What master cylinder bore size

[Van B]

67 Camaro with Baer 6S six piston front and PBR rear with manual brakes.

I asked around a little at Motorstate Challenge. Most say I need 1" bore and I have one saying 1 1/16.

I would like the line ports on the left. Part numbers or OEM applications appreciated.

Opinions?

[MarkM66]

What are you running now, and why do you want something different?

[Bow Tie 67]

Jeff,

I'm running the Baer C4 setup, using a C5 master, not sure if this helps.

Matt

[Van B]

What are you running now, and why do you want something different?

Currently have 13/16 that will not move enough volume. Brakes have never performed like they should.

[dipren443]

Currently have 13/16 that will not move enough volume. Brakes have never performed like they should.

Would you like for me to send you a brake force spreadsheet?

[jaybee]

Please tell me more about the brake force spreadsheet. I'm planning out a braking system that isn't in the aftermarket and at some point will face this same issue.

[yellow heap]

I run a 1 in master in the heap-with great results
the way to optimise master cyl. size is to add up caliper piston(s)surface area
and use that number to size the bore size in the master
I've played around with many manual combo's and the 7/8 15/16 or 1 in. seems to cover most normal car brake systems(manual) with the 1 in being used in the majority of apps.

[Takid455]

I would like to see a copy of the brake force spreadsheet

[dipren443]

It is nothing more than an Excel spreadsheet that allows you to enter a bunch of variables of your braking system and spits out calculations for pedal force. I am searching for it now. It is tucked away somewhere on my external HDD. I will post a snapshot of it here and anyone whom is interested, I will email it.

Nick

[jaybee]

Awesome, please count me in. I'm assembling components from different sources and would like to at least be in the ballpark the first time it hits the road. Or for that matter know that I haven't put together front and rear bits that are hopelessly mismatched.

[RSX302]

http://www.jakelatham.com/radical/info/brake_calculators.shtml

I play with this..Best one I've seen yet..

If you are not getting enough caliper pressure to stop the car then you want to reduce in master piston size to increase caliper pressure. Trade off is a longer pedal throw as the mc piston gets smaller.

If the Baer 6S caliper are similar to the Wilwood's SL6's, then I would start out with a 7/8'mc. I didn't have much luck with the Wilwood's SL6's and the 7/8" on mine, still needed more, but I think it's due to the car weight. If you're running over 3500lbs, I think you should look at power assist and then you can run a 1 3/16" mc (ABS Power Brakes Inc. as an example)

I say 3500 but I think it's more what you are planning to do with the car. Since my car weighs in at 3800lbs, the SL6's on 13" rotors are just too small for a manual brake set-up trying to pull 1g. I need to put race pads in it with a 3/4" mc to make it do it. My rotors will be gone in no time. With the power assist, I'm hoping to get the same level of braking and go back to a street pad. (less dusting, no sqeeling etc)

[Van B]

Interesting Ron. Baer has told me 1 1/16 knowing I am running manual brakes. I assume they feel I need to move more volume of fluid. Car is was 3026 without the A/C evaporator case, so it is 3100 max right now.

Answers have not been exactly abundant.

[RSX302]

Interesting Ron. Baer has told me 1 1/16 knowing I am running manual brakes. I assume they feel I need to move more volume of fluid. Car is was 3026 without the A/C evaporator case, so it is 3100 max right now.

Answers have not been exactly abundant.

I've also had a hard time getting correct info on brake stuff. It made me dig into it and learn more.

I take the info from the tech lines with a grain of salt. Sometimes you get good info and sometime you don't. I think the phones are manned by minimum payroll people. Sometime it can be very sad!

I'm far from being an expert with brakes, just going with what I've dealt with and learned on my car.

Questions:
What piston sizes are in the Baer 6S's? Wilwood SL6's are 1.62/1.12/1.12(4.03sq/in)
What are your plans with the car? Road Race 1+g's? Street .7-.8g's etc...all boils down to the tire and the amount of stick before it locks up.

There is a huge difference in braking requirements going from .7 to 1+g's as well as increased weight of just 500 lbs...increased rotor size is a big help as well.

I can't imaging a manual 4 wheel disc brake system using a 1 1/16" mc unless it uses huge caliper pistons. (5.5+ sq/in front etc) Maybe on a power assist system.

[clevorguy]

I have cobra breaks on my 70 mustang, 4 piston front, 2 piston rear. I plan on running stock ford cobra MC and hydroboost. The MC is 1 1/16 bore.

