Boxster Project: Brakes: Parts

Here's a quick reference to the various parts that will be mentioned in detail below.

	Boxster	Boxster S
Porsche Front Pads Set	986.351.939.xx	996.351.939.xx or 996.352.940.xx * or 996.352.949.xx *
Porsche Rear Pads Set	996.352.939.xx	996.352.939.xx
Pagid Front Pads Set	U2407	U2405
Pagid Rear Pads Set	U2406	U2406
Porsche Left Front Rotor	986.351.401.xx	996.351.405.xx
Porsche Right Front Rotor	(same as left)	996.351.406.xx
Porsche Left Rear Rotor	986.352.401.xx	986.352.403.xx
Porsche Right Rear Rotor	(same as left)	(same as left)
Caliper Bolts (4)	999.067.041.09	999.067.041.09
Porsche Left Front Caliper	986.351.421.xx	996.351.425.xx
Porsche Right Front Caliper	986.351.422.xx	996.351.426.xx
Porsche Left Rear Caliper	986.351.423.xx	996.352.421.xx
Porsche Right Rear Caliper	986.351.424.xx	996.352.422.xx
Brake Wear Sensor	996.612.365.xx	996.612.365.xx
Retaining Pin Kit	996.352.959.xx	996.352.959.xx
Front Rotor Thickness	24mm new, 22mm worn	28mm new, 26mm worn
Rear Rotor Thickness	20mm new, 18mm worn	24mm new, 22mm worn

* - These are updated Boxster S part numbers that have a different anti-squeal dampening design.

Notes

In Porsche part numbers, the last two digits are a revision number, which increase over time as Porsche makes minor changes to the part. I denote the revision number here with "xx". For example, the last set of OEM front pads I picked up for the Boxster were revision 16, so they had a part number of 986.351.939.16.

When you replace a rotor, the caliper is first removed by undoing the two caliper bolts that attach it to the hub. Porsche officially recommends that you re-attach the caliper with two new caliper bolts. However, many people feel that it's perfectly OK to keep using the same caliper bolts if they are in good, clean condition. And in fact, some Porsche service departments take this view as well. If you decide to purchase new caliper bolts, part number 999.067.041.09 contains four bolts—enough for two calipers.

The wear sensor part consists of a short wiring harness that plugs into a terminal attached to the suspension, and runs to the caliper where the individual sensors slip into a hole in each brake pad. You do not always need to replace the wear sensor. It's only necessary if the old sensor has worn through (triggering the warning light) to the point where it will always be "on". If you replace pads often, you may want to stop using the sensors altogether and zip-tie them out of the way.

The caliper part numbers are listed here only for reference, and do not need routine replacement.

The retaining pin kit consists of the retaining pin, the cotter pin that secures it, and the spring clip over which it fits. Porsche officially recommends changing these parts with every pad change. However, almost everyone seems to agree that it's perfectly OK to keep using the same retaining pin, spring clip, and cotter pin unless they show some sign of a problem. And in fact, Porsche service departments rarely replace these parts and often don't even stock them!

You have a lot of choice in parts. For street use, it's probably wise to simply stick with the Porsche OEM (Original Equipment Manufacturer) parts that are tried and true. But you do have other choices, and depending on what you want out of your braking system, you can benefit from aftermarket parts where their design fits your use. Just be aware that there are trade-offs.

Brake Pads

Porsche

The stock pads are pretty good. For street or autocross use, it's hard to recommend something else. For frequent track use, though, there are better choices. Pros: They have a fairly long lifetime, are quiet, and don't give off a whole lot of brake dust, so your front wheels don't get dirty too quickly. Cons: They can wear quickly when subjected to hard track use. Recent revisions of the stock pads (rev 15) have been known to exhibit "taper wear" in these conditions, and wear very rapidly in the last half of their life as they get thinner and dissipate heat less efficiently. They exhibit eventual fade under track conditions. These cons really don't apply to street use.

