Lost my brakes while doing a drivers ed.

[JackT]

Prior to the drivers ed I replaced my master cylinder, rebuild the front calipers and replaced my brake lines with stainless steal lines. I also put Hawk Plus pads all around. While doing a drivers ed last Friday, the brake pedal would go to the floor when the brakes would get real hot. The brakes would then come back when they cooled off. We manually bled the brakes at the track but it didn't help.
Anyone have any idea what the problem is?

[deoxford]

You are boiling your brake fluid.
You need to drain the system, and replace with a higher temp, brake fluid.
Also look in to some cooling.
Don't forget to drain the brake fluid, the fluid in the now is no longer good.

[VincentVega]

You are braking too much. Just kidding, sort of.

Make sure you use high temp fluid and bleed early and oftern. Search for ideas on brake cooling as well.

[sammyg2]

BTDT.
Put in DOT-4, try to get as much of the old stuff out as possible.
Hook up some sort of cooling vents to the front rotors, make sure your calipers are releasing fully and not hanging up.
If possible take some weight out of the car.
That's all I can think of without spending serious $$$

[JackT]

Thanks Derek,
When I changed the master cylinder, I put in new blue racing brake fluid. This was all done last week.
Are these symptoms consistant with a bad brake cylinder?

[sammyg2]

If the fluid is new it shouldn't be moisture saturated enough to lower the wet boiling point that much. My guess is a caliper is dragging.
Did the car pull at all when the brakes first started to go away?
Removing the rock shields behind the rotors might help too.

[JackT]

Also thanks Chris and Sammy,
I have been doing drivers eds in this car for a number of years and never had a problem with the brakes. One of the calipers started sticking a few months ago so I rebuilt the front calipers6 weeks ago and replaced the brake fluid with the blue stuff. The front calipers started sticking again at the next drivers ed so I had the calipers rebuilt again and put new blue brake fluid in. The calipers were still sticking with the new rebuilt calipers so we replaced the master cylinder and replaced the blue brake fluid again. This is getting pretty expensive.

[JackT]

Sammy, the brakes were not pulling before I would lose them. They would get soft then the next time I applied the brakes they would go to the floor and gradually bring me to a stop as I was running off the track. Now I know the pucker feeling I always hear about.

[smdubovsky]

Did you run the Hawk HP Plus pads before you had problems? They are a street application pad and may not survive the track. I would swap in a set of Hawk Blues for the track. Who knows - you might be going faster w/ more experience The HP Plus might have been alright before and now aren't enough. The pads won't DIRECTLY cause the low pedal, but they could be causing you to brake too much/too long (as the pad overheats its friction coefficient drops) -> boil the fluid -> which WILL cause the soft pedal.

SMD

[JackT]

SMD, I did run the Hawk HP Plus before. I wish I was "going faster, with more experience". This would happen within 10 minutes of being on the track, as soon as the brakes got hot.

[Richard C2S]

Drew,

I encountered a similar problem several years ago. It turned out that I had not properly bedded in the new brake pads and they were gassing. Happened the first day of a drivers' ed event. I frantically bled the brakes at lunch time - and still had the problem in the afternoon. But the next day they were fine.

I agree with the comments above. Get some cooling to the brakes. I use the AJ USA kit. Use better pads. The high performance street/track pads just won't do it.

[}{arlequin]

you didn't mention whether you put in new rotors... having everything else up to spec, EXCEPT the most important item sorta defeats the purpose....

do a search on "brake fade" and you'll have plenty of reading about your options

-bedding pads is crucial, bedding rotors, actually
-remove dust shields
-if you have access to a pyrometer, put it on all 4 corners after a normal drive, see if any one is considerably hot/hotter, this would point you to a dragging caliper. new, square seals have a tendency to do that, problems w/ hyperextension etc.
-get some cooling in there as well

[smdubovsky]

Drew,
As others have pointed out, cooling is clearly your problem IF the rest of the system is in good shape (which is sounds like - new MC & rebuilt calipers). Overheating the brakes could be damaging the seals - causing them to drag? You SURE your not going faster? Energy is MV^2 - doesn't take but a few mph more to make brakes go from marginal to not working. Even newer stickier tires can make that difference.

Since your running ATE Blue fluid, there isn't MUCH better. Try removing the rotor rock guards (as already pointed out). Its esentially free. Different pads will help alot (the dedicated track types - Hawk Blue/HT-10, Porterfield R4 (not the R4S), etc.). Ducting will help immensely. Any one of these changes might be enough to get you over the edge - for now. Even so, you WILL eventually go faster and need to do the others SC brakes are plenty w/ the right combination of pads and cooling (ask the PCA stock class guys).

FWIW, my "new" SpecE30 came w/ ??? street pads. First track day - I figured how bad can they be? Lasted TWO brake zones on the warmup lap before the pads overheated - Visibly smoking Pulled in and stuck my track pads in and tossed the others in the dumpster... Problem solved.

SMD

[tobluforu]

I have done many track days-not racing in my 72 with stock brakes. Yes they are drilled-big deal in some people's minds, yes I use Ferado pads and yes I use blue fluid as well. My 72 is not all that fast, but I have run that car at sears point a whole bunch of times without the pedal ever going to the floor. This is not to say that bigger brakes are not needed, but if the prob was not there before, then I would look as other people stated at the calipers sticking, better pads needed......

[rattlsnak]

I had the same issues,. ONCE,. heres your anwer..




But other than that, you defintely need some cooling, and if you dont want to go with a huge setup, you should at least look into installing <84 carrera brakes.

[cmcfaul]

Happend to me once. turned out to be a front brake piston was leaking (I had rebuilt all 4). It would only leak when very hot. Kind of scarry going into a turn knowing you are too fast. Learned to spin with a lift however.

Also, my 73 e has seen many, many track days on stock M calipers. Granted I will burn through a set of front racing pads in just over a day of DE but very little fade.

Chris

73 911 E

[Danskman]

Also, once you've cooked the pads, they become useless for the track. They will have become glazed from the overheating, and possibly even have multiple small cracks. Chuck 'em.

[Plavan]

Mark Scott had that same problem with the Hawk pads. He raced and came in and the pads were smoking! He switched back to the Ferodos and the problem went away. I think those Hawk pads run way too hot.

[Jeff Alton]

These have not faded yet..........







Cheers

[Bill Verburg]

You boiled the brake fluid, both it and the pads are now trash

you may want to read this

for a T, just better cooling and good track pads usually does the trick.