34 21 947 Precision-turning both rear brake discs on both sides

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IMPORTANT: Always precision-turn both sides of both brake discs on one axle.

Observe Max. machining dimension per friction ring side, see 34 21 REAR BRAKE DISCS E83 .

New brake linings may only be installed if the brake disc thickness is greater than or equal to the minimum brake disc thickness (MIN TH), see 34 21 REAR BRAKE DISCS E83 .

Brake discs of M models (Compound brake discs) must not be machined!

Only one brake pad set may be used up on brake discs which have been lathe-turned to minimum thickness (MIN TH), see 34 21 REAR BRAKE DISCS E83 .

Stationary brake disc lathe:

In the case of stationary brake disc lathes, the brake disc must be removed, see 34 11 220 Removing and installing/replacing both front brake discs .

Please refer to the lathe manufacturer's instruction manual for the exact procedure.

IMPORTANT: Only BMW-approved brake disc lathes may be used!

Fig 1: Stationary Brake Disc Lathe

Courtesy of BMW OF NORTH AMERICA, INC.

Mobile brake disc lathe:

In the case of mobile brake disc lathes, only the brake caliper has must be removed, see 34 21 745 Removing and installing/replacing left or right rear brake caliper .

The brake discs remain on the car.

Please refer to the lathe manufacturer's instruction manual for the exact procedure.

IMPORTANT: Only BMW-approved brake disc lathes may be used!

Fig 2: Mobile Brake Disc Lathe

Courtesy of BMW OF NORTH AMERICA, INC.

After fine-grinding the brake discs, measure the thickness difference, see 34 21 REAR BRAKE DISCS E83 inside the braking surfaces at 8 points with an external micrometer.

Fig 3: Measuring Brake Discs Thickness

Courtesy of BMW OF NORTH AMERICA, INC.