Brakes are for sissies!

That being said, I'm a grinder by trade and work with many types of metal. Yes, stainless is a poor conductor of heat.

I used to maunfacture brake pistons - steel, stainless and alot of aluminum -  and had discussions with Hayes Brake engineers. 69Mini mentioned "clean the piston surface with scotchbrite" Wha??? Use an abrasive to clean a piston? Absolutely. Surface finish of the piston is important. A super smooth/shiny piston is not good. A slightly rough finish (25-40rms) is optimal. The grain of the finish should be around the piston, not up and down. ()))) not ()==) The reason is, is that the seal can 'grab' the piston and 'pull it back' a few thousandths when pressure is released, thereby reducing contact heat transfer.

It is all about managing heat , I used 20 slots about 1/8 inch wide with a end mill not a ball mill, to open up the air flow  as much as possible   i put in high temp oven fiberglass  then pressed in a stainless steel cap that had ceramic plasma sprayed to the back , the back side of the pads were polished , a .020 thick stainless  shim was put between the pad and the cup, I opened up the  bridge of the caliper to allow more air in, coated the caliper with heat conductive back oxide , I used performance friction 93 pads. And I would brake harder and later then most, the brakes did give problems If I used them to much , one point is not to rest on them , stomp and push hard and get off , that way you put heat in and let it dissipate , I used special high temperature seals I made on the  lathe, can not remember the material  but it was silicon based , but it was very high in temperature ability.  I also had my car set up to slideways  i.e. many corners others braked for I just threw it a bit sideways and did not touch the brakes.

the machining of the caliper pistons shown in the photo is a step in the right direction, but I would remove more piston material so as to further reduce the contact area between pad and piston.  I would make the machined grooves both wider and deeper unless there are issues with the outer seal contacting the piston and causing problems.  I'm not recommending it, but some people race without the outermost seal, perhaps to avoid problems of it contacting the machined areas of the piston.  Some have also used thin sheets of stainless steel between pad and piston to even further reduce heat transfer.

hunter2, was the bent BINI at Blackhawk the one that was placed on the pole even though it didn't have the fastest time to justify it?  Shortly after the start, the BINI ended up getting in the way of two well-driven and faster classic Minis who were having a real battle.  Anyway, one or both of the Minis spun, contact occurred and one of the Minis contacted the BINI causing it to DNF with a damaged steering rack.  I never heard the part about BINIS dropping out with brake problems.  Too funny since they were supposed to be the heroes of the meeting.  Unfortunately, they just picked the wrong track for their 2700 pound bulk.  That plus they raced against a driver who had many years of experience racing Minis very successfully at Blackhawk.

Mini Meet East Meets West at Blackhawk Farms in 2004 only the Classic Minis finished the Mini Challenge...all the MINIs went out with brake problems (one was bent).

the track is Blackhawk and other drivers have also had problems with overheating brakes in Minis.

It may not be obvious from this track diagram: http://www.blackhawkfarms.com/tracktour.cfm   but Blackhawk has a lot of heavy braking  from medium to high speed for such a short course(1.95 miles) and the brakes never get much chance to cool.  There are also a few very slow turns which also serve to keep the brakes from cooling.  Yet another factor, not just at Blackhawk, is that some Mini racers have the brake bias adjusted so far to the front that the rears effectively contribute very little braking, thus overworking the front brakes.

I have personally seen a Mini come off of the track and proceed to drip brake fluid at a fast rate beyond its melted front seals.

 

That was going to be my suggestion.  If there is a brake failure that occurs on one track only, perhaps it has something to do with driving style?  Are the others who race Mini's having this problem as well?  If not, I would suggest the driver is over using his brakes.

 

R

Wilwood's Thermlock is another heat barrier.

 Tulka

The turning operation would be beveling the piston edge to reduce the contact area. The slots should probably be done in a mill. I like the round slots instead of square to avoid stress raisers since there is a lot of heat cycling going on in the caliper pistons.

The split pipe collet I find quick and handy for both lathe and milling setups.

Cheers,

Kelley

Yes, I sent you the video clips and pix, but I also have gone through 2 hard drives since then and only have the pictures, no videos, I'll search and see if I can find if I uploaded some of them,

I have been told by a few Mini racers that brakes are for getting through tech, then just barely needed once on the track, I guess it takes a few years to get to that level, B.S. Levy told me to stay away from Mini's, too expensive and he lost his brakes after 2 laps in a mooched Mini, he didn't say who's Mini,

apologies for going way off topic...