	Boxster	Boxster S
Porsche Front Pads Set	986.351.939.xx	996.351.939.xx or 996.352.940.xx or 996.352.949.xx
Porsche Rear Pads Set	996.352.939.xx	996.352.939.xx

price per set is usually between $100 and $120 (front and rear prices differ)

Pagid

Pagid makes several flavors of brake pads: blue, orange, yellow, and black. Each color has different friction, heat, durability, pad wear, and rotor wear characteristics. Orange seems to be the preferred compound for track use on street cars. I have used the Pagid Orange pads and can comment on them. Pros: Wonderfully durable and long lasting under hard track use, perhaps 3x the life of the stock pads. Much more fade-resistant under hard track use. Nice pedal feel under hard braking. Cheaper in the long run because they last so long. The extra life also means you don't have to replace them as often. Cons: Somewhat dustier than stock pads. As time increases between track events, they get noisier; hard braking seems to quiet them back down. They are designed to work well at somewhat higher temperatures (as experienced at the track), so in theory they don't grip as well at cold street temperatures. More expensive than stock pads per set (but they are cheaper overall because they last so much longer).

These are Pagid's numeric codes for the colors:

Blue: RS 4-2
Orange: RS 4-4
Yellow: RS 9
Black: RS 14

These are Pagid's numeric codes for the various Boxster pad sizes:

	Boxster	Boxster S
Pagid Front Pads Set	U2407	U2405
Pagid Rear Pads Set	U2406	U2406

price per set is usually between $160 and $250 (front and rear prices differ)

Note that when you buy from a particular distributor, they may use their own part number codes! And the Pagid part numbers shown above are independent of which Pagid "color" you choose. Make sure to state the Pagid pad color and your exact car model and year, front or rear.

I can definitely recommend the guys at Livermore Performance <http://www.livermoreperformance.com/> as an excellent source for Pagid brake pads.

Others

I've seen positive reports from people using Mintex pads on a Boxster (Mintex "Silver", also known as Mintex "Red Box"). Hawk, Performance Friction, and Porterfield are other popular brake pad brands for high performance cars. I haven't heard much feedback about using these on a Boxster. The guys at Livermore Performance carry Hawk and Porterfield pads as well.

Notes

My experience has taught me to always bring a spare set of brake pads with me when I go to a track event, just in case. Especially with the stock pads--if they aren't nearly brand new, you can't be certain they'll last the whole weekend.

After installing a new set of the Pagid pads, you should follow the "bedding-in" procedure instructions that come with the pads. This is important for getting the new pads to properly mesh with the old rotor surface under the proper temperature conditions. It involves a series of braking sequences at particular speeds.

Brake Fluid

For street use, the kind of fluid you use is not as important as the condition it is in over time. Of course, you have to use a proper type of fluid. For track use, the fluid's boiling point becomes more important. Brake fluid and water are essentially non-compressible. When you press the brake pedal, pressure is translated through the brake system and the fluid into a force that presses the brake pads against the rotor to slow the car. Brake fluid itself does not contain water, and that is important. Brake fluid has a boiling point much higher than that of water. But brake fluid is hygroscopic, which means that over time it absorbs water. Water in the brake lines is not in itself a problem for pedal feel (water being non-compressible just like brake fluid), but it is a major problem because of what it becomes under the extreme temperatures of hard brake use: it easily boils, leading to air bubbles in the brake lines. Those air bubbles are compressible and make the brake pedal go soft. Under the harshest conditions such as at the track, the temperature in the system can become hot enough to boil the brake fluid itself, or whatever minor amount of water it has absorbed. Thus the need for brake fluids that have high boiling points.

So the symptom of air bubbles in the brake lines (or more commonly referred to as "boiled brake fluid") is a squishy brake pedal. Pumping the pedal will firm it up, so the deterioration is at least not catastrophic and is somewhat recoverable, but the squishy feeling may return on the next lap or even on the next corner. Boiling of the fluid in the brake lines first occurs in the hottest part of the system: near the brakes. "Bleeding" the system means draining some fluid out from each brake and then topping up the reservoir, thus ridding the system of the fluid at the corners that is most likely to contain air bubbles. "Flushing" the system means pushing all of the old fluid out, essentially bleeding until you've replaced all the fluid.

