Boiling brake fluid?

[scottbooth]

I did some searching and think I know the answer to this, but wanted to get a reality check...maybe someone has seen this before.

I did a DE day at Gingerman yesterday in my 78 SC, and had a lot of fun, but I know I am still braking too early in some spots and staying on the pedal too long (unintentional trail braking). Stuff to work on, I know.

A couple of times during the day I noticed the brakes getting soft, but it never got serious, and the pedal would firm up and be OK for the next run group.

Toward the end of the day I noticed that the fluid level in the reservoir was getting low. I started out with about 1/2" of empty space at the top of the reservoir, and probably lost another 1/2" of fluid by the time I noticed it. Basically the level moved from the top of the metal band that holds the reservoir, to the bottom of the band.

Is it possible that boiling the fluid would push that much out of the reservoir through the vent hose, with what seems like a lot of expansion room in the reservoir? Or should I be looking for a leak somewhere? I did change the fluid a couple weeks ago, so there is a chance that a bleed screw is leaking. I will obviously check this out also. But the pedal does not sink under steady pressure as I think it would if there were a leak.

Either way it looks like I need to put some cooling ducts on the front, and learn how to drive. Given that my ability is probably the weak link here, I will install the coolers first and wait for my driving ability to catch up.

Thanks
Scott
78 SC

[911pcars]

Except for external leaks (did you check?), it might depend on the type of pads you have. Max. braking is going to put some wear in the friction material. When the pad thickness gets thinner, the piston extends further out and the volume of the hydraulic system increases. Could be normal wear. Check brake pads to verify.

Sherwood

[scottbooth]

Hi Sherwood,

I did not see any obvious signs of leaking - there was no fluid on the floor or in the trunk, and the pedal would hold firm under pressure instead of sinking slowly to the floor as has happened in the past when I did have a leak in the hydraulics. But I did not pull the wheels at the track to check for leaks at the calipers - instead I just topped off the reservoir and took it easy for the last session.

Pad wear is a possibility. I am using Pagid Orange pads, which have 10+ track days on them. At the end of the day I checked the pads that were easy to see (the outside ones) and they are probably down to around 4 or 5mm. I am not sure where they were before as I have always made subjective measurements (enough pad to last a track day, or not) instead of precise ones. As a best guess I think they may have lost a mm or two yesterday, so maybe that explains the change in fluid level.

Thanks for the info.

Scott

[DohertyCM]

Answer some questions....

what kind of fluid are you useing...

When was the last time you changed your fluid? not just bleed, but changed all of the fluid....You might be surprised and what comes out...

Get the racing blue fluid for your car, it will not boil as easily as the others...

Also you should change out your fluid once a year. Water will collect in the system and will cause your brakes to boil faster.
The pressure has to go somewhere and out it will go thru the tube, and when the water boils away or goes to vapor your fluid will go down. Also as pads wear the fluid will go down......

Also get some drilled rotors....they are cheap now days and will also help you from boiling your brakes. You seem to be using good pads, so also change to braided brake lines..This helps with rigidity...

Last thing dont ride with your foot on the brake...seems like common sense but I found myself doing it.

I thought I would chime in with my lessoned learned..

[scottbooth]

Good questions.

I am using ATE blue fluid that was changed 2 weeks ago. Right after I changed the fluid I did a 2-day DE at Grattan and had no problems with brakes. I did not bleed the brakes or change the fluid between the Grattan event and yesterday at Gingerman, though probably I should have at least bled the calipers.

I do change the fluid every year, sometimes once during the driving season as well. I know some people change it before every event, but I was thinking it should be OK for a bit longer than that. And time is limited so the track prep routine tends to get simpler as I go on.

Braided lines would be a good upgrade. I used them for a while years ago but changed back (long pointless story).

I think the main thing is probably my technique. As I get faster I am working on getting my braking points in the right place. The problem is that when I mess this up and start braking too early, I often find myself dragging the brakes until the turn-in point, even though I have already slowed the car enough. I need to work on separating out "off the brake" from "turn in" so I can leave a pause in between them and "save" the corner even if my original braking point was early. I am sure this would keep the brakes much cooler, and reduce pad and rotor wear as well.

