4wheel disc brakes

[5spd540]

What is the big difference in the bore of the master cylinder. I was looking at a wilwood 7/8 1in and 1 1/8 bore and just dont know what to order

[Ron.in.SoCal]

Master cylinder bore needs to be matched to your brake caliper fluid volume requirements (i.e. pistion total sq area). It wiould hellp if you listed what brake/brand model you have.

Our resident expert Tobin will jump in w the exact spec for you...

[5spd540]

I have 12in fronts with a duel piston d52 1le set up and 2002 4th gen camaro rears with a 12in rotor and single piston

[5spd540]

I am thinking of the wilwood calipers but have not decided yet

[5spd540]

Anyone know anything on this

[5spd540]

Well I just took a shot in the dark and got a 7/8 bore master

[T/Aaron]

Use 7/8 for manual brakes and 1 or 1-1/8 for power.

[5spd540]

What is the big difference in the 1in vs the 1 1/8

[Ron.in.SoCal]

I dunno, 1/8"? :D

JK Sir! Bore size must be matched to caliper piston diameter (and pedal ratio) to ensure good pedal modulation and not too much pedal movement. Keep reading, there's lots of info on this topic here.

[Ron.in.SoCal]

Here's an overall discussion on the topic:


[COLOR="#0000FF"]Basically stopping the car goes like this:

Lets assume a maximum effort stop where you are pressing on the brake pedal with 100lbs of force. Using a 6:1 pedal ratio, that force is up to 600lbs at the pushrod for the vacuum booster. IIRC vacuum boosters give about 3:1 assist. Now you have 600*3 = 1800lbs of force on the master cylinder push rod. Assuming the MC has a 1.25" bore, that is 1.227 sq in. Fluid pressure is measured in PSI, pounds per square inch. 1800/1.227 = 1467psi. Pressure is constant in a closed system, so 1467psi at the mc is 1467psi at the caliper. Now assume we are using 4 piston calipers with 1.75" pistons. Caliper piston area is 2*(1.75/2)^2*3.14 = 4.8 sq in. Now the fluid pressure is evenly distributed on the pistons. The total force on the pistons is 4.8sq in*1467psi = 7041lbs. That force is transmitted through the pad and is applied to the rotor. But there are losses in that transfer due to sliding. Lets assume the coefficient of friction between the pad and rotor is 0.4, a common value for street pads at low temperature. So the force on the rotor is 7041*0.4 = 2817lbs. Now that is acting on a moment arm from the center of the hub to basically the center of the pad. Lets assume a 14" rotor which would net a moment arm of about 6". So the moment at the center of the hub would be 2817 * 6 = 16900 in lb or 1400 ft lbs. That 16900 in lbs acts on the tread of the tire. Lets assume a 26" tire, so the moment arm is 13". The force on the tread would be 16900 / 13 = 1300lbs. So what who cares. Lets assume this is a heavy pro touring car with grippy tires. On a max effort deceleration a lot of weight transfers forward. So lets say during the deceleration the weight on the tire is 1250lbs. If we assume the grippy tires have a coefficient of friction of 1.0 between the tire and road, that means we can tolerate 1250*1.0 = 1250lbs of tread force. So based on all these calculations, we are using 1300/1250 = 104% of the available grip. In other words the tire will lock up.

[5spd540]

here's an overall discussion on the topic:

thanks

[5spd540]

Nobody can put some info on this

[makoshark]

Do you plan to run or are you running power or manual brakes? 7/8" for manual brakes and 1" to 1 1/8" for power, basically. There's more to it than that, but that is the gist of it. I recommend calling Wilwood and discuss what you need with them. That would be your best source. They will answer the questions you do not know to ask, so you'll get better feedback with them on the phone than on here without knowing all the details we all need to properly answer what your seeking.

[Apogee]

Nobody can put some info on this

What sort of info are you looking for, specifically? As Ron already stated quite well, you need the bore size of the master cylinder to be sized relative the the rest of the brake system, including not only the caliper piston bore sizes, but also the pedal ratio, booster/gain multiplier, rotor diameter and even pad compound. Moving up or down a 1/16" in MC bore sizes in the range we're talking about here, 7/8" to 1-1/8", results in about an 11-12% difference in pedal travel and effort. As the bore size gets smaller, both the pedal travel and output pressures increase. Alternately, as the bore size gets bigger, both the pedal travel and output pressure decrease.

With your current D52/LS1 F-body front/rear caliper configuration, you have a somewhat substantial mismatch in terms of caliper piston area from front to rear with too little rear bias. If you're going to err one direction, that's the direction to go, but it's less than ideal. The D52 front calipers have 2-15/16" diameter pistons which equates to 6.7 square inches of piston area. The rear LS1 F-body calipers have 45mm diamter pistons, or 2.46 square inches of piston area. In your application, switching to the Wilwood D52 caliper with 6.28 square inches of piston area would be a step in the right direction in terms of front to rear bias, however not a very large one IMO.

HTH,
Tobin
KORE3

[5spd540]

I got it figured out now without all the techanal bs. Thanks to wilwoods tech help