I know the caliper pistons aren't huge by any means, but I don't know the exact specs.

[Van B]

Total piston area is 4.66 sq. in. when calculating one side of one caliper. I found one of the pads hanging up in the pad guide (was not moving at all). I am thinking a somewhat small change may give me what I need after talking with Frank and others. Frank is thinking I would need Superman legs to get the pedal to move with 1 1/16 bore.

Still seeking input...

[andrewb70]

Jeff,

I am using a $25 15/16" MC in my GTO. C6 Z06 calipers in the front C4 in the rear. Its a manual setup and I think it works very well.

Andrew

[jaybee]

http://www.jakelatham.com/radical/info/brake_calculators.shtml

I play with this..Best one I've seen yet..

Hey, that if VERRA nice. Just playing with it I've learned a thing or two about braking systems. Thanks for linky.

[Van B]

Jeff,

I am using a $25 15/16" MC in my GTO. C6 Z06 calipers in the front C4 in the rear. Its a manual setup and I think it works very well.

Andrew

I still have your PM on that in my box and you were trying to tell me that over two years ago. I have a thick head. I seem to remember the ports for the lines on the right, or engine side. Is that correct? There is supposed to be one made for export that has the line ports on the left (fender) side and is 1" bore.

I would be willing to try 15/16, but I would like to do it without re bending a new set of lines.

Jeff

[Apogee]

CPP sells a C3 Corvette style master cylinder with a 15/16" bore for disc/disc applications. I would hope that they are ported on both sides, but can't say for sure since they don't have any info posted up on the website about them yet.

Given that the Baer calipers you have are only slightly larger than a comparable C5/C6 set up with ~4 sq. in. of piston area, the 15/16 bore MC would seem to be optimal for a manual installation like yours. The 1-1/16" recommendation by Baer seems out in left field. Not sure where they came up with that. Pads will certainly have an impact as well...do you know what you're running? There might be a two letter coefficient of friction (CoF) code on the side or back of the pads, some thing like EE, FF, or GG, representing the approximate CoF ranges of the pads.

Tobin
KORE3

[andrewb70]

I still have your PM on that in my box and you were trying to tell me that over two years ago. I have a thick head. I seem to remember the ports for the lines on the right, or engine side. Is that correct? There is supposed to be one made for export that has the line ports on the left (fender) side and is 1" bore.

I would be willing to try 15/16, but I would like to do it without re bending a new set of lines.

Jeff

Ports are on the left side. Should be a bolt in and just require minor fiddling with the push rod.

Andrew

[rrunner68]

I'm currently running a 1 1/16" manual with my Wilwood 4 pistons on all four corners, and I believe there is a lot left to be had. Once I can find the bcuks or a trade, I'll be going to a 1" or smaller.

[andrewb70]

Raybestos PN MC39946

RockAuto has them on sale for $62.79 with a 30 day warranty

Andrew

[Van B]

Raybestos PN MC39946

RockAuto has them on sale for $62.79 with a 30 day warranty

Andrew

Did you have to shorten the pushrod? Should have one here this afternoon from Advance Auto Parts. Under $30.

Looks like the port toward the front goes to rear wheels?

[andrewb70]

Did you have to shorten the pushrod? Should have one here this afternoon from Advance Auto Parts. Under $30.

Looks like the port toward the front goes to rear wheels?

You will have to be resourceful with the rod. I cut the end of the rod that came with the MC, threaded it and used the clevis from my old rod.

Correct, front port goes to the rear wheels.

Andrew

[Van B]

Here is an update. I ordered the 15/16 MC that Andrew suggested. It looked virtually identical on the outside to the one I had in the car, so I was happy I wouldn't have to bend lines, etc. I got it mounted in the car on Saturday and when I got the other one out I decided to measure the bore in the old one just to double check and get an exact size. I had gotten a rough measurement of 13/16 or 7/8 when I tried to measure it in the car, without cracking the lines. I could have cried when I measured the old master on the bench...you guessed it, 15/16.

I bled the system anyway, just in case the old master was bad. Tonight I took it for a spin to check it out. Needless to say I was ready to be disappointed. I am happy to say that for whatever reason, they work. I must have had a bad master from the start. I would say they are about 95% better than they were, so I may still have some air in the lines.

Thanks to Andrew, Frank at Prodigy, Kyle Tucker, Jeff Schwartz and everyone else who replied in this thread or to whom I have spoken in the last month. All of you have been infinitely more helpful than the company who sold me the system.