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Checking Brake Rotor Thickness
 
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Pelican Technical Article:

Checking Brake Rotor Thickness

Kerry Jonsson

Time:

30 minutes30 mins

Tab:

$0

Talent:

*

Tools:

Micrometer

Applicable Models:

Mercedes-Benz W211 (2003-09)

Parts Required:

Wheels

Hot Tip:

Measure in a few spots around the caliper

Performance Gain:

Verify they need to be replaced

Complementary Modification:

Bleed brakes at the same time

When you step on your brake pedal you are really pushing a piston in a hydraulic system. This compresses the brake fluid and forces it through the brake lines to the caliper. The caliper pistons then act on the brake pads and the brake pads rub up against the rotors. This action creates friction that slows down the brake rotor and therefore slows down the wheel. This friction between the brake pad and rotor causes both components to wear out. Brake pads are made of a softer fiction material and wear out faster. Brake rotors have high iron content to dissipate the heat from the friction so they last longer. When you have your wheels off you should check the brake pad and brake rotor thickness to determine if they need to be replaced. If the car undergoes spirited driving the brake rotors can overheat causing them to warp. Also, if a brake rotor becomes too thin it can fail and come apart causing brake system failure. In this tech article we will go over checking the replacement specifications of the brake pads and rotors.

Front Brake Rotor

Minimum Thickness 25.4mm (1.00in)

Rear Brake Rotor

Minimum Thickness 8.3mm (.300in)


In order to check your brake rotors and brake pads you will need to lift and support your vehicle. See our tech article on jacking up and supporting your vehicle.

Using a micrometer fit it over the brake rotor and rotate the dial adjuster until the two measuring surfaces are flush with the brake rotor.
Figure 1

Using a micrometer fit it over the brake rotor and rotate the dial adjuster until the two measuring surfaces are flush with the brake rotor.

Measure the brake rotor thickness in at least 10 spots around the rotor.
Figure 2

Measure the brake rotor thickness in at least 10 spots around the rotor. Use a marker to mark the measurement to make sure you are not duplicating measurements.

Using a depth measurement tool seat the red ring of the tool on the back of the brake pad at the exposed pad in the caliper.
Figure 3

Using a depth measurement tool seat the red ring of the tool on the back of the brake pad at the exposed pad in the caliper. Push on the back of the tool until the plunger rests on the brake rotor. A clear plastic ring will record where the depth was set to. This is the factory BMW tool but the Mercedes Benz factory tool is similar.

Looking at the depth measurement tool we see the clear plastic ring has recorded the depth measurement.
Figure 4

Looking at the depth measurement tool we see the clear plastic ring has recorded the depth measurement. These pads are getting close to needing replacement. Mercedes Benz uses a single piston caliper on the 211 non-AMG models. You cannot measure the inside pad with this tool. This tool assumes the brake caliper is floating properly on its pins and providing even brake force distribution. Look inside the inspection hole of the caliper to verify the same thickness of both brake pads.

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Comments and Suggestions:
Barndoggy Comments: I'm confused by the minimum thickness of the rear discs stated here. The rear discs on my 2005 E320 4Matic Wagon are vented, so it's impossible for them to be as thin as 8.3mm. They'd have to be nearly as thick as the fronts, at 25.4mm. Am I missing something? Thanks!
June 7, 2016
  Followup from the Pelican Staff: That info was for the subject vehicle model.

There other options available.

for example, one at 19.4 and one at 24. - Nick at Pelican Parts
 
Amateur mech. Comments: I don't see the Min. Thickness of front and rear brakes rotors ?
December 5, 2015
  Followup from the Pelican Staff: There is a table in the article body with that info. - Nick at Pelican Parts  

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