Brake Fade - could it be discs?

[jcas]

Hi All,

I have an E30 that has been standing for about a year, and is suffering extreme fade when the brakes get hot (track temps rather than road). I have flushed the brake fluid for new stuff (ATE super blue so I could see when the new fluid was through), and fitted new EBC yellowstuff pads. The brakes seem fine on road (though lacking bite) and passed an MOT ok. However on the track as soon as some decent heat built up there was no braking force at all. The pedal still felt firm though so I don't think its fluid or an air lock. I changed back to the old pads but exactly the same thing happened. Could it be the old discs causing the problem having not been changed since standing? Or any other suggestions?

Thanks,
James

[Crash Test Dummy]

If I recall correctly they are solid discs, which will do nothing in the way of cooling.

Try and find so vented discs or [may not be an option as my BMW knowledge is pretty poor] try and upgrade brakes of a higher spec'd car.

If the latter is not and option and you are finding your brakes are still fading then set up some ducting to the brakes, although there is more to it than just adding a duct. If its not done properly you will end up with stones caught between the disc/pad causing scores in the disc.

[shouldbworking]

Have the brake hoses been changed? might be worth a close inspection.

[Crash Test Dummy]

shouldbworking said:

Have the brake hoses been changed? might be worth a close inspection.

Not trying to sound like a smart ars but what effect could this have on brake fade?

[Paul Drawmer]

jcas said:

Hi All,

I have an E30 that has been standing for about a year, and is suffering extreme fade when the brakes get hot (track temps rather than road). I have flushed the brake fluid for new stuff (ATE super blue so I could see when the new fluid was through), and fitted new EBC yellowstuff pads. The brakes seem fine on road (though lacking bite) and passed an MOT ok. However on the track as soon as some decent heat built up there was no braking force at all. The pedal still felt firm though so I don't think its fluid or an air lock. I changed back to the old pads but exactly the same thing happened. Could it be the old discs causing the problem having not been changed since standing? Or any other suggestions?

Thanks,
James

Hmm puzzling. If I've got it right, your brakes work OK cold, but fade when HOT. If your brake fade is the type where you have firm pedal, but the car doesn't stop, then the problem is overheated pads. The pads produce a gas as a product of combustion which reduces the friction, so you don't stop.

Problem is that you've fitted yellow stuff which is good for 800C, so I'm reluctant to say they are getting too hot, since even on a track day; with a road car thats very very hot. Are these new pads properly bedded in? If they have just been fitted and then not bedded in, maybe they are only working on the high spots which have got very high temperatures.

Brake friction material doesn't just rub on the metal disc to get friction. Modern materials work with a deposited layer of friction material on the disc it self to get the best stopping power. For this reason, changing material can sometimes have lengthy bedding in period to build up the required deposits on the discs. Do EBC yellow stuff have the bedding in compound on them (A reddish layer)?

[shouldbworking]

Crash Test Dummy said:

shouldbworking said:

Have the brake hoses been changed? might be worth a close inspection.

Not trying to sound like a smart ars but what effect could this have on brake fade?

Im thinking along the lines of collapsed internally or possibly even have dirty great bulges in them that could be changing the feel of the brakes under pressure and it not actually being brake fade which would have to be down to either the fluid boiling or the pads being the wrong compound, both of which are apparently ruled out. Im also thinking along the lines of different types of brake fluid being used as stated potentially causing problems.

[Crash Test Dummy]

shouldbworking said:

Im thinking along the lines of collapsed internally or possibly even have dirty great bulges in them that could be changing the feel of the brakes under pressure and it not actually being brake fade

Not sure on the physics of bulging pipes etc although surely this would have been noticed all along, not just on track days. So wouldn't give the same symptoms as brake fade?

Sorry to disrupt your thread, although its all relevant

[52classic]

I would suggest a sticking caliper due to corrosion whilst standing.

My thinking is that the brake is not releasing entirely and therefore heat is accumulating in the unit inducing the pad problem which others have described. E30 stuff is cheap enough at breakers so I would change for another set of calipers and see if there's any change.

Having had experience of old brake flexis swelling under load I would certainly relace them all before I considered taking an old car near a track.
The Aeroquip thin ones seem to improve efficiency anyway, something to do with the volume of fluid in the pipe but not sure of the exact physics involved.

[Sam_68]

52classic said:

I would suggest a sticking caliper due to corrosion whilst standing.

That was my first thought, too.

[neiljohnson]

Is the fluid your using a silicone based product? If so its not compatible with the abs systems fitted to the Bmw (bosch i think) as under heavy braking it can froth inside the abs pump causing the problem you describe.
Making a few assumptions here but may be worth looking into.