Once I noticed this I started working on it, as you know there can be a lot going on out there so it takes some practice to get it all together.

Thanks for the suggestions.

[Bill Verburg]

Also get some drilled rotors....they are cheap now days and will also help you from boiling your brakes

Please do not follow this piece of advice, there are NO DRILLED 911 ROTORS that are good for track days, 930 yes, 993 yes, 911 no.

Even if you have good 930 or 993 rotors, the driling will not keep the rotors cooler. The purpose of drilling is to alow outgassing of the plasma layer that will try to build at the leading pad -rotor interface, works similarly in the rain as well.

[scottbooth]

Thanks Bill. I had heard that the 911 drilled rotors tend to crack.

What about slotted rotors? Does this help anything? Some have said that it has many of the benefits of drilling without the cracking issue, others say don't bother.

I need to check my rotors more carefully but they are looking kind of worn so they may be on the (rapidly growing) winter project list.

Thanks
Scott

[MichiganMat]

Oh man, you're kidding me Bill. I just put drilled Zimmermans on my Targa, should I inspect them regularly? What is the lifespan of them? I've got some pretty serious cooling going to them, will that help them last longer?

what a bummer.

[Bill Verburg]

What about slotted rotors?

I haven't heard or seen any additional issues due to slotting, The slots help w/ out gassing and water as well as holes do.

I've got some pretty serious cooling going to them, will that help them last longer?

Keeping the rotors as cool as possible is numero uno wrt pad, rotor and fluid life expectancy.

[LarryP]

Don't apply your brakes as you roll to a stop after your session, either. Cut your motor and ease the clutch out. Ths will help keep the rotors from cooking the calipers and fluid.

[masraum]

drilling and slotting can cause the rotors to crack, but drilling is worse. There have been lots of threads and pics here and on the miata board about NOT using drilled rotors. Not only will they crack (question of when not if), but they can eventually fail catastrophically(sp).

Solid rotors have a higher heat capacity than drilled rotors. Removing mass removes metal that can absorb heat which is what brakes are designed to do.

Here's an interesting page
http://flashoffroad.com/Maintenance/Brakes/BrakeRotors.html

[KTL]

Check the overflow tube near the driver's front of the car. That's where the fluid would have spit out. And Sherwood's point is a good one too. As your pads wear down, the fluid level drops.

I can support Bill's concerns about the rotors. My friend Jay (Jay Auskalnis here) has drilled SC rotors on his '78 SC lightweight and he developed a significant crack connecting at least three holes radially, after a 2 day event this past weekend. Rotors are junk now and being replaced with solid ones.

[911pcars]

Regarding the master cylinder vent tube. I'd direct the end into a container of some sort. You may not normally corner at max. g's for the fluid to vent through this line, but all it takes is an inadvertant overfill. Brake fluid is corrosive and is a fine paint remover wherever it ends up.

Do you know where the end of your vent tube line is?

Sherwood

[Jay Auskin]

Originally posted by MichiganMat
Oh man, you're kidding me Bill. I just put drilled Zimmermans on my Targa, should I inspect them regularly? What is the lifespan of them? I've got some pretty serious cooling going to them, will that help them last longer?

what a bummer.

Matt--

I went a year on a set of worn x-drilled rotors. A second problem with the cross-drilled is they develop deep grooves due to the holes. This wears pads out very quickly. If it's just street use, don't worry about any problems.

Yep, like KTL said, my SC has an overflow in the left front of the car. I sprays over the underside nicely. Unfortunately, it did not take the paint off my pink calipers.

[DohertyCM]

The slotted rotors are not only to vent the gasses but also to slice the glazed portion of the pad off of the rotor. They wear pads out faster. But they are a good product and dont crack like the drilled rotors do.

Personally I have been running a set of brembo cross drilled rotors for almost 2 years now, on and off the track and they still look great with no cracks. Maybe its the product, maybe it is in how you treat them.

