Master cylinder bore size for 4 wheel power disc brakes? - Vintage Mustang Forums
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post #1 of 8 (permalink) Old 07-13-2019, 01:15 AM Thread Starter
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Master cylinder bore size for 4 wheel power disc brakes?

I've been looking around and have been getting mixed answers for the ideal bore size for a power 4 wheel disc brake setup. I'm running Wilwood 6 piston Dynapro calipers up front and 4 piston dynalites in the rear. I recently picked up a 1 1/16th power 4 wheel disc master cylinder from a 1996 Mustang V6. Would that bore size be ideal for my brake setup or should I get the 1 in bore MC from the 1999-2004 Mustang V6s?
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post #2 of 8 (permalink) Old 07-13-2019, 02:08 AM
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Quote:
Originally Posted by 66goldcoupe View Post
I've been looking around and have been getting mixed answers for the ideal bore size for a power 4 wheel disc brake setup. I'm running Wilwood 6 piston Dynapro calipers up front and 4 piston dynalites in the rear. I recently picked up a 1 1/16th power 4 wheel disc master cylinder from a 1996 Mustang V6. Would that bore size be ideal for my brake setup or should I get the 1 in bore MC from the 1999-2004 Mustang V6s?



As compared to a 1" bore M/C, a 1 1/16 bore will deliver lower line pressure at any given foot pressure, but pedal travel will decrease. 1" bore will deliver 127+/- PSI @ 100lbs leg pressure, whereas a 1 1/16 bore will deliver 113 PSI+/- @ 100lbs leg pressure. So the net difference is 11 PSI and some undetermined (though likely marginal) decrease in pedal travel for the larger bore. ....Course, its not precisely that simple, because your brakes don't end at the master cylinder, and there's a booster and pedal ratio to consider as well, so the pressure differential won't be just 11 PSI. In general though , if we assume at least one of those bore sizes is suitable for the calipers you are using, then it seems highly likely the other would be as well. I would note that you typically see a 1" bore on manual brakes - (higher pressure at a given leg pressure because there is no boost) and larger bores on the scale of 1 1/8+ for power brakes. Now as both the vehicles you quote clearly had power brakes, I can only assume that is all factored in, but a 1" bore on a power brake is a little unusual - I've only ever seen that in the transition years between factory drums and factory disks, but I don't know much of anything about modern brake systems. Additionally, 4-piston calipers are commonly paired with 1 1/8 - 1 /11/64 bore masters - what piston arrangement came with the donor vehicles?




If you are interested, and willing to do the math, you can calculate your total piston area, the total pressure delivered through the ratio of the brake pedal, to M/C bore, to booster and then see how said pressure will act on your pistons. the best resource I've found is here: https://www.joesracing.com/master-cylinder-math/


Allan
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Last edited by Treozen; 07-13-2019 at 02:15 AM.
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post #3 of 8 (permalink) Old 07-13-2019, 06:05 AM
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I would call Wilwood.

Chris (Sussex, WI)

289 w/AFR 165, T-5z, 3.55T-loc, Granada Discs and 6 bolt Moto-Lita Steering Wheel
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post #4 of 8 (permalink) Old 07-13-2019, 12:09 PM
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^ What he said.
And one can't design a brake system without knowing the particulars on those Wilwood calipers.....

And we don't know the car we're dealing with.

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post #5 of 8 (permalink) Old 07-13-2019, 01:06 PM Thread Starter
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The car that I'm building the braking system for is a 1966 Ford Mustang. Currently the master cylinder and booster in the car is off a 67 Mustang with power discs up front and drums in the back. The reason why I went with a SN95 Mustang MC is because its a factory power 4 wheel disc MC with no RPVs in the front or rear brake circuits.
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post #6 of 8 (permalink) Old 07-13-2019, 04:28 PM
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Quote:
Originally Posted by GT289 View Post
And one can't design a brake system without knowing the particulars on those Wilwood calipers.....


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Here's the chart. You'll need to do the math for the caliper piston sizes. It'll probably show that
1 1/16" is the best master cylinder bore..... won't know until you drag out the calculator however.

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File Type: jpg Mustang MC info.jpg (77.3 KB, 11 views)
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post #7 of 8 (permalink) Old 07-13-2019, 04:48 PM
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I have a 1 1/16" master cylinder on my car. It has the Granada disks up front and no power booster. The pedal is high and firm, even with DOT 5 fluid. The brakes work well and have great feel. It's really a chore to drive though. Gives me legs cramps. I was told it would be ready for a power booster when I was ready to do that. I should try a smaller than 1" master.
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post #8 of 8 (permalink) Old 07-13-2019, 08:13 PM
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Quote:
Originally Posted by cougar70 View Post
I have a 1 1/16" master cylinder on my car. It has the Granada disks up front and no power booster. The pedal is high and firm, even with DOT 5 fluid. The brakes work well and have great feel. It's really a chore to drive though. Gives me legs cramps. I was told it would be ready for a power booster when I was ready to do that. I should try a smaller than 1" master.
In general, the correct master for manual brakes (disc front, drums rear) is 15/16"
That would be an 1/8" reduction in bore size on your car....... a massive reduction in leg force required.
Get some good brake pads too. You'll never need to go power brake.

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