Master Cylinder Sizes

I know there is a lot of conversation on this site about this. Much of it is over my head. I saw that someone put together a MC calculator and it made my hair hurt.

I have 13” Corvette front brakes and 11” rears with a hydraulic clutch.

Is there an average size that would be best?

From what I’ve read I’m looking at a Wilwood 3/4 clutch, 3/4 front and 7/8 rear.

Does that look about right?

I’ve also read that this process is a trial and error process and I need a place to start.

Thoughts?
 
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Good question. I have also gone back and forth on size for best results. Is the main criteria brake disk size? Brake caliper size?


Richard
 

Howard Jones

Supporter
The biggest factors are, peddle ratio, master cylinder size, pad friction value and caliper piston sizes.

My GTD has, 1.75 diameter piston X 4 willwood superlight calipers on the front, 1.38 X 4 willwood superlight calipers on the rear, 5/8 diameter master cylinders (tandem system) and 12 X 1.25 rotors on all four corners. The effective peddle ratio is 6.5 to 1 (with GTD peddle box and OEM power brake system).

17 inch wheels were necessary.

This car will out brake any car I have every run across at a track day on good summer only street tires and hot race pads. With street use brake pads it still will throw the passenger out of the seat if I stand on the brakes. Pads are Willwood B's and C's with fiction values in the .55 - .62 range.

I built my SLC with the above as a baseline. As of now I have the 6 piston willwoods on the front 1.62, 1.25, 1.25 pistons, 1.25 X 4 pistons on the rear, 13.06 X1.25 rotors on the front, 12.88 X 1.25 rotors on the rear with 5/8 diameter masters. The Tilton peddle box is 6.6 to 1. As of now I have some pretty cheap pads, willwood E's, on the car but it still stops very well. FV = .48. It will get better pads latter.

So there are two examples, You will need to determine your caliper piston sizes. Your peddle box is 6.6 to 1 just like mine, and you rotors are in the same ball park.

3/4 or 5/8's are my guess for masters, if your calipers piston diameters are near the examples above.

And.......yes there will be some trial and error involved.

Here are the FV charts.
 

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You have a few dependencies, namely disc diameter, caliper bore diameter, pedal length/ratio, clutch size etc.
Like Richard said, you have to start somewhere and then test the clutch for effective release, and put your car on a brake tester at your local test station to check for front/rear balance, excessive pedal travel etc.
As a rough finger in the air, I would start with the master cylinders you describe, and find out what you get. Then change the m/cyl diameters to debug any operational issues. Practice beats theory every time.

Good luck, Tony.
 

Terry Oxandale

Skinny Man
I'm using 3/4" all the way around, with 1.75/1.88 pistons on 12" rotors, on all four corners, and the feel is great (Tilton peddle assembly) with 2 turns toward front bias.
 
The biggest factors are, peddle ratio, master cylinder size, pad friction value and caliper piston sizes.

My GTD has, 1.75 diameter piston X 4 willwood superlight calipers on the front, 1.38 X 4 willwood superlight calipers on the rear, 5/8 diameter master cylinders (tandem system) and 12 X 1.25 rotors on all four corners. The effective peddle ratio is 6.5 to 1 (with GTD peddle box and OEM power brake system).

17 inch wheels were necessary.

This car will out brake any car I have every run across at a track day on good summer only street tires and hot race pads. With street use brake pads it still will throw the passenger out of the seat if I stand on the brakes. Pads are Willwood B's and C's with fiction values in the .55 - .62 range.

I built my SLC with the above as a baseline. As of now I have the 6 piston willwoods on the front 1.62, 1.25, 1.25 pistons, 1.25 X 4 pistons on the rear, 13.06 X1.25 rotors on the front, 12.88 X 1.25 rotors on the rear with 5/8 diameter masters. The Tilton peddle box is 6.6 to 1. As of now I have some pretty cheap pads, willwood E's, on the car but it still stops very well. FV = .48. It will get better pads latter.

So there are two examples, You will need to determine your caliper piston sizes. Your peddle box is 6.6 to 1 just like mine, and you rotors are in the same ball park.

3/4 or 5/8's are my guess for masters, if your calipers piston diameters are near the examples above.

And.......yes there will be some trial and error involved.

Here are the FV charts.
Thanks Howard. You’re obviously very knowledgeable about this. I think my set up is similar to the second scenario on your SLC, I’ll also be using 17” wheels.

Thank you for your comments!
 
You have a few dependencies, namely disc diameter, caliper bore diameter, pedal length/ratio, clutch size etc.
Like Richard said, you have to start somewhere and then test the clutch for effective release, and put your car on a brake tester at your local test station to check for front/rear balance, excessive pedal travel etc.
As a rough finger in the air, I would start with the master cylinders you describe, and find out what you get. Then change the m/cyl diameters to debug any operational issues. Practice beats theory every time.

Good luck, Tony.
Thanks Tony!
 
I'm using 3/4" all the way around, with 1.75/1.88 pistons on 12" rotors, on all four corners, and the feel is great (Tilton peddle assembly) with 2 turns toward front bias.
Hi Terry, I’ve read where many guys have different sizes for front and rear. You have 3/4 on all 4’s and it works well? That’s great.

What I’m learning about bore size is that is in fact a trial and error proposition.

Thank you!
 
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