Discs,drums, m. cylinder

I have searched this site high and low and I know this question has been asked and answered but I can't find the answer so here goes. I am installing GM pre 78 calipers on the front and a 70 Nova drum rear end in my 35 coupe. I am using 39 pedals and have a CE adapter to mount the master cylinder to this pedal assembly. I am not using a brake power booster but a dual reservoir master cylinder that is for a 77 ford mustang 2 disc/drum set up. Without going into details I screwed up this master cylinder and have to purchase a new item. This MC has a 15/16 dia bore and I was wondering if this is the correct diameter for my disc/drum set up or should I go to a larger dia MC. Any part store and master cylinder P/N would be helpful.My apologies if this is redundant and if so, any direction to the correct post is appreciated.

 

Bought a manual disc/drum kit for the Dart project and 15/16" is what they supplied - but for power brakes you could go larger. The brakes are spongy on the Dart, so I got them to send the next size up in my Mopar app which is 1 1/32". We will see, could be the peddle will now be rock hard, and that's not good either.

On my COE with power '73 GM truck disc/drum I just put in a 1 1/8" Fenco # NM1521 and it works fine. Had a 1" before that and it worked fine. The '73 truck app actually calls for a 1 1/8" bore. Power is obviously more forgiving.

 

Yup bigger is better for power brakes, but not for manual. You'll want to stay with a 1" bore MC or less for manual brakes so the 15/16 will be fine. Or 7/8".

Rockauto has some good prices on dual reservoir MC's that were made for vehicles with manual disc/drum setups from the factory. Think I used one meant for a '72 c10 to use in my 64 c10.

 

Here's a link that talks about several different GM MCs, along with part #s. I'm using the first one, the "C3" that was used on Vette's, Camaros, etc. It's a 1" bore and is made for a disc/drum application. Available at Napa.

Chris

http://www.trifive.com/forums/showthread.php?t=33201

 

I would try what you have 1st and work from there. The factors you did not mention are pedal ratio and caliper and wheel cylinder piston size and will affect the end result.

I would not try anything larger that 15/16" MC piston on a manual brake system. The pedal gets too hard for most. Just ask all the SSBC kit users with manual brakes and a 1" MC.

The key will be to find out if the MC you have can supply enough fluid volume to the calipers and wheel cylinders you are using without running out of pedal stroke/fluid volume. If the car stops like you want and the pedal still has 20% or so of stroke left you should be good to go.

This is hot rodding. Try what you have and fix it if it doesn't work...

 

You don't want to use manual brakes as they are very hard on the hands.

 

You can also use the 79 Lincoln Zephyr master cylinder. (same size pistons) The brakes lines are on the other side. If your master is backwards under the floor, then the lines come out on the frame side... away from the exhaust pipes.

 

Thanks for all the input. As Mr. Mom would say .937 or 1.125.....whatever it takes. You guys all know about second guessing so I'll replace what i have and give it a go. I was so excited when i picked my MC up at Napa, ( I have a simple life) that I pushed the pedal rod into the mc piston bore not knowing it was a one way clip. I did this at the counter while they were ringing up the sales !!!! I was dreaming about chucking the rod in the lathe and turning some threads . At least now I have a real clean "core" for a $9.00 exchange ! Again, thanks for learning me, you guys are the best. See you on the road !!