Brake question....

Hydraulic pressure will depend solely on the size of the master cylinder and the lever length of the brake pedal. Brake clamping power will be dependent on these as well as caliper puck size. A bigger master cylinder piston will give you a more solid pedal feel with less travel but your hydraulic pressure will be less as will your clamping force. A smaller culinder will be the opposite. Softer pedal and more travel but higer pressure and clamping force. On the caliper side a smaller caliper puck size will give you less clamping force than a larger puck for the same size brake pad.

Blaine

When I built the MGB I put disk brakes in the rear and larger brakes up front. I replaced the MG master with a wilwood. In looking for the proper size I had a spreadsheet I worked it from one end to the other.

It started with:
The coefficient of the brake pads,
the number of brake pads,
The caliper pistons, numbers, bore,
the rotational distance of the pad contact,
The tire diameter
The weight distribution,
Difference in these variable with the front and rear,
MC diameter
Pedal to MC ratio,
and a number other things.

All this works back to required pedal force and required MC volume.

In the end a smaller bore gives you more travel, less pressure and a better feel until you run out of volume.

There are a few more things involved then what it seems on the surface.

The best place to look for this information is either on the WILDWOOD Site for the Ford Motorsport site. Both explain the relationship between the master size and the caplper size.

Ron

quote:

Originally posted by comp2:

All this works back to required pedal force and required MC volume.

In the end a smaller bore gives you more travel, less pressure and a better feel until you run out of volume.

I assume you are talking about caliper bore size here? A smaller MC bore will only increase the operating pressure at the expense of more pedal travel and a softer pedal. Technically the calipers will clamp harder with a smaller MC (if you can push the pedal far enough).

Blaine

Turbo, trying to calculate this stuff is full of possibilities for error. Assuming you want to modify your brakes, here's a real-world baseline: I run vented rotors the same dia & thickness as stock solid rotors, Wilwood Superlite 2s in front with Porsche 911S (front calipers) in the rear, stock pedal lengths and a late GM power brake assembly with stepped master cylinder bores as converted for the Pantera by Precision Pro-formance. The car uses no shuttle valve, aeroquip lines and a manual Kelsey-Hayes proportioning valve, all plumbed to generate adjustable pressure in back with full pressure in front (stock plumbing is exactly backwards of this). To get a verifyable adjustment, I added small liquid filled 0-2000psi gauges permanently mounted on the brake lines. The combination is adjusted for about 1100 psi on the fronts and 950 on the rears with the engine at idle, using firm but not panic-stop foot pressure. This gives a nice pedal feel with outstanding stability under heavy braking, without over-braking the fronts in the rain. Mid-engined MR-2s use a temporary plug-in gauge set that screws into a front and rear bleeder screw to verify the balance of their non-adjustable proportioning valve settings, and they're pretty close in pressure to what I found to work well with our Pantera's assembly. This should give you a starting point without wearing out your calculator.