Brakes

[davbell22602]

Whether you’re studying for an upcoming ASE brake certification test, expanding your knowledge or honing your brake repair skills, this “course” is for you. While there are no grades and no pop quizzes or tests, and it’s not even a pass-fail course, the credit you’ll receive will be thanks and appreciation in the future from your customers and employer for a job well done.

Of course, the goal of this course is to help you do better brake jobs and avoid common mistakes that often result in comebacks, unhappy customers and lost time and wages. However, if your instructor wants to create a test out of the material here, we advise you to study this article thoroughly, and we expect you’ll score well.

Lesson One: The Basics
Obviously, brakes are an essential safety system because they stop the vehicle. If the brakes can’t do their job, there’s no telling what might happen. So it’s important to make sure every brake job you do is done correctly and to your customer’s satisfaction. There are no exceptions!

First, a rule to live by: A basic brake job does not consist of hanging a set of pads, giving the rotors a quick turn and sending the vehicle out the door. Quickie brake jobs may seem like an easy way to make a buck, but they are less than complete.

Always replace pads with quality parts.

“Complete” means “full, finished, ended, perfect or made whole.” If you are doing a “complete” brake job, therefore, you should inspect everything and replace anything that is worn, broken, defective or out-of-specification to restore the brakes to like-new condition.

But what about parts that are marginal or questionable? Is it OK to reuse brake hardware? Should the calipers be rebuilt or replaced if they are not leaking? What about wheel cylinders or the master cylinder? What about brake fluid? Is bleeding the air out of the lines all that’s necessary, or should the fluid always be changed?

Many times you have to make judgment calls when deciding what to replace. For years, “industry accepted practice” was the criteria by which most technicians based their decisions. What’s wrong with that? For starters, everybody had their own standards, and it was often hard to get people to agree on many of the finer points of brake service.

For example, should brake linings be replaced only when they are at or below minimum thickness (as defined by the vehicle manufacturer), or is it OK to replace them if they are still above minimum thickness, but getting thin? This is your call when doing a four-wheel brake job because, in most instances, the front pads are worn more than the rear shoes (or pads).

The front pads typically outlast the rear linings by a margin of two or three to one. If the rear linings are still well above the wear limit, there’s no need to replace them. But if they are getting close to the limit, replacing them now may save your customer the cost of another brake job later, as well as possible brake problems down the road.
In some states, such as California, the law stipulates when certain parts may or may not be replaced. Such rules are designed to protect consumers from unnecessary repair expenses, but they also create a roadblock to common sense in some instances. Even so, you have to live by the rules or suffer the consequences.

Lesson Two: Inspection Checklist
All of the following should be inspected when doing a brake job:

* Master cylinder: A low level may indicate worn linings or a fluid leak.
* Brake lines and hoses: Visually inspect them for leaks, severe corrosion or damage.
* Calipers and wheel cylinders: Check for leaks or cracked or missing dust boots.
* Disc brake pads: Measure thickness and check for cracks or separation from backing plates. Also, look for uneven wear between the inner and outer pads, which may indicate a caliper problem.
* Brake shoes: Measure their thickness and check for cracks or looseness.
* Drum hardware: Check for loose, discolored or badly corroded parts.
* Warning lights: Make sure the brake warning light and ABS light come on when the ignition is turned off, and make sure the lights go out and stay out while the vehicle is driven.

Finally, if possible, test drive the vehicle and take note of brake pedal feel and braking action. Pulsation in the pedal usually indicates warped rotors. A low pedal may indicate worn linings or air in the brake lines. A pedal that slowly sinks indicates a worn master cylinder, and noise may indicate loose or worn pads, missing shims or other brake problems.Check the parking brake for travel, the ability to hold the vehicle when stopped and release.

Lesson Three: Servicing
Once you’ve inspected the brake system, you can recommend what parts need to be replaced and why. A few

A low fluid level in the master cylinder maybe a sign of worn seals.

recommendations you may have to make during the subsequent brake job may include any or all of the
following:

* New linings, front and rear.
* Resurfacing of both rotors and drums (or replacing them if they are badly worn or cracked or hard spots are found).
* Replacing drum hardware and caliper bushings/pins/sleeves.
* Rebuilding or replacing calipers and wheel cylinders (depending on mileage and condition).
* Replacing brake hoses if they are leaking or damaged.
* Replacing the master cylinder if it is leaking or worn.
* Changing the brake fluid and bleeding all of the lines.
* Inspecting wheel bearings (repacking on older vehicles).
* Lubricating all critical areas, such as caliper slides and shoe pads with a high-temperature, moly-based brake grease.
* Adjusting the parking brake.
* Replacing ABS components as needed (such as a defective wheel-speed sensor, hydraulic modulator, accumulator, pump or relay).
Inspect all hydraulic lines.

