BASIC BRAKE SYSTEM SERVICE
Any time your vehicle needs brake work, you should ask yourself, "Is this something I really want to do myself?" If you don't
feel competent enough to tackle a do-it-yourself brake repair, don't! Brakes are a critical safety item that must be serviced
correctly. Don't take chances if you have doubts about your own capabilities. Pay a professional to fix your brakes.
But hey, this is a brake book for do-it-yourselfers, so you probably won't even be reading this section unless you were ready to
do the work yourself. So let's proceed and get through the preliminaries before we tell you how to do first class brake repairs.
Brake work is not difficult to do, but there are some safety precautions you must keep in mind before you proceed. Brake work
requires you to raise your vehicle so the wheels can be removed to provide access to the brakes. This sounds simple enough
but can create a potentially dangerous situation if not done correctly:
* First, work on a level surface to minimize the risk of your vehicle rolling or moving when the wheels are raised off the ground.
* Second, place the transmission in Park (automatic) or in gear (manual) to prevent your vehicle from rolling before you jack it
up. If you're not going to work on the rear brakes or raise the rear wheels off the ground, set the parking brake, too. But if you
need to work on the rear brakes, use chocks to block the wheels.
* Loosen the lug nuts before you raise the wheels off the ground. This makes the job much easier and eliminates the danger of
pushing or rocking the vehicle off the jack.
* Place a pair of sturdy safety stands under the chassis as soon as the vehicle is raised. The stands should be positioned
under a structural component such as the frame rails, engine cradle or some other solid point that isn't going to move. Do this
before you remove the wheels and before you start to work on the brakes. Never, repeat never, crawl under a vehicle that is
supported only by a jack. Relying on a bumper jack or floor jack alone to hold a vehicle up is gambling with your life!
* Avoid exposure to brake dust. Your brakes will be dirty and coated with dust from the worn linings. The dust may contain
asbestos, and even if it doesn't brake dust isn't something you want to breathe. When the wheels are removed, wash off or
clean the brakes with brake cleaner. Some aerosol brake cleaners contain toxic or carcinogenic chemicals, so note any
precautions on the product's label before using (like warnings to use only in a well ventilated area). Also, never blow off the
brakes with an air hose because this will force the dust into the air.
* Heed all the warnings and cautions throughout this book. Where various procedures or repairs might get you into trouble,
we've tried to alert you to the potential dangers.
* If your vehicle has Hydro-Boost or integral ABS with electrohydraulic power assist (Teves Mark 2 ABS, Bosch III ABS, Delco
Powermaster 3 ABS, Bendix 10 and Jeep ABS), you must fully depressurize the high pressure accumulator before starting any
brake work. On Hydro-Boost applications, this is done by depressing the brake pedal 4 to 6 times with the engine off. On the
integral ABS applications, you have to depress the brake pedal 30 to 40 times with the ignition off.
* Be careful not to splash brake fluid on your vehicle's finish. Brake fluid can cause paint to streak.
* Wear eye protection if you do any pounding or chiseling.
DOING A COMPLETE BRAKE JOB
Now that we've covered the safety precautions, let's move on to what's involved in doing brake work. More specifically, let's
talk about the importance of doing a "complete" brake job.
A complete brake job is the opposite of an "incomplete" brake job that overlooks things or leaves some things undone. We're
talking about ignoring a leaky caliper or wheel cylinder that needs to be rebuilt or replaced, reusing old drum hardware that's
badly rusted or weakened with age, forgetting to lubricate shoe pads and caliper mounts so these parts can move freely,
reusing old grease seals to save a few bucks, not changing the brake fluid or bleeding the lines because it's takes too much
effort, not even checking the condition of the rear brakes because you're only replacing the pads up front. Things like these
can get you intro trouble -- if not now, then at some point down the road.
So anytime your vehicle needs brake work, think in terms of doing a complete brake job. That doesn't mean you have to
overhaul the entire brake system if it only needs a new set of linings. But it does mean doing a thorough inspection of your
entire brake system so you can identify any additional items that might need adjustment, repair or replacement, and also doing
those things that are necessary for preventative maintenance (like lubricating the caliper slides, shoe pads, changing the fluid
and bleeding the lines). This may sound like a lot of unnecessary extra work, but it will usually save you money and trouble in
the long run because it helps to prolong the life of your brake system while assuring optimum brake performance and safety.
