Date: Sat, 28 Feb 1998 22:40:31 CST
Reply-To: Joel Walker <JWALKER@UA1VM.UA.EDU>
Sender: Vanagon Mailing List <Vanagon@vanagon.com>
From: Joel Walker <JWALKER@UA1VM.UA.EDU>
Subject: All You Wanted to Know about Brake Fluid ... :) <long>
Content-Type: TEXT/PLAIN; charset=US-ASCII
Car Care by Rik Paul Motor Trend, APril 1998
Are you getting all of your stopping power??
The importance of brake flushing
Brake fade is somewhat akin to brain fade. Reaction time is slower,
usually snappy performance is replaced by a dull, mushy feel, and in
critical situations the slow response time can be disasterous. While
there are several mechanical reasons for this type of condition, one
of the most overlooked causes is contaminated brake fluid. Most car
owners are well aware of the importance of maintaining proper fluid
levels in the vehicle, and reliably check to make sure that the brake
fluid is mainained between the minimum and maximum marks on the
reservoir. After all, if there's too little fluid, it's possible for
air to be sucked into the lines, which can result in a spongy pedal
feel and inefficient braking performance.
The importance of flushing the brake system ... taking the old fluid
and replacing it with new ... is often not so well recognized. In fact,
a few years ago, Motor Trend Senior Road Editor Mac DeMere needed to
get his vehicle's brake system flushed and call a local gas station for
a price. The person he talked to ... even with never having seen Mac's
car ... told him that procedure wasn't necessary. When Mac pressed for
a price anyway, the person again fervently stated that his vehicle's
brake fluid didn't need to be changed. Finally, Mac simply called
elsewhere. One of the problems is that flushing the brake system if
often not specifically listed in many vehicle's routine maintenance
schedule, which could cause an unknowledgeable person to think that the
procedure wasn't necessary. In fact, manufacturers usually specify a
general inspection of the brake system and leave it up to the mechanic
to know when to flush the fluid.
Why is flushing important? Conventional glycol-based brake fluid is
hygroscopic, which means that it absorbs water. This is important, in
order to keep condensation in the brake system from causing corrosion.
However, eventually, the fluid will absorb all the moisture it can hold,
reaching its point of saturation. Several things can happen at this
point. Unabsorbed moisture can begin to collect in the system, causing
corrosion in critical areas; the water can cause seals to swell and
deteriorate, further contaminating the fluid; and the boiling point of
of the fluid drops beyond recommended levels. This means that under
high-heat braking conditions, such as during hard braking or repeated
brake application while descending a mountain, the fluid will start
boiling sooner, which will reduce braking performance. The pedal can
begin to feel spongy, and as braking efficiency drops, it takes longer
to stop the vehicle.
How do you know when the system should be flushed? Most maintenance
schedules that do specify it recommend changing the fluid every two
years or 30,000 miles. If you live in an unusually humid climate, it's
better to plan on doing it every year. However, your eyes can tell you
when the time has come. Fresh brake fluid is transparent and has a
slight amber-colored look. As the fluid absorbs moisture, it takes on
a darker, cloudy appearnace, which tells you it needs changing. This
can also be verified empirically. For instance, Phoenix Systems (Dept.
MT, 3555 E. 42nd Stravenue, Tucson, AZ 85713; (888) 749-7977), a
company that specializes in professional brake system tools, markets
a Brake Fluid Tester ($370) that reads the boiling point of a sample
of fluid. Fresh brake fluid has a boiling point of about 400 degrees F
or higher. As it absorbs moisture, however, the boiling point will
gradually drop. Phoenix Systems recommends that if its tester shows a
fluid's boiling point to be below 330 degrees, the system should be
flushed.
When adding new brake fluid, be sure it's the appropriate type for your
vehicle; it will be listed in the owner's manual or marked on the
reservoir cover. Conventional glycol-based formulas are designated as
DOT 3 and DOT 4, which differ mainly by their boiling points. While the
two are compatible, DOT 4 has a higher boiling point, so if your vehicle
is designed for DOT 4, don't substitute DOT 3. If DOT 3 is recommended
for your car, you can use either type. Castrol also markets a brake
fluid called LMA, for Low Moisture Absorption. This is formulated to
last longer than conventional types because it takes longer to reach
its saturation point, and also boasts a higher boiling point.
It's important to note that DOT 5 brake fluid, which is silicon-based,
is NOT compatible with conventional fluid and should NEVER be added to
a system using DOT 3 or 4. DOT 5, which has a purple color, doesn't
absorb moisture, and has a higher boiling point. It's NOT recommended
very often for late-model cars because its lack of moisture absorption
INcreases the chance of corrosion, and since it can be compressed, it
can cause the brake pedal to have a spongy feel. It's also much more
expensive.
Certainly never pour any other type of fluid, such as power steering
fluid, ATF, or motor oil into the brake system, as those petroleum-
based fluids will deteriorate the seals and other rubber components,
potentially causing brake failure. In addition, if using DOT 3 or 4,
be careful not to spill brake fluid on a painted surface, as it can eat
away the paint. If this happens, clean up the spill immediately and
wash the area with plenty of water.
Whenever you add the brake fluid, it should come from a fresh, sealed
container. This is, again, due to its hygroscopic characteristics.
Fluid that has been exposed to air for any length of time can absorb
water vapor, reducing its capacity to absorb moisture in the brake
system. When buying brake fluid then, always get the smallest container
that will do the job. If you're just topping off a master cylinder, for
instance, purchase a small bottle. If doing a complete flush, get a
large container. Any leftover fluid should be sorted in a tightly
sealed bottle and used within a few weeks. It's false economy to use
brake fluid that's been sitting around for an extended time.
