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Loosen the lug nuts on each wheel while the weight of the
car is on the wheels. The lug nuts are usually torqued very high, and
impact guns may not loosen the nuts. |
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Jack the car up and place jack stands in place. NEVER
work under a car supported by a floor jack...always use a good pair of
jack stands.
Place the stands under the rubber bumpers to prevent
damage to the under body.
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Remove the lug nuts and wheels. |
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Drive out the two retaining pins using a small diameter
punch. Another safety note, always wear safety glasses when hammering on
metal.
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You may need to use a metal dowel rod to drive the
retaining pins out completely. The punch will only go in so far due to
it's shape. |
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Clean off any corrosion on the retaining pins using a wire
wheel brush. |
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Also, if the ends of the pins are dented and dinged, put a
nice flat face on them using a bench grinder. Don't over do it, just
enough to make the end flat. This will help you get them out easier the
next time you do the brakes. |
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Unplug the wear sensor from its receptacle. Note in this
photo that there was only one wear sensor on my car. In a correctly
rebuilt system, each brake pad has its own wear sensor. |
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Remove the spring clip from between the pads |
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Pry each pad out from the caliper using a Philips
screwdriver. Select one that fits into the holes of the pads. Work each
side out a little at a time. |
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Continue until you are able to pull the pad out. |
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Quite a difference between old and new pad thickness.
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If you need to have your rotors cut (machined), continue
with these steps. If you see deep grooves, or a wavy surface on either
face of the rotor, you should have it cut. If the rotor looks flat,
smooth, and no gouges, you may be able to leave it as is.
Personally, I always have my rotors cut when changing
pads. I like to start off with a flat, even rotor.
Minimum allowable rotor thickness for cutting is 28
mm.
Absolute minimum thickness is 27.4 mm
New thickness is 30mm.
Cut a length of wire about three feet long, and string
it through the top of the spring, and then into the caliper. You will need
the wire to support the caliper when it comes off.
Remove the two 19 mm bolts from the back of the caliper.
They are on very tight. You will probably need that breaker bar to loosen
these bolts. |
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Remove the caliper from the spindle, and tighten the wire
to support the caliper's weight. NEVER let a caliper hang by the brake
line. It could be damaged.
Now is a good time to clean off all the dust. Remember
this dust is harmful! Do not inhale it! This is especially true if you use
compressed air to blow it off...it'll go everywhere.
Also, DO NOT step on the brakes until the calipers are
back on. The pistons could pop out of the caliper, and then you really
have a mess on your hands.
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Here is a close-up of the pistons in the caliper. These are
4 piston calipers, 2 on each side. The metal discs are heat shields to
protect the rubber boots around the pistons from the heat created by
stopping.
Make sure there is no brake fluid leaking out anywhere.
These pistons should be completely dry. If you see oil, there is a leak
somewhere. Time to rebuild or replace the caliper.
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To remove the rotor, remove the 5 mm fastener as shown.
This fastener holds it onto the hub.
Again, although my rotors looked pretty good, I always
like to have them cut.
Once I removed the left side pads, I saw that one of the
pads wore in a tapered manner. Measuring the rotor across its face showed
that it was also tapered. Definitely needs resurfacing.
One of my rotors was extremely stubborn coming off. I
had to use penetrating oil, and with a good piece of wood against the back
of the rotor, hit the wood with a ball peen hammer to drive the rotor off
the hub. I don't like to do this, as I've heard sharp strong impacts can
damage the sensors on the spindle. Sometimes though, you need to do what
you have to get the job done. We'll see what happens when I get it all
back together. |
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New disc thickness = 30 mm
Wear Limit (minimum thickness) = 27.4 mm
The wear limit is also stamped on the rotor. |
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While you're at this level of detail, it would be good to
check the hub bearings.
Pry the cap off with a flat blade screwdriver. Work it a
little bit out, then move to a new spot and work some more. Repeat this
until you can remove the cap. |
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Whoa! First time I've seen MB wheel bearing grease...very
pretty!
Spin the hub, and feel for any grittiness, grinding, or
stiff spots. If you feel any of this, pull the bearing out, clean it
thoroughly, and inspect for damage or wear. Replace and repack if
necessary.
Mine felt fine. I used a bit of the clean excess in the
cap, and forced it into the bearing. |
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Make sure there is no loose rust on the cap, and gently tap
it back in place using the rubber-face hammer.
My cap had dings in it from someone using a metal
hammer. |
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Next, we need to retract the pistons into the caliper
housing.