Let's say your vehicle needs new pads up front. There's no need to replace the rear shoes as long as the rear linings are in
good condition. But if the shoes are marginal or have been contaminated by fluid leaks or grease, they also need to be
replaced -- along with any other drum components that are not in good condition. Even if the shoes are still within service
limits, you should ask yourself if they'll last as long as the pads you're replacing up front. If not, then now might be a good time
to replace them.
Whether or not the calipers and wheel cylinders need attention will depend on their condition. Any sign of leakage or sticking
calls for immediate repair or replacement. And even if they're not leaking, sticking or frozen, you should consider rebuilding or
replacing them for preventative maintenance.
DECIDING WHAT'S REALLY NECESSARY AND WHAT ISN'T
One of the pitfalls of do-it-yourself brake work is that you don't have anyone looking over your shoulder to hold you
accountable for what you do or don't do. A professional brake technician has his employer and customer to worry about as well
as his own reputation. In some states, there may also be a regulatory agency that serves as an auto repair watchdog. In any
event, a professional has to guarantee his work. If a problem occurs during the warranty period, he has to fix it for free. So
there are numerous incentives to do the job right the first time.
As a do-it-yourselfer, on the other hand, you are your own boss. Except maybe for your spouse or a nagging mother-in-law,
you're accountable only to yourself and your own conscience. Even so, it's important to remember what's at stake. You don't
want to take chances with your brakes because the consequences of doing a halfhearted job could be deadly. So the
responsibility is yours for deciding what needs to be fixed and what ought to be fixed for preventative maintenance.
Repairs that should always be made include any brake parts that are worn out, broken or damaged. Brake linings worn down
to minimum specifications, for example, would need to be replaced because they might not be able to create enough friction to
safety stop your vehicle. They may also damage your rotors or drums, which will end up costing you even more money. It's the
same story if you find a leaky caliper, wheel cylinder, master cylinder, brake valve, hose or steel line. Leaky components must
be repaired or replaced because fluid loss could lead to brake failure.
WHERE TO START
Every brake job should start with a thorough inspection of the entire brake system, including the antilock brake system if your
vehicle is so equipped.
* First, start with a warning light check. Turn on the ignition to verify that the brake warning light (and ABS warning light if your
vehicle has ABS) comes on. The light(s) should come on momentarily for a bulb check, then go out if no problems are present.
No light? Then you've found a bulb that needs replacing or a wiring problem. If the light comes on and remains on (does not go
out), then further diagnosis will be required to find out what's wrong.
* Apply the brakes and start the engine. Does the pedal drop slightly? That's good because it indicates a good vacuum
booster. No boost may indicate a leaky booster diaphragm or vacuum connection.
* How does the brake pedal feel? Is it firm? A soft or mushy-feeling pedal usually indicates air in the lines or leaks. A pedal that
slowly sinks is a classic symptom of a worn master cylinder. Is the amount of pedal travel normal? A low pedal may indicate
worn linings, the need for adjustment, defective or frozen drum brake adjusters or a low fluid level.
* Check your stop lights (taillights & center high mounted stop light. Do all the lights come on when you press on the brake
pedal? No lights may indicate a defective or misadjusted stop light pedal switch, a wiring problem or burned out bulbs in the
* Apply the parking brake. Does the pedal or handle work smoothly? Is it adjusted properly? Does the brake light come on? No
brake warning light may indicate a bad bulb or defective or misadjusted parking brake switch. Does the parking brake hold the
vehicle? Put the transmission into gear while the parking brake is applied. If should hold the vehicle with the engine idling. If it
fails to hold the vehicle, it may need adjustment or repair. Now release the parking brake. Failure to release fully means the
linkage or cables need attention.
* Turn the engine off, place the transmission in park (or gear if you have a manual), open the hood and check the fluid level in
the master cylinder. A low level may indicate a leak or worn linings. Also, note the fluid's appearance. Dark discoloration
indicates moisture contamination and the need for a fluid change.
* If you're working on somebody else's vehicle or one that you haven't driven for some time, take it for a short drive to test the
WARNING: Do not test drive any vehicle that does not have a full pedal, adequate brake fluid or enough brakes left to safely
bring it to a halt!
