Brake
System Flushing
Contents:
Introduction:
Did
you know that you should regularly flush your brake fluid?
Most people don’t and here is why you should do it,
regularly.
Brake
fluid is hygroscopic. That
means it loves to absorb water like a sponge and likes it so much it
will suck water right out of the air.
As it absorbs water two bad things happen.
First is that it causes the boiling point of the fluid to go
down reducing braking performance, and second, the moister causes
the brake fluid to become corrosive and can damage brake system
parts, very expensive brake system parts.
The
brakes generate lots of heat and the fluid in the brakes can get
very hot. If it gets
hot enough it can boil, and when it does it goes from a liquid to a
gas. Remember back in
school you leaned that fluids don’t compress well?
That is the whole concept behind hydraulic brake systems.
The brake fluid does not compress so it passes energy from
the master cylinder that is connected to the brake pedal to the
wheel cylinders, or calipers where the pads press against the rotors
or drums to stop your car. This
all works well as long as the brake fluid remains a liquid.
If it gets to hot it will boil and transform its self from a
liquid to a gas. Remember
air is a gas and you can really compress it, a lot.
You can take a lot of gas and compress it and put it in to a
small place like a scuba tank. The bad thing is that it will not transfer energy to the
brake pads like liquid brake fluid can.
Once
your brake fluid boils, your brake pedal can go right to the floor
and have little to NO affect on getting the brakes to stop the car.
This has happened to me several times in my work cars, but
NEVER in any of my personal cars.
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DOT
Types and Boiling Points:
DOT
3 brake fluid has a minimum boiling point of 400 degrees Fahrenheit.
DOT 4 has a minimum boil of 450 Degrees.
DOT 5 and 5.1 has a minimum boiling point of 500 degrees
Fahrenheit, but they are not compatible with normal brake systems
and are used in special racecar brake systems.
DOT 5 is a silicone fluid and will foam in ABS systems and
you will have no brakes. DOT
5.1 is non-silicone, but neither one is compatible with the Toyota
brake system so forget about it.
If
your system is labeled for DOT 3 you can use DOT 3 or 4 and they can
be mixed if needed. I
use DOT 4 in my vehicles.
The
minimum boiling point ratings are as the fluid sits in its factory
sealed container. As
soon as you open the container it starts to absorb moisture and the
boiling point starts to drop. When
you add brake fluid always make sure you do so from a factory sealed
container.
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Corrosion:
As
brake fluid absorbs moisture it can become corrosive and damage very
expensive brake system parts like a $1400 ABS modulator pump.
A few dollars spent regularly flushing you brake system can
save you thousands down the road especially in modern brake systems
with all kinds of fancy stuff like ABS, Traction Control, Vehicle
Skid Control, and so on. Your
brake system should be flushed yearly, but never longer then every
two years.
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Flush
your brakes:
Brake fluid absorbs water from the atmosphere, lowering its boiling point
and causing corrosion, particulate contamination, microscopic
particles of rust and rubber accelerating the wear of very expensive
brake components. This is why you should fully flush your brake
system every year, but never more then every two years.
In addition, whenever the hydraulic system has been opened
like when a component is replaced, the system must be bled of air.
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Flushing
Methods:
The
brake pedal method:
This
can be done with two people or one with a “one man bleeding
kit”. The one man bleeding kit has a check valve that you attach to
the wheel cylinder so air does not get drawn back into the system.
Everyone
knows about this method, but few know how bad it can be. Normally the piston, which is connected to the brake pedal,
only travels so far in the master cylinder.
When using the brake pedal flushing method, the piston can
travel much further down in the master cylinder and contact an area
that has never been touched by the piston or its sealing O-ring.
If the area has corrosion in it you can ruin the O-ring in
just one pass and then you will need a new master cylinder.
This is most likely going to occur in a vehicle where brake
flushing has not been done as often as it should have been.
If it has been neglected then you should only have it power
flushed.
Knowing
that and you want to proceed you should check the shop manual and
make sure that your brakes can be flushed this way.
Some GM cars cannot and they can only be flushed with a
special computer that interfaces with the ABS system.
I can tell you that my 96 4Runner can be flushed this way.
Determine
how far down the brake pedal normally goes and put a block of wood
under it to prevent it from going further down to prevent O-ring
damage. Next using a NEW turkey baster, not a used one so you do not
contaminate the brake fluid and system.
