The rotors job in disc brake systems is to provide something for the caliper and pads to clamp on.  This creates friction and friction helps stop the vehicle.

Rotors must be smooth and flat for proper braking and capable of absorbing and dissipating a lot of heat.   Vented rotors have cooling fins between the rotor faces and solid rotors do not.

When rotors are worn unevenly or have hard spots that are causing pedal pulsation when you apply the brakes, it’s probably time to resurface the rotors.  If you find the rotors are rough or badly scored, it’s also a pretty good idea to turn the rotors.  However, if they are cracked or damaged, you need to replace rotors.

When you are checking your brakes, you should also check the rotor thickness.  Use a micrometer to make sure they are not worn beyond the minimum “safe” specification.  In this photo, I just used a set of Central Tools (3M113) 0 to 3″ Storm Swiss Micrometers to check the specifications.  Mind you, this was a new rotor, but it’s important to check for flatness.   According to the shop manual for an 88 Chevrolet Camaro.  “Thickness variation can be checked by measuring the thickness of the rotor at four or more points around the circumference of the rotor.  All measurements must be made at the same distance in from the edge of the rotor.  A rotor that varies by more than 0.013 mm (0.0005 inch) can cause pedal pulsation and/or front end vibration during brake applications.  A rotor that does not meet these specifications should be refinished to specifications or replaced.”  Imagine that!  Such a small difference on one side of the rotor can cause pedal pulsation!

You can see the vents in the caliper from this picture. I am measuring the caliper here with a Central Tool Storm Value Line micrometer which you can buy here: Central Tools (3M113) 0 to 3″ Storm Swiss Micrometer

Here are some specs for Rotor Tolerance.

According to the Shop Manual for an 88 Camaro, the lateral runout of the rotor should not be over 0.13mm (0.005 inch.)  A rotor that does not meet the lateral runout specifications should be resurfaced or replaced.

Front Disc Brake Rotor

Maximum Rotor thickness   26.5mm or 1.043″

Minimum Thickness after refinish     24.84 or 0.98″

Discard hickness.  24.5mm or 0.965″

Rear Disc Brake Rotor

Rotor Thickness Max                   26.47mm  or 1.042″

Minimum Thickness after refinish   25.04mm or 0.986″

Discard Thickness     24.3mm or 0.956″

Light scoring of the rotor surfaces not exceeding 0.38mm (0.015 inch) in depth, which may result from normal use, will not affect brake operation.

You maybe wondering why there is a discard thickness.  The reason is that a rotor that is turned too thin or worn may not be able to absorb and dissipate heat quickly.  This can make the brakes run hot, accelerate pad wear and reduce braking effectiveness to the point of brake fade.   Too much heat and the rotor itself may fail in operation!

Another thing to check for is rotor run out.  Lateral run out is the movement of the rotor from side to side as it turns.  Excessive run out will kick the pads out as the rotor turns, creating excessive clearance that requires increased pedal travel when the brakes are applied.

The instructions in the manual says that the lateral run out should not be over 0.005 inch.

As for Rotor surface finish, the manual says that light scoring of the rotor surfaces not exceeding 0.38mm (0.015 inch) in depth, which may result from normal use, will not affect brake operation.  The optimum speed for refinishing braking surfaces is a spindle speed of 200 rpm.  Crossfeed for rough cutting should range from 0.254-0.152mm (0.010-0.006 inch) per revolution.  Finish cuts should be made at crossfeeds no greater than 0.051mm (0.002 inch) per revolution.  Always use sharp cutting tools or bits!  Dull or worn tools leave a poor surface finish which will affect initial braking performance.  Vibration dampening attachments should always be used when refinishing braking surfaces.  These attachments eliminate tool chatter and will result in better surface finish.

Mike Mavrigian and Larry Carley wrote in Brake Systems: OEM & Racing Brake Technology some interesting tips

1.  Applying a non-directional swirl or cross hatch finish by lightly sanding the rotors with #120 or #150 grit sandpaper after the rotors have been turned is a good way to guarantee quiet operation.

