Hello Danny:

I misspoke when I wrote 'valve' - I should have written 'seal.'

Yes, the interior diameter of the cylinder is 13/16" and since the seal is designed to seal it, it should also be 13/16". The seal I have definitely looks smaller than the seal currently mounted on the piston. My question is whether the shaft on which the old seal is mounted pushes the outer radius of the seal outward enough to add 1/16" to the final diameter. That seems like a lot to me and highly unlikely. The only reason I did not pull the old seal off is because I was afraid that I would destroy it only to prove the new seal was the wrong size, resulting in an undrivable car.

Cheers,

Pooch