Brake question for track guys

[ChrisGTS]

Hey everyone,

I have a 2006 Coupe that goes to about 4-5 track days per year. I have a brake issue that I want to get your opinions on.

Last summer, I did a track day in really hot weather -- so hot that my red front calipers turned a brownish red from the heat. I noticed afterward that the rubber dust boots around my front brake pistons were very ragged and looked like they had been melted. The brake fluid did not boil. I put the dust boots on a list of things to replace but I have not done so yet.

I have done several track events since then, and I have been noticing two things. First, the car feels very unstable under full braking -- even in a straight line, if I nail the brakes really hard the car twitches back and forth, left and right, and I think it is getting worse. I have to brake early and with less force to keep the car straight.

Second, the last two sets of front track pads I have gone through have been much more worn on one side of the car than the other -- like the passenger side caliper is working much harder than the driver's side. My guess is that this is what is causing the car to be unstable under braking.

So that brings me to the questions:

(1) Do you think that the brake pad wear difference indicates that one of my calipers is not working correctly?
(2) Do you think that this is what is causing the instability in straight-line braking?
(3) Do you think that the solution is to rebuild the front calipers and replace the seals inside the pistons, on the theory that they are compromised and impairing the operation of the pistons on one side?

My inclination is to rebuild the calipers, since that is what I suspect is going on. If it helps, I am using stock calipers, EBC dimpled/slotted rotors, Mintex front pads and stock Brembo pads in the rear. For track events, I run the following alignment specs:

Front: camber -2.3, 0 toe, caster about 4.5
Rear: camber -1.5, 1/8" toe in

Thanks for any advice you may have.

Chris

 

[Tabs1]

You seriously overheated the calipers. Get them rebuilt.

 

[Achilles99]

Who has parts kits, and has anyone rebuilt them personally? I've heard it isn't hard, any FAQ's out there to do it on the Gen III calipers?

 

[Dave Scott]

1) yes
2) yes
3) yes

 

[mjorgensen Woodhouse]

A little more caster will help stability, and just a touch of toe in the front would also, but will compromise cornering. If the calipers were so hot that the red powder coat burnt the fluid would have been boiled beyond belief! Maybe you have hot drake pad residue burnt onto them from the Mintex pads?

I would also suggest using the same compounds and brands of pads front and rear as this changes the initial "bite" of the pads and the stability of the car. The dust boots will deteriorate on any caliper at the track so you will be replacing them often. Check the calipers for sticking before you rebuild. If the move smooth in the bore then you don't need to and they are very durable so I would be shocked if they actually needed this. Replace the fluid entirely when you do this.

 

[fireball]

Instability is almost always a brake balance issue (front / rear) - but I don't think that's what's going on here.

Since you changed rotors and pads it gets difficult to sort the balance out. The factory set-up was balanced - that is to say that the fronts ALWAYS lock up before the rears do. The rotor change and the mixed set of pads changed that. Maybe for the better - but maybe not.

Anyway, the piston boots are fine and will not affect the braking in the way you've mentioned. Long term they should be replaced - especially if you drive in a salty environment. They do, however, indicate that you have put a lot of heat into the brake system.

It's my opinion that you did overheat the fluid and that a bleed is on order. I believe that a bleed, a new set of pads and a 'refresh' of the rotor will make everything right. It's my opinion that you do not need to rebuild the calipers. An upgrade to Castrol SRF or to Motul 600 brake fluid would be a very good idea.

Why? I think that one side has develped an air bubble and the other side hasn't. That's why your left and right side are wearing differently.

BTW, refresh your brake rotor with garnet paper. (read this for details StopTech : Balanced Brake Upgrades the garnet paper section is 3 paragraphs up from the section titles Myth #2)


Greg

 

[Achilles99]

That's the max caster you can get on the front of a Gen III when running that much negative camber. I tried on my car as well and got the same results.

My calipers turned a little brown as well during a track session, and the fluid didn't boil at all.

I tried Mintex on all four corners once, DON'T DO IT! My rears locked up way before the fronts. I guess it depends on pad compound, YMMV with other pads.

Fireball - Good suggestions, but I know Chris did all the things you suggested because I helped him do it New Mintex pads, new rotors, new fluid (ATE). Chris and I have the same setup, except I use stainless lines. I wonder if somehow the rubber hoses are flexing differently on one side and not the other?

 

[ChrisGTS]

Mark, thanks for the response. Regarding the color change on the calipers, I don't know whether it is baked-on brake dust or that the paint got "cooked," but whatever it is won't come off! And the brake fluid did not boil -- I was using brand-new Motul that day and the pedal was firm and the brakes working fine through the end of the day.

Regarding the seals inside the pistons -- if those aren't the problem, what could it be that is causing the pad wear to be so uneven from one side to the other? My street pads don't show this -- only the ones I use at the track.

With the pad compounds, my friend Achilles99 who posted above tried running Mintex front and rear at one event and told me that it caused the car to be very unstable under braking, and we have heard that from other people too, so we have intentionally been using a less aggressive pad in the rear and it seemed to help stability. His car is darting around under heavy braking too, by the way, but he doesn't have the uneven pad wear that I do.

Anyway, thanks for your thoughts on this issue.

Chris

 

[ChrisGTS]

Greg, thanks for your response, but I don't think an air bubble in the line is an issue. I completely change my brake fluid before every track event, and I alternate between ATE Super Blue and ATE Amber so that I know when I have completely flushed the lines. And I have had two different sets of front pads wear unevenly like this, so I am thinking it is something in the brake system itself -- whether the calipers or something else.

Chris

 

[Achilles99]

I'm running stainless lines, Chris is not. I'm running R888's, he's running PS2's. I have Stoptech Rotors, he has EBC. Other than that, similar setups.

I wonder if the rubber hoses are flexing on Chris' car unevenly?

I think my darting may be the front tires... I checked both fronts and they are corded. That wouldn't solve Chris' problem, though, as his tires are new.