FAQ 17.5


Brake Wear

Reading the disc brake pads

Brake Squeal

Hard disc brake pads versus soft ones

Brake pulls

Discussion on each part of your braking system:

  1. Disc brake pads & drum brake shoes

  2. Hardware (disc & drum hardware, rotors, drums & machining)

  3. Hydraulic System (master cyl, booster, wheel cylinders, calipers)

  4. Misc. (wheel bearings & grease seals)

  5. Labor related services (bleeding & flushing the brakes)

BRAKE WEAR --- Let me start out with my favorite saying, "Brakes are like a new pair of shoes. If you put them in your closet and never use them, they never wear out". Now, if you drive like my wife, you're going through front brakes every 8,000 or so miles like she does on her Suburban. If you're like me, you'll get 30,000 to 45,000 miles out of your front set of brakes and 50,000 to 60,000 miles out of your rear brakes. It obviously depends on how you drive, what you pull, how far you go without applying the brakes and in my wife's defense, how late you are to the basketball game!

Expect to pay between $110 and $250 to properly replace your front OR your rear brakes. That estimate can easily double if drums or rotors need to be replaced or if any repairs have to be made to your calipers, wheel cylinders or master cylinder. 85% of all of the brake jobs we do are within the above range.

READING THE BRAKE PADS --- A good technician can read the old disc brake pads and know what may be wrong or if everything is okay:

  • If the inside pad is worn more than the outside one, the caliper needs to be serviced or replaced because the caliper piston is hanging up.
  • If the outside pad is worn more than the inside one, the mounting hardware is causing the caliper to hang up and not slide. The repair is to replace the mounting hardware and lube the slides.
  • Even wear is what you want. A slight variation in thickness from one pad to the other is OK. 

Otherwise, if there isn't a symptom seen in the wear of the pads, if there isn't a fluid leak, then don't authorize a caliper or wheel cylinder repair.

BRAKE SQUEAL --- As you apply the brake pedal, the calipers squeeze the pads to the spinning rotor to stop it.  During this time, the pads rock forward and backward, side to side and shake and vibrate inside their containment cavity inside the caliper.  That is what causes the noise or what is commonly called "brake squeal".

Brake squeals are created by the pads moving and vibrating like a guitar string.   The pads are positioned inside an opening in the caliper.  The caliper squeezes the pads on the rotor surface to slow and stop the spinning wheel. The squeal is caused by the BACK of the pad (which is steel) rubbing on the steel portion of the caliper or caliper piston. The squealing noise IS NOT created by the front of the pad rubbing the spinning rotor. 

If you can keep the pads from moving or vibrating, you won't have any brake squealing.   We use a variety of ways to hold the pads in one place:

  • We bevel the leading edge or lower edge of the pad to eliminate the 90 degree angle between the rotor surface and the pad.  We grind the square lower corners and end of the pad to make them round corners and bevel the pad to a 45 degree angle.

  • We install new hardware to hold the pad firmly in the caliper.

  • We make sure to apply the brakes which squeeze the pads to the rotor, THEN we bent the tangs which hold the pads in place.

  • We spray a glue like substance on the back of the pads to help glue them to the caliper pistons which they rest against and are squeezed by. Some suggest the use of a special brake grease, I think that is a bad idea.

March 30, 2001


Can I polity disagree, #1 about your use of pad glue and #2, you non use of moly grease?

Extensive testing has proven that what you want is a movement of the pad...to release the dynamic stress that builds in the friction material. When deceleration occurs and stick_slip generates that deadly harmonic energy, it must be dissipated and unfortunately there are only two paths for it to go. One is back through the rotor (that is why you must put a solid based lubricant on the spindle faces before reinstalling the rotor) and the other is, out through the back of the pad. If you glue it down you actually turns it into a magnet (higher density) for the energy to collect in, where as if it is loose an free it becomes more like a piece of wood in nature and hat dull, dead, dampening object has a harder time holding the frequency it is flooded with.

In some of our SAE testing we did with Ford, I found some interesting and unexpected results I'd like to pass on. Maybe I can try and summarize about 30 pages of documents we developed to give you the meat of the study. What it says basically, is that noise is generated by one or possibly both of the following:

The rotor to pad contact surfaces, or

the pad to caliper contact surfaces.