2.  Clean the rotors after they have been resurfaced.  The microscopic debris that’s left on the surface of the rotors can become embedded in new pads, causing them to squeal.  use soapy water, a stiff brush and then dry the rotors before they are installed.  Brake cleaner and solvents do as thorough a job. (I’m assuming because they don’t actually scrub the brake rotor.)

3.  Rotor run out is usually fixed by going to the dealership to get an on car rotor resurfacing.

4.  To tell if the rotor is smooth enough after its been resurfaced, give it the “ballpoint pen” test.  Draw a line on the rotor with an ordinary ballpoint pen.  If it leaves an unbroken line, the rotor should be smooth enough.  If not, take it back to have them redo the job.

5.  Apply heat emitter coating to the vanes

6.  Stress relief the rotor using cryogenics or vibratory stress relief.  This will help prevent rotor warping and heat-cracking.

7.  Some rotor hats have a black coating.  Don’t remove or paint over this coating.  Black will help to promote heat dissipation from the hat.   Also, this may be a special heat emitter coating.

Rotor Bedding:

Use pads that have already been bedded.  Use the brakes gently at first from initially low speeds, and progressively increase to normal racing speeds, but continue to use gentle braking pressure when applying the brakes.  Do this for about 10 miles or so.  After this, apply the brakes hard for 3 applications.  During this final braking, you want to raise rotor temperature to at least 600 degrees F., and possibly up to about 800-1000 degrees.  (You need to apply temperature indicating paint for this procedures.)

New rotors are referred to as “green” rotors, and require a slow break-in period.  Don’t hammer new rotors on the first few laps.  Allow them to build head slowly, eventually up to race temps, then allow them to cool completely.

After that, change your pads and repeat the above process with new pads.

However, I’ve noticed different bed in procedures depending on the manufacturer and you should consult the manufacturer of your bedding procedures.

For example, my manufacturer recommended the following procedure for the rotors:
1. Make 6-10 stop at approximately 30-45 mph,
apply moderate pressure
2. Continue with 2-3 hard stops at approximately
40-45 mph
3. Do not drag the brakes
4. Let your brakes cool for about
20-30 minutes.

When I asked them about the used or new pads they replied:

It would be best to use the new pads or the pads you are planning on using so the brake pads can also break in and embed with the rotors.

So contact the manufacturer of your rotor and ask!

The GM Brakes found on third gen Camaro’s are usually front disc and rear drums or both front and rear discs.

This post is going to talk about the general theory of disc brakes, which really comprise of three main components: A caliper, Rotor and a pair of brake pads.

When you step on the brake pedal, pressure from the master cylinder goes to the caliper forcing one or more pistons to squeeze the inner and outer brake pads against the rotor.  This creates friction, which slows the vehicle and produces heat.  When the brake pedal is released, the caliper loosens its grip, allowing the square cut seals around the pistons to retract the pads slightly. The rotor also helps kick the pads back slightly too.

Many of the advantages of disc brakes can be attributed to the rotor/disc.  If you have a ventilated rotor, it draws air through the center of the disc and it is discharged along the outer edge.  This is what allows disc brakes to not fade as bad as drum brakes.  It dissipates heat.  Sometimes you’ll find the splash shield is shaped to channel the flow of air over the exposed rotor surfaces.  However, I don’t believe GM originally shaped their splash shields to channel air in through the splash shield from the factory.

I only say this because of an old Hot Rod article from July 1982.

http://www.thirdgen.org/hotrod-shootout-camaro-prep-july1982

You’ll notice on page 33 the caption reads that Dick Guldstrand bent the backing plate to allow for more cooling to the brakes.
Calipers:

There are two basic varieties of calipers:  Floating or fixed.