Porsche recommends flushing (completely replacing) the fluid every 2 years. If you take your Boxster to the track, you'll want to flush it at least once per year, and you may want to bleed the system (remove the most abused fluid) every couple of events. Fortunately bleeding and flushing can be easily done yourself, with the help of a little bit of bleeder equipment listed in the next section. It's most convenient to just take a few extra minutes to bleed the brakes while you're changing wheels or pads.

Brake fluid is nasty stuff. It will damage paint. Warnings on the can say it can damage your internal organs if absorbed through the skin. Take precautions to not get it on your skin and on your car: wear gloves, use rags, be careful, and wash your hands after doing brake fluid work. Always take used brake fluid to a proper recycling or disposal facility (many auto parts stores and auto service facilities will take used motor oil and brake fluid).

Porsche

The mystery is, what brake fluid does Porsche put in the car at the factory? It is reported to be Ate TYP 200. In any case, it does not matter, in this sense: a given Porsche dealer or independent mechanic may well use something different in their service bays, and unless you ask for the specific information you won't know for certain what is in your car. That's OK: the mechanic will certainly use a proper "DOT 4" fluid that works with the brake system. And it is OK to mix different brands of DOT 4 fluid in the system at the same time; you need not ensure that the entire system is completely flushed and filled with the same fluid. For street use, any DOT 4 standard fluid is fine. You can find various DOT 4 fluids at car parts stores. All other things being equal, the higher the rated "boiling point", the better, in principle.

("DOT 4" is a standard defined by the U.S. Department of Transportation that defines certain characteristics of the fluid for compatibility and performance.)

Ate

Ate ("AH-tay") makes two flavors of DOT 4 brake fluid that are very good and well suited to track use. As mentioned above, Ate TYP 200 is reportedly what Porsche puts in at the factory. Ate Super Blue Racing is blue-colored. Ate TYP 200 is almost clear, somewhat gold-colored, and is often refered to as "Ate Gold". The Ate Blue and Ate Gold are essentially the same fluid, but with a different color. When flushing the system, if you alternate between blue and gold, it's easier to see when you've flushed out all of the old stuff. Ate is not easy to find in car parts stores, but here are a couple of sources:

Parts Heaven. Located in Hayward, California. Online at <http://www.partsheaven.com/>

OG Racing. Located in Manassas, Virginia. Online at <https://www.ogracing.com/>

Motive. Located in Berkeley, California. Makers of the Motive PowerBleeder (see below). Online at <http://www.motiveproducts.com/>

Motul 600

I haven't used Motul but it comes highly recommended by those who do serious racing. On the plus side it has a higher boiling point than Ate. On the minus side it has less resistance to water absorbtion (it is more hygroscopic), so it's more suited to track usage where you're willing to commit to frequent flushing in order to keep it fresh. So compared to other types of fluid, if you leave it in the car too long, it will absorb water more quickly and that will lower the boiling point, defeating the whole point of using it in the first place. That's why it's probably a poor choice for street cars. Once source is Motive.

Bleeder Equipment

If you're going to bleed or flush your brakes, you need either an assistant or a little bit of special equipment. When bleeding or flushing, you need to open each of the two bleeder valves located on each caliper (one at a time). However, this can allow air into the brake lines, which is bad. With a helper, you have one person to open and close the valve and another to press and release the brake pedal, making sure that the pedal is released only when the valve is closed, so that releasing the pedal doesn't suck air in. You can avoid the need for a helper with a pressurized bleeder, or with special one-way bleeder screws. They're both quite inexpensive and handy.

Speed Bleeder Screws

From Speed Bleeder at <http://www.speedbleeder.com/>, these screws replace the stock bleeder screws. They have a "one-way check valve". When the screw is in the closed position, it is like a normal closed bleeder screw. When it is in the open position, it lets fluid out when you provide pedal pressure, like a normal bleeder screw, but won't let air in when you release the pedal, unlike a normal bleeder screw. Thus you can open the valve, go to the driver's seat, and pump the pedal several times to bleed fluid out of the valve, with the check valve preventing backflow of air into the system when you let the pedal up. I have these on my Boxster and I find them very handy. They're easy to install because you just remove the old screws and put in the new ones, and then do your first bleed. Speed Bleeder screws let you bleed your brakes with only an extra 10 minutes effort if you're already swapping your track and street wheels.

