Master cylinder help

[dwhip361]

I'm sure this has probably been asked many times before,but I haven't been able to find a thread with a similar situation. I have a 72 Duster that came with power drum brakes. I have switched the fronts to disc and rear to 10 in. drum. What I need us a master for power disc/drum. Most of the stuff I see people doing is manual brakes. Could I use one from a 72 coronet? Any help would be appreciated. Thanks

 

[Inertia]

Rock Auto has them..

RAYBESTOS Part # MC36406 More Info {Professional Grade; Bore Size=15/16" Number of Ports=2 Primary Outlet Size=9/16x20 Secondary Outlet Size=1/2x20}
Front Disc Brakes; Rear Drum Brakes;

http://www.rockauto.com/catalog/more...117&cc=1088760

Your push rod should be fine...

hope it helps

 

[dwhip361]

Are power masters and manual masters any different?

 

[BillGrissom]

The main difference is that the manual brake rod has a rubber bushing on the end to secure it in the piston. I think a manual MC piston has a step or taper to capture the bushing, though it might self-lock in just a smooth bore.

A manual MC also has tapped holes on the back to mount a piston retainer-rubber bellows, which usually comes on rebuilt MC's (often w/ the rod). The boot keeps dust from the passenger compartment from getting in the piston bore, though old ones usually split or fell off.

Also, a manual MC with a failed piston seal will usually spill brake fluid into the cabin, dribbling down the inner firewall and floor, removing paint, and causing rust. Power MC's dribble down the booster onto the firewall but not on my cars w/ DOT 5.

 

[mvh]

Also, depending on the year, the stock replacement MC listed may have a different bore for manual or power applications. The 15/16" one listed above is correct for power brakes. The one for manual would have a 1-1/32" bore. The bigger bore creates higher pedal resistance and shorter travel -- it may seem illogical that the power brake MC would have a smaller bore, but the reason is that the longer pushrod changes the mechanical advantage at the pedal. At any rate, the bore size doesn't affect interchangeability.

 

[BillGrissom]

-- it may seem illogical that the power brake MC would have a smaller bore, but the reason is that the longer pushrod changes the mechanical advantage at the pedal. ...

That is certainly the reason in GM A-bodies where the power rod bolts to the pedal in a different place and angles upward. In Mopar world, the rod would be a very minor effect (same angle for both). That main reason is the lever arrangement in the "stand-off brackets" that are used with the power booster.