Master Cylinder bore Size

[mdauth]

Need help, I changed my pedals in the car. For the brakes I have a dual master cylinder with a balance bare with a 6 to 1 ratio and the calipers are from a stock Mustang II. Wilwood told me to use a 7/8” bore for the front and 1” bore fort the rear. Anyone have any suggestions. Thanks, Mike

[mickmate]

Are the brakes Mustang front and rear? Can you count the pistons and measure there diameter?

[Rick Parker]

Why second guess their recomendations, that's their business.

[Ital-cobra]

I have to agree with rick.

[Tom Cimino]

The way I understand it is the smaller the master cylinder bore, the less pedal pressure it takes to apply the brakes. This also increases the pedal travel. I too have dual master cylinder/balance bar, but with 3/4" bores. The brakes are marginal at best. If this theory holds true, the 7/8" and 1" bore sizes would require more pedal pressure, which in my case, would not be a good thing. Front brakes are Wilwood Dynalite and rear are Lincoln Mk 8 discs. Always looking for upgrade info.

[strictlypersonl]

Wilwood Dynalites are available with bores from 1.75" to 1.38" diameter. That's a 40% difference in area (and pedal pressure). If you factor in the rotor diameter, you can end up with a bad combination.

But, some of this is "culture shock". We're too used to power brakes, and have gotten lazy.

[Dwight]

I don't think the size of the cylinder bore has much to do with pedal pressure. The length of the pedal (pedal ratio) has more to do with the amount of foot pressure needed to apply the brakes. The master cylinder bore size has to be matched to the size caliper pistons. Disc take more fluid than drums. The pedal should not over travel the mc piston, bottoming out. This will damage the master cylinder. So pedal travel = mc piston travel = correct amount of fluid to the wheel calipers so they travel the full range to close the pads. or something like that.

There is a lot to a well engineered brake / clutch system.

There are a few guys on this site that know a lot about brake systems. Let hope they post so we can all learn.

Dwight

[mickmate]

Cylinder bore has a lot to do with pedal pressure. That's why it's measured in psi. You change the bore a little and it changes the si(square inches) a whole lot. A couple of guys that know something about brakes have already posted BTW. Even if Mike just knows how and why the components he has work or don't together he's ahead of the game in my opinion. Knowing what's under your butt does a lot for understanding it's and your capabilities.

[john chesnut]

Mickmate is correct. Cylinder bore has alot to do with pedal pressure. The smaller the volume of fluid that you are trying to push through an orvice the less force required. A 1 inch front and 7/8 rear MC was recommended to me for the Corvette brakes in my cars. The brakes were almost non existent. Very scary. I switched them out to 3/4 and 5/8 and the brakes now are fantastic. The pedal travel is almost nil and the clamping force is great. I use 2# residual valves to keep fluid from draining away from the wheel cylinders as my Master cylinders are lower than the wheel cylinders. The residual valves are installed in the brake lines as close to the MC's as possible. For drum brakes use a 10# residual valve.
I use a 2# residual valve in my hyd throwout line as well as it keeps pedal travel to almost zero. John

[undy]

Larger M/C bore = less fluid pressure, more volume = shorter foot stroke.

Smaller M/C bore = more fluid pressure, less volume - longer foot stroke.


If you lack stopping power then a smaller M/C will increase pressure. This is assuming your balance beam is adjusted correctly. I was plagued by poor stopping power and now run 5/8" on the front and 3/4" on rear which took care of the problem in my case. It was downright scary before I changed my original setup (1" on the front, 7/8" on the rear).

Dave

[Ital-cobra]

undy are you also useing corvette set up? Thats what I have C4 corvette brakes 3/4 front, 7/8 rear and stopping is a little scary.

Joseph

[undy]

Originally Posted by Ital-cobra

undy are you also useing corvette set up? Thats what I have C4 corvette brakes 3/4 front, 7/8 rear and stopping is a little scary.

Joseph

Nope, running the 12.18" 4 piston Wilwoods in the front with Ford Exploder discs/calipers in the rear.5/8" in the front w/ 3/4" in the rear would definately reduce your pedal pressure requirement.

Dave

[Tom Cimino]

Lots of good info here. My Dynalite calipers are 1.75". I'm planning to change my pedal assembly out for the Wilwood 6.25:1 ratio pedals. Maybe I'll try the 5/8 bore M/C first. That would be a cheap fix, if it works. Go fast cars need stop fast brakes!