Lesson Four: Linings
When replacing brake linings, always replace same with same or better. In other words, pads should be replaced with ones made of the same basic type of friction material as the original.

In some applications, non-asbestos, organic or low metallic pads can be safely substituted for semi-metallics to reduce noise potential. But the trade-off may be shorter pad life and decreased resistance to heat fade under hard use.

For best results, recommend a premium-grade replacement lining. Many linings today are “application engineered” to match the brake requirements of specific vehicles.

If you are installing a loaded caliper assembly with pads already included, the pads should have the same approximate friction characteristics as the ones on the opposite side (if only one caliper is being replaced).
Always use the same type of friction on both sides of an axle to reduce the risk of creating a brake pull.

Lesson Five: Rotors and Drums
Unless the rotors and drums are in near-perfect condition (no scoring, minimal runout, etc.), resurfacing is a must to restore the friction surface. Resurfacing does shorten the life of rotors and drums because it removes metal, so use the shallowest cut possible to conserve iron and extend the life of these parts.

Measure runout at the rotor and bearling flange.

On-car resurfacing is recommended for vehicles that are especially sensitive to rotor runout or where rotors are difficult to remove, as in trapped rotors, for example.

If rotors are worn to minimum specs or can’t be resurfaced without exceeding the minimum or discard specs, they must be replaced. It’s the same with drums. If the inside diameter exceeds maximum specs, or a drum can’t be resurfaced without exceeding the limit, it must be replaced. There are no exceptions! Also, both drums should have about the same amount of wear. If the difference is greater than about .040-inch, both drums (or rotors) should be replaced, even if only one is at or near the discard limit.

Rotors should also be replaced if they have hard spots due to the fact that changes in the metallurgy extend below the surface. Turning the rotor may temporarily restore a flat surface, but the harder metal will still remain and cause the rotor to wear unevenly. Usually, within a few thousand miles, pedal pulsation will return.

As for drum hardware, self-adjusters, return springs, shoe springs, etc., and disc hardware, caliper slide pins, bolts, bushings, sleeves, etc. - anything that is obviously worn, damaged or badly corroded should always be replaced. On high-mileage vehicles (with more than 100,000 odometer miles), new hardware is recommended.
If a return spring or shoe spring is stretched or discolored, it has suffered heat damage and must be replaced. Many brake experts say it’s a good idea to replace springs anyway when doing a brake job, regardless of their appearance. Why? To assure like-new brake performance and minimize the risk of a comeback.

Lesson Six: Fluid
Every brake job (complete or not) should include a fluid change. Still, surveys have found that half of all cars and light trucks 10 or more years old have never had their brake fluid changed — even when they’ve had the pads replaced once or twice.

Note: If the inside diameter exceeds maximum specs, or a drum can’t be resurfaced without exceeding the limit, it must be replaced. There are no exceptions!

The reason it’s so important to change the fluid each time is because you can’t judge the condition of the brake fluid by its appearance alone. Some fluid darkens as it becomes contaminated with moisture, while others don’t discolor. The only way to know for sure is to test it with a brake refractometer, chemical test strips or an electronic tester.

Brake fluid is hygroscopic and absorbs moisture through tiny pores in brake hoses and seals. Over time, it can pick up quite a bit of water, which increases the fluid’s viscosity, lowers its boiling temperature and increases the risk of internal corrosion in the brake system.

Always top off brake fluid

 

[davbell22602]

Always top off brake fluid.



Tests have shown that, even after only a year of service, brake fluid in the average vehicle can contain as much as 2% water. After 18 months, contamination levels can reach 3% and continue to climb to 8% or more as time goes on. As the amount of moisture in the fluid goes up, the boiling temperature comes down. Corrosion inhibitors in the fluid also break down, increasing the risk of internal corrosion inside the brake system.

The type of brake fluid required depends 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 check the owner’s manual for the requirements. Remember, too, that DOT 5 silicone fluid should never be used in any vehicle equipped with ABS.

