braking capacity

[chris parker]

prices are all in the new catmonster four brakes are £258.75 and six's are 3£311.25 for calipers with handbrake operation approx £70-80 more than the same caliper without
hope this helps speaking to hispec at the nec the handbrake operates on only one piston from one side but they did look cool

 

[Julian West]

Chris,

I was wondering about the capability of the H-brake, being that it only works on one piston especially with 1100 kilos of GT40 to hold on a hill!!!

However it looks beautifully made & I'm sure Hi-spec wouldn't sell anything they're not happy with.

What's the general consensus as to the differences between 4-pot & 6-pot calipers? The 6-pots are tempting, but aren't they a bit 'Max Power' & do they actually provide better braking than 4-pots?

 

[Lee]

I was also wondering about this. The 4 pot and 6 pot calipers actually use the same brake pads. I guess the 6 pot will have more surface of fluid touching the cylinders so may dissipate heat a little bit better? As you say Julian, it might be a bit Max-Power, particularly on the back.

 

[chris parker]

when i spoke to the chaps at hispec they said the four and six pot calipers used the same alloy block but the six pot gave better feel on the brakes apposed to a better braking capacity but the calipers would be the same size. the handbrake only operates on one side and i too wondered if it was going to be ok and if it only operates on one side surley over a period of time it could warp the disc
i guess hispec have already looked into this and would not sell a product that was not going to do the job due to a lot of unhappy customers i think i'm going to go for them on both front and rears
chris

 

[Ricky]

I have a few questions that maybe Dave Wharran or others may be able to comment upon.

I presently have Willwood 4 spot front & rear calipers on my RF (superlight & dynalites - both without bridge bolts, just pins to retain the pads) these are working on 13" front & 12" rear rotors. I am now using 0.625” front & rear m/c's instead of my original 0.75” m/c’s which was done after reading Dave’s post on braking capacity. The pedal ratio is 3.5:1. A Tilton balance bar with remote adjuster, hard steel lines and braided flexible lines are also fitted to the calipers. Wheels are 17”.

This appears on the surface to be similar to Dave’s brake setup except for the pedal ratio.

For the spec of the brakes I am still not really happy with the stopping power of the brakes at the track (or on the road really) and during a track session on the weekend found that they seam to be aerating the fluid causing quite a long pedal with little power. The pedal is still long even after the system has been left for a few days, hence the thought of aerated fluid. (Longer than normal)

The brakes were bled when I fitted the smaller m/c’s and the pedal felt quite reasonable but stopping power was only marginally increased and the pedal has never really been “Hard”

I am now making a new pedal (5.25:1) to increase the leverage and line pressure, but before changing back to the original 3/4" m/c to reduce pedal travel I wanted to find out what kind of pedal travel is the accepted norm. I am concerned the extra leverage will increase the travel even further.

In addition to hopefully correcting the system I will do the following

• Check for runout in the rotors (I am sure they are ok)
• Check rotors and pads for glazing and deglaze if they are
• Fit residual pressure valves to front & rear m/c’s
• Re-bleed the brakes again
• Consider different pad compound (from memory the existing ones are Polymatrix A compound)

So what pedal travel is acceptable and what other things can be done without spending mega $$ on changing calipers etc to improve the system.

Any help is appreciated.

Regards,
RV

 

I could be wrong here, but I would double check before using residual pressure check valves. I was always under the impression they are meant for drum brakes only where there are springs pulling everything back. With calipers, it is the seal inside which does the final pull to get the pad pressure off the rotor. The check valve would eliminate this, causing dragging brakes.

 

[Bill Musarra]

Eric,
According to "Brake Systems OEM & Racing Brake Thecnology" residual valves are used in certain aplications. If the master cylinder is located below the horizontal plane of the calipers, you will need a residual valve (2# for disc, 10# for drums). It prevents rhe fluid form flowing back to the master cylinder wihtout causing the brakes to drag. If the MC is above, you might get away without one for the drum aplication, if the spring pressure is not excessive, but if you are below as GT40s are you don't have a choice.
Bill

 

[Ricky]

The RPV I intended using was the 2lb wilwood version. The 10lb version is strictly for drum brakes. I think I must be getting some back flow of fluid causing the longer travel so figured I could not really go too far wrong in fitting them. With the setup I have the m/c's are definately level or slightly lower than the callipers.

 

[Trevor Booth]

Rick,
Check the end float in your front & back wheel bearings. Excessive end float can knock the pads back.

 

[Mike Dozier]

Clarification....I believe it's the FLUID level and not the
master cylinder location that must be above the calipers.
So if you are using remote reservoirs mounted high enough,
you won't need these valves.