That leads us to the following conclusion... we need to adjust these two areas with the latest "proven and tested" technologies so that they work in accordance with known, engineering principals for energy and heat dissipation.

This is where we looked at the various solutions and wives tales that were out there and then tested each of them to determined if they did what everyone thought they did. We tried every conceivable way to insulate, isolate, glue, attach, float and separated the pad from the caliper piston. For the second stages, we changed the rotor surface profiles dozens of ways. After running hundreds of test at several laboratories, we compiled all the test results to find which combination produced the best RA, FEI and Hz results... and for both short term and long term situations.

These tests and many others that are used in the labs, truly give unerring, consistent results that prove beyond a doubt what concepts, materials, devices, etc are correct.

One area of particular interest to our company was again, the surfaces of contact for the parts in the brake system. For the last 15 years in Europe we have researched the metallurgy field and have developed what is now the number one used metal treatment system for reducing surface tension and resultant, related wear. Most all the trains and lifting rail cranes in Europe, many OE manufactures of vehicles, and a large percentage of the heavy steel fabricating industry use the REBBS systems daily to save millions of dollars in wear and unnecessary labor annually.

Well you may be asking, what does this do for me? I hope it gives you pause to look into the new technologies that are available to the automotive industry, especially with respects to servicing and maintaining brake systems. One area I am especially interest in having you consider, is your use of the "glue" type product on the back of the brake pads. I know you alluded to your preference to glue over grease but I wanted to mention that all European and now most every American brake manufacture (Raybestos, Wagner, Bendix, Autospecialty, Qualitee, Performance Friction, etc, etc, etc) frown on a glue type product for pad backs. What they do specify is moly based synthetic lubricant that allow the pad to move freely, wear evenly and also dissipate heat and energy properly. (See our original OE Approved Pastelub 2400F Synthetic "Dry-Film" Brake Lubricant on our website, www.gwrauto.com.)

There is a difference between greases and lubricants and you need to be careful which you use... Make sure it is the correct, tested and proven product for that area of the brake assembly. You might enjoy reading the article I wrote for Undercar Digest last year on lubricants and brakes, I will e-mail you a copy if you did not get to see it.

I want to encourage you to look into this subject more when you get the time and even call me if you want to talk about it. We do have a website www.gwrauto.com that discusses the subject in a broader format (incorporates the full 5 step process for eliminating brake service comebacks) so you may want to surf through that also. It displays and explains several specialty tools, conditioning treatments and the supplies we have developed the last few years, along with of course, the GWR procedure.

I have enjoyed sending this and hope you likewise enjoy reading it.


Gary W. Roy



Thank you for taking the time to educate me. I learn a lot in the shop BUT I learn more from folks like you who take the time to help me better understand these kind of issues. Thanks again.

Mark Salem

So readers, I left my comments above about not liking grease and using glue, so the above letter would make sense. After reviewing Gary's letter and calling a few other brake experts, I have changed my mind and now our shop no longer uses glue on the back of the disc brake pad and we now use the appropriate disc brake pad grease.

Last, almost all disc brake pads make some noise. Some worse than others. It seems that like other things in life, you can't always have your cake and eat it too.

Better Life expectancy Worse
Better Black dust or soot Worse
Worse Squealing Best
Worse Rotor wear Best
Even Performance Even

Brake dust, we are now being told, is related to the quality of the steel brake rotor. Evidentially, they tested the black soot on front wheels and found that soot was metal from the rotors. So, at least today, it appears there is a big difference in brake rotor quality and that quality may show in more or less dust on your front wheels.

As far as I am concerned, there is not enough of a difference between OEM pads and the aftermarket pads to fall on the side of one or the other.  I use both.  It is also clear that the same companies that make the aftermarket pads, make the OEM pads.

I think brake repair is one area that is oversold. I think too many wheel cylinders and calipers are replaced and/or rebuilt because of what may happen. Brake repair, suspension work and shock and strut replacement are the areas you're most likely to be ripped off.

Car pulls while braking.

When your car pulls when braking, it is caused by a suspension problem or a braking problem. I'll cover both in detail for you.

Suspension pull --- This one is tough to find, but here's a way to find out quite easy.  IF your pull comes and goes or if your pull switches sides or pulls to one side then to the other for no apparent reason, try this.  Back up kinda fast and slam on the brakes, then drive the car normally and see what happens and see which way the car pulls when braking.  As soon as it has pulled to one side or the other, stop and back up again, then slam on the brakes.  Then drive it again.