Our use my favorite, a large sterile medical syringe. Clean
the outside of the master cylinder and reservoir to make sure no
dirt can get into the brake system.
Remove the cap and use the turkey baster to remove as much of
the old fluid as you can and top it off with new fluid from a
factory sealed container. Then
go to the wheel cylinder that is furthest from the master cylinder. On most cars that will be the right rear wheel, on the 3rd
generation 4Runner with ABS it will be the left rear wheel.
Apply a 10mm box end wrench to the bleeder valve and a clear
tube that goes into a collection container and you are ready to
start.
Tell
your helper to apply pressure to the brake pedal while you open the
bleeder valve. Have
your helper tell you when the pedal is against the block of wood and
hold it there until you close the valve.
Let him know to let the pedal up.
It is important that he allows it to come all the way up for
a few seconds while the master cylinder refills.
Keep going until you see nice new clear fluid free of bubbles
coming out of the bleeder valve.
Stop and move to the next closest wheel to the master
cylinder and so on until you get them all. It is very important that you never let the level in the
master cylinder reservoir drop below the MIN mark or you may get air
into the system and have to start all over again.
Once you complete the last wheel, top off the reservoir and
go for a careful test drive. If
the brakes are mushy that means you got air into the system and have
to do it again until you get it all out.
Now you are done until next year.
Here
is another nifty idea. There
is a company called Speed Bleeder
that sells a replacement bleeder
valve that has a check valve built right in.
It looks like it would speed up the bleeding process
especially if you had to do it by yourself.
The only thing is that for the speed bleeder to work properly
the threads would have to remain air tight so the valves would have
to be removed from time to time to apply more thread sealant.
Reverse
Injection:
There
is some new equipment out that is for reverse injection of brake
fluid. The idea here is
that you force new fluid into the wheel cylinders through the
bleeder valve and flush the old fluid back out the master cylinder.
I
have one of these systems and flat do not like it.
I just do not think I can get the bleeder valve clean enough
so I do not force dirt into the brake system.
I also feel that the fluid in the wheel cylinders is where it
gets the hottest and maybe in the worst shape and I sure do not want
to force the worst, dirtiest brake fluid backwards through the ABS
modulator pump and the rest of the brake system.
I
may just be old fashioned here, but I just do not think this is a
good idea.
The
reverse injector system can also be used to apply suction to the
bleeder valve and such the old fluid out the bleeder valve.
I have tried this several time and I keep getting air sucked
in past the threads of the bleeder valve into the wheel cylinder and
it appears to me that I can not get all the air out of the wheel
cylinder. Overall the
only thing I like about my reverse injection kit is the nifty
collection bottle that I use when power flushing the brake system.
Power
Flushing:
Power
flushing is the ticket for flushing the brake system and you do not
have to worry about damage to the master cylinder like in the brake
pedal method.
The
professional power flushing systems have a big aluminum gadget that
looks like a beer keg. It
has two chambers in it that is separated by a diaphragm.
One side of the diaphragm is the new brake fluid and the
other is compressed air. A
hose is clamped on to the opening of the master cylinder reservoir
to supply the reservoir with fresh fluid.
The tank is hooked up to the shops compressed air line and
puts about 15 PSI on the diaphragm which forces the new fluid into
the master cylinder reservoir and keeps it under positive pressure.
Then all your have to do is go around to the different wheel
cylinders and allow the fluid to flow out until you see nice new
fluid coming out of the bleeder valve.
This works really well, but the equipment is expensive and
you need shop air to drive it.
I
just found a power flusher tank that works really well for the do it
yourselfers.
I
got one from Motive Products
and it sells for $49.95 for model PBU101.
It
works the very same way as the professional power flushing systems,
just on a smaller scale. You
connect the hose with the universal adapter to the opening of the
master cylinder reservoir and dump two quarts of new fluid into the
tank and pump it up to 15 PSI and then run around and bleed it out
of the wheel cylinders. I was able to flush the brake systems in all three of my
vehicles in about an hour and a half.
It is fast and really easy to use.
For the money it is a must have item.
Many shops charge well over $100 to flush a brake system.
You can get one of these tanks and do it yourself for $49.95
for the tanks and $20 in new fluid.
From then on all you need is the fluid.
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