MurcoRS

There are a lots of members who are trying to do brake system repairs for the first time and hopefully this thread will help with some basic and a few more advanced diagnostics and repair procedures.
Let's start with the basics...
First and most importantly - BUY 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! Don't skimp on the brakes!
Brake fluid - You must replace it every 12K mile or once a year. 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 form, 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 as it has a higher temperature rating and is less suceptible to breakdown in high-performance use.
Wheel cylinders - If you have drum brakes on the rear of your 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. Ever wonder why your shoes last 2-3 times as long as your pads? 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 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 essentially rendering the rear drum brakes useless and overworking the fronts causing excessive heat, wear, and dramatically increased braking distances.
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).
Calipers - 70% of your braking power is right here and most of you will have the standard 78mm single piston GM standard mid-size caliper. These are a stout piece for around town driving and the large bore is fairly resistant to sediment binding when maintained properly. For high-performance use they are marginal at best but this is a maintenance and repair thread so lets fix what you have. The most common problem afflicting calipers is sediment bind due to poor maintenance. The heat cycling calipers go through is staggering and the large-bore calipers tend to "cook" the fluid under heavy use and flushing the fluid yearly 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? Your's 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. 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 and unless your car's brakes have been horribly maintained your's shouldn't have these symptoms.

Difflock

Makes me ashamed to say that all I've done regarding my calipers is check for leaks and how much brake pad material is left. I will be getting the fliud changed soon.
Saying that, there's about a litre of new DOT 4 in the system because I've replaced the rear brakes (cylinders, lines, shoes)recently
Thanks for the info.
Mark.

MurcoRS

We have covered the basics for maintenance and pad/shoe problems, lets get deeper!!!
The newest 3rd gen f-body is already 13 years old. A minimum of 13 years of wear, tear, some neglect, and just normal use can cause more difficult to diagnose problems in the hydraulics.
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!
Need more? 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 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 reservior
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 30K miles on your master cylinder. The extra heat will damage the springs (heat-stress) and seals (hardening) inside the master.
Proportioning/Combo valve - Our cars use a 3-function combination valve (proportioning valve, metering valve, and brakelight warning switch) and are prone to many of the same problems as the master.
The prop valve is an umbrella-shaped seal that ONLY REACTS AT PEAK SYSTEM PRESSUREs! It is designed to keep the rear-end from locking-up and is designed to close off the rear brakes at a specific pressure, allowing no additional pressure. The excess pressure is fed to the fronts.
The metering valve is designed to pressurize the rear brakes FIRST, under light pedal application, to promote more even braking. On drum brake cars it can hold up to 125 psi before allowing any fluid to the fronts, simply to overcome the force of the return springs and engage both front and rear brakes simultaniously. Disc/disc metering valves operate at lower pressures as it only takes about 3-5 psi to move a piston.
If EITHER of these valve fail or the springs are weakened, you will have excessive brake wear on one end of the car. Drum to disc rear conversion? CHANGE THE COMBINATION VALVE DURING THE CONVERSION or you will tear up your new rear brakes!
Headers + 30K miles? Notice how close the combo valve is too the headers? Remember how springs and seals deteriorate when exposed to high heat? Replace your combo valve ASAP!
Got nasty fluid in the master? Guess what else needs replacement?!

Conv90RS

Good info Murco

EDIT: I revived this oldy because I had a question about flushing my brakes, but after I posted I found this thread.

MurcoRS

Bumped this up as I see a lot of basic questions being posted... Hope it helps!

I want to address another issue, specifically regarding adjustable prop valves. I've been blasted on here 100 times for this but I'll stick to my guns... If your car is driven on the street, use an OEM prop valve. Varying loads, road conditions, tires, weather, and suspension wear are all realities the OEM valves will cover, even though it is biased to the front. If you are having other problems with your brakes, particularly the rears, do not just slap on an APV to solve the issue! This is a band aid at best and flat out dangerous at worst! If you don't have the technical skill to diagnose and repair a problem, don't work on it until you've learned about it! Also, please don't jump to the next level and modify a brake system you know little to nothing about! If your rear calipers aren't working properly, fix them. I'm sure someone on this forum has done the APV, set it up in perfect conditions to balance his pressures, then did some trail braking going into a corner in the rain and flown off the road *** end first. Problem is, they may not have lived to bac me on this. I'm not trying to flame anyone, I'm just saying go to a library and learn about the brakes before messing with them. Their are a lot of knowledgable folks on here, their are people who should be banned from giving any advise on the brake board, and their are 1000's of professional mechanics who don't know squat about proper brake repair. Think I'm full of it? 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!!!! Good luck!!!

MurcoRS

In revisiting the brake forum I'm seeing a lot of questions posted that are answered in this thread. Let's make it a sticky...