If the pull is there and apparent then when you back up fast and slam on the brakes, the pull goes away for some time, the problem is probably caused by something in the suspension that is loose.

You see, there is nothing in the brake system that causes the brake pull to change sides or come and go.  But by shifting the suspension in the opposite direction it normally is loaded to (by driving backwards and slamming on the brakes) you are rearranging the suspension and often times right after you back up the pull will be gone for some period of time.  The key here is that if the brake pull ever comes and goes or switches sides, it's probably a suspension problem.

Brake pull created by a brake problem --- Brake pulls can be caused by a sticking caliper or one not working at all.  A sticking caliper causes a pull to the same side. One that is not working or frozen, causes a pull to the other side.   So when you have a brake pull to the right, it could be a frozen or non-operational caliper on the left or a sticking one on the right.

A brake pull is almost always to one side and stays there and gets worse the hotter the brakes get and the more you use them.  When we encounter a brake pull, we switch brakes pads side to side one at a time.  The last time Eddie did the front brakes on my Suburban, it ended up with a bad brake pull to the right.  After a week or so and the pull didn't go away and only got worse. 

Eddie and I decided to just switch the inside front disc brake pads side to side, otherwise put the drivers side inboard disc brake pad on the passenger side and vice versa.  For a few days, the pull was gone, then the pull came back, even worse, BUT to the other side, now it pulled left hard. 

So we knew the pads were the cause of the brake pull.  After a week, we replaced all the pads.  The brakes have been fine for over two months, clearly it was the pads causing the brake pull.

If after swapping the inboard pads, the brake pull stayed the same, we would have swapped the outer pads, then the brake rotors.  Each time we would have monitored the brake pull and determined if the pull changed sides, was better or worse.

Our next move would depend on what happened after each change.  If the pull stayed to the right, no matter what we did, we would test the "squeeze" pressure of each caliper and if the difference exceeds 300 pounds side to side, we replace the calipers.  BOTH OF THEM.  If you decide to change one caliper, you will always end up changing the other because the new one will work better than the old one and cause a pull to the side of the new caliper.

Customers often make a mistake when dealing with their shop over a brake pull. Instead of working with the shop and test driving the car for a week to measure the repair attempt, they insist the pull be fixed and be fixed right now.  We don't allow that to happen to us.  If you are not willing to work with us and help us fix your car, one step at a time, then perhaps you need to find another shop.

Brake parts discussed . . . piece by piece!


1) Brake pads front or rear (disc) $75 - $185

Replace based on visual inspection and wear, expected or average intervals for front brakes would be from 8k to 50k miles. Expected or average intervals for rear disc brakes would be from 15k to 100k miles depending on primary driver habits. Pad wear tells you the following:

  • Inner pad wear = points towards a defective caliper
  • Outer pad wear = indicates caliper not sliding properly, hardware needs to be cleaned or replaced.

2) Brake shoes front or rear (drum) $65 - $105

Replace based on visual inspection and wear. Expected or average intervals for front drum brake shoes would be from 15k to 50k depending on primary driver habits. Expected or average intervals for rear drum brake shoes would be from 30k to 100k depending on primary driver habits.

The rear shoe on either front or rear brakes will always wear more than front shoe, slight uneven wear is normal and acceptable.


3) Hardware kit front or rear (disc) $22 - $85

Most brake hardware manufacturers say replace hardware for obvious reasons, like they make the stuff and want to sell the heck out of it. Think of that as one extreme. The other extreme of this same issue is replace based on visible symptoms. No one says never replace the hardware. If the outer pad has excessive wear, more than the inner pad, that clearly means the caliper is hanging up and not sliding smoothly. A cleaning or replacing or the hardware would be appropriate. You can clean them if they are only greasy or dirty, you would replace if the hardware is pitted, corroded, bent, or worn.

4) Hardware kit for drum brakes, front or rear includes springs (drum) $20 - $65

Again most of us simply look at the springs and can see, we can tell if they are bent, stretched or need to be replaced. We mentally compare what we see with what we know "NEW" looks like. HOWEVER, many brake experts say change all of the shoe springs and hardware at each brake job, some say every other brake job (60-120k intervals) and the last group will say as needed.

