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Rear Brake Pad Replacement
 
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Pelican Technical Article:

Rear Brake Pad Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$18 to $50

Talent:

**

Tools:

Punch, hammer, pliers, flathead screwdriver

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

New pads

Hot Tip:

Clean the caliper mounting surfaces

Performance Gain:

Car stops better

Complementary Modification:

Replace Rotor or disk

In general, you should inspect your brake pads about every 25,000 miles or once a year, whichever is less. You should replace them if the material lining of the pad is worn down to less than a quarter inch of material on the pad. In reality, most people don't inspect their pads very often, and usually wait until they see the little brake-warning lamp appear on the dashboard which will not help you on the W123 because there is no brake pad wear sensor on the rear!

If you let the pads wear down enough, you will get to the point of metal on metal contact where the metal backing of the pads are contacting the brake discs. Using the brakes during this condition will not only give you very dangerous and inadequate braking, but will also begin to wear grooves in your brake discs. Once the discs are grooved, they are damaged and if you have drilled or slotted rotors there is no way to repair them. The smart thing to do is to avoid this problem and replace them at the correct times.

Safely jack up and support the rear of the vehicle and remove the rear wheels. Please see our article on safely lifting and supporting your Mercedes W123.

Brake pads should always be replaced in pairs. If you have not bled your brakes in a while this is a good time to give them a good bleed and get fresh fluid in the system. Please see our article on bleeding your brakes.

The rear brakes on the W123 are a dual piston caliper and both pads (red arrows) can be replaced without removing the caliper.
Figure 1

The rear brakes on the W123 are a dual piston caliper and both pads (red arrows) can be replaced without removing the caliper.

Use the appropriate sized punch and tap out the retaining pins (red arrows).
Figure 2

Use the appropriate sized punch and tap out the retaining pins (red arrows). If you don't have a punch you can use a small screwdriver in a pinch.

The retaining pins will probably be covered in brake dust so make sure to clean them before reinstalling.
Figure 3

The retaining pins will probably be covered in brake dust so make sure to clean them before reinstalling.

Keep pressure on the retaining spring while removing the pins and then remove the spring.
Figure 4

Keep pressure on the retaining spring while removing the pins and then remove the spring.

Depending on how worn your rotors and pads are you will need to compress the pistons back into the caliper.
Figure 5

Depending on how worn your rotors and pads are you will need to compress the pistons back into the caliper. Use a large set of pliers or channel locks and squeeze the pads and the flat area of the caliper (red arrows).

While you are pushing the piston back in you will be forcing brake fluid back into the system and up into the reservoir.
Figure 6

While you are pushing the piston back in you will be forcing brake fluid back into the system and up into the reservoir. Make sure to check the fluid level (red arrow) in the reservoir as you do this and be prepared to remove some fluid as needed.

Use a flathead screwdriver and pry the pads out from the caliper; if they have anti squeal pads on the back they will stick in there pretty good.
Figure 7

Use a flathead screwdriver and pry the pads out from the caliper; if they have anti squeal pads on the back they will stick in there pretty good.

You will need to push the piston all the way back into the caliper to install new pads so before you remove the old pad use the pliers to compress the pistons all the way in remembering to check the level of fluid in the reservoir.
Figure 8

You will need to push the piston all the way back into the caliper to install new pads so before you remove the old pad use the pliers to compress the pistons all the way in remembering to check the level of fluid in the reservoir. You also want to clean up the area where the pads rest against the caliper (red arrows), this area gets a lot of brake dust on it and that can lead to squealing brakes. Inspect the rubber dust boots (yellow arrow) around the pistons for any damage to them or leaking fluid, if you find any it is time for a caliper rebuild or replacement

While this pad has plenty of life still on it, if the pad gets below a quarter of an inch of material change it right away.
Figure 9

While this pad has plenty of life still on it, if the pad gets below a quarter of an inch of material change it right away. Installation is the reverse of removal and don't forget to pump the brakes a few time before you drive to move the pads into position.

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