15/16" MC with 2.75" calipers any problems with stopping ?

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rustytoolss

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Just put 2.75" calipers on my car. Should I use the 1 1/32" MC , or the 15/16" MC ? this is for a manual front disc/ 10" rear drum system. Thanks
 
I would go with 15/16" master cylinder.

When I originally replaced my single pot m/c. I went with a 1 - 1/32". I never liked the stopping power. 2 years ago I switched over to a 15/16" and it's perfect!!
 
anyone using the 15/16" MC have any problems with the pedal travel being to much, Or not having enough fluid volume for thier system ?? using the 2.75" calipers.
 
Fyi the area of the 4 pistons in 1 KH caliper is 8.4 but you can only use the area of 2 pistons due to their opposing nature* So the resulting area is about 4.2 sq in and your single 2.75 caliper is about 5.9 sq in.

15/16 piston area is about 3
1 inch piston is about 3.14
1 1/32 inch piston Is about 3.25

Simple math can get you the respective ratios for the combonations.

Then measure your brake pedal and get its ratio

A little more math and you can get final ratio.

* Thanks goldduster318 for noticing my error. The mythbusters proved it with a head on collision between two cars and one car and a block wall. Same amount of damage.
 
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Fyi the area of the 4 pistons in 1 KH is about 8.4 sq in and your single 2.75 caliper is about 5.9 sq in.

15/16 piston area is about 3
1 inch piston is about 3.14
1 1/32 inch piston Is about 3.25

Simple math can get you the respective ratios for the combonations.

Then measure you brake pedal and get its ratio

A little more math and you can get final ratio.

You don't count the opposed pistons the same way in brake calculations as you do with a sliding caliper. Since it's clamping on both sides of the rotor but moving half as much it's going to basically half that. The single 2.75 piston is acting on both pads simultaneously.
 
Once filled, calipers require very little volume to apply pressure, a few drops actually.
Pedal travel is less than 1/4 inch difference, 1 1/8 to 15/16s.
Rear drum brake adjustment has far greater effect on pedal travel .
 
I'll be the odd man here and say that with my wildwood forged dynalites (front disc) and smaller bore rear drum I was running a 15/16" MC for a few years. I do have power brakes, so not manual like the OP. Anyway, I never liked the stopping power because the pedal almost went all the way to the floor. This was fully bled, everything working fine. I switched to a 1-1/8" MC and everything is right now. Not too much travel, since I have power assist, the pedal is not too firm.

With that said - isn't the 15/16" MC designated for the manual brake setup? In the end, if you try one and it doesn't feel right, it doesn't cost much to try the other size and see which works best for your setup.
 
It's simply a pump, with a removable residual pressure valve to maintain slight pressure in rear wheel cylinders with drums .

I run 3/4 inch M/C with my Supercalifragilistic 4 piston calipers on my roundy-round cars .
Pedals at the top, and very solid, - locks up all 4 - 8" in Hoosier slicks, hot or cold ! !
 
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I run a 15/16 master and 2.75 calipers on two cars, both stop fine. I use an adjustable prop valve in the line going to the rear drums and bypass the factory distribution block. Both cars are manual brake, and the pedal feels nice
 
Residual valves were installed to keep the wheel cylinder rubber cups in contact with the cylinder wall, preventing leakage.
Newer W/Cs have a spring with a "spreader" to mechanically hold the cups against the cyl wall, no need for residual valves.
If you know your rear W/Cs have the spreader spring, no residual valve needed.
Not sure, - or no spring, install the R/valve .
The residual valve will have no effect on W/Cs with the spring .
 
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I don’t have a residual valve on either car. Got all my parts from Napa except the prop valve from summit.
 
I don’t have a residual valve on either car. Got all my parts from Napa except the prop valve from summit.
I have the same set up on my 68 Barracuda. Wilwood front disc. 11” rear drums with Adjustable Summit in line valve to the rear.
 
Residual valves were installed to keep the wheel cylinder rubber cups in contact with the cylinder wall, preventing leakage.
Newer W/Cs have a spring with a "spreader" to mechanically hold the cups against the cyl wall, no need for residual valves.
If you know your rear W/Cs have the spreader spring, no residual valve needed.
Not sure, - or no spring, install the R/valve .
The residual valve will have no effect on W/Cs with the spring .
Do you mean the long spring and the 2 steel pieces that go in the cups?
 
I don’t remember the application, but they are aluminum with plastic reservoir... also have two bolt mounting.
 
The one I used was a MP 4 bolt.

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