Try a couple of low speed gradual stops. How do the brakes feel? Do you feel any pulsations in the pedal? Pulsations usually
indicate warped rotors that need to be resurfaced or replaced. Does the pedal feel soft or spongy? There could be air in the
lines? Is pedal travel excessive? The brakes could be worn or need adjusting. Do the brakes pull to either side? Uneven
braking could indicate fluid or grease contaminated linings, or a bad caliper or wheel cylinder. Do you hear any unusual
noises? Scraping sounds could indicate badly worn linings or loose debris inside a brake drum. Squealing may indicate worn or
loose pads. Do any warning lights come on when you apply the brakes? A warning light could signal loss of pressure in one of
the hydraulic circuits.
If the brakes are working normally, try a panic stop from about 35 to 40 mph.
WARNING: Do not attempt this if you're already detected a brake problem or the brakes are defective.
Again, note how the brakes behave. Braking should be even, the pedal should remain firm and there should be no unusual
noises or sensations. If the vehicle is equipped with ABS, you may feel pulsations in the pedal and hear clicking or buzzing
noises from under the hood. This is normal for most ABS systems and does not indicate a problem. The ABS system should
prevent the wheels from locking up and allow you to make a safe, controlled stop. If the vehicle does not have ABS, the rear
wheels may lock up and skid depending on how hard you brake and traction conditions. This too is normal for vehicles that do
not have ABS.
* Remove a front wheel and measure the thickness of the brake pads. If worn down to minimum specifications or if wear
indicators are making contact with the rotor, new linings are needed. If the pads are still above specs, you might consider
replacing them anyway if they're near the end of their service life or if they're noisy.
* Note the condition of the rotors. Deep scratches or grooves indicate a need for resurfacing. Measure runout and parallelism,
too. If out of specs, resurfacing or replacement is needed. Are there discolored spots, heat cracks or warpage? These may
also indicate a need for rotor resurfacing or replacement.
* Note the condition of the calipers and caliper mounts. If the pads are worn unevenly, the caliper is hanging up and is not
centering itself over the rotor. This would indicate a need for disassembly, cleaning (or replacing) and lubricating the caliper
slides or bushings with brake grease. If you see any signs of fluid leakage around the caliper piston seal, it would tell you the
caliper needs to be rebuilt or replaced.
* Check the condition of the rubber brake hose. If cracked, frayed, worn, damaged or leaking, it needs to be replaced.
* Pull a drum and inspect the drum surface, brake shoes, hardware and wheel cylinder. If the shoe linings are at or below
minimum specifications, you need new shoes. If the linings are still above minimum specs but are getting thin, consider
replacing the shoes anyway. Any wetness or leakage around the wheel cylinder means it needs to be rebuilt or replaced.
* Check everywhere for leaks: the master cylinder, proportioning valve, steel brake lines, all rubber hoses, and ABS
components if your vehicle has ABS. Have a helper apply the brakes while you look underneath. Rubber hoses should not
expand under pressure. Any hoses that are swell under pressure need to be replaced.
GENERAL GUIDELINES ON BRAKE REPAIRS
* Always reline brakes in matched axle sets. In other words, do both front wheels, both rear wheels or all four-wheels. Never do
just one wheel on the right or left side as this can cause the vehicle to pull towards one side when braking. Also, use the same
type, grade and brand of friction material on both sides. Mismatching friction material side-to-side may also cause uneven
braking and a brake pull. Keep this in mind if you're buying a single "loaded" caliper assembly that comes complete with new
pads. You should also replace the pads on the other caliper so both will have the same friction material.
* If you're replacing brake linings, use the same type of material as the original. Replace semi-metallics with semi-metallics,
never asbestos or NAO. Replace NAO with NAO. Replace asbestos with asbestos or NAO. You can also upgrade from from
asbestos or NAO to semi-metallics if the friction supplier offers such linings for your vehicle application.
* Premium quality linings will give you the best wear life, noise control and brake performance. If you can't afford the best, then
go with standard grade replacement linings. Avoid economy grade linings.
* Have your rotors and/or drums resurfaced when relining the brakes unless they're in perfect condition. New linings require a
smooth surface to rub against for maximum braking effectiveness. A rough or grooved rotor or drum will wear linings rapidly
and reduce braking effectiveness. Warped rotors or ones with excessive runout can also cause annoying pedal pulsations.
* Rotors and drums should always be resurfaced in pairs. As a rule, there should be no more than .010 in. difference in rotor
thickness or drum diameter side-to-side.
