COMMON BRAKE QUESTIONS
Kryderacing has been
in the “Trackside Service” business for many years. Along the way we have
been asked many questions. Brake parts used under racing conditions undergo
severe abuse. Analyzing them is always a learning process for both ourselves
and our clients. Among the more common brake problems we have encountered
are the following.
PROBLEM: “Boiling” of the brake fluid
Assuming no leaks, the explanation is simple. The solution may be difficult. Air in the system is usually the result of the fluid reaching a temperature where it “boils”. Once that happens you will need to bleed all of the fluid’s air bubbles out of the system. To keep it from happening in the future you need to lower it’s operating temperature and/or raise the fluids boiling point. Lowering the operating temperature usually requires modifications to the vehicle and we will leave that discussion to individual vehicles.
As far as raising the boiling point of the fluid is concerned let’s start with some basics. First, be sure the fluid is fresh. Fluid boiling points slowly drop with time. The usual cause is moisture from the air slowly being absorbed by the fluid. This diluted fluid has a lower boiling point than fresh fluid. So make sure the fluid is fresh and the reservoir cap seals properly. If you are using fresh fluid and it still boils you might want to consider a higher boiling point fluid. The DOT rating is a good indicator, but can be misleading.
The DOT ratings are based on “dry” and “wet” boiling points. For example, a DOT 4 has higher boiling points than a DOT 3. But it is possible to have a DOT 3 fluid which will handle your boiling problem better than a DOT 4. Obviously this can be very confusing. The reason this is possible is because of the “wet” boiling point portion of the test. This portion of the DOT test is designed to show how good the fluid is after it has been in the car for a while and absorbed a certain level of moisture. In other words, the DOT ratings also take into account aging of the fluid. Another way of saying this is that the “dry” boiling point is for fresh fluid and the “wet” is for old fluid. What if you had a fluid which had a very high “dry” test result but didn’t age very well and tested poorly for the “wet“ portion of the test? Several racing brake fluids fit this description.
So what is the solution?
If you are going to change the fluid frequently because of your track activities,
don’t go solely by the DOT rating. Look for the “dry” boiling point temperature
on the labeling. That reading represents the conditions under which you
are using the fluid. Obviously there are other factors to consider, but
this “dry” boiling point is one of the more critical if you are worried
about boiling your fluid.
PROBLEM: Silicone brake fluids
We don’t see this
problem much anymore. Thank goodness. Most of the people we have met who
used silicone fluid bought it because it was rated DOT 5. Sounds good,
but like the story above, there are other things to consider. Silicone
fluid offers big advantages at not absorbing moisture, but racers we have
talked with do not like the “feel” of the pedal with silicone brake fluids.
Note: Do not confuse “silicone” with “synthetic”. They are two very different
things and we have had great luck with the Motul synthetic.
PROBLEM: Rotor Grooving (“Record” appearance)
What is happening
is the temperature has reached a level where it is boiling the metal surface
area of the rotor. As in the case of boiling fluid the two basic approaches
are to either use better components, or lower the temperature. Usually
people blame either their brake pads or rotors and they decide to replace
one or both of them with better components. In a problem talked about above,
we used better brake fluid to cure a boiling problem. But, using better
pads and/or rotors may not be the best approach to cure the record appearance.
While there are definite differences in the quality of rotors, unless you
go to non-ferrous materials such as carbon (very expensive) the boiling
points of the metal do not vary drastically. It would be a better use of
your time and money to initially concentrate on lowering the temperatures
through the use of air ducts, brake balancing front-to-rear, and other
PROBLEM: Picking the proper brake pad compound
If you are looking for a simple answer as to what brake compound you should use, forget it. If you talk to a factory engineer from one of the leading brake pad manufacturers you are likely to end up being more confused than when you started. That’s because they want detailed information about your exact usage. That goes beyond the model of car and type of racing you do. Even the driving style of individual drivers (both drivers being very talented) can result in different pads being recommended.
Our suggestion is to consult with several sources. We at Kryderacing will be happy to talk with you and tell you our recommendations based on what we have seen at racetracks and what we know from our industry contacts regarding the latest products.
Problem: Improper brake fluid bleeding
Over the years we have seen lots of different ways to bleed brakes. A lot of very successful racing mechanics say their method is the only way that works. But different mechanics have different methods. Who is right? From what we have seen of all these seemingly correct methods, they have one common factor: DO NOT MOVE THE FLUID RAPIDLY THROUGH THE LINES. If you ever see your mechanic rapidly pumping the brake pedal in order to bleed the brake, find a new mechanic. If they are slow and methodical, you are probably getting a good bleed job.
Rather than go into
a long detailed explanation of any particular procedure, we suggest you
go to “www.baer.com/bleeding”
for one of the more thorough explanations. The Baer website has an extensive
Q&A section on brakes and many other questions are answered.