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Rear Brake Rotor or Disc Replacement
 
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Pelican Technical Article:

Rear Brake Rotor or Disc Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$60 to $150

Talent:

**

Tools:

Rubber hammer

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Rotors

Hot Tip:

Clean the hub face

Performance Gain:

Car stops better

Complementary Modification:

Bleed brake system

Other than physical damage, there are basically two ways your rotors can go bad on your Mercedes. The first way is they just wear out. All rotors have a minimum wear thickness on them (that is usually stamped on the rotor) and once they get below this thickness they need to be replaced. If you are going to measure the thickness of the rotors make sure to measure in several places as rotor can wear unevenly. The second way they go bad is by warping. If you are feeling a pulsing in the brake pedal when braking and it is proportionate to the speed of the vehicle, you probably have a warped rotor. This is usually caused by hot spotting the rotor by late braking then keeping the pad fully depressed on the rotor while stopped. Rotors can also get heavily grooved and this can also be a cause to replace them.

When replacing your rotors, it is always a good idea to replace them in pairs. You should also replace the brake pads as well--especially if the rotor was heavily grooved. You want to start with two flat surfaces (the rotor and pad) rubbing against each other when seating the new brakes. This will lead to better brake performance and eventually longer life from the components.

This is also a good time to give the system a good bleed and get all of the braking system "like new" again.

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

You will need to remove the brake caliper to replace the rotor so please see our article on replacing your rear brake calipers for additional assistance.
Figure 1

You will need to remove the brake caliper to replace the rotor so please see our article on replacing your rear brake calipers for additional assistance.

The rotor is held to the hub by the clamping force of the wheel lugs.
Figure 2

The rotor is held to the hub by the clamping force of the wheel lugs. There is a single locating pin (red arrow) on the hub that the rotor sits on and this pin is only for helping keep the rotor in the right position so the lugs line up.

There is a good chance if the rotor has been on for any length of time that it will be rusted and corroded onto the hub.
Figure 3

There is a good chance if the rotor has been on for any length of time that it will be rusted and corroded onto the hub. First make sure the parking brake is off and try and remove the rotor by hand. It is heavy so be prepared for it when removing. If you cannot get the rotor off by hand you will need to hit it with a rubber mallet to free it up from the hub. Once it "let's go" make sure it doesn't fall off.

Before installing the new rotor this is a good time to check the condition of the parking brake shoes (red arrow) and mechanism.
Figure 4

Before installing the new rotor this is a good time to check the condition of the parking brake shoes (red arrow) and mechanism.

Make sure to clean the mounting surface of the hub to give a good clean flat mounting surface.
Figure 5

Make sure to clean the mounting surface of the hub to give a good clean flat mounting surface. Installation is the reverse of removal and now is also a good time to adjust the parking brake; please see our article on parking brake adjustment.

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