* Rotors or drums that are worn down to minimum specifications, or cannot be resurfaced without exceeding the minimum or
discard specifications must be replaced.
* New hardware is recommended for drums and calipers. Replace hardware items such as the retaining clips and return
springs. Heat and age weakens these components. Self-adjusters should also be replaced if found to be corroded or frozen.
Use high temperature brake grease (never ordinary chassis grease!) to lubricate the self adjusters and the raised shoe pads
on the backing plates. New mounting pins and bushings will help keep disc brake calipers sliding freely. Slides and bushings
should also be lubricated with high temperature brake grease.
* Don't overlook the wheel bearings when relining the brakes. Check for looseness by rocking the wheel in and out. Check for
roughness or noise by spinning the wheel by hand.
Greasable wheel bearings should be cleaned and inspected. If worn, cracked or damaged, the bearings need to be replaced. If
good, the bearings need to be repacked with high temperature wheel bearing grease. Never reuse old grease seals (they
usually leak). When wheel bearings are reinstalled, they must be set with the correct amount of preload (not too tight or too
loose). Wheel bearing adjustment procedures vary, so always refer to your shop manual for the specifics on your vehicle. Note:
Though most front-wheel drive vehicles have sealed front wheel bearings, the rear wheel bearings on many are greasable --
and often neglected.
* It is not absolutely necessary to rebuild or replace disc brake calipers or drum brake wheel cylinders when doing a brake job
-- as long as these components are not leaking or sticking. Even so, most experts recommend rebuilding or replacing them
anyway for preventative maintenance.
* Always replace the old brake fluid with fresh fluid after relining the brakes, and bleed the brakes to remove air bubbles from
the lines. Brake fluid absorbs moisture over time, which lowers its boiling temperature and promotes internal corrosion.
Replacing the fluid every couple of years for preventative maintenance or when relining the brakes will prolong the life of the
hydraulic components while assuring maximum brake performance and safety.
Never reuse old brake fluid or fluid from a container that's been left open for several days or longer. The fluid will be
contaminated by airborne moisture and unsuitable for further use.
* Always use a torque wrench to final tighten wheel lug nuts. This is a much more accurate method than using a four-way
wrench, breaker bar, ratchet or impact wrench.
* Break in new linings gradually. Avoid sudden stops or hard braking for the first 150 to 200 miles. This will minimize the risk of
glazing new pads.
INSPECTING YOUR BRAKE LININGS
How often should you check your linings? It depends on the type of driving you do. Checking the linings every six months or
once a year would be a general guideline. Stop and go city driving will wear the linings much more quickly than open highway
driving because the brakes are used more often. So if most of your driving is down in town, you might want to check the linings
more often. The same holds true if you do a lot of driving on hilly or mountainous terrain. And if you have an aggressive driving
style or do any weekend racing, better plan on checking your brake linings on a much more frequent basis.
Disc brake pads can be easily inspected by removing a front wheel, but the rear drums also require pulling a drum.
It's difficult to accurately judge lining wear by appearance alone, so always measure the exact thickness of the linings at their
narrowest point to determine whether or not they're still within acceptable limits. If the linings are at or less than the minimum
thickness specification (refer to a shop manual), you need new linings. Don't put off replacing the linings too long because the
minimum thickness is based on the design of the brake system (how far the caliper pistons, wheel cylinder pistons and
self-adjusters can safely travel) and the type of linings used (bonded, molded or riveted). Bonded and molded linings can
generally tolerate more wear than riveted linings. But if wear either type too far, you can chew up your rotors or drums.
New linings would also be needed if the wear indicators on your disc brake pads are making contact with the rotors. The
indicators will make a loud high pitched squeal to warn you it's time to replace the pads.
The linings should also be replaced if they are found to be contaminated with brake fluid or grease (regardless of wear), or if
they show uneven or taper wear. Replacement would be needed if the difference in thickness from one end of the pad to the
other is more than 1/16th inch (1.5 mm) on fixed calipers, or 1/8th inch (3.0 mm) on floating calipers.
ROTOR & DRUM RESURFACING
Resurfacing rotors and drums unnecessarily will obviously reduce their useful service life, but in many instances resurfacing is
necessary by the time the linings are replaced. The general rule here is to resurface when necessary, and don't resurface
when it isn't necessary.
