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changer ses plaquettes

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(Click on any photo to get a large version of it.)

Figure A. Major brake parts, colorized.

  • Red: cotter pin
  • Yellow: retaining pin
  • Dull Green: spring clip
  • Blue: brake pad (backing plate)
  • Light Blue: brake pad (material, not much left here)
  • Orange: rotor where it's in the caliper
  • Bright Green: outer bleeder screw (inside screw is just out of frame top)
  • Light Purple: caliper bolts
  • Dark Purple: rotor placement screw (between lug bolt holes on rotor hat)

Note that in these pictures there are no wear sensors attached. If you have wear sensors attached, you have to orient the spring clip such that the little hook that guides the wire leading to the outside sensor (shown here on the bottom edge) is on the end (above or below the retaining pin) where the guide slot on the caliper is located. This varies from corner to corner on the car, because the same caliper part gets mounted in a different orientation. These pictures are of the left front corner of the car, so the guide slot is above the retaining pin (just above the cotter pin), so the hook would be on the top side--the spring clip therefore would be reversed from what you see here. (Since the wear sensors are not installed in these pictures, the orientation of the spring clip does not matter, and I just happened to put the spring clip in "upside down".) Don't worry, when you have the sensor wires, it will be obvious what to do.

1. Using pliers (needlenose work best), remove the cotter pin that holds the big retaining pin in place. See figures B and C, with the cotter pin colorized red. The pin is small, so keep track of it!

Figure B. The cotter pin, highlighted in red.

Figure C. Removing the cotter pin.

2. You may notice that in the above pictures, there is no wear sensor harness. That's because I've stopped using the wear sensors. If you still have your wear sensors installed, you'll need to detach them from the old brake pads. The outer one will come out first. The inner one probably doesn't have enough slack to pull out until after you've removed the retaining pin in Step 3 below. See figures D and E, two older photos from my first pad change, with the sensors in the pads colorized red. These two photos are from the opposite wheel, so they're reversed from the other photos here. Tweezers work best to press the friction tabs and pop them out (if you have needlenose pliers with a small, sharp tip, they might work). You can either leave the wire hooked under the tab in the spring clip, or detach it.
Note again that these two pictures are from the right front wheel, so the sensor wire guide slot is below the retaining pin. You can see the sensor wiring harness feeding through the guide slot in the caliper in the first picture below. Thus the spring clip is oriented with its guide hook on the lower half.
Howard Graff points out that if you find it impossible to remove the wear sensor from the brake pad, you can simply take the nearest tool, throw it across the room, and swear loudly.

Figure D. Outside pad's wear sensor, colorized red.

Figure E. Inside pad's wear sensor, colorized red.

3. While pushing down on the spring clip, slide out the big retaining pin towards the inside. See figures F and G. If you've previously used a little bit of anti-seize paste on the contact areas of the pin when installing it, it should slide out easily by hand while you're pressing down on the spring clip. If not, you will probably need to tap it out with a hammer and a nail punch or some other small bolt.

Figure F. Sliding out the retaining pin. One hand is pushing down (toward the center of the wheel hub) on the spring clip, while the other is pulling the retaining pin out towards the inside of the caliper.

Figure G. Removing the spring clip and sliding the retaining pin the rest of the way out.

* Boxster S Note:

Some Boxster S brake pads come with "vibration dampers" that quiet the brakes by dampening the vibrations that would otherwise result in a squealing sound. One type of damper consists of little weights near the top of the pad; this does not affect your ability to proceed to Step 4.

However, another type of damper consists of a thin plate glued to the brake pad backing plate, and two nubs that make contact with the pistons either with a friction fit or a sticky substance. This prevents you from simply lifting the pad out as you would normally do in the next, because the pad is attached (by friction or goo) to the pistons.

If you have the glued-on backing plate dampers, you need to remove them before you can lift the pads out. You can do this at this point in the process, using a putty knife or x-acto knife to separate the thin vibration damper plate from the old brake pad's backing plate. Or, if you are going to have to remove the caliper anyway (for example, if you're doing rotors in addition to pads) you may find it easier to remove the caliper first [ Changing Brake Rotors ] and then you'll be able to remove the pads by popping the friction fit thing out of the piston; this leaves the damper still attached to the pad, which you can cut away and transfer to the new pad if you're replacing the pad.
4. Now the pads are free and clear. You can just lift them out. However, if you are going to immediately put the new pads in, you'll need to compress the pistons to make room for the new thicker pads. The easiest way to do this is use the old pads to push the pistons back into the caliper. A simple technique I use is to simply stick a screwdriver or other prying device into the retaining pin hole in the pad backing plate, and pry the pad, as in figure H, to squeeze the pad back against the pistons. The point of this is to push the pistons back into the caliper so that the newer, thicker pads have room to slip into place where there is currently only room for a worn, thinner pad. Alternatively, you can buy a "pad spreader" for about $10 at an auto parts store (I saw one at Sears) that inserts between the pads and works like a reverse vise. You could also use pliers to grab the backing plate and caliper where the retaining pin holes line up, and squeeze them together, using a rag to protect the caliper surface from getting scratched up.

