MC Piston size

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bobscuda67

bobscuda67

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I am having a issue stopping my car. It has manual Kelsey Hayes disc up front and 10 by 2 1/2 inch drums out back. The brake pedal is rock hard but I have to use both feet just to stop it normally at a light. The brakes won't lock up and I could never stop it in a panic. When I rebuilt the brake system 10 years ago I think I used a 1 1/8 bore master, which would explain the rock hard pedal. But I can't remember for sure.
I was thinking of using a aluminium master with the 2 bolt flange. What size bore would I need? Is the 1 1/32 bore that much easier to push than a 1 1/8 bore? Or is a 15/16 master the best for manual disc?
What year of cars had aluminium master cylinder should I look for? I know I need a 4 bolt to two bolt adapter, and I have an adjustable pushrod already.

I was hoping someone that has already done this could help out. Thanks.
 
This is getting into stuff that's too much for my brain.....BUT, I remember in the MP catalog, there USED to be two different master cylinders. One had a large bore and the other a smaller bore with a longer stroke. One was for better pedal feel, the other was for better stopping effort. That's about all I have, but I remember that pretty clearly. It sounds like the one you have is for better pedal feel and I THINK those work best with a power booster.

Of course, I could be completely dead WRONG about all of this so take it with a grain of sand. lol Just trying to help.
 
Thanks for the advice guys. i guess i'll have to try a smaller bore master. Does anyone know the part number of the aluminum 15/16 bore master cylinder that would work on my car.
 
yes..should be 15/16" but for sure no larger than 1"
why not stock cast iron master cylinder?
 
I put a 7/8"D MC (for ABS) from a ~96 Plymouth Breeze on all 3 of my 60's Mopars. I bought several new for $25. Indeed, today I bled one I just put on my 65 Newport (2-4 bolt adapter on booster). I have a stiff pedal (engine off) and normal pedal travel, even though I am using DOT 5 (silicone). Many here, who have never used DOT 5, claim it is "spongy". On my Valiant, I will run booster-less. Front drums there, but that size should tame your disks.
 
ir3333 said:
yes..should be 15/16" but for sure no larger than 1"
why not stock cast iron master cylinder?
Click to expand...

Hell, I don't know. I was thinking since I'm replacing the cast iron one I have, I might as well use the aluminum one. I'm having a hard time finding a aluminum master that's not $100.00. Also I have to have one that has a hole for the pushrod.
 
The 1 you want fits 70-2 a bodies with manual disc,try rock auto 1st
 
I'm looking for a part number for either 15/16 or preferably 7/8 bore 2 bolt master cylinder. For manual KH disk with 11x3 drums. I replaced the calipers because each calipers had a froze piston with some reman unit's , now I'm have some problems with getting any pressure in the lines and I'm leaning toward the master cylinder being damaged.

Any and all help is always appreciated
 
srixon4406 said:
I'm looking for a part number for either 15/16 or preferably 7/8 bore 2 bolt master cylinder. For manual KH disk with 11x3 drums. I replaced the calipers because each calipers had a froze piston with some reman unit's , now I'm have some problems with getting any pressure in the lines and I'm leaning toward the master cylinder being damaged.

Any and all help is always appreciated
Click to expand...

You likely got a ton of air in there,, keep bleeding ,
 
bobscuda67 said:
Hell, I don't know. I was thinking since I'm replacing the cast iron one I have, I might as well use the aluminum one. I'm having a hard time finding a aluminum master that's not $100.00. Also I have to have one that has a hole for the pushrod.
Click to expand...

My car 68 cuda, 73-76 A body discs, 10 x 2-1/2 rear drums.

First: had a 15/16" bore MC. It's listed for a 74 A body power disc brakes but run manually.

Second: went to Auto Zone and had them pull a bunch of aluminum MC's off their shelves. I was looking for one that had the recess in the piston for the pushrod rubber retainer. Found one (think it was for a mid 80's Dodge truck but the bore was 1-1/8". I wanted aluminum to save the weight.

Third: found a slightly used vintage Direct Connection aluminum 1-1/32" MC that had really low miles because it was used on a race car for less than a year. Maybe so, but it was gummed from sitting up so I disassembled and cleaned it before installing. It's still on the car with a Wilwood adjustable prop valve.

************

Of the three combinations I've tried, here's what I think.

The 1-1/8" pedal was way too hard! I really had to concentrate on pushing the pedal at stop lights. With one foot only, the car tended to creep if I wasn't careful.

The 1-1/32" is OK, firm but not too hard.

If you want to get it right the first time, go with a 15/16" bore. Order a power brake master cylinder from a 73-74 A-body but run it manually. You'll love it. DC used to list a couple MC's with different bores so they may be out there somewhere.
 
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