My 70' SS has the rectangular master cylinder as opposed to the round one. Are they both correct? I'm assuming mine is original but don't know for sure. I'd like to replace it with a new detailed master cylinder/booster combo and would like to get the right one. Thanks for your help.

The front of the master cylinder should have a machined surface, in the shape of a half moon. Look for it and the stamping on there. Also, the underside will have a casting # that ends with 409.

The rectangular is correct for a 70 a the round is correct of 68 and 69.If yours has the original master and booster just have then restored or replated

The front of the master cylinder should have a machined surface, in the shape of a half moon. Look for it and the stamping on there. Also, the underside will have a casting # that ends with 409.

There should be a "BB" stamped on the machined surface that Tim is referring to.

I have planty of the correct BB cores if You need one and we also replate the boosters with thye Correct Cyanide Caduimn versus the TOO shiney gold chrome like EPA user friendly Alakilide cadiumn that is curently available. Jim 302-420-4743

Thanks for all your help, very much appreciated.

They were also used on 1970 Monte Carlos. I have 2 BB master cylinders and 2 original power brake boosters off Monte Carlos.