Got a spongy brake pedal? Did you do a pad or caliper replacement and you need
to bleed and flush the brake system? This repair is a good idea when doing any
kind of brake replacement because brake fluid becomes dirty from the pistons of
the brake master, caliper and wheel cylinders rubbing against the metal housing
of each component. These pistons hold pressurized fluid by using rubber seals that can
withstand the chemical properties of the fluid.
Hydraulic pistons slide inside the housing when the brake pedal is pressed
down and are held in place by the housing bore hence the metal on metal wear.
This wear will cause leaks due to scores in the housing bore which the seal cup
cannot seal against therefore causing a leak. A fluid change also removes moisture and contaminants which cause
rust pits in the housing bores which also lead to leak failures.
This fluid is subject to extreme pressure and heat, the boiling
point of the fluid is much higher then normal fluids of its kind which is important for different applications, higher boiling points
(severe duty) and anti-lock braking ABS systems which require a high quality fluid,
Distinctive ratings define the chemicals in which
the fluids are produced from such as mineral oil, ester glycol and synthetic oils. Many of these fluids are not compatible, make sure to add and flush your brake
system with the manufacturers recommended fluid.
Avoid accidental fluid spillage, because it is corrosive. If
you do accidentally have a spill clean it up with soap and water quickly. Always
add fluid from a sealed container to avoid dirt and moisture contamination.
Here is a list of brake repairs or replacements that warrant a bleed or
I have created this guide to show you how you can do it yourself without
using a fancy power bleeder and saving you from going to a repair garage.
I will go over this problem in detail further down in the article and how to
complete this service. Watch the following
video and then read through the following article to gain additional
added information, though appearances may vary, the procedure is the same on
Locate and identify the brake master
cylinder fluid reservoir, fluid cap, lines, and fluid level sensor. Check the
master cylinder for leaks between the master and brake power booster using a
flashlight and a small mirror which is a sign of component failure. This is a
sign the seals inside the master have failed and there is no reason to continue
this procedure until the master has been replaced. If no leaks are present
continue with this guide.
Before opening the master cylinder cap use a shop towel to wipe it clean. This
will help keep dirt out of the reservoir which can cause seal failure by
contaminating the fluid.
Next, grasp the lid and twist it counterclockwise to remove while gently lifting
it upward. Some caps have a fluid level sensor which is will have wires attached
to it, simply wipe off any excess fluid and set it off to the side.
If a screen is present in the reservoir remove it with a twisting motion then
insert a suction device which most of you have in the kitchen (turkey juice
remover). Have a small plastic container to release the old fluid into to
discard. Avoid spillage if you can and rinse with water if an accidental spill
occurs. Some reservoirs are designed with a dual chamber, a small hose will need
to be attached to the suction device get over the divider in the middle of the
Try to get as much fluid out as possible as to not contaminate the new fluid.
If all the fluid cannot be removed it will mix with the new fluid and most of it
will be flushed out when the process begins.
Then, carefully pour the new fluid into the reservoir, you may need to use a
funnel to aid in this process. Continue adding until the fluid reaches the full
line and then remove the funnel. Most systems use a DOT 3 or 4 fluid but if you
are not sure consult your vehicles owners manual.
Wipe off an access fluid then reinstall the reservoir cap.
Locate all four brake fluid bleeder fittings
located near the top of each caliper or wheel cylinder which may have a dust cap
over them. The system bleeder screw can be fairly tight because bleeder screws
seals against a taper fit seat in the valve. When loosening apply WD40 or equivalent to aid
in rust removal, use a 6 point wrench
or socket is best to avoid rounding.
Using a small screwdriver or pick remove
the bleeder dust cap. Place it to the side to be reinstalled, do not discard.
Then place a boxed end wrench and rubber hose
positioned onto and over the bleeder. A rubber hose is helpful to avoid fluid
contamination from getting onto the pads or shoes, access fluid should be hosed
off with water once the job is completed.
Now it's time to start the bleeding process, start with the right rear and then
the left rear, then head to the front and do the right front and then finish
with the left front. Open the first bleeder valve while the opposite end of the
rubber tube is in a fluid catch container.
Have a helper push down on the brake
pedal slowly and hold even pressure downward.
Fluid will then start to flow out of the bleeder or tube. Air bubbles will be
in with the fluid stream if air is present in the system.
As the fluid flow slows down tighten the bleeder valve while maintaining
pressure on the pedal. Do not allow the pedal to come upward while the valve is
open or it will such air back into the system and then you will need to start
the bleeding process all over again.
Never pump the brake pedal as this will cause additional air to get into the
system. There is a very small orifice inside of the master cylinder that allows
fluid down into the fluid chamber, pumping the pedal cause's air to be sucked in
through the seals of the master creating more problems.
Once the bleeder valve is closed, allow
the brake pedal to slowly return to its normal position. While servicing each
wheel observe brake fluid level in the reservoir and refill as needed. Continue this process at each wheel
until clean fluid is present with no air bubbles being expelled from the bleeder
valve or hose.
Add additional fluid to the reservoir to keep the master full. Do not allow
the fluid to become empty or air will be pumped into the system.
Refill the fluid to the full line of the reservoir and reinstall the lid.
Using a shop towel wipe any spilled fluid and rinse with water if needed.
Then start the engine and check brake pedal operation which should be firm
toward the top of its travel. If the pedal is on the floor or spongy there is
air still in the system. This means the brake shoes are out of adjustment, the
master cylinder is bypassing internally or the system has a leak.
Brake pedal goes to the floor
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