Front GM Delco Morraine Brake caliper from a third gen camaro

Floating calipers are mounted on slides or bushings that allow the caliper to move sideways when the brakes are applied and released.  They typically have a single piston located on the inboard side of the caliper and are used because they are simpler, and less expensive to manufacture than fixed calipers or ones with multiple pistons.  The stock GM Brakes used on third gen Camaros are floating calipers.  Both the two piston 1LE brakes found mostly in the 88-92 “High Performance” brakes, or the regular “Non-High Performance” disc brakes are floating calipers.

A caliper can contain 1, 2, 4 or 6 pistons.  The pistons are relatively large in diameter and short in stroke to provide high pressure on the friction pad assemblies with a minimum of brake fluid displacement.   The hydraulics are the same as drum brakes.  Press the brakes, the master cylinder pushes the brake fluid into the wheel cylinders and against the wheel pistons in the brakes.  GM used “non-high performance” 1 piston delco morraine calipers and starting in 1988 (in only about 4 cars according the thirdgen.org), the 2 piston 1LE “high performance” calipers.  The delco morraine calipers were fitted to 10.5″ disc rotors and the “high performance” to 12″ discs  (I think it was more like 11.6″ to be exact, but it’s commonly referred to as a 12″ rotor.)

When the brakes are applied on a vehicle with a single piston, floating caliper, the piston moves outward and pushes the inner pad against the rotor.  This forces the caliper to slide inward slightly and pull the outer pad up against the rotor.  When the pedal is released, the caliper slides out slightly as the pads are kicked away and retract from the rotor.  Thus, the caliper is constantly moving in and out as the brakes are applied and released.

Floating calipers like the one found in third gen F-bodies must be free to move if it is going to do its job properly. If the caliper slides or bushings are rusty, worn or damaged, the caliper will not work properly and the pads will wear unevenly.  If there is more wear on the inner pad than the outer one, the caliper isn’t sliding.  A sticky or frozen caliper may also cause the brakes to drag if the caliper does not slide so the outer pad can kick away from the rotor.  This may cause increased wear on the outer pad as well as a steering pull to one side because of the constant drag.

As for rebuilding calipers.  With prices so low on the stock rebuilt Delco Morraine GM calipers, I’m almost going to say it’s better to replace your calipers.  Although, if you’re on a really tight budget, you should consider rebuilding the front calipers when you change your pads.  (The rear calipers I found were difficult to rebuild as they are locking calipers.  In my case, it was just cheaper and easier to buy new rear calipers.)    If there is no pitting on the bores of the pistons, just take some 600 grit or finer crocus cloth/emery paper and polish it lightly with some brake fluid.  Or use a drill powered brake hone.  But if you have to increase the diameter of the bore by more than  0.002 inches, replace your calipers.   The only reason that rebuilding calipers are recommended is because when you push the pistons back to replace the pads, any dirt or corrosion on the pistons may damage the rubber piston seal in the caliper.  As the seal hardens with age, or deteriorates against the constant rubbing of the pistons, there is more of a chance of the seals leaking brake fluid (and thereby failing.)

Here’s a good article on rebuilding calipers from Circle Track magazine.  Again, I found it easier to just buy re-manufactured rear calipers, although this method worked O.K on the front calipers for me.  I used this article to guide me in rebuilding my gm brakes.

http://www.circletrack.com/chassistech/ctrp_1108_brake_caliper_rebuild/

2 different brands and sizes of brake fluid that is compatible with some GM Brakes

If the brake lines in your GM Brakes are arteries, brake fluid would be the life blood that does the work. Brake fluid must be able to flow freely at extremely high temperatures (260 degrees C, 500 degrees F) and at very low temperatures (-75C, -104F). Brake fluid must also lubricate the parts it comes in contact with as well as fight corrosion and rust in the brake lines and various brake assemblies and components. With all the rusted GM brake lines in the news right now, I’m wondering if it’s because certain models may have the non-teflon coated brake lines from the factory or if the brake fluid was not flushed and changed according to GM maintenance schedules. In my opinion it may be a combination of both as most vehicle owners never think twice about flushing the brake fluid in their cars.