Part numbers:

Boxster bleeder screw: SB1010S (you need 8 screws, optionally one more if you want to also replace your master clutch cylinder bleeder screw, although I think I just read somewhere that the clutch bleeder screw is not replaceable)
Price: $7 per screw ($56 for a set)
I recommend also buying a piece of the surgical tubing they sell that fits the screws properly. I don't recommend using their fluid baggie because it's small and not very durable. Use a resealable plastic water or soda bottle instead.

Motive Power Bleeder System

From Motive Products at <http://www.motiveproducts.com/>, this system is a pressurized bottle that you fill with brake fluid, pump up, and then attach to the Boxster's fluid reservoir. You can then safely open a bleeder screw and fluid will exit due to the pressure, preventing backflow of air into the system, and without the need to even use the brake pedal to supply the pressure. Compared to Speed Bleeder screws, it seems to me that the Motive system has the following pros and cons. Pros: no need to walk back and forth from wheel to brake pedal to release the fluid, so you can eyeball the fluid as it comes out, no need to top up the reservoir after doing each wheel. Cons: it's a medium-sized piece of equipment you have to take with you to the track, and you have to fill it with enough fluid to complete the job rather than just topping up as much as necessary, thus potentially consuming and generating more used fluid that has to be recycled.

Price: from $45

Rotors

The Porsche OEM rotors are fine. However, there are alternatives in part source and treatment. Reportedly, the Porsche OEM rotors are made by Zimmerman, and Porsche adds a grey paint coat to the hats and fins to prevent surface rust. You can find the unpainted Zimmerman rotors as an aftermarket part, for considerably less. You might want to then spray paint the hats and fins yourself using something like Rustoleum.

Cryogenic Treatment

From Diversified Cryogenics at <http://www.frozenrotors.com>, where they take a rotor and put it through some kind of deep-freeze process (sorry for all the techno-jargon ;) ). The freezing process does something to the material that makes the rotor last longer and makes it less prone to fading and warping. It sounds like voodoo, but it really does work, especially with regard to a reduced rate of wear. Diversified Cryogenics will freeze rotors you ship to them, but they also have the OEM parts in stock and you may actually be able to get a set of frozen rotors from them cheaper than you can get the factory parts from Porsche. You can also get these frozen rotors from some parts catalogs such as Performance Products. The part numbers will vary, so specify your model and year. If I were buying a new set of rotors, I would buy them directly from Diversified Cryogenics, already frozen.

Personally, I think that frozen rotors and Pagid Orange pads are a great combination for performance and long life on cars that see a lot of track time.

Cross-Drilled or Cast-In Holes

Unlike the 2.5/2.7 Boxster rotors, the Boxster S rotors come with holes in them. The last word I saw was that these rotors use cast-in holes (not drilled) that are then finished off by drilling to counter-sink the edges.

In theory, the holes in the rotor have several purposes and benefits:

• More total surface area in contact with the air means improved cooling.
• Less unsprung weight, by a tiny amount.
• Better evacuation of water in the rain.
• Better evactuation of gasses from pad out-gassing.

Of course, there are also a couple of drawbacks:

• The edges of the holes have a "cheese grater" effect of wearing the pads more quickly.
• The holes can lead to uneven pad wear, which in turn can lead to uneven rotor wear.
• Cracks can develop around the holes.

Cast-in holes are supposedly superior to cross-drilled holes by reducing or eliminating cracking around the holes. With cast-in holes, there is no drilling because the rotor is formed with the holes simply part of its shape. This supposedly reduces the amount of cracking. However, you may see minor cracking even on stock Boxster S rotors. With cross-drilling, it seems in practice to be almost inevitable that cracks will develop around some of the holes over time. Minor surface cracking is not a problem. If the cracking gets bad enough, it can create an uneven surface, start wearing the pads more severely, and if it gets even worse, a crack can connect two holes and cause actual breakage. It is beneficial to "counter-sink" or "chamfer" the hole edges so that the hole is tapered inward.