5) Shims (disc only) $12 - $45

I know of nothing written that I have ever read that suggests a mileage interval for changing of the shims. Typically they come with the brake pads or hardware kit, and if not, they simply need changed based on the condition you find them in when you remove the old disc brake pads. Worn, bent, crushed or discolored ones would fall into the "replacement " category.

6) Drums $65 - $425

We measure them to determine what they have in overall diameter. (i.e. 12.050 or 12 inches and 50 thousands), how big they can be before we must discard them which is called "turn to" or "machine to" or a "discard" number like 12.90 and how deep any grooves are that must be removed. If the overall diameter is 12.050 and we have a groove we need to remove that is .043 deep and the minimum thickness is 12.090, this drum will end up too big in diameter to machine or refinish or use again. It would have to be replaced.

7) Rotors $45 - $360

We measure them to determine what they have in overall thickness (i.e. .960 or 960 thousands), how thin they can be before we must discard them which is called "turn to" or a "discard" number like .920 and how deep any grooves are that must be removed. If the overall thickness is .960 and we have a groove we need to remove that is .043 deep and the minimum thickness is .920, this rotor would have to be replaced.

8) Machining, turning, resurfacing drums and rotors

The auto repair industry is in turmoil over when to machine rotors and drums. Everyone agrees that if the rotor or drum is warped, too thin (rotor), too big (drum) or is grooved beyond repair, the drum or rotor should be replaced. Up until 1997 or so, we always resurfaced, machined or turned drums and rotors during every brake job. Over the last four years, GM and others now say if the drum or rotor surface is clean, not warped, not grooved and the surface is "acceptable", simply scuff up the surface with sandpaper like material and reinstall it. MAP says "Friction material replacement does not require drum or rotor reconditioning unless other justifications are met.".

The repair industry is slow to respond to drastic changes and half will follow the "new" recommendations and the other half will continue to machine each rotor and drum during brake services. I have chosen to leave it up to the tech to make the decision whether to machine or not.


9) Master cylinder $90 - $3000

There are NO mileage requirements for the replacement of a master cylinder. One needs to be replaced when the following symptoms are either given by the driver / customer or found during the brake inspection:

  1. The back of the master cylinder is leaking brake fluid into the power brake booster or down the front of the power brake booster.

  2. The brake pedal slowly sinks to the floor as I apply steady pressure and the brake fluid level is consistent and OK and the brake system is not consuming any brake fluid or have any brake fluid leaks.

  3. The brake fluid level is full and the red brake light is on. If the parking brake switch isn’t on (bad parking brake switch) and the brake fluid level isn’t low (brake fluid leak somewhere else in the system like a leaking wheel cylinder or caliper), then the red brake light means uneven pressure between the front and rear brakes or in a diagonal system, uneven pressure between one diagonal circuit and the other.

10) Power brake booster $140 - $950

There are NO mileage requirements for the replacement of a power brake booster. One needs to be replaced when the following symptoms are either given by the driver / customer or found during the brake inspection:

  • The brake pedal is rock hard and you have 16-18 inches of vacuum being delivered to the power brake booster by the running engine.

  • The application of the brakes causes the engine idle to deteriorate because the power brake booster is bad and causing a big vacuum leak.

11) Front calipers (disc) OR Rear calipers (disc) $75 - $395

There are NO mileage requirements for the replacement of a caliper but there is often a "service" requirement which means we should inspect the caliper for symptoms that may point to a specific repair. A caliper can be addressed in one of two ways, rebuilding it or replacing it ONLY when the following symptoms are either given by the driver / customer or found during the brake inspection:

  1. The inner brake pad is worn far more than the outer disc brake pad.

  2. The caliper is leaking brake fluid.

  3. The caliper’s dust boot is torn or no longer functioning as it should.

The choice to rebuild (low parts cost, high labor costs, in house warranty) or to replace with new or rebuilt calipers (high parts cost, low labor costs, warranty by others) is made by shop management or the parts department or the technician. All of the above options (rebuild or rebuilt or new and who makes the decision) are well within industry standards.

12) Front wheel cylinders (drum) OR Rear wheel cylinders (drum) $45 - $265

This is the one where our industry is widely divided. With respect to symptoms:

  1. Some say pull back the dust boot, if you see brake fluid you must "service".

  2. Some say all wheel cylinders have fluid under and behind the dust boot, "service" only if you see an external brake fluid leak.

