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FAQ Brakes

WHAT SHOULD BE INCLUDED IN A "COMPLETE" BRAKE JOB?

A complete brake job should restore the vehicle’s brake system and braking performance to
good-as-n60w condition. Anything less would be an incomplete brake job.

Brake components that should be replaced will obviously depend upon the age, mileage and
wear. There is no pat answer as to which items need replacing and which ones don’t. It’s a judgment call.

A complete brake job should begin with a thorough inspection of the entire brake system;
lining condition, rotors and drums, calipers and wheel cylinders, brake hardware, hoses,
lines, and master cylinder.

Any hoses that are found to be age cracked, chaffed, swollen, or leaking must be replaced.
Make sure the replacement hose has the same type of end fittings (double-flared or ISO) as
the original. Don’t intermix fitting types.

A leaking caliper or wheel cylinder needs to be rebuilt or replaced. The same applies to a
caliper that is frozen (look for uneven pad wear), damaged or badly corroded.

Steel lines that are leaking, kinked, badly corroded, or damaged must also be replaced. For
steel brake lines, use only approved steel tubing with double-flared or ISO flare ends. Leaks
at the master cylinder or a brake pedal that gradually sinks to the floor tells you that the
master cylinder needs replacing. The rotors and drums need to be inspected for wear, heat
cracks, warpage, or other damage. Unless they are in perfect condition, they should always
be resurfaced before new linings are installed. If worn too thin, replace them.

Wheel bearings should be part of a complete brake job on most rear-wheel drive vehicles
and some front-wheel drive cars. Unless bearings are sealed, they need to be cleaned,
inspected, repacked with wheel bearing grease (new grease seals are a must), and properly
adjusted.

Rust, heat, and age have a detrimental effect on many hardware components. It’s a good
idea to replace some of these parts when the brakes are relined. On disc brakes, new
mounting pins and bushings are recommended for floating-style calipers. High temperature
synthetic or silicone brake grease (never ordinary chassis grease) should be used to
lubricate caliper pins and caliper contact points.

On drum brakes shoe retaining clips and return springs should be replaced. Self-adjusters
should be replaced if they are corroded or frozen.

Use brake grease to lubricate self-adjusters and raised points on brake backing plates where
shoes make contact. As a rule, tapered roller bearings are not preloaded. Finger tight is
usually recommended. Ball wheel bearings usually require preloading.

As a final step, old brake fluid should always be replaced with fresh fluid.

HOW THIN CAN ROTORS/DRUMS BE SAFELY TURNED?

If a customer wants drums turned to a size outside the limits cast into the drum, you must
refuse. They cannot be turned thinner than the minimum thickness specifications stamped or
cast on the rotor or drum itself. A drum or rotor worn or turned too thin may not be able to
absorb and dissipate heat quickly.

This can make the brakes run hot, accelerate lining wear, and reduce braking effectiveness.
It can also lead to rotor or drum arpage and a pulsating brake pedal.
Most drums are cast with enough thickness to allow 0.090" of wear. In other words, the
difference between a drum’s diameter when new and its discard diameter is 0.090," but that
doesn’t mean you can machine a drum right up to the 0.090" limit. You should never turn a
drum that’s worn more than 0.060" beyond its original diameter.

The 0.060" limit leaves a 0.030" margin for additional wear. If you turn a drum that’s worn
more than 0.060," or if the drum ends up being more than 0.060" larger after turning, there
may not be enough metal left to handle normal wear until the next brake job.

The 0.090" discard limit is the maximum acceptable wear the drum can safely handle before
the metal is too thin. Any drum worn beyond 0.060", or that would be over 0.060" larger
after resurfacing, should never be turned on a lathe, it should be replaced.

Like drums, the amount of wear a rotor has experienced will determine whether or not it can
be resurfaced. The two-key rotor dimensions to take into account are minimum refinish
thickness and discard thickness.

Wear is checked by measuring diameter with a drum micrometer. If the gauge shows
enough metal left to safely ‘turn it, the drum can be resurfaced to restore and true the
surface.

Minimum refinish thickness is the limit for resurfacing the rotor. If the rotor has worn to the
point where its thickness will be less than the specified dimension after resurfacing, the rotor
should be replaced.

Discard thickness is the maximum acceptable wear limit. Once the rotor is worn beyond
discard thickness, it must be replaced. The difference between discard and minimum refinish
thickness is the margin the vehicle manufacturer believes is necessary to allow for normal
wear between brake jobs. It varies considerably from one vehicle manufacturer to the next,
and according to vehicle size and type of brakes used.

The margin specified on most domestic passenger cars is around 0.015." The range is
0.020" to 0.030" for most imports. A few, such as Jaguar, have as much as a 0.050" difference between minimum refinish thickness and discard thickness.

Measuring at various points around the rotor will reveal any variations in rotor thickness or
parallelism. Both surfaces of the rotor must be within the manufacturer’s specified
tolerances for parallelism, otherwise the rotor can cause excessive pedal travel (by kicking
the pads too far out as it turns), front end vibration, pedal pulsation, and chatter. Parallelism
specs recommended by various vehicle manufacturers range from as low as 0.0001" to as
high as 0.0008." Refer to reference charts to determine how much correction, if any, is
needed.

Another critical rotor dimension is runout. Lateral runout is the movement of the rotor from
side to side as it turns. Excessive runout will kick the pads out as the rotor turns, creating

excessive clearance requiring increased pedal travel when brakes are applied.

Runout is checked with a dial indicator while the rotor is still on the car. If run-out exceeds
the recommended limit, the rotor must be resurfaced or replaced.

Drums and rotors should always be inspected for heat cracks, distortion, damage, and hard
spots prior to resurfacing. Cracks, damage and hard spots call for replacement. If distortion
can’t be eliminated within the limits of resurfacing, replacement will also be necessary.

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