Manuel, someone sent me a short video of my car, right after that race, I remember the file information showed it was from a Kodak camera, was that you? I tried to make a miniature animated GIF from a few frames of that video, but never got the file size small enough to make a decent avatar. I lost the video (and 3 years of other important stuff) when my laptop ate its hard drive. Oh well. I read the rules before going vintage. I went to a Sebring HSR event just as a spectator, I found the HSR chief of tech, I had my old SCCA log book and some current photos of the car. I asked him a bunch of annoying questions. It came down to this: I had to take off the Gp5 flares and slicks, and run Gp2 flares with treaded tires. That's all they required me to change. Even old race cars are required to have modern safety equipment, fuel cells, safety harness, fire system, etc. If rules allow a brake upgrade over stock brakes, then it becomes a matter of cost to me; when I found that 6-pot racing brakes cost less than stock Cooper S brakes it was a no-brainer. But in racing, I found no performance advantage in the KAD brakes over the old S brakes (which probably is an indication of my lack of skill/bravery) but they should have an advantage in a crash-avoiding, life-saving situation, so I want them on the car. I do bring my old Cooper S front brakes with me when I go to the track, they are my spares.

now back to topic... Kelly suggests a simple way to mount the piston in a lathe. That is good, but I just don't see any point in mounting it in a lathe, I don't see any turning operation to be done on a piston as the workpiece. For milling, I would take a block of scrap aluminum or even a piece of wood, face off top, bottom and two of the sides, drill a hole bigger than the piston, then saw this block-with-a-hole-in-it in half, sliced across the hole diameter. Wrap the piston with leather or vinyl or paper or whatever, put it in the hole, clamp it in the milling machine vise, mill some slots, Bob's your uncle.

The simplest fixture for the lathe would probably be to take a short piece of aluminum pipe and turn it allow the piston to slip inside. Split the pipe on one side so it can clamp down a bit on the piston. Fit the split pipe with the piston inside in the chuck and turn. You could use the same thing on a mill. All you really need to do is protect the piston from marring by the clamps or chuck.

Cheers,

Kelley

What did they say when you ran Barber ?, I took this entering the back straight,

 

Manuel, make a fixture to mount them on the milling machine. The ones that 69Mini shows in his photo look like the slots were milled with a ball-end mill.

I believe you when you say SVRA wouldn't let you run modern brakes, and I am pretty sure VDCA just uses the SVRA car prep rules. My car was an SCCA race car in the 60s, I would have to make a lot of changes to my car to make it comply with their notion of a "vintage race Mini". I would be changing so many things that my car would no longer be representative of its own history, it just seems wrong so I don't run with them. HSR only requires you to keep the same style of brakes that were originally on the car, in other words disc front, drum rear, if you have 10" wheels you should be able to run HSR.

When I got my car it had Wilwood Dynalite calipers, a west coast VARA legal car, I knew they were not legal in HSR, SVRA, VDCA but thought I would wait until tech said something, but then I discovered they are too close to the wheel to run anything but Keizers because they are flat across the center bead to bead, I tried GB's, Wellers, Mamba's, nothing would clear the calipers so I bought the Cooper S ones, now my question is how do you put the pistons in a lathe to bevel them without damaging the contact surface ?.

Not me, just the experts I associate with.  When you are in town, I'll take you to see the experts race shop.  These guys don't apply to run the Historics, they are asked what they are bringing.

Great pictures Dave. Thanks!! Since when have you become such and expert!!!

cutting reliefs in the pistons not only alllows some air to cool things, but it reduces the contact area between pad and piston, thereby reducing heat transfer.  The race track in question is a real brake abuser, probably much worse than any other tracks that Minis race on in North America.  Come to think of it, the driver in question is also a bit of a brake abuser.

Got this from the Mintexracing site: " For Group N or production based classes using production based calipers, it is strongly urged that mild-steel brake pistons are removed and replaced with stainless steel or titanium alternatives. Cutting slots in the face of the pistons so that air is able to vent to atmosphere is also recommended. A production piston is typically hollow and if it is not ventilated for use with the F-Series material the air inside the piston becomes superheated from the backplate of the brake pad and this heat transfers to the fluid. "

MM lists the Cooper S stainless steel brake piston as 1.75" diameter. I looked at the thermal barrier pistons on the Wilwood site. These are coated aluminum, with a stainless insert. They have 1.75" diameter pistons in different lengths.

Thanks Neal.  I have a back up set in my tool box so I figured it was worth taking a picture.  Yes, the dust seals are still in place on my brakes.  Since adding air ducts and machining the pistons, I've been able to run a full season without replacing the seals.  Before, I got to practice replacing the seals at the track.  An additional 4 slots should allow more airflow around the piston.  Adding the bevel will reduce the contact area on the pad plate even more.