Master cylinder question
 

Can I use a disc/drum master cylinder on a drum/ drum car

Don't think so!
In all the years I worked as a auto parts counter man I always sold one for each, never one part number for both"

thanks steve i know they are two seperate parts but im curious if it will work

The drum type master has a check valve to keep some fluid pressure in the system when the brakes are NOT engaged. If you dont have this the brakes will be spongy or won't work on the first push of the pedal.

I did not know this.

Called a residual valve.

...and GM quit using residual valves in 1970. See "Note" under figure 2-5:

http://hbassociates.us/Delco_Brake_Manual_03.jpg

I always heard that disc brakes require more fluid (volume) to make them move. If you use a disc m/c on drums, the drums will over-extend (drums don't need as much volume). If you use a drum m/c on discs, the disc won't clamp all the way. You can look up specs on disc v. drum m/c's and see the bore in the disc m/c's are larger, which means as the piston moves down the bore, more brake fluid is displaced in the disc m/c than in the drum m/c.

Disc caliper has a bigger piston, but (except for low-drag calipers) also has less travel to apply the pads to the rotor. Drum wheel cylinders have to move much farther to take up the clearance between the shoes and the drum. There may be a difference in the diameter of the master cylinder piston(s), but that's a tuning tool to achieve desired pedal effort/pedal travel more than a way to push more/less fluid due to the demands of the wheel cylinder/caliper.

A disc master cylinder needs a larger reservoir of fluid due to the fluid "permanently" transferred from the master cylinder to the disc caliper as the pads wear.