Brake Discussion...

[Daryl Smith]

Due to some of the discussions on the forum, and the age of the brakes on my car, I felt the need to renew or upgrade my brakes....Initially at least it was going to be an upgrade....the Z aluminum caliper with vented rotors...after a few comments and research....well I don't really need those....and I started reading more, comparing, and doing some calculations with the 'pedal ratio' issue.
There are options:
Z32
240Z
Volvo (solid/vented)
Toyota
Stock
Custom aftermarket (Willwood, Baer,...)
Eventually a cheaper lighter floating caliper system may be adapted....

I almost went back to stock, but, the cost is getting out there. Add that the stock single master cylinder is not available and I threw in the towel. Done.

For the way I drive, and the mountains and hills here, I felt I should have vented rotors as I have experienced some brake fade at different times, not a lot, but some. I also plan to do some autocross with my brother as a second driver...
SO, I went with the Volvo vented conversion, even tho I'm not real happy about the extra weight. (I haven't weighed them yet, but I am expecting several extra pounds.)

I'm also looking for a short dual master cylinder to adapt to the low windshield car (my '66), which is what got me on to the calculations...

The pedal ratio is listed in the Clymer manual @ 3.9 (page 168). I did my calculations @ 4:1 for simplicity.
With the pedal ratio I began looking at 2 parts of the braking equation - (1)brake line pressure and (2)clamping force.
Brake line pressure = (pedal force in lbs. x pedal ratio)/master cylinder area (sq. in.)
Clamping force = brake line pressure (psi) x caliper piston area (sq.in. of BOTH or ALL pistons)

Without going through all the #'s the stock system, with 50 lbs. pedal force, has 3210 lbs. clamping force.
Just 1/16" step up in master cylinder bore diameter brings that down to 2711 lbs., a 499 lb. decrease!

Changing the pedal ratio, by moving the pedal 1/2" down (4.8:1)
Stock system with 50 lbs. pedal force would have 3851 lbs. clamping force (+640 lbs)
13/16" master cylinder with 50 lbs. pedal force would have 3253 lbs. clamping force (+43 lbs)

Given that the actual clamping force seems to be the # that's important, what should the target clamping force be on a 2000 lb car with 11.18 in. solid discs?
How does that change with a vented 11 in. disk, if it does, heat dissipation being better?
At what point does the clamping force change become noticeable? 100 lbs? 250 lbs??

Thanks for reading.

[fj20spl311]

The pedal ratio is listed in the Clymer manual @ 3.9 (page 168). I did my calculations @ 4:1 for simplicity.
With the pedal ratio I began looking at 2 parts of the braking equation - (1)brake line pressure and (2)clamping force.
Brake line pressure = (pedal force in lbs. x pedal ratio)/master cylinder area (sq. in.)
Clamping force = brake line pressure (psi) x caliper piston area (sq.in. of BOTH or ALL pistons)
.

email sent on calculations.

The pedal ratio in the factory manual is listed at 4.3 IIRC
Line pressure for disc brakes should be a little over 1000 psi.

Choice of brake set-up is dependent on what size wheel you run.
My suggestion is pedal ratio as close to 6:1 as practical for manual brakes.
Vented rotors, 20-24mm or 0.81 depending on the type, either 11 down to 10 1/2
Calipers of equal or larger piston area with larger pads.
The Volvo has just a tiny bit smaller piston area, its OK. Toyota is a better option. Early Z is much smaller piston with larger pads(EDIT: same size pistons), not so good(EDIT: better pads, make it a good choice). Later Z, or skyline, 10% larger area makes it a good option. I prefer the narrower rotor models.

I am working on using aluminum Wilwood GM single piston calipers with 0.81 x 11" rotors, but its stalled right now. You might want to pick up that project.

Jag 2 1/4 Dunlop pistons a good option if you need to be stock, but no vented rotor is a problem.

brake calcultor

If you want to include your drum brakes, I worked some changes that make a pretty good calculation.

