Brake info..

I'm always impressed with the depth of technical knowledge of fellow forum members.Way beyond what I will ever know ! I read questions regularly about brakes on on our cars which are usually concerned with the efficient working of the braking system.Just out of curiosity I began to wonder what sort of pressures and temperatures our brakes work at.Just for a car driven by the average enthusiast for normal road use.Really just tobe aware of what the braking system has to cope with. Does anyone know ? Your thoughts would be appreciated.

Leonard. I can tell you that you can hit 1000 psi with a regular MGB brake master cylinder. That's about 70 kilogram-force/square centimeter.

kelvin

Up in the shop I have a copy of a five hundred page tome on brakes published by ATE, and a copy of the fabled Little Blue Bosch Book, the one before they yanked the directions on how to make a nuclear bomb. ;-)

You don't really want to get to technical with this stuff or they will carry you away in a straight jacket. LOL

Basically, brakes are nothing more than machines that convert kinetic energy into heat and then dissipate that heat into the atmosphere.

How efficiently any particular system does that places it here or there in the "good brake" pecking order.

There is absolutley nothing wrong with drum brakes that a little more size and a little more maintenance will not cure. Porsche resisted disc brakes for years and won lots of races with their drum thingies. Porsche, and MB for that matter, included "exercising the brakes" in their larger maintenance service. That meant that you had to remove the drums individually and have one guy press the brake pedal while another one watched to see that the cylinder pistons didn't pop out of the cylinders. Several cycles of that was supposed to make sure that the cylinder/piston working surfaces were in good shape, but it added about an hour to the shop visit.

The difficulty with drums is that in order to dissipate more and more heat from heavier (mass) and faster (velocity) cars they have to be made larger and larger, mostly to get the heat gone quickly and keep the drums themselves from distorting and reducing their contact with the friction shoes.

Disc brakes have the advantage of hanging out there in the wind with all kinds of surface area to catch the breeze and take the heat energy away. With them you can certainly improve things by making them larger in diameter, but it is easier to just make the discs themselves thicker, more mass to absorb the energy, and/or increase the surface area of the friction pads.

The discs and drums function, as I say, as a heat sink storing the energy and then throwing it off as cooler air passes over the surface.

Temperatures? That depends on lots of things. Start with the velocity and mass of the vehicle, compute that energy and then decide how quickly you you want to get rid of it. If you don't make it go away quickly the energy will build up in the mass of the disc and eventually the old iron hat will get red hot. Porsche sells ceramic discs as an option on some of their cars that will sustain over a couple of thousand degrees and still not melt. Of course they cost about two thou a disc, and that is before you buy the pads that work with them. LOL

Pressures? Hydraulics are a strange realm. I don't think that I have ever read a definitive paragraph on just how much pressure is applied to any given caliper or wheel cylinder, but if you have time and the inclination, I suppose you could start with the actual pressure applied to the pedal by your foot, deal with the leverage through the pedal arm, work that into the diameter of the master cylinder bore and toss in the face area of the caliper piston before you computed that with the larger pad surface. Drums would add another dimension when you had to figure in the leverage of the shoe and then that against any given point of contact between the friction material and the drum.

I use to have an old rubber boot heel attached to the end of a length of lumber that pivoted on a wood screw. I pushed on one end of the board and the heel rubbed against one of the rear wheels of my soapbox go-kart. It worked well enough to keep me out of the storm drains and I was happy.

Slotted and cross drilled rotors ( discs after the Greek and disks after the Romans ) are IMHO a big waste of money for anyone who drives within or any where near legal limits. Even with the old solid iron OEM MGB discs I can't recall ever experiencing brake "fade" or boiling my fluid.

After typing all of this I now realize that I probably didn't answer your specific questions, but I put too much time in it for the delete button so I think that I'll post it anyway. Cheers, Jack

For the real curious Pegasus racing supplies sell temp indicating stickers and
paint that changes colors under cartian temps .. 800deg C //1471 F ..
Temp labels sell in sets of 6 labels (varied temp within a range )
Avail in sets ranging from 149 to 199 F the lowest set,
466 to 554 F the highest set at about 24 dollars a set if stickers.

You can see the pressure in the braking system reaching above 2,000 P.S.I. and temperatures in excess of 450 degrees. This is why the factory reccommends replacing the brake fluid every 2 years due to moisture contamination which can lead to boiling and a spongy pedal. I know a gentelman who used to travel to Germany each Summer in the 50's. He would go to the Mercedes factory and purchase a 300 SL and bring it back to the states. In '56 their was a horrendous crash at Nurenbergring and Mercedes pulled out of sponsering racing. The gentleman hurried to the factory to pick up his car, but was told that it was no longer available. After a long discussion, they let him have a race car instead. Now, at the time, Mercedes was still using drum brakes. They were huge affairs with aluminum housings surrounding a cast iron center. The brake shoes had 5 different materials on each shoe to give maximum efficincy. He still has the car to this day and says the beakes are the best he he has ever used. RAY