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Pelican Technical Article:

Brake System Overhaul

Mitchell Sam Rossi

Applicable Models:

 
Porsche 911 (1965-89)
Porsche 912 (1965-69)

Figure

This article was originally published in HPBooks' Porsche 911 Performance: Building the Ultimate 911 for High Performance Street or Road Racing, by Mitchell Sam Rossi. Rossi is a contributor to European Car, Road & Track, Sport Compact Car and the Los Angeles Times. As part of our selection of vintage 911 must-reads, this book provides a comprehensive look into the high-performance modification of 911's for the street and track. Covering topics ranging from engine building to chassis strengthening, this 144-page guide will certainly take your venerable 911 to the next level of performance. Click here to order this book.

It may sound counter intuitive, but good brakes are one of the most important elements in producing fast times around a racing circuit. It is a matter of the braking point, that is, the very instant the driver lifts his foot from the throttle pedal and begins to induce the brakes to slow his car and set the suspension for the next turn. The later the driver makes this transition, the longer he can lengthen the straightway and thus increase the distance he has carried his maximum speed. In wheel-to-wheel racing, this is the "late braking" benefit and is paramount when fighting for position. Be itFormula One or Formula Vee, if two cars are evenly matched in horsepower and torque, nine out of ten passes are done at the end of the straightaway.

The S original aluminum calipers and Koni shocks.

In 1969, the 911S braking system was improved by the addition of the Ate one-piece S-type front aluminum calipers. These larger calipers incorporated two 48 mm pistons squeezing 11.1 inch ventilated front discs. At the rear, the car was equipped with steel M-type calipers similar to those of the E and T models. These clamps use 38 mm pistons and surround 11.3 inch vented plates.

Cast out of an aluminum alloy, the S calipers not only reduced the unsprung weight but also have the benefit of dissipating large amounts of heat developed by the front brake rotors. In the physics of stopping a car, the brakes transform kinetic energy into frictional heat generated by the brake pads pressing on the rotating disc. Quickly dissipating this heat increases the braking system's efficiency and avoids brake fade or worse, brake failure.

Front brake pads (left) vs. rear brake pads (right).

With the S, after several years of non-use, the brake system was in need of a complete overhaul. Neglected brake fluid is notorious for two things, absorbing water and wreaking havoc on rubber components.

Removed front S calipers (left) and rear M calipers (right).

Restoring the Calipers

Taking the calipers off the car is a simple operation, but be sure to use the proper line wrench to remove the hydraulic lines, as a standard open-end wrench will invariably ruin the fittings. Inspecting the front and rear calipers verified my fears. Time had disintegrated the rubber dust covers that surround the brake pistons and allowed moisture to seep into the cylinder bore.

Beginning with the aluminum calipers, and with the high hopes of saving the pistons, I removed the dust covers as delicately as possible. To unseat the seized pistons, I employed a high pressure air hose and nozzle. Placing a narrow piece of wood into the center of the caliper, a blast of air was shot into the hydraulic line hole. Take care; the piston explodes from the cylinder bore with the force of a small howitzer. If you are lucky, both pistons will pop free. I was not so fortunate.

Air pressure blasts out stubborn brake pistons.

To dislodge the second, the hydraulic connection line that links the left and right sides of the one piece caliper was removed. This isolated the brake fluid chamber behind the remaining piston. Taking extreme care to keep my fingers safe, I again injected the compressed air and shot the piston into the wood block.

The rear M calipers are built from two halves and thus the piston chambers can not be isolated. If one of the pistons sticks in the bore, use a long forked C-clamp to hold the loose piston while injecting air into the chamber of the other. Although it is not shown, lay a rag across the caliper before using the compressed air, otherwise, you may get a face full of dirt, dust and grimy fluid.

With the pistons removed, lift out the rubber seal, or in my case, the remnants of the seal, with a small wooden or plastic pick to keep from marring the cylinder bore. Once the calipers are completely dismantled, you can clean them with any number of brake cleaners from the local automotive shop.

For reconditioning, I had the M calipers and their associated hardware gold zinc coated. While you may be tempted to anodize the aluminum brakes, the steel pins in the cylinder bore will cause the calipers to be damaged during the electrolysis process.

Dismantling the S aluminum calipers.

Once the S calipers were cleaned, I discovered light pitting along the outer edge of the bore. As the pistons ride on the rubber seals, this was not a serious problem. The outside diameter of the pistons, however, had also been gnawed by the corrosion. This pitting would certainly result in the loss of hydraulic pressure.

To rebuild the S calipers correctly, I opted to replace the spoiled pistons with new stainless steel units. While the replacement pistons are expensive, these original 911S calipers are still the choice clampers of many early car enthusiasts and autocross racers.

Luckily for me, the pistons from the M calipers were in better shape and only needed polishing with a Scotch Bright pad and a bit of effort. The aggressive pad was also used to cleaned out the cylinder bores.

Brake components are cleaned and re-zinc coated in preparation for assembly.

