ECR Repairs

[MINI-P]

In my opinion as someone with FWD experience you need some work on your spin recovery skills.

Well...I think I RECOVERED from the spins pretty well. :) Especially the one in T4. I went all the way around and kept on going. Now, I could use some work on my spin saving skills fo sho!

I learned that brake fluid goes bad over time even if you don't use it. The car had two days at Hallett on that fluid and nothing else. Also, the front pads were getting a tad thin and both of my brake duct tubing had gotten crushed so no cooling from those (I need to find a new way to route them where my 9" rims don't hit them). I flushed the fluid at the track and went out for a truncated session and all was well.

[MINI-P]

You need 3-3.2* front camber, 2.5* rear, the rest is fine.

I'll shoot for that next time. Hopefully I can get 'er done before Hallett. I think I'm gonna be a little gun shy going into T2 until my brakes earn my trust and respect again.

[MINI-P]

What pads are you running?

Just saw this part of your post. DTC 60 front and 30 rear. Have not had issues before. I think I let the pads get too thin. Should have swapped them out before I went but though I had enough. I need to learn that ECR = New front pads.

[SirHustlerEsq]

Rears are overheating; run 60s all the way around, you have a bias valve. Even with 138whp I'm still boiling the rear brakes and losing pressure on cool-down and I run 60s. We need a proper BBK for the rear with a vented rotor, but that will never happen.

Route the ducting through the sway bar. If you need some 2.5" I think I have some extra you can have.

I always check-up on the pedal going into any corner with extreme consequences like #2 at Hallett.

[altiain]

Typically the pedal will not go to the floor when a pad overheats, even if it is crumbling. You will still feel some pedal resistance (since the pistons physically have nowhere to go if the pad is still there and the fluid is good). What will happen is you will step on the pedal and get a resistance, but little change in velocity.

If the pedal goes to the floor or offers little resistance, this is 99.99% of the time caused by boiling the fluid. The fluid turns to gas in the lines, and gas is compressible. Now the pedal can travel because it can compress the gas in the lines far easier than it can compress the piston against the rotor.

If you've ever boiled your brakes, they need to be completely flushed before going on track again. You should also make a habit of bleeding before every event.

To me brake fluid is the single most important fluid in the car. If I skimp on the oil, it will cost me $$$ in the form of a damaged engine. If I skimp on brake fluid, it could cost me a serious injury or worse. I recommend Motul RBF600 or Castrol SRF, with regular (every 6 months or every 2 track events) changes.

[SirHustlerEsq]

If the pedal goes to the floor or offers little resistance, this is 99.99% of the time caused by boiling the fluid. The fluid turns to gas in the lines, and gas is compressible. Now the pedal can travel because it can compress the gas in the lines far easier than it can compress the piston against the rotor.

When the design temp range is exceeded fluid temps skyrocket. When I ran DTC30s the pedal went to the floor; switching to 60s made it all stop. I suspect this is something to do with pedal pressure and friction. Any engineers want to chime in?

I think it's increadibly unlikely that he's boiling the fluid considering that we have the same brake set-up and such different results.

[OZMDD]

Besides the fact that altiain IS an engineer, I'll add that as a physics teacher his argument is the most sound. Hydraulic brakes are essentially mechanical in nature, and the brake fluid (any liquid) is incompressible, so it acts as a mechanical component that exerts equal pressure on all parts of the system. The area of the two pistons determines the force multiplication. The only possible explanations outside of his would involve some mechanical portion of the system developing additional play. While I'm not an expert on pad chemistry, I'd wager that they are not liquifying or contracting.

While his explanation is correct, I might be able to clarify: I suspect the culprit is actually WATER that has been absorbed by the fluid, which can boil fairly easily, and can also re-condense fairly quickly when the heat is dissipated by the brake fluid. The less-dense vapor and hot fluid will naturally rise in the system while cooler material is denser and will move down. This might be the reason that brakes which have gone to the floor can quickly recover.

Now, the issue of pad fade is another factor, but not one that should cause a pedal to go to the floor. Exactly which part of his system failed first isn't known, but I think the pedal issue points pretty squarely to overheated fluid on at least one corner. A failure in the master cylinder, piston or proportioning valve orifices would be unlikely to self-correct.

As for similar brake setups and different results, the number of unknown variables in 20 year old cars makes it impossible to say.

With that, let me disclaim that I might also be totally wrong. :)

[SirHustlerEsq]

When a pad goes over it's MOT, it ceases making friction as designed and then additional pedal pressure is needed to stop the car.



When this happened the pedal went to the floor. I swapped pads to Hawk Blue that day and the pedal was fine.

[OZMDD]

I see what you mean. The pad itself failed and the backing plate bent, so is fits the description of "mechanical portion of the system developing additional play." It allowed too much piston travel as you cooked away the pad trying to generate stopping force, thus resulting in a bottomed-out pedal. I don't think it contradicts the previous fluid argument, but does demonstrate another way brakes can fail.

The best solution to this is to own an NC, which have perfect brakes that never fail. :)

[altiain]

When the design temp range is exceeded fluid temps skyrocket. When I ran DTC30s the pedal went to the floor; switching to 60s made it all stop. I suspect this is something to do with pedal pressure and friction. Any engineers want to chime in?

I think it's increadibly unlikely that he's boiling the fluid considering that we have the same brake set-up and such different results.

Heh.

Trey, as Mike pointed out, I am a degreed and licensed mechanical engineer with over 10 years of powertrain development experience and a painfully thorough knowledge of hydraulic systems.

Mike makes a good point about water in the brake fluid. Brake fluid is hygroscopic in nature, which means it absorbs moisture. The water does not chemically react with brake fluid. It is merely suspended in the fluid mixture. That means that any water in the braking system that comes in contact with a hot spot - like the back side of the piston - will boil. When it boils it becomes gaseous, and therefore compressible. When any part of the fluid system turns to gas and becomes compressible, your pedal travel can increase. When your pedal goes soft, it is due to localized boiling and compression of the resulting gas volume.

However, even "dry" or fresh brake fluid is a liquid. As such it has a boiling point, and if you exceed this point you will vaporize the fluid. The presence of water merely lowers the effective boiling point by allowing for localized boiling at lower than fluid design temp.

The design temp range of your brake pads has no impact on the basic laws of thermodynamics. Your brakes turn kinetic energy into heat energy. That energy has to be dissipated to somewhere. Most of it is radiated out to the atmosphere from the rotors, but the calipers, hubs, wheels, and anything else in contact also absorb some of that energy.

If anything, once you exceed the design temp range of your pads the energy conversion curve will actually begin to taper off, since the coefficient of friction between the rotors and the pads will decrease and you will be converting less kinetic energy into heat (i.e., not slowing down as quickly or in some cases at all).

This is a pretty simplified explanation. The actual behavior of multi fluid mixtures in closed loop systems under dynamic pressure and temperature conditions can get very complicated. I'm certainly no expert, but I have spent several years designing and troubleshooting very complex hydraulic control systems for mobile off highway equipment.

In short, if the pedal went to the floor, it was because the fluid vaporized. Either that, or you have a leak in your brake system. There is nowhere else for the fluid to go if it remains in a liquid state, where it is incompressible for all intents and purposes.

[SirHustlerEsq]

Okay.

[black roadster]

Okay.

That's it? You're losing your edge Hustler.