All the answers about brakes

[RACER X #99]

Got a question about brakes??? You will probably find the answer here. www.wilwood.com

McCranky

[Toivo]

Didn't find answers to these:

1) Does anyone sell an aftermarket hydraulic power brake setup (in combination with power steering)? Or is there someplace to learn how to adapt a DOHC 4.6L hydraulic power steering/braking system?

2) Electric vacuum pumps for power brake boosters...what is the expected life on these? Are they noisy, bothersome in other ways? Most importantly, do they work?

3) If I'm not producing enough vacuum for power brakes, what's happening to my automatic transmission?

4) What's involved in converting to totally manual disk brakes? Do I need to change the mounting/lever point on the brake pedal or just learn to press harder? Would a different master cylinder help here?

Thanks

and the Master Power Brakes site doesn't answer these questions either, I'm sure there are major liability issues with brake system modifications.

[RACER X #99]

Auto trans, power steering, power brakes?????

Are you talking Cobra or Cadillac?
Cranky

[Toivo]

Originally posted by RACER X #99
Auto trans, power steering, power brakes?????

Are you talking Cobra or Cadillac?
Cranky

...and a stereo I can actually listen to. I've got a heater too!
My wife doesn't have the thighs for the clutch that would be needed which I think is a good thing.

[750hp]

Racer X - if only that were true about Wilwood answering questions.....

I've emailed them on three separate occasions over a period of a month for the following answer :

What size master cylinders do I need?

The details:
I have a Wilwood 6.25:1 ratio pedal box with bias adjustment, Wilwood 6 piston GNIII calipers and Wilwood SuperLite 4 piston calipers at the back, Wilwood pads and I have #4 lines to the front calipers and #3 to the rear. I want Wilwood Composite master cylinders.

This can't be too hard to work out surely!!! I haven't ever received an answer from them

Can anyone help?

[Richard Hudgins]

Craig,

You need to provide a couple of more bits of information.

1. Weight of car
2. CG height and CG location (longitudinal)
3. Front piston sizes
4. Rear Piston sizes

With the above, the proper size MC's can be determined.

Without, it is just a guess.

[750hp]

Richard, here's where I sheepishly admit that my main priorities (mistakenly) originally lay in the horsepower side of the car equation.....

I don't know the CG height or location (and I have no idea what's involved in the measurement/calculation of same). I can only say that my motor seems to sit about two inches further back than the ERA 289FIA mounting location



Other than that accurate assessment ( ), the car really is like any other plain old Cobra replica chassis in design. As such, if you have a "ballpark" CG height in your mind for the average Cobra it'd be pretty safe to use it.

The weight is 2420lb

The caliper piston sizes are:
Front - 1.75", 1.38", 1.38"
Rear - 1.75", 1.75"

Front and rear rotors are both 13" diameter - cross drilled, ventilated and slotted on the front, slotted and ventilated on the rear.

Richard, I'm embarrassed to ask for advice when I can't tell you a definitive answer required to accurately answer my question. In any case, if you think you have a pretty good idea of what bore size I'll need, I'd be happy to hear from you!

Thanks very much,
Craig

[Richard Hudgins]

Craig,

Well I will take a wild ass guess here as to your sizing.

With a 6.25 to 1 pedal ratio, 100 lbs pedal force gives you 625 lbs of MC force. (100 lbs pedal pressure is about where you wish to achieve lockup)

Therefore with the below MC sizes:

.625 dia = .3068 area 625 lbs force = 2037 psi line pressure.
.750 dia = .4418 area 625 lbs force = 1421 psi line pressure.
.875 dia = .6013 area 625 lbs force = 1039 psi line pressure.

Therefore with your caliper areas being:

front = 5.3967 sq. in.
@ 2037 psi = 10993 clamp pressure per rotor.
@ 1421 psi = 7668 clamp pressure per rotor.
@ 1039 psi = 5607 clamp pressure per rotor.

Rear = 2.9914 sq. in.
@ 2037 psi = 6093 clamp pressure per rotor.
@ 1421 psi = 4250 clamp pressure per rotor.
@ 1039 psi = 3108 clamp pressure per rotor.


Assuming a CG height of 17 inches and a 48-52 longitudinal location, the optimum F/R ratio for a one G stop is in the 1.2>1.35 to 1 range.

Looking at the pressure and clamp numbers above, it seems that you will need to use the .8750 diameter master cylinder for the front and the .750 for the rear. This will give you a F/R ratio of 1.31.

Also, the above combination will give about .55>.6 inch master cylinder travel for both units.

The balance bar will give you approximately a 1.6 to 1 adjustment range to fine tune to the bias.

In closing, the above information was compiled after a few adult beverages, therefore accuracy of information and the application of same must be checked by someone who has a clue, as I certainly do not.

[RACER X #99]

Craig,
I knew I had this info but just had to find it. Right from Wilwood engineering,

GN caliper 2 per mc, piston 1.75-1.38-1.38 6 pistons = 7/8-1" mc
SL caliper 2 per mc, piston 1.75 4 pistons = 7/8-3/4" mc
SL caliper 2 per mc, piston 1.38 4 pistons = 7/8-3/4" mc
SL caliper 2 per mc, piston 1.12 4 pistons = 7/8-3/4" mc

Hope this helps,
Cranky

[750hp]

Geez Richard - if that was compiled after the result of a few adult beverages, I might have to start drinking some more

Thanks for not only the end result, but the reasoning and calculation behind it.

And Cranky, thanks for Wilwood's own sizing. I couldn't find it!!! It backs up what Richard had calculated, so I know what I'll be ordering on monday.

Thanks again guys,
Craig