smithk993

New info my son forgot to share. He had put Hawk HT10 on front and left the used stock on rear. Also the car seems to get into the ABS lock up very easy now. Could this be the culprit to overheating?

Not sure if it makes any difference but my son had mounted HT10's (less corrosive dust) rather than Blue's.

I'm probably just looking for someone to sympathize with but here's my story from today's VIR Driver's ED.

My son was driving my 95 BMW M3 in the B run group in the first session of the day. Had completed just 4 laps when on the 5th lap going into turn 1 after the front straight, the pedal went to the floor. Fortunately, he got the speed down and spun once he left track but contacted the tire wall with the entire right side. No injuries just lot's of body work.

The prior lap, the brakes were good and he said he got into the ABS just a bit so decided to move his brake point back couple of car lengths.

The car has stock BMW rotors and he had just put on HAWK race pads. The brake fluid had been completely flushed two weeks earlier and then bled the brakes the day before after changing pads using the PowerBleeder.

After the mishap, the brakes seemed to be OK. I took the car for a couple of full braking stops and got the car to skid and ABS to kick in. On the way home, we rode the brakes for a while and got them hot. Seemed to cause a similar problem, with the pedal going to the floor and very little brake.

I guess what I'm looking for, is some good solid ideas on what went wrong. Losing brakes at the end of the long straight is not something I want to think about. The temperature was around 90 degrees but we had only done 4 laps when the failure occurred. I sure want to get back on track bu really need some ideas as to how to approach and build confidence in the car. We had the car on 5 prior DE with no problems. Only difference was this was the first outing with the HAWK pads. Prior was using Ferrodo intermeditate.

Thanks for the comments.

Robert Henriksen

My first thought is that BMWs are 'ultimate driving machines' for the road... but circuit driving places a significantly higher demand on the brakes' heat sink capacity. Porsches have typically had over-engineered brakes for street driving; but come into their own on the track. Not so for BMW.

But the second thought I've got (re: no problems during 5 previous DE weekends) is that for your car, your home track, your driving style/speed, etc, the brakes were okay; but after 5 weekends, the rotors had gotten thin enough that they didn't have the requisite mass to dissipate the heat.

I noticed the same thing (w. less drama) when I replaced the rotors on my 993. I hadn't experienced failure, but I'd boil the fluid & get spongy pedal. That problem was greatly reduced with new, full-thickness rotors.

You could just put new rotors on, or look at upgrading the stock system.

JC in NY

Barring mechanical failure brake pedal going to floor is boiled fluid. Fluid is getting too hot. Try using brakes less, using a brake fluid with a higher boil point or cooling brakes with ducting in that order.

smithk993

Car had ATE Super Blue fluid. While I had experienced some brake fade with the Ferodo pads previously, never had the total loss of brakes before. Anything about the
Hawk race pads that would contribute to higher temperatures?

Rotors are definely on their last round as they have a significant outer lip.

SundayDriver

Sorry to hear about your problem. It sounds like it was the fluid boiling.

Rotor wear, IMO, will have little effect as the difference in mass bewteen new and worn is pretty small. Pad thickness and fluid are the big items. How is the pad thickness? Once you go past about half way, you will be transferring a lot more heat into the fluid - It is more than possible to wear the pads in a single day.

ATE fluid is good, but not super high temp. In a big heavy car (to me any production car matches that) you can get huge amounts of heat. While ATE is adequate for the Porsches, it is not for some others. It is also possible that the different pads have more grab and produce more heat than your old pads. It is a tough thing to sort out unless the pad thickness is way down - then you have found the culprit.

It is a little late now, but when that happens a pump or two on the pedal will usually return 80-90% of the braking capacity (been there done that a few times).

Robert Henriksen

Pad thickness is another good idea. I've heard that different pad compounds can affect the ability to deal w. high heat loads & moderate the boiling issue, but couldn't quote you which pads are better than others.

smithk993

Is there any problem with topping of the brake fluid with fluid that has been previously opened? The fluid was still in the original can with cap secure and had been used two weeks prior to flush the system.

I have heard that fluid will absorb moisture.

os993

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by smithk993:
<strong>Is there any problem with topping of the brake fluid with fluid that has been previously opened? The fluid was still in the original can with cap secure and had been used two weeks prior to flush the system.

I have heard that fluid will absorb moisture.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">If the ATE Super fluid container seal was only broken two weeks ago, you're fine. I'm personally particular to open brake fluid containers and I wouldn't use anything that's been open for longer than a few months.