TIPS for the Do-It-Yourselfer
Brake flushing is much like bleeding air from the system. The most
common method is the tried-and-true two-person procedure. It's easier
done than described. First remove the lid from the master cylinder
(be sure to clean around the lid first, to prevent any dirt from
falling into the reservoir). Here, you start at the wheel farthest
from the master cylinder, and slip a piece of clear plastic hose over
the bleeder valve; it should fit snugly. Place the other end of the
hose into a clear containe, such as a glass jar or plastic milk carton,
submerged in brake fluid. Have an assistant pump the brake pedal a few
times to build up pressure, then on a downward stroke, hold the pedal
depressed slightly. While he's holding the pedal down, use a wrench to
open the bleeder valve just enough to let a surge of brake fluid
escape into the hose and container. Your assistant should then slowly
depress the pedal to the floor and hold it there long enough for you
to immediately close the bleeder valve again to prevent air from being
drawn back into the lines.
The key here is to keep the fluid level in the master cylinder above
the minimum mark by repeatedly adding fresh fluid. Once you begin
seeing fresh, clear fluid (with no air bubbles) coming out of the
bleeder valve in place of the old, dark fluid, you can tighten the
valve and move on to the next wheel. Repeat this procedure on all
four wheels, working your way toward the master cylinder, which should
be your last bleeding point (unless another sequence is recommended
in the vehicle's service manual).
In these days of modern technology, there are easier alternatives to
this age-old procedure. For instance, you can buy a bleeder hose with
a one-way valve, that allows fluid and air out, but doesn't let it
back in. This eliminates the need to repeatedly open and close the
bleeder valve during each pump of the pedal. Just make sure that the
fit of the hose on the valve is tight enough that it doesn't allow
any air to seep in through the connection. Russell Performance
Products (Dept. MT, 225 Centress Blvd., Daytona Beach, FL 32114;
(904) 253-8980) also makes a one-way bleeder valve, called the Speed
Valve, with which you can replace your stock valves. This works the
same as the one-way hose and eliminates any concern about air leaks
at the connections. Either method makes it possible for one person to
do all the work, although you still need to check when clear fluid is
flowing out of the valve.
Vacuum pumps, such as the popular Mity-Vac models made by Neward
Enterprises (Dept. MT, 9251 Archibald Ave., Rancho Cucamonga, CA 91730;
(800) 648-9822), can also be used as a one-person flushing procedure
by drawing fluid out through each bleeder valve, without the need for
someone to pump the brake pedal. The company also markets the Mityfill
Automatic Fluid Feeder, which can be attached to the master cylinder
to provide a constant supply of fresh brake fluid as you're removing
the old fluid, eliminating the need to be constantly check the fluid
level.
Perhaps the most sophisticated tool for both bleeding and flushing
brake systems is the Phoenix Injector, produced by Phoenix Systems.
This has the capability of either injecting fluid into the system or
pumping it out, to allow a variety of one-person techniques to be used.
For instance, in split-system designs (most vehicles produced in the
last couple of decades), you can pump fresh fluid into one bleeder
valve, while the old fluid is simultaneously extracted from the
opposing valve. Or the system can be pressure flushed (a professional
technique normally requiring expensive hardware) by pumping fluid
through the system from each master cylinder reservoir port, while
again collecting the old fluid at each bleeder valve. Or it can be
used to vacuum flush a system, acting as a conventional vacuum pump.
For bleeding, the Injector also allows reverse fluid injection, which
removes air bubbles by forcing them upward and out of the master
cylinder, requiring a minimal loss of fluid. The Phoenix Injector is
a professional-caliper instrument, and understandibly isn't cheap;
depending on model, it runs $70 to $305.
Regardless of which flushing method you choose, when you're done, be
sure to top off the level in the reservoir and install the lid securely.
Assuming all mechanical components are in order, your brake pedal should
have a strong, firm, confident feel, and the system should be working
at maximum efficiency, ensuring you'll get the most from your brakes.
TIP of the Month: The Masters of Our Own Cylinders
Even if there are no leaks in your car's brake system, the fluid level
in the brake master cylinder will still gradually go down. This is
important to keep track of, because it is a good indication that it's
time to check the vehicle's brake pads and/or shoes for wear.
As the friction lining on pads and shoes wears down, they are pushed
out farther to maintain good braking contact with the rotors or drums.
This, in turn, requires that more fluid be drawn from the master
cylinder. Eventually, this will be evident in the master cylinder
reservoir as the fluid level drops to near the minimum mark.
Be sure to check your brakes at this point, and don't forget to top
off your fluid.
----------------------
Unca Joel's warning: if you add fluid BEFORE you replace the pads
or shoes, you may regret it later (after you've forgotten that you
added that fluid!) when you do change the pads/shoes. the new pads
and shoes are thicker, and will push the fluid back up into the
master cylinder reservoir ... and all that fluid you added may spill
out!!!
so if you're gonna add fluid, make yourself a note somewhere to watch
out for spillage when you replace the pads/shoes. :)
---------------------------------------------------------------------
For Vanagons
You have FIVE bleeder valves. The fifth one is on your hydraulic
clutch slave cylinder (on the transmission, between the rear wheels).
This fluid also needs to be bleed/flushed periodically (whenever you
do the wheel cylinder bleeder valves). I think it's easier to reach
from up top, through the engine compartment. And yes, you have to
pump the CLUTCH pedal (instead of the Brake Pedal). :)
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