Brakes 101 - Function & Maintenance

[Murco]

This thread is a repeat for those who either already do their own brakes or want to learn to do them properly. This is good knowledge to have for the DIY'er...

My name is Russ and in a previous life I had my own brake shop and then worked as a technical consultant for Bendix training technicians and hopefully this thread will help with some basic and a few more advanced diagnostics and repair procedures for those who want to work on their brakes. This is mostly for disc/disc systems but disc/drum and drum/drum systems use the same basic information.

Let's start with the basics...
First and most importantly - USE THE HIGHEST QUALITY PARTS YOU CAN AFFORD!!! These are your brakes, the number one safety feature of your car. If the car doesn't run, you won't die. If your brakes don't work you can get killed or injured or end-up killing or injuring someone else! Don't skimp on your brakes!

Brake pads - Unless you really intend on doing a lot of racing stick with OEM brake pad materials and use pads and rotors from the same company. Ceramics are touted as the be-all, end-all brake pads. Not so much... While they run cooler and create less dust they are much harder than organics and semi-metallic pads, they will often increase your braking distances, and are very hard on standard rotors. Ceramics were developed by European manufacturers for their heat resistance in high-speed braking, but the cars equipped with them also have what are known as "soft-rotors" that are designed to be replaced along with the pads. Here is the kicker - some cars come with ceramics, some have organics, and some had semi-metallic. Check your applications before buying ceramics

Brake fluid - You must replace it every 2years or 24K miles! Surprised? Most are and domestic US manufacturer owners manuals say not a word about it, but check every Japanese or European car's owners manuals and they will recommend every 1-2 years. Brake fluid is similar to motor oil in that it is designed to encapsulate the moisture and sediment in brake systems but it only has so much capacity to do so. As it ages the boiling point drops, deposits collect, and problems start becoming more expensive to correct. Flush and bleed the brakes after every other oil change and you'll avoid 70% of common brake issues. I recommend DOT 4 fluid or Castrol LMA fluid (low moisture absorbtion) as it has a higher temperature rating and is less suceptible to breakdown in high-performance use. The only down side to the LMA fluid is you need to change it more often as it won't encapsulate as much moisture.

Wheel cylinders - If you have drum brakes on another car and over 15K miles on them I will bet the wheel cylinders are either leaking or sticking. I'll also bet alot of folks here think they are supposed to leak and operate just fine like that. THEY ARE NOT SUPPOSED TOO!! Wheel cylinders operate at far higher pressures than calipers just to open the return springs, much less stop the car. Peel back the dust boots on the ends and if you find any brake fluid at all (assembly grease is OK) go ahead and replace them. Often, wheel cylinders will blow their seal during a hard stop, squirt tiny amounts of fluid, then draw air into the lines when you release the pedal. This essentially renders rear drum brakes useless on a disc/drum car, overworking the fronts causing excessive heat, wear, and dramatically increased braking distances. It will also cause spongy brake pedals, more so on drum/drum cars. If you have the hardware off check to see if the cylinders move freely back and forth, about 1/4" of travel. If they stick, replace them, it's cheap insurance!

Hardware - Anytime you replace pads or shoes replace the caliper hardware and/or return springs as well. These items are cheap and allow the system components to slide and return properly. Worn caliper hardware will cause uneven pad wear from the leading-to-trailing ends. Worn return springs will cause heel-toe shoe wear (different wear in leading and trailing shoes). To lubricate the hardware do not use silicone-based lubes, use a proper brake grease.

Calipers - These are a stout pieces for around town driving and the dual piston units are fairly resistant to sediment binding when maintained properly. The most common problem afflicting calipers is sediment bind due to poor maintenance. The heat cycling calipers go through is staggering and the larger-bore calipers tend to "cook" the fluid under heavy use and flushing the fluid every 2 years max is essential to keep these working well. Binding is diagnosed through the pads, look for uneven wear, pitting (numerous small holes on the pad face), and scoring (the pads look like the surface of an old LP record). I would recommend rebuilding the ones on your car before getting remans, no matter how cheap they are. Why? Because your calipers have been in service recently, you know their history, and they haven't been sitting in a junkyard for who knows how long awaiting rebuild while exposed to the elements. It's also very inexpensive, about $8-12 per corner and all you'll need is some compressed air, a green scotch-brite pad, and some hydraulic assembly lube to rebuild them. You would probably be stunned if you opened a reman caliper for an older car. Many will have heavy corrosion pitting on the piston, scored bores, corrosion scarring, and heli-coiled line and bleeder threads. None of these conditions are acceptable your brakes shouldn't have these issues.
PHENOLIC PISTONS - These are usually found in light trucks but some cars are heavy enough to need them as well. This means there is another potential issue you will run across as these cars accumulate age and mileage. These are phenolic pistons...