As long as your rotors and drums are in relatively good condition (smooth and flat with no deep scoring, cracks, distortion or
other damage), there's no need to resurface them when doing a brake job. But they're not in good condition or you've had a
problem with noise, resurfacing is recommended.
The factors that determine whether or not resurfacing is really necessary include:
* Surface condition. This is the most important criteria. Scoring, pitting or other minor surface imperfections should be cleaned
up to restore the surface to like-new condition and to minimize noise. If a rotor or drum is cracked, however, it must be
* Lateral runout on rotors. This must be measured with a dial indicator against the face of the rotor. If rotor wobble exceeds
OEM specs, re indexing it on the hub (if possible) may help reduce runout. A better solution here is to have the rotor resurfaced
in place with an "on-car" lathe. Many vehicle manufacturers now recommend this technique, which unfortunately requires
expensive equipment that only a dealer or brake shop would have. But the equipment does a fantastic job and cuts the rotor
true to its axis of rotation.
* Rotor warpage. Variation in the thickness of the rotor or uneven spots on either rotor face will cause the brake pedal to
pulsate or shudder when the brakes are applied. Flatness can be checked by placing a straight edge against both faces of the
rotor. Thickness must be checked with a micrometer at six or more points around the rotor.
If parallelism between rotor faces exceeds OEM specs (generally about .0005 in.), or if the rotor is warped or has hard spots
(which are often discolored blue or black), the rotor should be resurfaced or replaced. Hard spots that develop from
overheating or uneven tightening of lug nuts can create raised areas on the surface that often extend below the surface. The
metallurgical changes in the rotor often cause the hard spots to return after a few thousand miles so replacing the rotor may be
the best long term fix.
* Rotor thickness and drum diameter -- If a rotor is close to or at the minimum thickness specification (which is stamped on the
rotor or may be found in a brake service reference book), it is too thin to be resurfaced and must be replaced. The same goes
for drums, except the critical dimension here is the drum's inside diameter (the maximum or discard diameter spec is stamped
on the drum or listed in a reference book),
Most experts today recommend a rotor finish of 40 to 60 micro inches or smoother for quite disc brake operation. This is
achievable with most bench lathes or on-car refinishing equipment. When you have your rotors or drums resurfaced, ask them
to remove the least amount of metal possible to maximize the remaining service life of your parts. Sanding rotors after they've
been turned with #120 to #150 grit sandpaper will leave a smooth, non directional finish that provides an optimum surface for
Rotors should also be scrubbed with a brush and soapy water before they are reinstalled. Resurfacing leaves a lot of metallic
debris on the surface which can embed itself in the new brake linings and cause noise problems. Even if the rotors or drums
have not been resurfaced, cleaning is recommended to remove dirt and grease (which can contaminate new linings and cause
uneven braking or grabbing).
As we've said already, it isn't absolutely necessary to rebuild or replace your calipers when relining the brakes. But not doing
so may be asking for trouble later on. A caliper that's leaking brake fluid, is damaged, has a frozen piston, or is causing uneven
pad wear obviously needs to be rebuilt or replaced. But what if your calipers aren't leaking? Should you rebuild them anyway
for preventative maintenance?
Those who subscribe to the "don't fix it unless it's broken" philosophy of brake repair think they're saving time and money by
leaving the calipers alone. Maybe so. But most brake experts say it makes sense to go ahead and do the calipers when the
brakes are relined. Here's why:
Brake calipers, like any other mechanical component, wear and corrode with age. Every time the brakes are applied, the
back-and-forth motion of the caliper pistons produces a slight amount of wear. At the same time, moisture is building up in the
fluid. After several years of service, the fluid may contain as much as 3% water -- which is enough to produce visible corrosion
in the caliper bores and on steel pistons. As the surface of the pistons become rough, they scour the seals with every
application of the brakes. Eventually this will lead to fluid leaks and pad contamination.
So even if a caliper isn't leaking, it's still aging inside. Rubber piston seals and dust boots harden and become brittle over time.
One of the jobs the piston seals do besides keep the fluid where it belongs is to help retract the pistons when the brakes are
released. When a piston moves out, it twists the square cut seal slightly. This helps pull the piston back when the brakes are
released to keep the pads from dragging against the rotors. But as a seal ages and loses elasticity, it doesn't do as good a job
of pulling back the piston. Consequently, the pads start to drag resulting in reduced fuel economy, a possible brake pull and/or
accelerated or uneven pad wear.
