Another Master Cylinder Sizing Question...

[Andrew Robertson]

Hi All,

Mclaren M1C replica, race only on slicks, about 900-950kgs with me in it, 40/60 weight dist, 17x9 fronts, 18x13 rears, Wilwood Superlite 6 pots with 4.04 sq/in piston diameter on both front and rears, and same 353mm rotors front and rear. Wilwood 6:1 ratio pedal box. Want a firm and short-ish pedal and don't mind effort as long as I can brake to the traction threshold at will.

After searching the archives seems it's very application specific, with 3/4 bores seeming too soft for several posters. I was leaning towards starting with twin 7/8, or maybe 7/8 back 3/4 front, and dialling in from there.

What do you think?

Also, what size clutch master fully strokes the Wilwood pull-type slave?

Thanks, Andrew Robertson

 

[Cliff Beer]

Hi All,

Mclaren M1C replica, race only on slicks, about 900-950kgs with me in it, 40/60 weight dist, 17x9 fronts, 18x13 rears, Wilwood Superlite 6 pots with 4.04 sq/in piston diameter on both front and rears, and same 353mm rotors front and rear. Wilwood 6:1 ratio pedal box. Want a firm and short-ish pedal and don't mind effort as long as I can brake to the traction threshold at will.

After searching the archives seems it's very application specific, with 3/4 bores seeming too soft for several posters. I was leaning towards starting with twin 7/8, or maybe 7/8 back 3/4 front, and dialling in from there.

What do you think?

Also, what size clutch master fully strokes the Wilwood pull-type slave?

Thanks, Andrew Robertson

Andrew, are you using a brake booster or no??

 

[Andrew Robertson]

Gidday Cliff,

no, unassisted. Andrew

 

[Bob Putnam]

My back-of-the-envelope calcs indicate that, with a 1.3G stop and 9" CG height (both values probably too low), you'll have a slight front weight majority under braking. Stick with equal M.C. diameters. With your low weight, you can probably get away with the 7/8" diameter, although the effort will be fairly high. And watch out for that first cold stop!

 

[Ian Clark]

A soft pedal doesn't make sense with this combination you should be fine. However you have 24 pistons to engage so the initial take up will use more pedal travel. Once engaged, it should be hard. Use top quality flex lines between the calipers and chassis, hard piping the rest would be the way to go.

Also the setup of the brake balance bar and pedal push rods requires a lot of experimentation to get right. A slight over correction can use a lot of travel and make finding the ideal balance almost impossible. You can be sure the final settings won't be 40/60 across the balance bar with equal length pushrods.

Properly adjusted you'll be ok.

Cheers