Brake fluid has to resist evaporation, however it’s also hygroscopic; that is, it readily absorbs water. This is why you should never open up the brake fluid reservoir cap if you can see the fluid level through a transparent reservoir. Never used brake fluid from an old container as you don’t know how much water it may have absorbed. Because of this “hygroscopic” quality of brake fluid, after a year of service, the brake fluid has about 2% water. After 18 months, the level can be as high as three percent. If you don’t change your brake fluid after several years, you could have as much as seven to ten percent of water in the brake lines. Thus causing your brake lines to rust! All the water seeps in through pores in the rubber hoses, seals, and through the fluid reservoir every time it’s opened for inspection (so don’t open the cap if you can see the fluid level from the sides.) So if you have GM brake lines that are rusty, ask yourself, when did you last bleed ALL the brake fluid from the vehicle (usually by pressure bleeding or “power bleeding”?

Three types of Brake Fluid:
DOT 3:  Conventional brake fluid with a minimum dry equilibrium reflux boiling point (ERBP)  of 205 degrees C (401 degrees F) and minimum wet ERBP (3% moisture contamination) of 140 degress C (284 degrees F.)

DOT 4:  Is a conventional brake fluid with a higher boiling point.  An ERBP of 230 degrees C (446 degrees F) and a meinimum wet ERBP of 180 degrees C (356 degrees F.)

DOT 5:  Is a unique silicone-based brake fluid witha minimum dry ERBP of 260 degrees C (500 degrees F) and a minimum wet ERBP of 180 degrees C (356 degrees F).  DO NOT MIX DOT 5 brake fluid with DOT 3 or DOT 4 glycol based brake fluids.  Even if you drain and refill your brake system with DOT 5 fluid, any residual glycol fluid will form slugs that may concentrate moisture.  If the fluid gets hot enough, the slugs may boil and cause loss of pedal.    Also, do not use DOT 5 in ABS brake systems as it absorbs air and foam when cycled rapidly through the ABS orifices.

DOT 5.1:  is a non-silicone-based polyglycol fluid and is amber in color.  It has the same boiling point as DOT 5 fluid.

Always use the type of brake fluid that’s specified by the vehicle manufacturer!

Some general guidelines:

-Avoid contact with brake fluid, it can cause irritation and is harmful/fatal if swallowed.

-Do not splash or spill DOT 3/4 brake fluid on painted surfaces (it will take the paint off!)  If you do spill, don’t wipe.  Flush immediately with water!

-Only use fresh brake fluid from a NEW sealed container.  Do not reuse old fluid or brake fluid from an open or unmarked container.

-Don’t open the master cylinder fluid reservoir if you don’t have to.

To keep your gm brakes working optimally, you need to flush the brake fluid in your gm brakes according to GM’s maintenance schedule.

GM Engineers Quiet Brake Squeal – Take a look at that! After announcing their plan to make longer life rotors, GM has now engineered less brake squeal into the rotors themselves. That’s just awesome! Hopefully one day GM will go backwards for all their older cars including third gen f-bodies.

Before installation, a picture of my new brake lines for my Camaro Delco Morraine brakes. These are brake lines for GM Brakes found in third gen F-bodies.

Brake lines are one of the most important things in your entire braking system.  If a brake line blows, you can lose at least 50-80% of your brakes.  When you step on your brakes, there can be almost 2000 psi of pressure going through those lines.

Air and dirt are the main enemy of your brake lines.  A small slow leak is almost just as bad as a sudden bursting of the brake lines because a small leak allows air to enter the hydraulic system.  Remember, air is compressible which means that when you press on the brakes, part of the pressure is used just to bend the air instead of forcing the brake fluid to press the caliper pistons of the brakes.

LEAKS ARE THE ENEMY!

