Need some help sizing master cylinder - Team Camaro Tech
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post #1 of 6 (permalink) Old Aug 1st, 17, 01:13 PM Thread Starter
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Charlie
 
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Need some help sizing master cylinder

I'm running hydroboost from a '93 astrovan, have c4 front brakes (1986) and getting ready to install 1990 c4 Corvette rear disc brakes. I need some advice as to what size master cylinder to use. If u have an application that would be great.Thanks!
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post #2 of 6 (permalink) Old Aug 1st, 17, 02:45 PM
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Re: Need some help sizing master cylinder

If me, I would leave it at the present size since going to discs all the way around.
The piston only retracts the resiliency of the square sealing ring.
Apply brakes, piston goes out, seal becomes a trapezoid, and seal is maybe 1/8 inch square at the most?
Release brakes and seal goes back to square shape, so piston moves maybe 5-7 thousandths?
Not much fluid moved in retraction.

But then, I'm not a brake expert.

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post #3 of 6 (permalink) Old Aug 1st, 17, 07:39 PM
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Re: Need some help sizing master cylinder

I've not run a hydroboost, too grabby for autocrossing we do. C4 caliper pistons are much smaller than stock Camaro. I think you'll need to be between 1" and 15/16"" MC bore size, but I have no personal experience with them. Look at Mustang master cyls. Problem to watch out for is some Hydroboost MC's have bolts on each side, others are up and down, so pay attention to that.

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post #4 of 6 (permalink) Old Aug 1st, 17, 07:51 PM
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Don
 
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Re: Need some help sizing master cylinder

Here is the math. I think you will have to make an estimation of the boost but you could assume similar to a vacuum booster for a first cut:

Brake sizing and selection tutorial featuring Ron Sutton and Tobin of KORE3

Here is the data/specs to do the math:

GM Brake Upgrade Option Measurements - Thirdgen F-body Brake Upgrade

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post #5 of 6 (permalink) Old Aug 2nd, 17, 05:31 AM Thread Starter
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I've been running this system for years and love it, it was overly sensitive and the solution was to drill a new hole in the brake pedal lever between the manual brake hole and power brake hole and that fixed it. I grafted a c4 front clip in the car years ago, used the c4 front brakes (12" rotors) because they fit my 15" wheels. I used everything from the Astro van (hydroboost, master and prop valve) and it has worked perfectly. I'm in the process of installing 1989 c4 rear disc brakes and that's why I was curious as to what master cylinder to use. I was going to get rid of the stock Astro van prop valve and put a wilwood adjustable prop valve in the rear brake line.
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post #6 of 6 (permalink) Old Aug 2nd, 17, 11:28 AM
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Re: Need some help sizing master cylinder

I use hydroboost, C5 13"/LS1 12" calipers and rotors, manual (upper) pedal hole and a 1.125" bore MC. It is perfect, not grabby at all for the street only driving I do. It'll stop on a dime.

If you care to compare the total piston area between your C4 stuff and what I have it might give you at least a sense of which direction to go IF you plan on using the upper pedal hole.


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