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

WARNING: This page is about a different car, the 2013 BMW 550i GT, 2012 BMW 550i GT, 2011 BMW 550i GT, and 2010 BMW 550i GT. However, it is still accessible from the selected car via links, so may be relevant.

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

Maximum machining dimension per friction ring side is 0.8 mm!

Observe MINIMUM BRAKE DISC THICKNESS (MIN TH).

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).

Stationary brake disc lathe

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

In the case of stationary brake disc lathes, the BRAKE DISC must be removed.

Please refer to the equipment manufacturer's Owner's Handbook for the exact procedure.

Fig 1: Identifying Stationary Brake Disc Lathe

Courtesy of BMW OF NORTH AMERICA, INC.

Mobile brake disc lathe

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

In the case of mobile brake disc lathes, the brake calipers and brake anchor plates must be removed.

The brake discs remain on the vehicle.

Fig 2: Identifying Mobile Brake Disc Lathe

Courtesy of BMW OF NORTH AMERICA, INC.

Please refer to the equipment manufacturer's Owner's Handbook for the exact procedure.

After fine-grinding the brake discs, measure the THICKNESS DIFFERENCE inside the braking surfaces at 8 points with an external caliper gauge.

Fig 3: Measuring Brake Surface Thickness Using Micrometer Gauge

Courtesy of BMW OF NORTH AMERICA, INC.