Check:

-the low fluid level in the master cylinder reservoir or wet spots on the driveway,

-dampness on the back of a brake drum or if the brake warning light comes on

Any of the above may mean an air leak in the brakes!

Obvious places for a leak include around the master cylinder, calipers, wheel cylinders or brake hoses or a line connection.  Not so obvious places to spot a leak are places where the brake line runs inside a frame rail, rocker panel, inside the floor pan or trunk.  Or the fluid could be disappearing into the engine through a leak in the power brake vacuum booster.  Check the inside of the brake booster vacuum hose and if you find fluid, the booster diaphragm is leaking.  This means rebuilding or replacing the booster.

If you are inspecting steel brake lines, look for dampness around connections or where there are bends.  Look for stains or corrosion and check for chafing, loose or missing support clips, kinks, dents or damaged armor.   Look for rust.  This is a major problem with some “newer” GM vehicles manufactured after 2000.  And they are not obvious leaks!  Sometimes the leak isn’t visible as the brake line runs through the frame rail or rocker panel or inside the car.

If you are inspecting rubber hoses, look for cracks, splits and breaks.  Rubber can bulge or swell over time indicating internal damage or deterioration.  The inner liner has problem broken and it’s time to replace the hose.  It helps a lot to have a helper depress the brake pedal while you observe each hose.  If you see a bubble or blister rise on any part of the hose or if the hose swells, replace the hose!

When you are changing the brakes, never allow the caliper to hang by its hose when doing brake work.  Always hang it from a piece of wire so that the weight of the caliper can’t damage the hose.

Odd things that can happen with brake hoses:

1.  The rubber deteriorates inside the hose and a small flap inside the hose lifts up and plugs the line.  This prevents brake pressure from reaching the wheel causing a brake pull when the brakes are applied.

2.  Debris in the brake fluid or a crushed or kinked steel line can block the line.  Sometimes the pressure will get through to press the brakes, but when you let go of the brakes, the blockage prevents pressure from releasing back to the master cylinder causing the brake to drag.

Brake lines are like the arteries in your body.  They deliver the fluid that does the work…in this case STOPPING THE CAR!

Make sure you inspect the brake lines any time you’re under the vehicle.  It doesn’t take much, just take a flash light and look at them.  Any bulges?  Any brake fluid anywhere?  Any rust on steel lines?  Any kinks or crushed lines?

Replace them!   And if you’re using steel, use “approved” double-walled welded steel tubing and tubing of the same original size.  (The size of the lines affects brake how much fluid hits the caliper.  Use the stock size or you will hurt brake balance!)

Whether you’re using steel lines or hoses, make sure you check the lines regularly and replace them if you notice a problem.  They are NOT supposed to last forever!  Although Teflon coated lines do last longer, if you can afford it, it can be worth it.

• Check out the Lukestaff site for some brake measurements on GM Brakes. This guy was one of the first people ever that figured out how to install Corvette Brakes onto third gen Camaro’s and through his project with that, the LS1 brake upgrade on third gen Camaro’s and Firebirds. If you want to go that route, you need to take a look at his site.

Look at that!  The factory is finally offering a performance option with their stock rotors.  Some Corvettes came with slotted and drilled rotors, however this is a game changer!   By heat treating the rotors in a controlled fashion, they are doing something similar to aftermarket brake companies.

Many aftermarket brake companies offer Cryogenic treatment for their rotors.  By lowering the temperature to a very low level and controlling the thaw rate, this aligns the molecules in the steel and increases the tensile strength of the rotor.  This improves the durability and life of the rotor.     The scientific explanation is that inside the metal are potentially brittle deposits called “austenites” that create the potential for cracking.   Deep freezing metal changes theses areas into harder, more uniform “martensites.”   Cryogenics also create a vast distribution of very fine carbide particles throughout the metal.  This is what helps align the molecules and improves the wear characteristics, by making the molecular structure denser.  When you cryo-treat a part, any internal flaws will be found!  This means that sometimes what you thought was a good part turns out to not be and instead of having the part break on the road, it gets broken by the stress relieving process of cryogenics.     This is a one time permanent process and changes the entire metal structure internally and will cure a rotor’s tendency to warp.  The tensile strength and ductile strength is improved.

