[Fot] brakes

[rob]

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 at verizon.net>
To: "rob" <19to1tr6 at comcast.net>; <fot at 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
>>_______________________________________________