Figure H. Compressing the pistons by prying.

Regarding step 5. Compressing the pistons is easier if you can open the bleeder valve to relieve pressure. See figure J. Otherwise, by compressing the pistons you are pushing back into the fluid system and actually raising the level in the reservoir, and there is a lot of resistance. You won't overflow the reservoir if you do it this way one wheel at a time, and press the brake pedal after doing each wheel, but you should keep an eye on it. This is a situation where the Speed Bleeder screws are nice: you can just open the valve, running the tube to your used fluid bottle, easily compress the pistons, and then close the valve. (It's not clear to me whether doing this with the standard bleeder screws could allow some air in.) Of course, you need to attach a bleeder hose to the bleeder screw; see the section on [ Bleeding and Flushing ] for that info. Don't worry about it on your first pad change--leave the bleeder screw alone.

Figure J. Opening the bleeder screw 1/4 turn.

If you are diligent about checking your brake pad wear (easy if you go to the track often and have the wheels off often, or are willing to assume the unseen inner pad is worn similarly to the visible outer pad), you might consider removing the outer wear sensor wire from the spring clip, and then using zip ties to move all the wear sensor cabling out of the way semi-permanently. Removing, re-inserting, and maintaining the wear sensors becomes more hassle than they are worth, if you don't need them to alert you to the condition of your brake pads. In addition, some aftermarket pads (Pagid, for instance) don't have the holes in which to insert the sensors, so if you're using such pads you'll definitely need to do this.
If you are going to install new rotors, jump ahead to [ Changing Brake Rotors ] and then come back here to finish up.

Installing the New Pads

1. If you've already compressed the pistons, the new pads simply drop right into place. If the fit is too tight, it means the pistons are not compressed enough. In this case, repeat Step 5 above to compress the pistons. As noted above, compressing the pistons is easier if you can open the bleeder valve to let the fluid out. Drop the new pads into place, as in figures K and L.

Figure K. Dropping a new brake pad into place. That is a brand new Pagid Orange pad; it's not colorized! The color permanently disappears once the pads heat up.

Figure L. New pads in place.

2. Porsche recommends replacing the retaining pin, spring clip, and cotter pin. Put a little bit of anti-seize paste on the retaining pin. This will make it easier to slide out next time. See figure M.

Figure M. Anti-seize paste on the retaining pin.

3. While holding the spring clip in its proper position and pressing it down against the edge of the pads and rotor, slide the retaining pin back in. Line the cotter pin hole up facing out so you can easily see where the cotter pin will go.
4. Put the cotter pin back.
5. If you're using the wear sensors, slide the each one down into its hole in the new pad, and the slot in the backing plate. If you're not using the wear sensors, make sure they are zip-tied out the way behind the hub.
6. If you previously opened the bleeder screw, close it.
7. Step on the brake pedal to seat the pads and level the reservoir. By doing so, when you compress the pistons on the next corner of the car, you won't cause the reservoir to overflow. Now the pad change is complete. See figure N.

Figure N. Pad change complete. (Wear sensors tied out of the way.)

Now is also a convenient time to bleed the brake fluid at this corner of the car, or to do this corner's part of a complete flush. See [ Bleeding and Flushing ] and then come back here to finish up.

Replacing the Wheel

Lift the wheel back into place and rotate it so that the lug bolt holes align. To do this on the front wheels, which turn freely, you'll have to hold the rotor still with one hand while you rotate the wheel with the other. Put the lug bolts back in and hand-tighten them with the 19mm socket. (You won't be able to torque them with the wheel spinning freely in the air.) An air gun or power drill fitted with a 19mm socket may make this step faster, but I am worried about cross-threading the bolts, so I always hand-tighten the bolts first.

Lowering the Car

Slowly lower the car down on the jack. Remember, if you use the rear jacking point, you only have to jack the car up twice to do all four wheels.

Torquing the Lug Bolts

I list this as a separate item because it is so important and so easy to forget. After lowering the car to the ground, you must torque the lug bolts to 96 ft-lbs. Find a routine that ensures that you'll either do this immediately after lowering one side of the car, or one individual wheel, or whatever. If you forget to torque the lug bolts, you'll heard sleigh-bell noises (rattling bolts, actually) as soon as you turn the wheel or exceed a walking pace, and if you keep driving the bolts may work their way out and wheel will come off. That would be undesirable.

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