As brake pads get thinner, the pistons that push the
pads against the rotors move farther out of the caliper. The new pads are
obviously much thicker than the old ones. We would never get them back in
place if the pistons aren't pushed back.
First though, you will need to
siphon some brake fluid out of the master cylinder reservoir. Remove the
cap and the strainer in the mouth of the reservoir.
Use a clean
turkey baster to pull out some of the fluid. Keep the reservoir cap off
for now. If you don't do this, the next step will cause brake fluid to
spill out of the reservoir.
It's a little tricky, because when one piston is pushed
in, the others want to pop out. You need to do this slowly and cautiously.
If a piston pops out of the caliper, it'll be a mess.
I use a Channelock pliers to push the pistons back. Be
careful not to squeeze the heat shields, they're very delicate. |
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Once I got two of the pistons somewhat pushed back in, I
used a thin piece of wood and a clamp to keep them seated while I worked
on the other two pistons.
Be careful not to crush any lines or hoses. |
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Place the freshly cut rotor back onto
the hub.
Put a drop of Loctite onto the rotor retaining fastener.
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Line up the holes in the rotor and hub, and install
retaining fastener.
Tighten snugly.
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The rotor installed. Notice the surface finish. This is
what you want to see on your rotors.
Notice that I wrote my name on the rotors, as well as
which side the rotor is. I like to have identifying marks on the rotors to
prevent the machine shop from giving them to the wrong person.
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Carefully cut the wire supporting the caliper, and assemble
the caliper back onto the spindle.
Place a good sized drop of Loctite onto each caliper
bolt, and assemble the bolts through the caliper into the spindle.
Torque amount is unknown, but I can tell you it was
pretty tight. I will try to find this info. |
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If your replacement pads have a peripheral pad (a) on them
as shown in the left diagram, do not use any anti-squeal paste. This is
per MB's instructions. Anti-squeal paste should only be used on pads
without the backing pad, as shown in the right diagram.
Update
8/30/05!
After completing this project, the front brakes are squealing a bit in
slow stops. I should have put on the anti-squeal paste after all. I will
find out where to apply the paste, and update this page soon.
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Note how the metal pads (c in the diagram above left) must
be oriented. The wide ear of the pad should line up with the wide ear on
the brake pad. |
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Insert the brake pad and the peripheral pad into the
caliper. Repeat for the other brake pad. |
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Drive one of the retaining pins through the caliper, brake
and peripheral pads as shown.
Assemble the spring clip under the retaining pin as
shown. |
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Install the other retaining pin while pushing down on the
spring clip. |
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The retaining pin must trap the spring clip as shown. |
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Install the pad wear sensor.
Note that it is possible to have one, two, or four
sensors in your application. Whatever you have, keep it that way, and
install the new sensors in exactly the same pad(s) and plugs.
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Make sure the sensor is seated squarely in the hole in the
brake pad. Carefully push the plug into the connector. Don't wiggle it too
much back and forth as the plug may break. |
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My car had only one sensor on each front caliper. Repair
literature states there should be one sensor for each pad. The connector
sockets for the wear sensors had one socket capped, and I could not remove
the cap. Rather than break something, I decided to install only the one
new sensor as I found it.
Assuming both inner and outer pads wear at the same rate
(not necessarily a safe assumption), one wear sensor could be enough. I
never let my brakes go that long, so I'm not all that worried about it. I
am also pretty sure that the next brake job will require new rotors, as
these are near their lower limit for thickness. |
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Give everything a good visual review. If it all looks good,
get in the car, and slowly push the brake pedal down. The car does not
need to be running. You will notice that the pedal goes down very far, in
fact it will probably go down all the way. Don't let it go that far
though, stop before it bottoms out. Release the pedal, and push down
again. Repeat this cycle until the pedal stops at the normal height.
Check the brake fluid level in the master cylinder
reservoir. Make sure it is between the MIN and MAX markings. Use only DOT
4 or higher brake fluid. Put the strainer and cap back on snugly.
This is an important step. The brakes will not stop the
car until the pistons push the pads into contact with the rotor. NEVER
drive the car until you've done this important step. Get out of the car,
and look everything over again. If there are no signs of leaks and
everything looks good, mount the wheels onto the car. Tighten the lug
nuts, and lower the car.
Start the car, and test the brakes BEFORE you put it in
drive to make sure they are functioning. If it feels good, give it a test
spin. Follow your brake pad manufacturers guide to breaking in the pads.
Different types of pads need different methods of break in.
Congratulations! Your brakes are done. |