When reassembling the calipers, be sure all important surfaces and channels are free of dirt and debris. Lubricate the new rubber seals with a DOT-rated brake fluid. I used Motul's RBF 600, DOT 4 racing brake fluid for the procedure as this would be the fluid I planned to use in the car's brake system during competition.

The Porsche tool helps to correctly align the brake pistons.

With the seals in place, slip the piston into the cylinder bore but not so far that you can not rotate the pistons by hand. To help the brake pads press evenly against the spinning rotors, the pistons are manufactured with an uneven face. A special Porsche tool is needed to set piston's alignment in relationship to the rotating brake disc.

When reassembling the M calipers, take care to moisten and position the four small O-rings in the center intermediate plates. These O-rings do not come in the standard rebuild kit and must be purchased separately from the Porsche dealership. As the retaining bolts are tightened, be sure the caliper halves are lined up properly. Then, torque each bolt working from the inside set outward.

Once the pistons are in place and aligned, wipe off any excess brake fluid. Insert the dust covers into the cylinder. Be sure the dust cover encircles the piston correctly. With the four calipers ready to be remounted, I turned my attention to the master cylinder.

The stock brake reservoir is sufficient for most brake upgrades.

The dual circuit master cylinder on the early 911 is positioned just behind the brake pedal assembly but outside the passenger compartment. Locate the brake reservoir in the trunk and withdrawal as much fluid as possible. A turkey baster works well, but be prepared to purchase another, as you are not going to want to return this one to the kitchen drawer.

The stock 19mm master cylinder.

Remove the steel under panel that covers the fuel pump and steering rack. The master cylinder is just to the left of the steering rack. Unplug the circuit failure switch located on the side of the unit. Disconnect the hydraulic lines. Be sure to use the correct wrench.

As the lines are loosened, there will invariably be brake fluid spillage so prepare yourself with a contingent of rags and paper towels. Take care to keep this liquid off the car's finish.

Often overlooked, the 911's pedal assembly should be inspected for wear.

Two retaining nuts hold the master cylinder to the floor panel. Once these are removed, the unit can be inched forward until a rubber boot is revealed. The boot surrounds the pushrod that is connected to the brake pedal. Working the boot free will release the master cylinder from the pedal assembly. The rod will remain attached to the pedal but will need adjustment upon replacement of the master cylinder.

The last two lines connected to the master cylinder are the solid feed tubes descending through the chassis from the reservoir. These are simply pressed into the top of the unit and can be pulled free as the master cylinder is removed from the car. Remember, these lines will still be filled with fluid so be prepared with a catch container and more rags.

A new master cylinder is a worthy investment.

Once the master cylinder is out of the car, I have only one suggestion. Place it on the highest shelf in your garage and never take it down. Yes, they are fairly simple devices and can be rebuilt by even the occasional weekend mechanic, but considering the importance of the master cylinder and the fairly inexpensive price for a new one, it is not worth rebuilding a bad unit.

For the project car's master cylinder, the cost of Performance Product's rebuild kit is about $60. A new unit, on the other hand, runs $190. One more time. A new master cylinder is a mere $130 more than rebuilding the worn-out original. These are the brakes, and the heart of the system is the master cylinder. With the exception of the steering rack, there is hardly a more important piece of equipment on your car.

When it is time to replace the master cylinder, simply work the removal steps backwards. Once the unit is in place, the trickiest part is to set the rod so that it has a 1 mm clearance with the unit's internal piston. This is done at the brake pedal assembly inside the car. The locking nut must be loosened so the rod can be turned either clockwise or counter-clockwise, depending on the need.

With the calipers repaired and the new master cylinder installed, the next step was to remove the factory's rubber brake lines and clear out the old brake fluid from the solid lines. With the high pressure hose in hand and shop rags tied loosely over their open ends, I systematically cleared all the lines.

Although the original rotors were covered with a rusty cinnamon hue, all that was needed to bring them to pristine condition was a quick turn on the race shop's resurfacing machine. Before turning a disc, however, be sure the rotor thickness is within the manufacturer's specifications.

If the S was destined solely for street use or concourse events, this would have been the point to reassemble the system. But as it was slated for competition, there were a few more upgrades to be added.

Stainless steel braided lines are a must for any Porsche that might see track time.

Because of the movement of the chassis in relationship to the brakes, rubber lines connect the calipers to the system's hard lines. Over time, even under normal use, these lines can deteriorate giving the brake pedal a soft, spongy feel. The ones on the S had gone in the other direction becoming stiff and cracked. But instead of replacing them with similar factory lines, I selected the sturdier stainless steel braided lines. These are a good upgrade even for a non-competition car.

Inner plates channel the air flow through the brake rotors. They are only to be used with some type of brake cooling system.

One of the best ways to maintain optimal brake performance is to dissipate the heat generated by the friction of the brake pads. This is best done by channeling cool air to the rotors and calipers, especially to the front brakes as they bear the greatest burden during a dive into a corner.

The Cooler Brake kit mounted on the 911's front struts.