  3. I say, all new and rebuilt wheel cylinders will show signs of brake fluid under the dust boot within a week. That test is too picky for me. I want to see brake fluid running down from the wheel cylinder onto the backing plate before we replace it.

With respect to options on ways to "service", the choice to rebuild (low parts cost, high labor costs, in house warranty) or to replace with new or rebuilt wheel cylinders (high parts cost, low labor costs, warranty by others) is made by shop management or the parts department or the technician. All of the above options (rebuild or rebuilt or new and who makes the decision) are well within industry standards.

13)  Rubber brake hoses (drum or disc, front or rear) $35 - $185

Unlike cooling system hoses that wear out from the inside out, brake lines wear out from the outside in. Some suggest that rubber brake hoses must be changed based on miles. Some say just look at them and compare them to what a new hose would look like. If the rubber brake hose is cracked, swelled, leaking or cut, replace it.

Most of us in the Phx repair industry believe that rubber brake lines can often last the life of the car in this dry and warm climate.


14) Wheel bearing repack, front or rear $50 - $150

This is really not a brake issue. It is a maintenance issue that does have a service mileage interval. Front and rear wheel bearings are either serviceable or sealed. Sealed bearings are not serviced and replaced only if they are bad. Serviceable wheel bearings can either be serviced using a mileage interval which may be every 25k miles to 50k miles. Because we regularly perform brake maintenance during that mileage frame, we simply service wheel bearings while performing brake friction service. Unlike the 70's and early 80's when we used to pack wheel bearings between brake jobs, we no longer perform that task because of improved lubes and greases.

15) Wheel bearings front or wheel bearings rear, renew $20 - $250

Wheel bearings and/or races are replaced when:

  • the bearings is found to be noisy or shedding metal or

  • the customer requests the wheel bearings be replaced to put them in "their" comfort zone.

16) Grease seals, A $3 to $8 part $8 - $50

Some say grease seals must be replaced everytime the hub is removed, some say if they are fine, not leaking and undamaged, then leave them and some never replace them because they say they never see a repair that is directly or indirectly related to a bad grease seal. All are valid arguments.


17) Bleed brake system $50 - $250

If the hydraulic system is opened, if a wheel cylinder or caliper or master cylinder is serviced or removed, the brake system MUST BE BLED.

18) Flush brake system $75 - $200

This is a brand new issue and I think it is based on economics. Years ago the master cylinder cost $68 and the labor was $45 to change it. So flushing the brake system every other year or every 30-60k miles for $65 - $75 to save a master cylinder or to extend it’s life, wasn’t money well spent. TODAY, many master cylinders can cost from $90 - $300 and a few can be $2200 so a $100 brake fluid flush is money well spent.

However, here is another viewpoint on brake fluid flushing that has equal merit:

Subj:    Brake comment
Date:    5/28/01 2:59:16 PM US Mountain Standard Time
To:    mark@salemboysauto.com

Hi Mark,

Read you section on brakes with interest. Allow me to introduce myself.  I'm
an a brake engineer currently working at a large brake part manufacturing company that I do not have their permission to mention. I got my start back in the 70s when Wagner Electric was still in the OE Business. I've been in the brake business about 25 years.

The value of brake system flushing is arguable. My vote is not to flush brake systems. The benefits are dubious in my measure and the potential for damage too great. True, it restores the anti corrosive additives and the boiling point of DOT 3. Still, brake fluid boiling is seldom an issue on modern autos and current corrosion protection measures do more than any additives in the brake fluid.

On the flip side, it's possible to create leaks due to bleeder screws that don't reseat properly, break off bleeder screws or even plug internal passages with the dirt flushed from the system. Master cylinder, wheel cylinder and caliper life is dependent on the quality of the corrosion protection measures used on the components inside the brake system and the quality of rubber sealing materials.

Anyway, if you have brake questions or wish to argue the point, feel free to
contact me.

Gerald "Jerry" Dreisewerd
Senior Design Engineer

So, there you have both sides of this brake flushing issue. You should be able to make a decision what's best for you...mark

After all of this research, after reviewing everything we could find, the bottom line is no part of a brake system has a mileage limit or a suggested replacement interval.

Each and every brake part is to be inspected and replaced based on it’s ability or inability to perform as it was intended or it’s inability to perform as it was designed.

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