MikeD

 

[Bill Musarra]

Mike,
you are correct. Didn't read far enough. In their recommendations they say, "Whenever possible, be sure brake fluid level is above both master cylinder and the brake calipers, to prevent "bleed down.""
Bill

 

[Dave Wharran]

Rick,
I replaced my .750 front MC with a .625. The rear is also a .625. Balance bar slightly to the rears. My pedal pressure vs stopping power is what I consider okay now. There is a fair amount of pedal travel, but not an overly amount. I can measure it tomorrow.
The brakes feel good now with stopping power increasing as rotor temp goes up. The pedal feel is not as hard as some other systems I've driven, but is not soft either. Never had any problems getting air into the system or boiling the fluid. I still need to get different pads to get rid of the squeeling at low pedal pressure, slow speed stops.

ERA had fitted residual valves on both front and rear MC's. I had problems early on with the fronts not releasing after a stop, so I removed the residual valve from them. Still have one on the rears.

There are Earl's teflon lined ss braided lines from the MC's to bulkhead fittings, steel tubing to each wheel, and Earls flex lines to each caliper.

One thing Baer cautions against is letting the angle of the pedal bar to the MC rod become greater than 90 degrees.

 

In a way there is not to much problems in selecting brakes, but if we like to take things a bit futher, brakes may becom quite difficult to select.
I am right now in the work of translating my Chassís book to English. If you people int the GT-40 forum is interested I may select a few words about brakes, for a new tread in a not to distant future.
Just a warning, my translation may not be correctley done,
and the book vresion has to be read by an English tecnichan before release. But I don mind a few laugh...
Goran Malmberg

 

[Ricky]

Thanks for the information.

I have made the new pedal which ended up at 5.5:1. I have refitted the .75" m/c as the pistons in the calipers are 1.75" as oppossed to the smaller ones noted in Dave Wharrans spec so figured the extra m/c capacity will be needed to reduce pedal travel. After reading about brakes being locked on / not releasing I did not fit the residual pressure valves but can fit these latter if need be. Now I just need to rebleed and I will let you know how it goes.

FYI, based on some calcs I did I figure the following line pressures as a comparison of the old system versus the new.

.625 m/c with 3.5:1 pedal and 75 pound pedal force = 840lb line pressure (Old System)

.75 m/c with 5.5:1 pedal and 75 pound pedal force = 1100lb line pressure (New System)

It will be interesting to see how much pedal travel difference there will be with the new set up given that I should end up with more effective stopping power.

Regards,
RV

 

Rick
Just a short not here, as you mentioned "stopping power".
The size of the caliper, pads and discs has very little to do with "stopping power". Those parts together with pedal lever and hydraulic balance affect pedal power needed and front to rear braking balance.
Ok, BALANCE is important to stopping power, in order to make use of all the rubber.

What counts is CAR BALANCE, weight tranfer under braking and rubber.

All other factors is to be calibrated against "HOW MUCH" braking we intend to do.
Regards
Goran Malmberg

 

[Trevor Booth]

check your calcs Rick.

 

[Ricky]

OOPs, You are right Trevor. I grabbed the wrong column in Excel.I grabbed the piston diameter in Inches rather than the Piston area in inches. and multiplied by 2 (being 2 m/c's)

The .625 + 3.5:1 setup should have been 856 lb & the .75 + 5.5:1 setup should have been 891 lb

 

[Chris Duncan]

Goran,

You are correct.

When the brakes are big enough to lock up the tires bigger brakes will not stop the car quicker.

""All other factors is to be calibrated against "HOW MUCH" braking we intend to do.""

"How much" is the question. Once you define what's big enough to lock up the tires then you have to determine how much repeated hard braking is required.

A given size may be adequate to lock up but with repeated hard stops will start to fail due to heat.

Larger brakes dissipate more heat for repeated hard stops, but they start to have negative effects in performance with greater unsprung, rotating, and overall weight.

I wouldn't necessarily go with the largest rotor that fits inside the wheel but with the smallest rotor that holds up to repeated hard braking without heat failure.

 

[Trevor Booth]

Rick , if you have 2 M/C and a balance bar set to equal, then your 75lb pedal effort is only 37.5 per cylinder. 37.5*5.5=206 per cylinder. piston area for 0.75=0.442 sq in. = 466psig. If you have an inline or tandem M/C the effort of 75 is to each cylinder.

 

[Ricky]

Well, I have been right through the system. The m/c's are changed, The new pedal is fitted. I have fitted bridge bolts to front and rear calipers (wilwood superlight & dynalight) Quick road test and MAJOR improvement in bite and reduced pedal travel. The rear pads have severe radial tapering due to caliper flexing but these and the front are to be replaced. I expect the pedal travel will reduce further with new pads.

I have had Hawke HP plus recommended by a dealer but what are other people using? Has anyone had any experience with Hawke?