Did I cook my brakes?

[nytebyte]

I went to the SVTOA on-track event at the Autobahn country club on Friday. Had a great time!

But, I think I might have cooked the brakes. On one of my runs, I took an instructor with me who made me really push it to the limit.

The next time I started up the car to go race, I noticed the brake pedal was VERY soft and almost went to the floor. I'm guessing the brakes heat soaked while I was parked, because they were perfectly fine on the track for earlier sessions.

I decided to go out anyway and see if the brakes would improve after the initial warm-up laps. If they didn't, I was going to pit for the day. Well, after one warm up lap, the brakes felt normal again and were fine for the remainder of the race.

After the race, I parked for a while. Vince was there with all his tools, and he let me borrow his infrared thermometer so I could take a reading of the front brake rotors. They were 270 degrees.

I let the car sit for a while, but when I came back and started up, the brakes were even worse.

They improved a bit on the drive home, but even after sitting in the garage all night, they are still soft this morning. They still stop the car, but they don't feel right. I also noticed that they are slightly slow to release as well.

My guess is that while the car was sitting after the races, the brakes heat soaked and boiled the brake fluid, leaving gas bubbles in the brake lines.

What do you think of this theory? Any other ideas?
Should I try to bleed the system, or should I just flush it and put in some better fluid?

I'm surprised this happened since I really wasn't driving that hard. Shouldn't the Cobra brakes be able to take a 30 minute run around a track?

Click to read more...

 

[blubyu]

Wouldn't hurt to try and bleed them. You probably boiled them like you said.

See attached file.

 

[JymBart]

If you are going to flush your brake system, .... now`s the time to flush out the stock dot3 brake fluid to a dot4. The dot4 has a higher boiling point and absorbs moisture better, ............. just be sure to flush out all of the dot3, ..... do not mix.

JymBart

 

[nytebyte]

Well, this afternoon I tried bleeding just the front brakes, figuring those were the ones that cooked. It worked and all is back to normal.

The fluid that came out looked OK and didn't smell burnt. I also didn't notice any air bubbles in the fluid, unless all the air had migrated to the top of the caliper near the bleeder valve. The pads and rotors look OK, although I probably don't have enough pad material left for another track session. I'll have to change the pads before then.

The brakes actually feel much better than they originally did before the race. I used some brake fluid that was rated for either DOT3 or DOT4. It said on the bottle that it was OK to use with existing DOT3 fluid.

I'll be changing all the pads eventually anyway and I'll just flush the whole system then.

 

[ShelbyGuy]

the ford brake fluid is the best thing you can get without spending money on stuff like motul600 and superblue.

go nuts with it.

dont be surprised if you burned the dust boots off the pistons. thats normal. they're soft rubber. a rebuild kit is cheap. very fun, very easy.

dont be surprised if you need pads. when a brake pad is more than 50% worn, its lost more than 65% of its effectiveness. its not linear. the thinner you go the less ability it has to absorb the heat.

 

[Mystic Terminator]

the ford brake fluid is the best thing you can get without spending money on stuff like motul600 and superblue.

go nuts with it.

dont be surprised if you burned the dust boots off the pistons. thats normal. they're soft rubber. a rebuild kit is cheap. very fun, very easy.

dont be surprised if you need pads. when a brake pad is more than 50% worn, its lost more than 65% of its effectiveness. its not linear. the thinner you go the less ability it has to absorb the heat.

Good article on brake fluid:

http://www.stoptech.com/whitepapers/brakefluid1a.htm

In many instances DOT3 is preferred over DOT4.

Ford Stuff is like $3.80/Pint and is 550 degree dry boiling point. Valvoline SynPower is a Synthetic w/ 480 degree boiling point and is about $4.00/Quart (Good for daily driver)

Stay away from silicone fluids for track since they are compressible and do not provide a linear pedal response.

And when I was @ Joe RizzaFord/Porsche a couple of weeks ago they sold me the Ford 550 degree brake fluid for a fraction of the cost of the Porsche fluid which has a LOWER boiling point. Porsche owners use brake fluid w/ 536 degree boiling point.

Stoptech has lots of information regarding brakes...

http://www.stoptech.com/technical/

 

[ChicagoMike]

I would think porsche has a lower boiling point because they have much better brake cooling ie brake ducts.

Something to think about in the future for the track racers is the brake duct cooling mod. KennyBrown sells a kit ($$$) or you can make your own somehow. Tubes run from the holes next to the fog lamps and up to the brakes.

 

[ShelbyGuy]

and hey its no big deal to bleed brakes on these cars. i carry enough duct tape and zip ties to keep anyone's car going. its more fun to be on the track than in the paddock area.

 

[Mystic Terminator]

dont be surprised if you burned the dust boots off the pistons. thats normal. they're soft rubber. a rebuild kit is cheap. very fun, very easy.

Do burned dust boots look like this?

 

[ShelbyGuy]

yup those are them. the piston seal is probably fine.