It looks like GM has done the same thing, however in reverse!  This is their way of improving the strength and life of the rotor.   I wonder how well their heat treated rotors will compare vs. aftermarket cryogenic stress relieved equivalent.

Both processes have the same goal.  To make the metal stronger and more stable and to reduce the potential for cracking, breakage and warpage!

Hopefully GM will roll this out to all their older vehicles including third gen Camaro’s, Firebird’s and Trans Ams!  Can you imagine having a genuine GM Brake that is treated similarly or better than a cryogenic aftermarket rotor?  That would be awesome!

But if they don’t, here’s a company that I think may be able to point you in the right direction.

http://www.woodworthheattreating.com/UltraWearPlusFNC.aspx

The proportioning valve’s job is to control the brake line pressure in the front and rear brakes.  Simply put, if the brake balance between the front and rear brakes are not correct, you’re going to lock up the rear brakes and cause the rear wheels to skid.

Usually you want the front brakes to receive more braking power than the rears.  The reason for this is because of the car nose-diving when you hit the brakes.  Braking tends to force down the front wheels, and lifts the rear end of the car up.  Typically rear wheel drive cars have 60-70% of the brakes geared toward the front.  In front wheel driven cars, this can be from 80-90% as the front wheels are also the drive wheels.

Here is a photo of the proportioning valve on a 1988 Camaro.

Inside the proportioning valve is a spring loaded piston that determines how much pressure goes fore and aft.  You can see the nut at the very front in this photo.  It’s important to buy the same proportioning valve that came with the same model/optioned vehicle if your original valve is defective.

The reason for this is that the factory has it precision calibrated to that specific optioned brake in your vehicle and it’s pretty darn close!

For example, there is a difference between proportion valves in the drum brake F-body cars and the four wheel disk cars.  (Even between the non-performance delco morraine brakes and the “performance” 1LE brakes, there is a slight difference.)

When the hydraulic pressure is applied to the wheel cylinder inside a drum brake ,the shoes are pushed out towards the drum.  When the shoes make contact, the rotation of the drum tries to drag the the shoes along, however since the shoes are anchored in place, the drum only pulls the shoes tighter.  This is why drum brakes are called “self-energizing” and require little additional pedal effort once applied.

Disc brakes are not self-energizing.  It requires increased pedal effort to squeeze the pads against the rotor.  Thus, the proportioning valve is different between the two cars.

Here is an interesting article from Stop-Tech regarding brake bias and the proportioning valve:

http://www.stoptech.com/technical-support/technical-white-papers/proportioning-valves

Here are some factors that affect brake bias from Stop-Tech’s site:

“Factors that will increase front bias

• Increased front rotor diameter
• Increased front brake pad coefficient of friction
• Increased front caliper piston diameter(s)
• Decreased rear rotor diameter
• Decreased rear brake pad coefficient of friction
• Decreased rear caliper piston diameter(s)
• Lower center of gravity (i.e. lowered vehicle)
• More weight on rear axle (i.e. loaded)
• Less weight on front axle
• Less sticky tires (lower deceleration limit)

Factors that will increase rear bias

• Increased rear rotor diameter
• Increased rear brake pad coefficient of friction
• Increased rear caliper piston diameter(s)
• Decreased front rotor diameter
• Decreased front brake pad coefficient of friction
• Decreased front caliper piston diameter(s)
• Higher center of gravity (i.e. raised vehicle)
• Less weight on rear axle (i.e. unloaded)
• More weight on front axle
• More sticky tires (higher deceleration limit)”

Generally, it’s best to leave your stock proportioning valve alone if you don’t have the testing equipment to get it right!  Stop-Tech seems to agree.

