Brake Pads

[A1990]

Originally Posted by Jeffvette

Go with a high quality fluid. Motul 600 or even Ford Blue fluid. That will help solve the problem of the soft pedal as mentioned before.


As for pads take a look at the Hawk HPS pads, they will do well for street use (don't require to much heat to function) and they will also serve as a good auto X or a couple of track days.

Are these the ones on DRM's site?

You can get them from tirerack which has a good price, along with great shipping.

[Tom]

The volume change with temperature of the calipers/lines/parts is minimal when compared to the displacement of the master cylinder. The temperature increase will not cause an increase in pressure like in a fixed volume gas pressure vessel where pv=nrt applies since the brake system is not a fixed volume system. The v is variable since you have moving pistons in the calipers and a moving piston in the master cylinder where the seal moves over a port open to the reservoir. Your mushy pedal that goes to the floor is caused by the fluid/moisture/contaminant mixture boiling and creating bubbles. The master cylinder does not have enough displacement to collapse the bubbles and adequatly pressurize the system before the pedal hits the floor. When the fluid cools and quits boiling the bubbles disappear and the pedal feel returns close to normal. This phenomenon used to be fairly common in mountain driving, like descending Pikes Peak, before modern brake systems that meet current government brake performance standards. Here is a link I put in another thread that shows how a tandem master cylinder works normally and with one system leaking: http://auto.howstuffworks.com/master-brake1.htm

[petefias]

Originally Posted by Tom

The volume change with temperature of the calipers/lines/parts is minimal when compared to the displacement of the master cylinder. The temperature increase will not cause an increase in pressure like in a fixed volume gas pressure vessel where pv=nrt applies since the brake system is not a fixed volume system. The v is variable since you have moving pistons in the calipers and a moving piston in the master cylinder where the seal moves over a port open to the reservoir. Your mushy pedal that goes to the floor is caused by the fluid/moisture/contaminant mixture boiling and creating bubbles. The master cylinder does not have enough displacement to collapse the bubbles and adequatly pressurize the system before the pedal hits the floor. When the fluid cools and quits boiling the bubbles disappear and the pedal feel returns close to normal. This phenomenon used to be fairly common in mountain driving, like descending Pikes Peak, before modern brake systems that meet current government brake performance standards. Here is a link I put in another thread that shows how a tandem master cylinder works normally and with one system leaking: http://auto.howstuffworks.com/master-brake1.htm

Exactly, the brake goes to the floor because the air bubbles caused by boiling brake fluid can compress. The normal liquid brake fluid does not compress and it operates the wheel cylinder/caliper pistons.

Here is an interesting question: why does the brake pedal go to the floor when you bleed the brakes one wheel at a time with a dual-piston master cylinder? According to howstuffworks the pedal should only go half way to the floor because of the separate circuits.

Peter '95 #442

[Patton]

Tom,... Funny, I just read exactly that from How stuff works right before reading your link, I love that site. Thanks very informative!

Jeffvette, thanks for the product suggestion!

Also, I am wondering what performance differance are there from pad to pad? Since i guess any pad has the ability to lock your wheel up so "grip" isnt really a performance trait... however consistent grip after heating to the surface of the sun is a different matter... also, the dust issue is a small concern of mine, function is my priorty. however which dusts the least while still maintaining the high temp performance without needing to be warmed up like you said jeff?? Still the Hawk?

Thanks guys.

[tomtom72]

Don't mean to hi-jack your thread, Francisco but this is very interesting. I have a Q for the guys that have been there & done this. Way back in the C2 & early C3 era there was a brake option called "J-56", if i'm not mistaken. Any way the pistons on the calipers had phenolic insulators on each piston to slow the heat transfer to the piston & fluid from the rotor. What would the C4's solution to that problem have been from the factory?

If I get what happened to Francisco, the fluid boiled from rotor heat transfer, right? Drilled & slotted rotors solve that problem along with the better brake fluid?

Thanks & my apologies to Mr. F

Tom

[Tom]

With one system leaking the pedal will go most of the way to the floor. You still have to move the other master cylinder piston seal past the port, move the caliper pistons, and use some travel to make up the volume increase under pressure of the components, like the flexible lines, and since one system is out you will generate higher pressures in the remaining system to get normal stop deceleration levels. You can typically generate pressures up to around 2,000 psi in hydraulic brake systems. I've driven vehicles with one system out and the long pedal travel is very disconcerting especially when the front system is leaking on a vehicle where the front brakes are on one circuit and rear brakes are on the other circuit. The government brake system performance standards have a one system out performance standard. In order to meet this standard some small, front wheel drive cars have a diagonally split system. The right front and left rear are on one hydraulic circuit and the left front and right rear are on the other since the two small rear brakes alone can not meet the stopping requirements. The temperatures at the interface between the pad and rotor during hard stops are very high. This heat is dissipated through both the rotor and the pad raising the temperature of both. This heat finds it way into the caliper and hence the brake fluid through conduction throught the pad material, to the pad backing place, to the pistons, and hence to the fluid as well as some through radiation from the hot rotor and pad to the caliper. Brake temperatures during testing are commonly measured by placing thermocouples in the brake pads. The thermocouples are placed at various depths below the surface and when you wear the pad away and expose the thermocouple to the interface surface you switch to the next deeper thermocouple. You can put thermocouples on the rotors but this is more difficult and not usually done since you have to get the signal across the interface from the spinning rotor to the non-spinning side.

[Patton]

Jesus, its Tom mania!

Umm,... Tom Alpha, dont worry about it, you arent hijacking at all! I like the question too, I figure the answer is yes btw.

Tom Bravo, Very interesting retrograde acceleration tidbits. I actually had no idea that they configured them diagonally on some cars. I think that would lead to a very dramatic momemtary yank to one side if there was a leak and a hard stop occured, wouldnt it?

Have any of you seen the video or read the article on the "Turbo Encabulator"?

Originally Posted by Patton

Also, I am wondering what performance differance are there from pad to pad? Since i guess any pad has the ability to lock your wheel up so "grip" isnt really a performance trait... however consistent grip after heating to the surface of the sun is a different matter... also, the dust issue is a small concern of mine, function is my priorty. however which dusts the least while still maintaining the high temp performance without needing to be warmed up like you said jeff?? Still the Hawk?

The difference in pads is the compund and how much "bite" they provide. Track pads are made to bite at higher temps that they encounter, and are horrible for street use, as they are not in their operating range.

Dust and braking capabilities go hand in hand. You want less dust, you get less perfomance, such as with the ceramic pads. You want great stopping power, buy PFC pads and watch the dust fly.

I still like the Hawk pads and it's what I use on my 4 piston set up.

Originally Posted by tomtom72

Don't mean to hi-jack your thread, Francisco but this is very interesting. I have a Q for the guys that have been there & done this. Way back in the C2 & early C3 era there was a brake option called "J-56", if i'm not mistaken. Any way the pistons on the calipers had phenolic insulators on each piston to slow the heat transfer to the piston & fluid from the rotor. What would the C4's solution to that problem have been from the factory?

If I get what happened to Francisco, the fluid boiled from rotor heat transfer, right? Drilled & slotted rotors solve that problem along with the better brake fluid?

Thanks & my apologies to Mr. F

Tom

The way to counter this in a modern caliper is with Stainless Piston compared to the stock aluminum.

The real issue with what happened is the fluid boiled due to not being changed frequent enough. it should be on your list to do every year, and more if you track your car (every event)