When boots get old, they often crack or split, allowing dirt and water to enter the piston bore area. The result can be
accelerated seal wear, piston corrosion and sticking. What's more, if the pistons are pushed back in to accept new pads any
dirt that's found its way behind the boots will be shoved back into the caliper bores. This too, can contribute to sticking, binding
So there are valid reasons for rebuilding or replacing the calipers when the brakes are relined.
The same arguments that apply to disc brake calipers also apply to the wheel cylinders in drum brakes. As long as they're not
leaking, sticking or damaged, you might be tempted to leave them alone and take your chances. But the seals inside are
aging, so rebuilding them for preventative maintenance will assure trouble-free operation.
A complete brake job also includes fresh brake fluid. Bleeding is necessary for two reasons:
1. To remove air bubbles that may have entered the system while repairs were being made, because of a leak or because the
fluid level got too low. The air must be removed because it is compressible and can prevent a full, firm pedal.
2. To remove moisture contamination. Brake fluid absorbs moisture over time, which lowers its boiling point and contributes to
internal corrosion. Changing the fluid periodically (every two years or when the brakes are relined) as preventative
maintenance rids your brake system of unwanted moisture, restores the fluid's boiling temperature and prolongs the life of the
hydraulic components by minimizing the potential for internal corrosion. This can be a really money saver if your car or truck
has ABS because of the high replacement cost of the hydraulic modulator assembly.
As a general rule, the sequence or order in which the individual brakes are bled is very important to get all the air out of the
system. The sequence varies from one vehicle to another, so always refer to the bleeding sequence specified by your vehicle
manufacturer. You'll find this information in a shop manual.
The most common procedure on hydraulic systems that are split front-to-rear (most rear-wheel drive cars and trucks) is to do
the rear brakes first, then the fronts, starting with the wheel furthest from the master cylinder. With systems that are split
diagonally (most front-wheel drive cars and minivans), the sequence is often right rear, left front, then left rear and right front.
Always use the type of brake fluid specified by the vehicle manufacturer (usually DOT 3, but DOT 4 in most European cars).
DOT 5 silicone fluid is not recommended for vehicles equipped with ABS. Use clean fluid from a sealed container, and discard
the old fluid.
BRAKE FLUID SERVICE PRECAUTIONS
* Always use the type of brake fluid that's specified by the vehicle manufacturer (usually DOT 3 but sometimes DOT 4).
* Avoid contact with DOT 3 and 4 brake fluids. It can cause eye and skin irritation, and may be harmful or fatal if swallowed.
* Be careful not to splash or spill DOT 3 or 4 brake fluid on painted finishes. It acts like a solvent and attacks the paint. If you
do spill, don't wipe. Flush immediately with water.
* Use only fresh brake fluid from a sealed container. Never reuse old fluid or brake fluid from an open or unmarked container.
* Don't leave brake fluid containers open. Close the lid immediately after use to keep out moisture. The same goes for the
master cylinder fluid reservoir. Don't leave it open unless you are adding fluid or bleeding the brakes.
BLEEDING THE BRAKES
Anytime the brake system is opened for repairs or to replace a hydraulic component such as a caliper, hoses, wheel cylinder,
etc., the system should be bled to purge all the air from the lines. Air is compressible so you don't want any in the fluid. So you
may have to bleed the entire brake system even if you only opened or replaced a single line. Air bubbles can quickly migrate
through the system, so in most cases you can plan on bleeding all four brakes.
A timesaving trick that can eliminate the need to bleed all four brakes is to clamp off the rubber hose to the brake prior to
opening the line to replace a caliper or wheel cylinder. The clamp will prevent air from backing up through the open line. When
you're done, just remove the clamp and bleed the one line.
When bleeding the brakes (or changing the brake fluid), any of the following techniques can be used: manual bleeding, gravity
bleeding, pressure bleeding or vacuum bleeding.
Regardless of which method you use, the hardest part of bleeding the brakes is loosening the bleeder screws without breaking
them off. If it's been years since the brakes were last bled, chances are the bleeder screws will be difficult to loosen. Apply
penetrating oil and allow it to soak overnight. The careful application of heat with a propane torch may help loosen stubborn
screws. Using a six-point bleeder socket or wrench is also a good idea to prevent rounding off the tiny screw.