While we’re on the subject, no parts in an ABS system should have to be replaced unless something has failed. Wheel-speed sensors can sometimes give bad readings if their magnetic tips become contaminated with metallic debris from the brakes. A simple cleaning may be all that’s needed to eliminate the problem.

Unfortunately, some wheel-speed sensors are sealed inside the wheel bearing assembly and cannot be replaced unless the entire hub assembly is replaced (at considerable cost). But, if that’s the only way to get the ABS warning light to turn off so the ABS system will function normally again, that’s what you have to do.

If you remember nothing else from this course, remember this: There is very little margin for error when doing brake work. Little mistakes can have big consequences. So, inspect the entire brake system end to end, identify any problems that need correcting, and replace all the parts necessary to restore the brakes to like-new condition.
That’s it. You’ve completed Brake Service 101. Now put what you’ve learned into practice.

 

[davbell22602]

Brakes Part 2
Debating a Complete Brake Job



One of the major issues with selling customers a “complete” brake job is that the components in the brake system do not wear at the same rate.


Most motorists know brake linings don’t last forever. Brake pads and shoes use friction to stop a vehicle, so every time the brakes are applied the linings experience wear. After so many stops, the linings wear out.
The rate at which the linings wear out depends on the frequency of use, how hard the brakes are being applied, the temperature of the linings and the wear characteristics of the friction material itself. Larger, heavier trucks and SUVs typically wear out their brakes faster than smaller, lighter cars.
Stop-and-go city driving obviously wears the linings down faster than highway driving. So does aggressive driving. Consequently, a set of brake linings on one vehicle might only last 25,000 to 30,000 miles when on a different vehicle they might go 50,000 or 60,000 miles.
As a rule, most brake pads and shoes should be replaced when the thickness of the friction material is worn down to minimum specifications (typically less than 1/8th inch of lining thickness) or when the surface of the pads or shoes is worn down flush with the tops of the rivet heads (riveted linings). Some brake pads have built-in wear indicators that generate a metallic scraping noise when the pads are worn out and need to be replaced.

Selling the Customer on a “Quickie” or a “Complete” Job
OK, the linings are worn and need to be replaced. Now what? Do you sell your customer a quickie “hang and turn” brake job (just replace the pads and turn the rotors), or do you sell them a “complete” brake job?
Brake linings and other parts that are obviously worn out, broken or leaking should always be replaced. But what about parts that are marginal or appear to be OK? Should drum brake hardware always be replaced, or can it be reused?
Should calipers or wheel cylinders always be rebuilt or replaced if they are not leaking, or should you leave them alone? What about replacing the master cylinder in a high mileage vehicle? Should you always flush the brake system and refill it with fresh fluid?
Some people might think you’re trying to rip them off if you recommend replacing parts that are still working, but are near the end of their service life. This is a hot button issue with consumer advocates and government regulators because they may see it as an attempt to sell unnecessary parts and services.
Nobody wants to pay for parts or services they may not need, so in some states (California) there are strict regulations covering the replacement of brake components. The rules say when you can and cannot replace various brake system components based on wear or condition.
A less draconian approach has been taken by the Motorist Assurance Program (MAP) to help technicians, service advisors and shop owners do a better job of selling brake repairs. MAP’s voluntary repair guidelines cover the brake inspection process and tell you when brake repairs are truly necessary, or when brake repairs can be recommended to improve braking performance or to restore the brakes to like-new condition.
Many times the person doing the brake inspection has to make a judgment call as to whether or not something should be replaced — which means their decision is often a judgment call.
For years, “industry accepted practice” was the criteria by which many technicians based their decisions. The trouble with this approach is that everybody has their own ideas about when certain brake parts should be replaced and why.
Take brake linings, for example. Should the linings be replaced only when they are at or below minimum thickness (as defined by the vehicle manufacturer) or is it OK to replace them if they are still above minimum thickness, but are getting thin?
This is a call that many technicians have to make when doing a brake job. Though it might not be absolutely necessary to replace the rear linings right now, doing so could save the customer the cost and inconvenience of having to replace them later. The best answer in this situation would be to discuss the situation with the customer and let them make the final call.