Phenolic pistons are used when a vehicle has the potential to boil brake fluid under expected braking conditions. Specifically, the heat generated by these heavy cars with their big wheels is pretty high. The steel pistons normally used in an automotive application would transfer enough of that heat to the brake fluid to boil it. The phenolic material is wood pulp, resins, and other organic materials that are formed under pressure then machined to final shape and sealed with an outer coating to prevent fluid incursion. These pistons are usually good for about 60-80k miles and what causes issues is the sealing surface of the piston wearing away allowing fluid to get inside the actual piston. The pulp begins to swell, the pistons become stuck in their bore, brakes drag, and I once had a customer pull into my shop with a rotor so hot it melted the bead of his tire.

Phenolic pistons are available through RockAuto for about $5-8 each and well worth it if you are doing a caliper rebuild, even if you aren't experiencing issues with them at the time. If you should be tempted to install steel pistons or you should get remans with steel pistons please know that you will experience brake fade under heavy use. Don't try to second guess the engineers on this subject, they know what they are doing!

Phenolic on the left, steel on the right. Replace phenolics with phenolics!


We have covered the basics for maintenance, lets get deeper...

[Murco]

MASTER CYLINDER - The master cylinder is the most important part of your car!!! Think about it, it's true!
Look inside your master cylinder reservoir for a moment and look at the fluid. Does it look like apple cider, tea, or coffee? It should be a golden clear color. If it's slightly darker (like tea) it's time for a change. If it's really dark (like coffee) and there is sediment at the bottom (wet black film) you have extensive seal deterioration and need a new master cylinder, PERIOD!
How about green fluid? Never seen it? Ask a neighbor who owns a 3 year-old ford if you can see his master cylinder. If he's like 90% of people, it's the OEM fluid and I'm willing to bet it's green! Green fluid indicates the copper in the brake fluid has started turning acidic from excessive moisture and is eating the brake-line inner coating and corroding them from the inside out. Fords do it quickly but after a dozen years or so I'll bet some of our board member's cars have this too.
Getting back to the blackened fluid - That film is particulates from the seals coming apart. Our master cylinders are made up of;
2 pistons (primary & secondary)
2 chambers (primary & secondary)
2 primary seals (named for pressure sealing, not location)
2-3 secondary seals (used for separation and sealing)
2 springs (primary & secondary piston return)
and a housing and reservoir
If one of the secondary seals goes bad you will still have a decent pedal but your brakes will wear one or the other end much faster than the other. You can usually identify this problem when opening a master cylinder cap and finding one chamber lower than normal and the other near overflowing. Replace the master cylinder.
If one of the primary seals is dead you will still have brakes but with a low pedal and little stopping power. Replace the master cylinder.
If one or both of the springs are losing tension the pedal will return slowly and drag the brakes after you release pressure. Replace the master cylinder.
Also, consider replacement if you have headers and more than 50K miles on your master cylinder. The extra heat will damage the springs (heat-stress) and seals (hardening) inside the master. Our one advantage to cars is the relatively large expanse under our hoods so the exhaust heat isn't directly under the master cylinder.

ABS Pump/Module - There have been 2 different generations of the ABS unit in our vehicles over the years and fortunately they have been pretty good as far as reliability and maintenance. However, you don't want to have too replace one as the sticker on one of these bad-boys will make you cry! When you have your brakes bled have the tech use his little handy OBDII reader to cycle the ABS pump to get all of the fluid flushed through it. Other than that it's nothing you need to do much about for maintenance.
Got nasty fluid in the master or the ABS system? Guess what else needs replacement?!
Remember, gravity does it's thing with particulates too so when you find it in the master cylinder/prop valve/ABS unit you'll certainly find it in the calipers/wheel cylinders.

Their are 1000's of "professional" mechanics who don't know squat about proper brake repair, and I'll back that up. Think I'm pulling your chain?? The first post in this thread contains more info than is covered in an ASE MASTER CERTIFICATION exam for brakes, all 25 questions of it!!! Think about that!!!!

[Murco]

Going back to "buying the best products you can" for a moment - when replacing rotors go with the "better-name" options (Brembo, Raybestos, Wagner) and avoid the low-dollar options. The better branded brakes will have more cooling fins, more chromium to inhibit corrosion, and better machining with truer surfaces.
I actually had a Camaro come into my shop a few years ago with the customer saying, "I put brand new rotors and pads on a month ago and ever since the front end is wandering." It was an '89 IROC and had the low-end rotors from one of the big-name retail auto parts joints. After getting it in the air and removing the wheels we discovered a consistent layer of surface rust, the hub of these cheap rotors weren't machined properly and his wheels had been sitting about 1/8" off the hub surface the whole time!
I'm not saying go buy the wiz-bang drilled and slotted stuff, they look pretty but do nothing on a street vehicle except crack and create extra dust. Just get high-quality rotors and pads from the same manufacturer and you'll be quite happy.