If a screw twists off, you have two options: forget it and move on to the next one, or replace it. If you can bleed the other lines
and get a firm pedal, it may not be necessary to replace the broken bleeder screw. But if there's air in the line and the pedal
remains soft or won't come up, then you'll have to replace the broken screw. This usually requires removing and replacing the
caliper or wheel cylinder unless you can get the base of the broken screw out with a reverse-twist extractor bit. Drilling out the
broken screw and re tapping the hole is also possible but also requires removal and/or disassembly of the caliper or wheel
cylinder so you don't end up with bits of metal inside the hydraulic system.
* Manual bleeding -- With this procedure you use the brake pedal to push fluid through the lines. The "bleeder screws" on the
calipers and wheel cylinders are opened one at a time (in the specified sequence, usually starting with the brake furthest away
from the master cylinder). A "bleeder hose" is then attached to the bleeder screw and immersed in a container partially filled
with brake fluid. The pedal is then slowly depressed to push fluid through the line to remove air. When the fluid emerging from
the bleeder screw is clear (no bubbles or discoloration), the bleeder screw is closed to prevent air from being drawn back into
the line. Check the fluid level in the master cylinder after bleeding each brake to make sure it doesn't run low and allow air to
be drawn back into the system. Then move on to the next brake in the sequence until all have been bled.
A variation on manual bleeding is called "surge" bleeding. This procedure is sometimes needed to remove trapped air pockets
in wheel calipers and wheel cylinders. The basic idea with this technique is to surge the fluid through the system so it will
entrap the air. You'll need a helper because it's a two-person job. You start by having your helper pump the brake very hard
and rapidly for about ten strokes. As he finishes the last stroke and holds the pedal down, you immediately open the bleeder
screw and let the fluid escape while your helper maintains pressure. You then close the bleeder screw and repeat until there
are no bubbles in the fluid.
Master cylinders can sometimes be tricky to bleed because air can become trapped in the bore, especially in vehicles where
the master cylinder is mounted at an upward angle with respect to the firewall. Raising the rear of the car with a jack so the
master cylinder is level can prevent air from being trapped in the front of the master cylinder while it is being bled.
If the master cylinder is being replaced, it should always be "bench bled" off the car before it is installed. This is done by filling
the fluid reservoir and attaching return hoses from the outlet ports to recycle the fluid back into the reservoir as the push rod is
On some vehicles with antilock brakes, a special procedure must be followed to remove air from the ABS hydraulic modulator.
Those that require a special procedure bleeding typically usually need a "scan tool" to cycle the ABS solenoids in the
modulator. The scan tool is plugged into the vehicle's onboard diagnostic connector to operate the solenoids. Scan tools are
pretty expensive, so if your vehicle requires this type of bleeding procedure you may have to take it to a professional.
* Gravity bleeding -- This is a method of bleeding the brakes that allows fluid to dribble out of the open bleeder screws by
gravity. It's a slow process and rarely used except in some import applications that require it because of metering valve
arrangements that prevent normal manual or power bleeding procedures.
* Pressure bleeding -- The preferred technique used by most professional automotive technicians because it's the fastest way
of getting the job done. Pressure bleeding (also called "power bleeding") uses a pressurized tank of fluid to force the old fluid
out of the system. The pressure bleeding equipment is filled with the appropriate fluid, attached to the master cylinder reservoir
with an adapter and pressurized with shop air. When the brake bleeder screws are opened, the fluid is forced through the lines.
On some brake systems with metering valves, the metering valve must be held open so the pressurized fluid will pass through
the valve. Special tools and clips are available for this purpose.
* Vacuum bleeding -- A less common but equally effective technique for bleeding the brakes. This process requires a special
vacuum tool that used shop air to create a vacuum siphon to pull fluid through the lines and out of the bleeder screws. Vacuum
bleeding does not require special adapters for the master cylinder nor do metering valves have to be held open.
The sequence or order in which the individual brakes are bled is very important to get all the air out of the system. The
sequence varies from one vehicle to another, so always refer to the bleeding sequence specified by your vehicle manufacturer.
You'll find this information in a shop manual.
The most common procedure on hydraulic systems that are split front-to-rear (most rear-wheel drive cars and trucks) is to do
the rear brakes first, then the fronts, starting with the wheel furthest from the master cylinder. With systems that are split
diagonally (most front-wheel drive cars and minivans), the sequence is often right rear, left front, then left rear and right front