Thanks to everyone for the input It looks like i will need a test day to
get these brakes set up the right way.
The rear at pressent have to much pad area ,it looks like they will need a
less grippy pad . and increase to a 7/8 bore on the rear master. thanks
rob
----- Original Message -----
From: "Richard Good" <goodparts@verizon.net>
To: "rob" <19to1tr6@comcast.net>; <fot@autox.team.net>
Sent: Thursday, June 04, 2009 8:16 PM
Subject: Re: [Fot] brakes
> Quite a few factors contribute to determining the master cylinder size
> needed. Weight balance of the car and other factors determine the amount
> of braking desired in the front vs. rear. Rotor size, pad material and
> caliper piston area determine the PSI of hydraulic pressure required to
> cause the desired braking in each circuit. Master cylinder piston area
> determines the amount of mechanical force required on the piston to
> produce the desired hydraulic pressure. And of course mechanical leverage
> determines the amount of force needed on the pedal to produce the required
> mechanical force on the master cylinder piston.
> Depending on the equipment used, the required pressure can be quite
> different in the front and rear circuits. Large rotors and calipers with
> four big pistons in the rear will not require much pressure to do alot of
> braking. If this is used with stock calipers in the front, alot more
> hydraulic pressure will be required in the front than the rear. A larger
> rear master cylinder will be required to keep the balance bar reasonably
> centered. With a single piston master cylinder, the front and rear
> circuits must be designed to produce the desired braking force with the
> same hydraulic pressure. Doing the same with a dual master cylinder will
> allow the use of two identical cylinders. Wilwood offers most of their
> calipers with a wide range of piston sizes to help in balancing the
> system. However, if you need to change the hydraulic ratio of an existing
> system I am sure one master cylinder costs less than two calipers.
>
> Increasing the hydraulic advantage by reducing the master cylinder piston
> area or increasing the caliper piston area or increasing the mechanical
> advantage will decrease the force required on the pedal. Going too far
> can make the pedal feel spongy. I once worked on a 550 Spyder replica
> that had "spongy" brakes. There was no problem locking up the brakes but
> it felt like there was air in the system. I finally gave up trying to
> bleed non existent air from the system and figured out that there was so
> much mechanical and hydraulic leverage that the calipers were over powered
> and flexing with little pedal effort. I reduced the mechanical leverage
> in the pedal by a large percentage and fixed the problem. Still plenty of
> braking without too much pedal effort and now a nice firm pedal. A larger
> master cylinder would have done the same thing. Of course if you go too
> far in that direction you will not be able to stomp hard enough on the
> firm pedal to stop the car.
>
> Richard Good
> Good Parts
>
> rob wrote:
>
>>Can anyone explain why a brake system with a balance bar and duel masters
>>would have different size masters ie a 5/8 bore for the front and a 3/4
>>bore
>>for the rear also can anyone sujest the correct size masters for a TR6
>>with
>>stock front brakes and rear disc brakes with a 4 piston willwood caliper.
>>Thanks rob
>>_______________________________________________
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