Tech Tips
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Brakes
Guidelines for a Complete Brake Job
When you're installing premium brake pads you should do everything else that's necessary to ensure your customer's brakes are safe and dependable. "Pad slap" brake jobs (replacing the pads and nothing else) only invite trouble down the road.
If the front disc brake pads are worn and need to be replaced, chances are other components in the brake system may require attention too. The most obvious ones would be the front rotors and calipers. But the rear brakes may need work also.
A quality brake job should cover every aspect of the system from the master cylinder to the calipers and wheel cylinders. This includes:
- Checking the level and condition of the brake fluid (changing the fluid is recommended to get rid of moisture contamination).
- Bleeding all the brake lines to remove trapped air.
- Inspecting the entire system for leaks (hoses, lines, wheel cylinders, calipers and master cylinder).
- Inspecting all the mechanical and hydraulic components in both the front and rear brakes (calipers, caliper hardware, wheel cylinder, drum hardware and parking brake).
- Replacing the front and rear linings (if necessary).
- Inspecting and resurfacing or replacing rotors and drums as needed.
- Inspecting wheel bearings (repacking on older vehicles).
- Lubricating all critical areas such as caliper slides and shoe pads with moly-based high temperature brake grease.
- Checking and adjusting the parking brake.
- Checking the ABS system (no warning light or trouble codes).
- Making sure the pedal is firm, the brakes operate properly, quietly and provide safe stopping power once the job is complete.
There's no excuse for not inspecting each and every component in the brake system. any parts that are out of specification, worn or damaged should always be replaced to restore brake performance and safety to like-new condition.
HYDRAULIC COMPONENTS
Calipers and wheel cylinders should be checked for leaks, severe corrosion or damage, and rebuilt or replaced if a problem is found. Pay close attention to the condition of dust seals and piston boots.
If a caliper or wheel cylinder is being rebuilt, do not reuse corroded steel pistons. Replace with new ones.
If a master cylinder is leaking externally or internally (pedal slowly sinks to floor), it must be rebuilt or replaced. Rebuilding aluminum master cylinders is not recommended.
Brake hoses in today's brake systems may have to withstand pressure of up to 2,500 psi so make sure there are no cracks, bulges, or damage to the hoses.
The type of brake fluid required will depend on the vehicle application. Always follow the vehicle manufacturer's recommendations. Most domestic and Japanese cars and light trucks require DOT 3 fluid while most European cars use DOT 4. But there are exceptions, so make sure you find out which type is required. DOT 5 silicone fluid should never be used in any vehicle equipped with ABS.
BRAKE ROTORS
New disc brake pads require a clean, smooth, flat surface on the rotors, otherwise brake performance will suffer. A rough surface will accelerate pad wear and increase the risk of noise. An uneven surface or variations in rotor thickness can cause vibrations, noise and annoying brake pedal pulsations.
Unless the rotors and drums are in near perfect condition, resurfacing should be considered a must to restore the friction surface. There should be no deep scoring or cracks, runout should be less than .003 in. (.060 mm), and thickness variation should be less than .0003 in.
When rotors are resurfaced, care should be used to minimize runout. this may require measuring hub and rotor runout on the vehicle using a dial indicator (and indexing the rotor on the hub to minimize runout or installing a tapered shim behind the rotor to correct runout), or using an on-car lathe that cuts the rotor true to the hub. Ideally, rotor runout should be less than .001 in. on the vehicle or on a bench lathe.
Measuring rotor thickness is an absolute must. If rotors are worn to less than the "discard" specification marked on the rotor, the rotor must be replaced. If the rotor cannot be resurfaced without exceeding the minimum "machine to" thickness specification, replacement is also required.
It's the same situation with drums. They must be measured when the linings are replaced. If the inside diameter of a drum exceeds maximum specifications or it can't be resurfaced without exceeding the maximum "machine to" limit, it must be replaced. Also, both drums should have about the same amount of wear. If the difference is greater than about .040 in., both drums should be replaced even if only one is at or near the discard limit.
It's the same for rotors. If rotors have hard spots (look for discolored patches on the rotor surface), replacement is the best repair option. Changes in metallurgy extend below the surface. Turning the rotor may temporarily restore a flat surface, but harder metal will still be there and cause the rotor to wear unevenly. With a few thousand miles the pedal pulsation will return.
BRAKE HARDWARE
Inspect caliper slide pins, bushings, sleeves, springs and shims for corrosion, damage and wear. Replace defective hardware as needed. Uneven pad wear can result if a floating caliper hands up and isn't free to move sideways on its mounts.
As for the drum hardware (self-adjusters, return springs, shoe springs, etc.), anything that is worn, damaged or badly corroded should also be replaced. If a return spring or shoe spring is stretched or discolored, it has probably suffered heat damage and must be replaced.
The cost of new springs and other brake hardware is only a small portion of a complete brake job. Replacing it can reduce the risk of a comeback and assure the best possible performance out of your new premium brake pads.
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