With this in mind, I installed two more upgrades offered by Performance Products. First was the use of air deflection plates that sit inside the front vented rotors. Normally, much of the wind that swirls into the rotor is lost through the hub. The plates block the openings, forcing a greater percentage of air through the rotor vanes.

The second and the most substantial addition to the front brakes were the Cooler Brakes system. This setup includes apair of aluminum disks, hoses and two shallow scoops. The disks bolt to the struts and fill the inner dimension of the ventilated rotors. The flexible hoses attach to the disks' two inch openings, then snake down between the strut assemblies and steering tie rods to the scoops which in turn, are fastened to the bottom of the A-arms. This system captures the air passing beneath the car and routes it directly to the center of the rotors.

The Cooler Brake kit air scoop mounts to the bottom of the A-arm.

While this is a huge improvement in brake cooling on a high performance street car, it is not the optimal setup for a racer. "You want to draw the air from the high pressure area at the front of the car," said Jaime Trimble of Race Technologies, a distributor for Brembo's high performance brake systems in the U.S. "This really forces clean air into the center of the rotors and out through the vanes."

The better way to find cool air for the brakes - an air dam scoop.

In order to tap into the air at the front of the S, the car was fitted with a special RS front spoiler that incorporated forward facing air vents similar to those of an RSR spoiler. From these vents, the hoses were fed around the trunk box and attached to the Cooler Brakes disks.

The last improvement to the car's brake system comes after everything has been reassembled and tightened to the proper torque specifications. This, of course, was the choice of brake pads. Performance Products offers Pagid pads for Porsche cars, but only two types, designated Blue and Orange, are available for the early 911. Pagid's Yellow pads are designated for long distance racing and are offered in sizes for the likes of the 993 Turbo.

For the dedicated club racer, the Orange pads are the best selection, but like fine tuning the suspension system, using competition brake pads on the street can have serious disadvantages.

"I would keep away from the Orange pads for the street," Trimble said, warning that the pads could actually damage the rotor if they are not run within their high temperature range.

Even if you drive the avenues like Hans Stuck, racing pads produce more brake dust than softer street pads blackening that hard earned polish on your alloy wheels. And of course, they have that tendency to announce your every arrival at the stop light with a deafening squeal.

Pagid's Blue pads are rated for high performance street, slalom and autocross applications and as I planned to continue driving the S on the highway and regain my racing legs at these lower speed events, they were clearly the best choice for the car.

At the track, I once saw a tee-shirt worn by an avid racer that read, "I don't brake until I see Elvis." The saying may not be very technical, but the message is true. With the rebuilt brakes and the upgrades mounted on the car, I was now confident the S would stretch the straight-aways a tad further than my competition or at least until I too saw the King.

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Figure
Figure 1

The S original aluminum calipers and Koni shocks.

Figure
Figure 2

Front brake pads (left) vs. rear brake pads (right).

Figure
Figure 3

Removed front S calipers (left) and rear M calipers (right).

Figure
Figure 4

Air pressure blasts out stubborn brake pistons.

Figure
Figure 5

Dismantling the S aluminum calipers.

Figure
Figure 6

Brake components are cleaned and re-zinc coated in preparation for assembly.

Figure
Figure 7

The Porsche tool helps to correctly align the brake pistons.

Figure
Figure 8

The stock brake reservoir is sufficient for most brake upgrades.

Figure
Figure 9

The stock 19mm master cylinder.

Figure
Figure 10

Often overlooked, the 911's pedal assembly should be inspected for wear.

Figure
Figure 11

A new master cylinder is a worthy investment.

Figure
Figure 12

Stainless steel braided lines are a must for any Porsche that might see track time.

Figure
Figure 13

Inner plates channel the air flow through the brake rotors. They are only to be used with some type of brake cooling system.

Figure
Figure 14

The Cooler Brake disk set into the brake rotor.

Figure
Figure 15

The Cooler Brake kit mounted on the 911's front struts.

Figure
Figure 16

The Cooler Brake kit air scoop mounts to the bottom of the A-arm.

Figure
Figure 17

The better way to find cool air for the brakes - an air dam scoop.

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Comments and Suggestions:
Chris Morse Comments: I am beginning to plan a brake upgrade to my 74 911. It will see occasional track use, so i would like to upgrade the brakes, that will fit in the stock 6x15 Fuchs wheel.

Is there a chart that lists Porsche brake component sizes, i.e. rotor thickness and diameter, caliper piston sizes, so that i may try to get the proper balance.

If i understand correctly, the stock M brake piston is 48mm and the rear caliper has 38mm pistons.

Any articles/threads/brake component charts would be happily received.

I will most likely use your fine front brake cooling set up with what ever i finally come up with.

I recently finished a massive brake upgrade on my 77 308, see garage.

Thanks,
chris
August 18, 2010
  Followup from the Pelican Staff: I don't know of any good chart like that. I'm also not sure what you mean by "balance", do you mean front to back? If yes, then you can insert a brake bias control valve between the two to prevent rear lockup. A good upgrade these days is to place the Boxster calipers on the fronts. - Wayne at Pelican Parts  

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Page last updated: Sun 10/15/2017 02:15:53 AM