Pros: better ventilation and cooling, therefore less fade. Cons: more likely to crack; the hole edges will be harsher on pads from a wear perspective (shorter pad life).

Slotting or Venting

Another common practice is to machine several angled slots in the rotor surface. The purpose is to provide a venting channel for out-gassing, almost as if the pad will push the gasses out along the slots under rotation. The slots can, however, have the same "cheese grater" effect on pads as holes do, making pads wear faster.

Pros: better out-gassing relief, therefore less fade. Cons: slot edges may be harsher on pads from a wear perspective (shorter pad life).

You can combine slotting and cross-drilling. Diversified Cryogenics will even sell you the entire package: slotted, drilled, frozen rotors. But again, for street driving there is probably little benefit to be had by drilling and slotting, and these do have downsides.

	Boxster	Boxster S
Porsche Left Front Rotor	986.351.401.xx	996.351.405.xx
Porsche Right Front Rotor	(same as left)	996.351.406.xx
Porsche Left Rear Rotor	986.352.401.xx	986.352.403.xx
Porsche Right Rear Rotor	(same as left)	(same as left)
Caliper Bolts (4)	999.067.041.09	999.067.041.09
Front Rotor Thickness	24mm new, 22mm worn	28mm new, 26mm worn
Rear Rotor Thickness	20mm new, 18mm worn	24mm new, 22mm worn

(The Boxster S front rotors are different left-to-right because the hole pattern is directional.)

Anti-Seize Paste

You only need anti-seize paste when replacing the rotors. However, it is useful for other things, and I find that putting a little bit on the brake pad retaining pin (see the section on pad replacement later) will make it easier to remove next time you have to change the pads. Other applications of anti-seize paste include lug bolts (you have to know where on the bolt you put the paste and where you must not put the paste).

Porsche's "Optimoly" anti-seize paste is about $25 for a toothpaste tube-sized container (part number 000.043.020.00). But you can get a comparable product at most auto parts stores for under $10.

Brake Lines

There is some debate on whether is it a good idea to install braided steel mesh brake lines. These replace the short rubber section of brake line that connects the inflexible metal brake lines affixed to the chassis to the caliper that travels up and down with the suspension. Braided steel brake lines are supposed to resist pressure deformation better than standard rubber brake lines (thus providing a firmer pedal feel), and provide better protection against damage from debris. However, there is the problem that the outer mesh will conceal any damage to or deterioration of the rubber line that it covers. Therefore, it may be better to install these brake lines only if you are committed to replacing them every 2 to 3 years before the rubber can have a chance to deteriorate.

About Tires

It should be noted that tires are more important than brakes in pure one-time stopping distance numbers. If you were to take two identical cars in a 60-to-0 braking test, equip Car A with Hoosier race tires and Toyota Corolla brakes, equip Car B with cheap street tires and Porsche Boxster brakes, Car A will stop in a shorter distance. Why? Because either brake system is perfectly capable of locking up the wheels once. What's left to affect the stopping distance is the ability of the tire to grip the pavement and slow the car down, and grippier tires will stop the car in a shorter distance.

So why do we want beefier braking systems? Because when we take the car to the track, or even down a mountain road, we need the brakes to continue to do the job corner after corner, lap after lap. That's where the most brake systems fall down, allowing excess heat to build up, leading to pad overheating, fluid boiling, and deteriorating braking power. If you were to take those same two cars from the above example to Laguna Seca and run 10 hard laps (20 minutes or so), you might find on lap 2 or 3 that the car with the inferior brakes would start to require dramatically longer braking distances as they withered under severe stress in the braking zone of turns 2, 8, and 11, while the Boxster brake system would make it through the session without much change in behavior. Beefier brakes dissipate heat better and don't have to work as hard to stop the car, and this means they are able to continue to do their job under harsh conditions for a much, much longer time. You may conclude from all of this that adding cross-drilled or slotted rotors, or "big red" Brembo brake kits, is probably a nice-looking waste of money on a car if it never sees the race track. Street driving simply does not put brakes under much duress.