On the drum brake F-bodies, you may also have a metering Valve.  This just holds off or delays the hydraulic pressure to the front disc brakes until the rear drums start to work.  I’m not sure if they actually combined that with the proportioning valve, when they do it’s called a combination valve.

Although there are magazines articles that say you can fool around with the spring inside the stock proportioning valve to get the back brakes to lock up sooner-the theory being that the rear brakes are not working hard enough, it goes against the fact that your front end nose-dives during braking, thus the front actually needs more brakes!  GM brakes have a specific proportioning valve for every vehicle they manufacture and GM usually had it very close to what the car needs!

The 82-92 F-bodies did not have traction control.  It wasn’t until the 93-94 F-body cars that Camaro’s, Firebird’s and Trans Am’s received ABS.

I found this aftermarket solution, but unfortunately it’s for bikes.

The fluid reservoir does exactly that.  It stores and supplies fluid to the master cylinders of your brakes.

GM brake fluid reservoir in a third gen camaro

Fluid is incompressible.  So it acts like a liquid linkage between the master cylinder and each of the wheel brakes.  When you press the brake pedal, the force is instantly transferred to the brakes.  The master cylinder has a push rod and a pair of pistons that exert force against the fluid in the cylinder bore.  When you push the brakes, the pistons in the master cylinder push against the fluid, which flows through the brake lines and pushes the caliper pistons outward to apply the disc brakes.  When you release the brake pedal, the spring loaded piston in the master cylinder returns to its rest position.  The fluid that was displaced by the pistons is pushed back to the master cylinder as the brake pads retract.

My Camaro has a plastic reservoir that is attached to a composite master cylinder.  It is held in place by a pair of O-rings.  The translucent plastic allows me to see the fluid level inside without having to open the filler cap-which helps keeps the system free of moisture and dirt.

You can see the min. line through the GM brake fluid reservoir. There is no need to lift the cap.

There were no fluid sensors for the brakes system in my particular model year.

Tips:

1.  Keep the reservoir full-but don’t over fill it!  Keep your fluid at the full mark, because it drops as your brake pads wear.  It if gets too low, air can be drawn in.  Unlike brake fluid, (yes, I know air a a gaseous fluid) air is compressible and will reduce hydraulic pressure, creating a soft and/or low brake pedal.  If you over fill the fluid reservoir, you’ll prevent the fluid to return after the brakes you let off the brakes.  Also, a little space is needed for the changes in fluid volume that results from temperature changes.

2.  Keep out anything that doesn’t belong in the reservoir.  No oil, no power steering, transmission, coolant, or water!  Anything with oil distillates in it can attack and ruin the rubber components in the brake system (O-rings etc.)  If you do accidentally get anything but brake fluid in the system, you’re going to have to disassemble, rebuild or replace the master cylinder, calipers and wheel cylinder and flush the system with new brake fluid.     Also, make sure you avoid getting dirt into the system as it acts as an abrasive and can plug up the master cylinder.

You can see the brake lines going to the front and rear of the vehicle

On the third gen, you have a dual master cylinder.  This is good because a leak in a single piston master system will cause you to have no brakes!

One half of the master cylinder works the front brakes and the other the rear.  (Front wheel drive cars split the system diagonally.)  The GM cars past 1980 had a special kind of master cylinder called a “quick take-up” master cylinder.  This design reduces the brake drag by using a stepped bore that delivers a large volume of fluid when the brake pedal is initially depressed.  This allows the caliper piston seals to retract the pistons when the brakes are released so the pads don’t drag against the rotors. The old method required the rotors to kick out the pads so they didn’t rub.  The drawback with this design is that the caliper pistons have to travel further when you apply the brakes and the reservoir has to hold more fluid.

If you compare a master cylinder from an 80’s GM car with some other car manufactures (think Honda) the GM brake fluid reservoir is huge!