[Murco]

Diagnosis -
If you currently have a brake issue here is the order of diagnosis, and this applies almost universally in brake repair...
The first thing to do is make sure the bottom-end is good. The calipers (and wheel cylinders) aren't leaking, frozen, or full of sediment. If they check out the next thing to verify is that the fluid hoses and lines are in good shape. No bulges or kinks in the hoses (if they have inner wall damage you'll usually have a significant pull under braking), no crimps or breaks in the hard-lines, and no leaks.
If all the lower components check-out flush the system and have someone (a dealer if necessary) cycle the fluid out of the ABS pump (if so equipped) to make certain you have no air in the system - which will give you the same indications you asked about.
If after these have all been checked, the fluid fully flushed, and you still have the same symptoms check your booster and the vacuum going to it. If you have access to a vacuum gauge check the booster vacuum, it should read no less than 14 inches at steady idle. If lower than that check the hose and fittings for cracks or leaks. You can use a can of starter fluid, just as you would a manifold or carb leak, running a spray along the length of the line listening for an RPM rise.
If you have good vacuum and feeder hose/fittings then have someone push the brakes with the engine idling, listen for the sound of a consistent air leak while they hold the pedal down - it's obvious when you hear it, a "whooshing" sound that continues while the pedal is held down.
As I said earlier, diagnostics starts at the bottom and you need to work your way up in the system. If you've followed these steps in order (which even if having the flushing done at a dealership should be well under $100 so far) and still have a weak pedal it is likely that the master cylinder is done. Now let's make certain!
Remove the master cylinder, using proper fitting wrenches for the lines, drain it, and clamp it securely in a bench vise. Put bleeding caps with tubes on the outlets (your local auto parts store should have some), refill the reservoir, and slowly push and release the plunger at the back using a screwdriver with the bleeder hoses in the fluid reservoir. Continue the push and release until the bubbles stop coming out of the hoses so you'll know the master is air-free, then remove and replace the bleeder cap with a block-off cap on the rear outlet and attempt to push the plunger again. If it's solid and won't move the primary side is good. Return the bleeder cap and hose to the rear and place the block-off cap on the front outlet and try to push the plunger again, You should be able to move it a little but maybe only a half stroke compared to when you were bleeding both outlets.
If you should go through these steps and haven't found an issue feel free to PM me and we'll start really digging.

As an example of how fun this stuff can be to diagnose I'll use my 1992 Lexus SC400 with ABS and Traction Control. It had a pedal pressure issue when I bought it (really cheap) except mine was constant. The car had 260k miles on it but was meticulously maintained with records going back to day one and looked perfect, like a new car. As with any used car I'd buy I immediately rebuilt the calipers, installed new pads and rotors, inspected the line and hoses, flushed the system, got a good pedal and felt I'd resolved the issue but expected more since the car had been maintained by the dealer all it's life and they would (hopefully) have done the same thing... After driving it for a few days I noticed the pedal started getting spongy again, a quick reverse bleed had bubbles in the master cylinder and looking through the lower hoses and lines again yielded nothing. In fact the hoses were recently replaced. I checked the tightness of the hose ends, all good. I checked the 16 line connections on the ABS module and found one that had a tiny amount of fluid on the outside, like the amount that you would leave if you bumped it with a wet hand! It was the line that provided fluid to the ABS pumps from the master cylinder and air was getting drawn into the system there. The 1992 traction control system was one of the first and, as you'd expect, it was convoluted and complex but it ended up being a $49 hose that got me a high mileage but nearly perfect Lexus for $800! I did contact the dealer afterward for info on the car and the service writer told me they had diagnosed a bad ABS unit and quoted the previous owner $3600 for a replacement, so then I knew why I got it so cheap. That was 18k miles ago and I still have a fully functioning brake, ABS, and Traction Control systems with no further troubles, although I can't imagine the original Master Cylinder lasting much longer!

After reading all of this, even if you don't do the repairs yourself, at least you have the knowledge to ask questions and sift-through any BS thrown at you and that's the whole point if this thread. I'm a brake geek (a geek in many ways) and trying to diagnose something without being there and doing all the things I'd do instinctively is tough so I won't pretend to be able to fix all issues with a brake system through forum posts. However, I am happy to provide all the expertise I have so that when you get into it yourself, or have it done elsewhere, you'll have the information you need to spend your time and money wisely.
Happy braking!

[dharris973303]

tech B disagrees, you're overthinking the simplistic