hot brakes

[n1gzd]

Hi,

After a few autocross runs my front brake disks (infrared thermometer) are about 350 degrees.
After a 25 minute lap session at NHMS my front disks are about 550 deg.
After a 1 hour lap session at NHMS my front desks were 850 degrees. I experienced no brake fade (performance remained very good).

Here is my question, given the maximum temperature that I saw, should I switch to some kind of super blue dot 4 racing brake fluid (higher boiling point)?

My 2003 9-3 Saab Vector has stock brakes with ABS (larger than other 9-3 models because it is the Vector). I am assuming that other than having a higher price and higher boiling point, dot 4 is dot 4 and this is compatible with the standard fluid (I already decided to use this in the car that I am still building).

I am assuming that if I did not experience any brake fade then I was never coming close to overheating the brake fluid in the line near my hot brake parts. Is this a valid assumption?

Thanks,
Rebecca

[Chrispy]

You definitely would want to switch out the brake fluid for a high temp fluid. DOT4 fluids are all compatible with each other so just do a full bleed with the new fluid and you're good to go. SuperBlue (or the gold ATE) is good upgrade for cheap money if you aren't really pushing the temp limits. My caliper temps were 460F which would have boiled an OEM grade fluid for certain.

[breakaway500]

Another item you may want to consider replacing/upgrading are your brake hoses,especially if your car has high mileage (which I believe yours does.. ).Track duty works parts very hard. A small ounce of prevention..

[WillM]

I am assuming that if I did not experience any brake fade then I was never coming close to overheating the brake fluid in the line near my hot brake parts. Is this a valid assumption?

I'm not an expert, but from what you have written, I wouldn't draw the conclusion that the fluid "was never coming close to overheating." The truth is, you don't know how close you were (or weren't). Its like heating up a pot of water to 210°F then turning off the heat, and claiming that the water was never close to boiling (water boils at 212°F at sea level).

At 850°F rotor temps, as measured with the car parked, I would recommend moving to a DOT 4 racing fluid like Super Blue, Motul 600, etc. That is freakin' hot.

[zip4zat]

Hi Rebecca,
Next time youre at the track take a temp measurement of your caliper right after you come in. Typically the inside trailing edge of the caliper will be the hottest. You will probably see a good difference between the inside and outside, leading and trailing edge. At any rate, this will give you a better indication of your brake fluid temp than the temps of your rotors will. I've seen well over 600*+ on my calipers on hot days.

As to the difference in DOT4 fluids, the critical number you should look at is the wet boiling point. This is what would differentiate the different brands, mostly the dry BPs are all relatively close (you'll get what you pay for, in this case). I think the wet BP has to do with what temp the fluid starts to boil if there is any (water) moisture absorbed into the fluid, someone can probably chime in on the technicalities here.

In either case, I know many have good success with the ATE, Motul RBF600, Castrol SRF (in order of $$$). Back in the day (I cant believe I just said that), the Ford racing brake fluid was good stuff but I dont know where you can get it anymore. That stuff was CHEAP!

On a side note, I have experience with some brands of brake fluid corroding the surface coating of the caliper pistons eventually pitting them rather serverely. I dont think you'll find this info anywhere unless you end up in touch with tech's for the OEM. I'll have to look back in my emails to remember exactly what brand it was, but it wasnt any of the ones I listed above.

[Chrispy]

Yes, wet boiling point is defined as brake fluid comprised of 3.7% water by volume.

The corrosion you saw is a sign that a brake fluid is unable to fully absorb the moisture in the fluid. This is something that the OEM fluids are very good at, but racing fluids not so much. If you do a partial bleed before every event it will help to keep the moisture out.

[DanDarcy]

Hi Rebecca;

I use the Ford High Performance brake fluid. It works well in a very heavy car (Mustang Cobra w/Brembo Brakes) and is real cheap, about $7-$8 a bottle. It is available at any Ford dealer. My cast iron rotors never go over 900 degrees but my aluminum hat two piece rotor have gone over 1200 degrees. I bleed the brakes before every event and only use fluid from an unopened bottle. I also use the Ford fluid in my Lotus.

[grovefromnh]

It's also important to remember to slow down after you get the checkered flag. Drive slow enough so that you don't have to use the brakes until you are off the track. Coming off the track after doing'one more fast lap' and parking the car will spike temps big time.