Barbecue Brakes

[Clark Griswald]

Spent the weekend abusing Sparky's brakes in god awful heat at Buttonwillow. I'm not sure what the air temp was, but it was definitely 100+ F. And the track temps where 150 F. Buttonwillow is one hell of place for a racetrack. It is in the middle of California desert. A real test of cooling systems.

My brakes are stock Carrera with pads assumed to be OEM.

The story actually starts before the event. Preping to go to the track I noticed my brake fluid was very low in the reservoir. This was odd because I never have had to top off the fluid before. No visible leaks.

I had run 2 DEs since I last filed the resorvoir. My conclusion was that in those DEs, the pads wore considerably allowing the pistons to move out and require more fluid.

Topped it off with ATE blue and got on my way. The pedal felt fine and had normal travel.

Middle of day two I came in from a session to find my peddle travel had increased substantially. I could smell brake pads cooking, and when I stopped I saw a small amount of smoke coming from the rear wheel wells.

I assumed I had boiled the fluid and promptly bled that brakes. No luck, still had a long peddle travel. But the brakes were there so I continued in the rest of the sessions.

What gives? No air in lines but I have a long peddle, even when the brakes are cool.

Another clue - inspecting the rotors showed that they are much smoother than before. Before the event, I had the typical ridges that develop on rotors with high miles. After this they looked like low mileage rotors, ridges greatly reduced. And trace amounts of material seemed to be stuck to a few spots on the rotors. Pad Material I assume. There is still good pad thickness, I have not yet pulled the pads to inspect.

I have three theories -

1) The pads and rotors wore down a great deal from the heat and abuse. Hence the pistons need to push out further. My caliper seals are 15 years old and may have lost some elasticity. The new piston position happened so quickly that the seals haven't had time to adjust to the new position. Hence they are returning the pistons back to the old position, requiring a long piston and peddle stroke for brakes application.

2) Rotors warped from heat, pushing the pistons in, requiring longer peddle travel. I don't feel any pulsing in the peddle.

3) Pads/rotors glazed reducing the coefficient of friction requiring heavy pressure and longer peddle travel.

What do you guys think?

---------------
Chuck Moreland '86 Cab - "Sparky", '77 Targa - "Sweet Pea"


[This message has been edited by Clark Griswald (edited 07-09-2001).]

[Planter91C2]

I'll take what's behind curtain number 1, Bob

[patalive]

Hey Chuck - - several suggestions:
-
In our PCA region (Potomac/Founders), the Tech inspection requires that brake fluid be changed every six months. I would immediately do that. Old brake fluid does pick up moisture after long periods of time.
-
Switch to track pads. You need a pad that will stand up to those high heat conditions - the stock ones won't do it. I once went out on a hot-day DE with green street pads and managed to fry them - splotches of pad material all over the rotors.
-
If you continue to do DEs at that location, I would invest in some brake coolers - They really helped my SC.
-
If they have never been changed, I would change the rubber brake lines immediately. Old ones will bulge under heavy stress and reduce braking effectiveness.
-
Were I in your shoes and planned to continue DEs, I would also have the calipers rebuilt.
-
Chuck
83SC

[Clark Griswald]

Patalive, thanks for the tips.

The brake fluid was changed about 4 months ago. Put in Stainless lines about 3 years ago.

I am actualy doing a complete brake overhaul this weekend so I know the problem will be solved. My questions are driven out of curiosity.

The new brake setup includes fresh cross drilled rotors, Ferodo pads, caliper rebuild, and I think I will take your advice about ducting some air to the fronts.

[Joe Bob]

I agree with the above, I would add.....

Get some Pagids oranges....
Bleed before every DE....
Change your fluid every other DE...

Loss of fluid does not mean, ooopsy fill it up. It means, change, bleed and inspect the system, including the pads.

MTZ
83 SC cab euro, everyday driver and closet race car....

[Bill Verburg]

Face it guys the brakes on the SC/Carrera were state of the art, circa 1969, and while adaquate for street use have become increasingly inadaquate for track work. Every year the cars have gotten heavier and more powerfull making the problem worse. Fluid, pads, coolers are all band aids that we have all tried over the years. They will only help at the margins. If thats where you are, great. But for serious track work you will need something more, unless your class disallows it.

[ppendle]

I had a similar prob about 3 mos ago...turned out that the outside (furthest from hub center)part of the stock rotors were wearing quicker than the inner part, causing the pad to rock upon engagement(with a faint creaking noise) with more pedal travel.

[Jim Smolka]

Also, keeping your brakes cool at the track is a good idea. Check out the tech article on adding brake ducts to you front rotors.

[campbellcj]

Chuck - You used your brakes?

Just kidding. I'm assuming the course you ran yesterday was way more brake-intensive than Saturday -- they said it was going to be a much tighter, slower & technical track.

I got to chauffer wifey to a baby shower (in her honor) yesterday instead of driving Buttonwillow I must say I was pretty damn frazzled after Saturday. I would have been a real zombie if I drove both days, and my poor little car would've been cooked. Damn it's miserable out there!

Chris C.

[This message has been edited by campbellcj (edited 07-09-2001).]

[Clark Griswald]

Chris,

You got off easy on Saturday. Sunday was even hotter. It was a battle to keep oil temps (and driver temps) under control.

Still a great time.

[jlex]

My guess is the brake fluid got too hot, it expanded, and you lost it out of the overflow tube. Because you lost it before the racing event, I'd suspect a sticking caliper that overheated the whole system.
I'm sure you'll find the prob when you inspect. Keep an eye out for one that's quite a bit more worn than the others.
regards,
jlex.