[mlwebb]

I like your calculations.
I don't know the answer to your questions, and am not quite on the road yet with my latest brake upgrade, so can't give you a report yet.
20 years ago I did the volvo/girling caliper mod/solid rotor, but didn't think it was significantly better than stock.
After thinking about it, this time I decided the main issue with roadster braking is the pedal ratio. I don't remember the exact ratio I measured for the stock brakes, but think 3.9/1 is optimistic. I replaced part of my firewall and put a set of Tilton pedals in (ratio adjustable 5/1 to 6.2/1), dual master cylinders, the Volvo /Vented Altima rotor, and Ebc yellow pads. I am quite curious about the result, should know in a couple weeks (hopefully).
So anything one can do to improve pedal ratio helps more than anything else, as far as I can see. That, and as small a master cylinder as you can get.
Michael

[fj20spl311]

Here are the numbers I get:

Leg Input force (pounds):50 lbs
Pedal Ratio: 4.1:1
Front:
Front Master Cylinder Diameter (inches):0.75 in.
Front Line Pressure: 232.01 psi
Front Caliper Piston Diameters:2.125 in.
Total Front Piston Area (one side):3.55 sq in.
Front Brake Pad cf: 0.4
Front Rotor Diameter: 11.18 in.
Front Pad Radial Height:~ 2" in.
Front Rotor Torque: 514.55 lb-ft
You need ~1200 lb-ft for 1 g stop

[fj20spl311]

I'm also looking for a short dual master cylinder to adapt to the low windshield car (my '66), which is what got me on to the calculations...

I don't have a single master cylinder car, so this suggestion might be from left field.

I would see if you can put a tandem cylinder/ pedal assembly, or even a triple.

You could start with a pedal plate from A&A
pedal plate

Maybe sandwich two plates with the firewall.

CNC Brakes, Tilton and Wilwood and others have pedal systems

[JT68]

I also have some nice options in process using aluminum calipers with a couple different rotor options. We can swap emails on details. I wouldn't necessarily discount the 240 caliper though, the piston is almost the same size as stock and works extremly well in practice. (Easily exceeds tire capability) I've used them for many years and they are excellent for the cost. You can buy great pads for them too so there is no fade even with a solid rotor. All these options work with the stock master which also has advantages (the bigger the bore master, the less fluid pressure you generate). Shoot me an email and I can update you on status.

Also, you don't REALLY need to go to the dual master. The single master stops as well as the dual does (all things being equal)/ j

[fj20spl311]

For some stupid reason, I was thinking the piston area was smaller on the 240Z caliper.

I stand corrected on the 240Z caliper. Its the same size and pad availability is the most important factor.

Changing the Cf of the pads can make a huge difference.

A single master cylinder will work better than a dual...its just a safety thing.

[Daryl Smith]

Irrelephant

[fj20spl311]

Its been a while since I went through the calculations.....I trust Jake Latham's calculator
http://www.jakelatham.com/radical/info/ ... tors.shtml
There are some assumptions. The pressure is applied at the center of the pad. pad area is ignored

The torque = Cf x clamping force x (rotor diameter - 1/2 the pad height)

If you look into the references listed on his calculator......

1200 psi is from my experience using the calculator and reading on disc pressure gauge requirement.

I was assuming you had a dual piston cylinder, so your calculations for the line pressure are correct for a single cylinder.
I would bet part of the reason the pedal ratio is wrong is it was design for a single piston and not changed when they went to a dual piston.

[Daryl Smith]

Irrelephant

[fj20spl311]

the chances of 1 g braking very slim.

Good pads, balance, 80 lbs pedal pressure, less weight are good goals

[Daryl Smith]

Irrelephant

[Daryl Smith]

Some good info here:
http://www.myturbodiesel.com/wiki/brake ... e-upgrade/

The first article below the main one is also very good.....

[SLOroadster]

I'd love to put an accelerometer in my car and see what I can pull under braking. Its less about the brake calipers, more about pads and tire. If you lack the tire, all you do is slide when everything locks up. Since no one is installing an ABS, its all about the tires. I have to say, with the KFP gold pads that have been heat cycled (fully bedded in) on 225/50/14 R compound tires, my car stops just fine. On the street, there is no way in hell I could overheat the brakes unless I'm stuck behind some truck doing 25 mph with no place to pass. I don't cook them off on the track, so on the street should be totally impossible.

Will

[fj20spl311]

I did figure out though, that if you don't change the front caliper piston area (or the rears), there should be no need to worry about front rear balance of the brakes....should.

One thing I took away from all my reading is you need a brake proportioning value to flatten the response curve of the drum brakes in a Disc - Drum system. The torque response for disc brakes is linear while the response for drums brakes is nonlinear X^2. The proportioning valve flattens that curve.