Brake Rotors, Checking, Ceramic Brakes

WARNING: This page is about a different variant/trim than selected.

Special tools and workshop equipment required

Carbon-Ceramic Brake Wear Tester:VAS 6813 , not illustrated
Dial Indicator - 0-10mm:VAS 6079

Fig 1: Dial Gauge
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Dial Indicator Bracket:VAS 6079/1 , not illustrated

Cracks

Fig 2: Identifying Stress Cracks In Ceramic Brake Disc

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-- Check the friction surface of the ceramic brake rotor:

The friction surface on a new ceramic brake rotor already has stress cracks which occur during the production process. These stress cracks are all different.
Stress relief cracks do not mean the ceramic brake rotor is faulty.
The stress cracks are somewhat visible and can be different from each other in strength.

Wear, Measuring

For a quick measurement: respective wheel installed or removed, brake caliper installed.
For an exact measurement: respective wheel is removed, brake caliper is detached and placed at least 50mm away from the brake rotor.
Brake rotor temperature between 0 and 40 °C (32 and 104 °F) when measuring.

Tip

Attention, when doing the quick measurement: the metal shield lowers the measured value.

-- Check and calibrate the Carbon-Ceramic Brake Wear Tester: VAS 6813 , if necessary refer to Operating Instructions.

The measurement device measures the damage to the carbon fiber reinforced material of the brake rotor. Due to temperature effects, carbon fibers of the inner structure of the brake rotor are damaged increasingly and the wear value lowers.

-- Measure the brake rotor at three locations -B-, 120° apart from each other, shown for measuring point "3" as an example.

Fig 3: Wear Indicator A Through D

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-- Position the Carbon-Ceramic Brake Wear Tester:VAS 6813 -2- with the roll-stops and the bottom, flat to the measuring point "1" of the brake rotor -1- -arrows-.

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-- Move the Carbon-Ceramic Brake Wear Tester:VAS 6813 along the outer edge -2- of the brake rotor until the laser beam points precisely at the -D- marking on the brake rotor.

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-- Read the measured value and note it down.

Fig 4: Wear Indicator A Through D

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-- Repeat the measurement at the measuring points "2" and "3".

-- Compare the measured values with the wear value -C- shown here as an example.

If a measured value is below the wear value -C- specified on the brake rotor: replace the corresponding brake rotor.

Chips/Broken-Off Pieces, Evaluating

Fig 5: Identifying Nicks Or Material Break Down On Friction Surface

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-- Check the friction surface on the ceramic brake rotor for any chipping and/or broken-off pieces.

Multiple chips/broken-off pieces -arrow- on a friction surface are permitted.
If there are any individual chips/broken-off pieces -arrow- larger than 1 cm² , replace the brake pad.

Edge Damage, Evaluating

Fig 6: Chips On Edge Of Brake Disc Are Caused By Mechanical Damage

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-- Check the ceramic brake rotor for damage to the edges.

Maximum permitted width/depth = 2 mm.
Maximum permitted length = 10 mm.
Maximum three edge damages.

Surface Changes

-- Check the friction surface of the ceramic brake rotor for topping application.

If a pad transfer layer is determined, then check the following:

-- Check the air routing to the brake rotor for completeness, correct securing and damage.

-- Check the brake pad quality.

-- Check the perforation holes for debris.

Clean the holes with a high pressure cleaner. Pay attention to the environmental and safety precautions.
Never work on the holes mechanically.

Brake Rotor Lateral Run-Out, Measuring

-- Only perform the measurement of the brake rotor lateral run-out, if the following conditions are met:

There are vibrations when braking.
Brake rotors are without damage
Wheels and tires are OK and balanced.

-- Tighten the brake rotor with five underlying wheel bolts or five other suitable bolts to the wheel hub. Tightening specification. Refer to WHEEL, CHANGING .

The completely installed bolts must not touch the wheel bearing housing behind!

-- Clean dirt and rust off the brake rotor.

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-- Mount the Dial Indicator Bracket:VAS 6079/1 -item 2- at a suitable location on the wheel bearing housing.

-- Mount the Dial Indicator - 0-10mm:VAS 6079 -item 1- with slight pretension and measure the lateral run-out at the dimension -a- from the outer edge of the brake rotor.

Dimension -a- = 10 mm

-- When measuring, slowly turn the brake rotor via the threaded connection on the drive axle outer joint either by hand or using a hand ratchet.

If the lateral run-out of the brake rotor is less than 0.06 mm: the brake rotor is OK.
If the lateral run-out of the brake rotor is greater than 0.06 mm: measure the lateral run-out of the wheel hub.

Wheel Hub Lateral Run-Out, Measuring

-- Remove the front brake rotor. Refer to BRAKE ROTOR, REMOVING AND INSTALLING, CERAMIC BRAKES .

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-- Mount the Dial Indicator Bracket:VAS 6079/1 -item 2- at a suitable location on the wheel bearing housing.

-- Mount the Dial Indicator - 0-10mm:VAS 6079 -item 1- with slight pretension and measure the lateral run-out at the dimension -a- under the holes for the wheel hub.

Dimension -a- = 5 mm

-- When measuring, slowly turn the wheel hub via the threaded connection on the drive axle outer joint either by hand or using a hand ratchet.

If the lateral run-out of the wheel hub is greater than 0.02 mm: replace the wheel hub.
If the lateral run-out of the wheel hub is less than 0.02 mm: replace the respective brake rotor.