SundayDriver

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by smithk993:
<strong>Is there any problem with topping of the brake fluid with fluid that has been previously opened? The fluid was still in the original can with cap secure and had been used two weeks prior to flush the system.

I have heard that fluid will absorb moisture.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Brake fluid, as you have heard, absorbs water which significantly lowers the boiling point of the fluid. Once the fluid is open (including the fluid in your master cylinder, it is subject to diurnal breathing - every time it cools it pulls in outside air which has some humidity. As it cools further, the water vapor condenses into the fluid. Repeating this cycle adds water to the brake fluid. This is worse in the master cylinder as it gets hotter, but it also affects an open bottle. It is worse when there is little fluid in the bottle (lots of space to pull in air). If the bottel is fairly full and you keep it at a pretty constant temp, it should be good for quite a while (months). If the level is low, I would use it within a couple of weeks or discard it - just not worth the risk.

Steve Weiner-Rennsport Systems

Hi Keith:

Good adivce above and I'd "second" all of it.

Hawk pads are rather notorious for this (increased heat) and I'll vote that your poor son experienced boiled fluid. The most important thing is that your offspring was OK.

As Mark pointed out, ATE fluid while very good (we use it here) its not the very best fluid one can buy. Cars we call "problem children" with undersized brakes that have strong tendencies to boil fluid get the Castrol SRF fluid. Its not a cure-all, but it does raise the bar somewhat and with effective brake cooling, helps keep this problem at bay.

Unless one wishes to upgrade the front brakes on the car to deal with this problem, I'd suggest the Castrol SRF fluid and ducting some high pressure air to the brakes.

Kristoffer

Steve would you use the Castrol SRF on 993s or just BMWs? My brakes still boil at times & any edge I can get helps!!!

Rezal

I've had brake fade before in different cars (300ZX Twin Turbo at Sears Point & Alfa Romeo Milano at Street of Willow Springs). Everytime, it's what it says, the brakes start "fade"ing. I've never had catastrophic brake failure where I went from brakes to no brakes immediately. Usually, the brakes starts feeling spongy and I either go into the pits or take it easy for a lap or so.

Ray Calvo

Keith, I have to go along with the others re boiled fluid. I have gotten very spongy pedal appications once or twice in a session of driving in my 993; in retrospect on the previous corner the pedal felt a little spongy from the brakes getting hot and probably boiling fluid, and I ignored the warning signs. Backing off for half a lap and the brakes were again form and braking normally, when again after a few hot laps of heavy braking they would come back. Stock (new) 993 rotors with Alan Johnson front cooling kit, Performance Friction 97 pads, and ATE Type 200 brake fluid.

Keep in the back of your mind (and tell this to Junior also) that an important aspect of driver's ed events is to be able to learn your car and to be able to distinguish small warning signs that all is not right before things escalate to an accident.

For info, I also have had bad experiences with Hawk pads re heat and boiling of fluid. Switched to Cool Carbon pads then Performance Friction 90 compound. Got much better success but didn't totally cure the problem (I live with it today).

drcollie

I've got many, many track sessions in BMW M3's. I went from track novice to instructor in an E36 M3 and along the way did many brake mods. The brakes are tough, and stop the car well.

VIR is not tough on brakes, especially at T1. So I'm going to rule out boiling as it's obvious you had fresh fluid, and ATE is adequate. In my experince with M3's, I think you didn't get a good brake bleed. You had air in the line somewhere and it worked its way up in that instance, and you lost the brakes.

If the pedal is spongy at all, there's air in there. Too often when bleeding, the person doing it lets the M/C cavity get too low on fluid on an M3 and you get an air pocket. Try doing a full rebleed on the car and change fluid color so you can tell on all the lines. Watch the fluid level in the M/C when you do it.

Stock BMW calipers are fine, switch to the Euro Rotors if you're warping stock ones, and duct the brakes if you're really getting them hot enough to cook off.

AW

Keith, sorry for your loss. At least your son is in one piece.

Are you sure the pedal went to the floor? Could it be related to break bed-in? Last time I changed brake pads on my car, I have experienced a brake friction issue: the pedal was not to the floor, but the brake did not stop the car. It felt like there was some oil on the rotors. I was expecting it because my mechanic warned me about this when using new pads. It occurred after 4-5 laps.

Following my mechanic advice, I did a cool down lap and aborted the session, That issue did not occur again.

ACW