Wear Rates
One of the major issues with selling customers a “complete” brake job is that the components in the brake system do not wear at the same rate. The front brakes typically wear two to three times faster than the rear brakes. Consequently, it may not be necessary to replace the rear linings until the second or third set of front pads have been replaced.
Time, mileage and the operating environment are all factors that affect the service life of parts in the brake system. Brake fluid is hygroscopic and absorbs moisture over time. As moisture accumulates in the fluid, it increases the risk of internal corrosion inside the calipers, wheel cylinders, steel brake lines, master cylinder and ABS solenoid valves.
Because of this, it’s not unusual to find corrosion-related failures in these components in high mileage vehicles that are operated in wet climates. Recommending a fluid flush for preventive maintenance would therefore be a valid suggestion.
And, if the fluid is more than three or four years old, changing it when the linings are replaced or other brake work is
performed would be a good idea.
Many technicians recommend rebuilding or replacing calipers and wheel cylinders as part of a complete brake job — and with good reason. Over time, rubber seals on caliper and wheel cylinder pistons harden and lose elasticity. This may cause the seal to leak.
Corrosion inside the piston bore can also accelerate seal wear. Pushing the caliper pistons back in their bores also causes the seals to rub against an area on the piston that may have become corroded and rough, which can accelerate seal wear, too.
So even if the caliper or wheel cylinder is not leaking when you replace the linings, eventually it will leak. Since there’s no way to know how long it will be before the brakes are serviced again, many technicians think that rebuilding or replacing these parts to restore the system to like-new condition reduces the risk of brake-related problems down the road — and they are right.
The point here is components in the brake system wear at different rates which cannot be predicted by time or mileage alone. That’s why a thorough inspection of the entire brake system is so important any time brake work is needed, or any time the brakes are experiencing a problem (noise, pulling, dragging, soft pedal, etc.).
A complete brake job, therefore, is (1) inspecting the entire brake system to determine the condition of all its major components so (2) you can recommend any repairs that are necessary to restore the brakes to
proper operating condition for safe driving.

Inspection Tips
The brakes are the most important safety system on a vehicle, so a complete brake job should cover every aspect of the system. It should start with a thorough visual inspection of the entire brake system.
This includes measuring lining thickness front and rear (which will require pulling BOTH rear drums), the condition of the lines, hoses, calipers and wheel cylinders, the appearance and condition of the brake fluid, checking pedal feel and travel, and the brake and ABS warning lights (lights should come on then go out when the ignition is turned on). Only after the inspection has been completed should any repair recommendations be made.
The ABS system is often overlooked when doing brake work on late model cars. If the ABS warning light is on, there is a fault that needs to be investigated. This will require plugging a scan tool into the vehicle’s diagnostic connector to read out the diagnostic trouble code(s). If the light is out (and is not burned out), it’s usually safe to assume the ABS system is functioning properly — unless the vehicle has been experiencing any unusual brake problems or the ABS system has been kicking in unnecessarily when braking normally on dry pavement. There may be an issue that will require additional diagnosis.
A test drive is an excellent way to evaluate overall brake performance. Unfortunately, many techs don’t have the time to test drive every vehicle they work on. Because of this, problems may be overlooked that may cause a comeback later.

The “Complete” List
Once the entire brake system has been inspected, a recommendation to the vehicle’s owner can be made as to what parts needs to be replaced. In most instances, a “complete” brake job will include the following:
• New linings front and rear.
• Resurfacing both rotors and drums (or replacing them if worn, cracked or hard spots are found).
• Replacing drum hardware and caliper bushings/pins/sleeves.
• Rebuilding or replacing calipers and wheel cylinders (depending on mileage and condition).
• Maybe replacing some brake hoses and/or the master cylinder (if leaks or problems are found).
• Test the brake fluid and, if necessary, flush the brake fluid and bleed all the lines.
• Inspecting wheel bearings (repacking on older vehicles).
• Lubricating all critical areas such as caliper slides and shoe pads with high temperature brake lubricant.
• Checking and adjusting the parking brake.
• Checking the ABS system for any fault codes, or replacing any faulty ABS components as needed (wheel speed sensors, hydraulic modulator, accumulator, pump or relay).
______

 

[crazy4offroad]

For me, brake fluid level is an indicator of pad wear. If my fluid is down a about 1/4 the way I check the pads and shoes, and replace as necessary. If you filled your reservoir, then noticed you needed new front pads, when you put them on the master cylinder will be overflowing because the new brake material will displace fluid in the lines. If the pads/shoes look OK I start looking for leaks, not just top it off.

I've always frowned on straight-up copy/paste posts. Without adding your own content it just seems like stealing someone else's work. I may be off-base with that comment, you may have posted this on another forum and did all the typing yourself. But it's a lot for me to sit and read top to bottom anyway.

 

[89Suburban]

Thanks for the info there Dave.