If you are on the track, you should change out your fluid ATLEAST once a year if not more, check your brakes and rotors prior to use.

BUT, I like my cross drilled, They work and they are cheap enough not to hurt my pocket if they should crack...also I have yet to boil my brakes since switching to these rotors with racing pads and the blue fluid.

But also I dont drive in the rain, and one cause of warping brake rotors is the heating and cooling of the rotor.

Im sorry Bill I am extremely happy with mine and they work really well. And no one accuses me of being slow or easy on the car on the track. BUT I will say this, I do inspection of the car and the systems all the time and will replace something if there is the slightess indication of a problem.

[Bill Verburg]

Originally posted by DohertyCM

Im sorry Bill I am extremely happy with mine and they work really well. And no one accuses me of being slow or easy on the car on the track. BUT I will say this, I do inspection of the car and the systems all the time and will replace something if there is the slightess indication of a problem.

Shall we make this a popularity contest? If so the vast majority of people that have actually stressed their brakes will report that drilled 911 rotors(we are talking SC or Carrera here) are not a good thing to own.

As I said above

Keeping the rotors as cool as possible is numero uno wrt pad, rotor and fluid life expectancy.

having a light car is obviously part of keeping them cool.

There are so many variations in individual chassis setups, motors, tracks drivers etc. that there is a continuum of solutions from unacceptable to overkill, drilled 911 rotors are closer to the unaccepatbale end than the overkill end.

again we are not talking about 930 or 993 or 996 or 997 rotors here.

[DohertyCM]

No popularity contest, I am just professing my sincere happiness with the product that i purchased and currently using.
Maybe its the product that I purchased....For instance, my rotors have what looks to be a third as many holes in the rotor than that one shown above. Maybe thats a factor...not as flexable as one with crap loads of holes like that one. . .I dont know. But as I said, I have not had a bad experience with them.

Respectfully speaking, i dont understand why the distinction between a 930 and a 911 as far as rotors go. Weight? Speed? would only increase the heat on the rotors. A lightweight car would not have to brake as hard.
Overkill no, i dont think its overkill. There are many other overkill products out there..

As I was saying, i have had great performance and I am very satisfied with the drilled brembos.
Now if you are talking full time track, I would not go drilled, I would go slotted. Given that, I believe that I would buy the rotors to fit the application you are going to be using them for.

[Craig 930 RS]

- I've been a vendor of Pagid brake pads for 3 1/2 years....based on personal experience and feedback from probably 100 911SC (and to a lesser extent) Carrera owners:

1) Drilled SC rotors for an SC - NO! Never.
Slotted - decent.

2) LOTS of cooling. AJ-USA kit a must.

3) Fresh fluid OFTEN. I would do a full flush several time per year, flushing the caliper fluid out each event. Overkill? Nope.
Motul is better than the old favorite ATE Blue. *Castrol SRF highly recommended for these brakes.

4) SC brakes are undersized for serious track work..........use the precautions mentioned or that pedal may go to the floor in a HURRY.

5) Higher friction pads wear rotors faster, create more heat, and will cause cracking more than cheapo pads.

You can't have it both ways --

[Bill Verburg]

Originally posted by DohertyCM

Respectfully speaking, i dont understand why the distinction between a 930 and a 911 as far as rotors go. Weight? Speed? would only increase the heat on the rotors.

The 930 rotors were designed from day 1 to incorporate the holes which are cast in. That and superior metallurgy make the holey rotors on those cars a world different from 911 rotors which were drilled as an afterthought. Brembo certainly has the metallurgy but the design details are not there.

I have the original patent applications for the 930 rotors somewhere here. I'll see if I can find it again.

[DohertyCM]

OK, I dont have an SC model, so I am not familiar with those model particulars. I do think that having a lessor amount of holes, driving style and pads plays a part...and of course you get what you pay for..

Change of subject...kinda ....

What do you think about the idea of placeing a titainium plate between the pad and the piston. I have seen this done on some other cars in articles because of the titainiums ability to shed heat rapidly. This prevents alot of heat transfering to the puck which boils your fluid.

Thoughts?