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Pelican Technical Article:

Brake Pads and Rotor Checking

Kerry Jonsson

Time:

1 hour1 hr

Tab:

$1

Talent:

***

Tools:

Brake pad thickness tool, micrometer, dial gauge with mount

Applicable Models:

Mercedes-Benz R129 (1990-98)

Hot Tip:

Clean the area with brake clean and measure in a few spots

Performance Gain:

Determine what brake work needs to be done

Complementary Modification:

Flush the brake system at the same time
As you drive your car you entire brake system gets a workout. This is the most important safety system on your car. Think about how many times you step on your brake pedal to get the car stopped. Brake components wear out over time and the more driving you do the more you have to maintain your brake system. How will you know when you should replace components? Mercedes Benz does have brake pad wear sensors in their cars to warn the driver the brake pads are low. There is no warning for the brake rotors. Brake rotors are hardened on the outside and have a softer core to help dissipate heat. If you let a brake rotor get too thin it can lead to rotor failure. Also if you feel a pulsation in the brake pedal or a vibration in the steering wheel under braking you may have warped brake rotors. Manufacturers do have component replacement specifications that can be checked with a few tools. In this tech article we will go over all the steps to check your brake pads and brake rotor specification.

Front Rotors Minimum Thickness 28mm (1.10in)
Rear Rotors Minimum Thickness 7.6mm (.300in)

    In order to check these brake components you should lift and support your vehicle. See our tech article on jacking up and supporting your vehicle. If you discover your brake pads or rotors need replacing see our tech articles on replacing your brake pads and brake rotors.
Using a commercially available micrometer measure the brake rotor thickness.
Figure 1

Using a commercially available micrometer measure the brake rotor thickness. Turn the hand dial in until both sides are flush with the brake rotor surface. You will probably not be able to remove the tool to see your measurement because there is probably an outer lip to your brake rotor from wear. You will have to look at the measurement with the micrometer in place.

Measure the brake rotor thickness in at least 10 different places to get a good idea of the overall thickness of the rotor.
Figure 2

Measure the brake rotor thickness in at least 10 different places to get a good idea of the overall thickness of the rotor. You can rotate the rotor to get access to more spots. Mark the places that you have measured with a marker so you do not duplicate measurements.

Working at the top of the caliper use a commercially available brake pad thickness tool (green arrow) to measure brake pad thickness.
Figure 3

Working at the top of the caliper use a commercially available brake pad thickness tool (green arrow) to measure brake pad thickness. This is the BMW factory tool but the Mercedes Benz tool is similar in design. Put the Red edge of the tool up to the back of the brake pad and the pin of the tool up against the brake rotor.

When you look at the tool you will see how much depth was measured by looking at the location of the plastic slide.
Figure 4

When you look at the tool you will see how much depth was measured by looking at the location of the plastic slide. Use the line in the middle of the plastic slide as you measuring point. Replace your brake pads when they are under 3mm to prevent damage to the brake rotors. Keep in mind this is a dual opposed piston designed caliper. You will not be able to quickly check the depth of the inner pad. Our tool assumes both pads are floating freely and wearing evenly, which they should due to the design of the caliper.

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