice didn't start until 1975. 1973 models used bolt GM #6271686 which had dimensions very close to those that I provided above.