Volkswagen owners may complain of a pulsating brake pedal when applying the brakes at highway speeds. The pulsation may also be felt as a vibration in the vehicle body. Additionally, the steering wheel may shake. The cause may be improperly machined brakes, and the condition may not be felt until several months after the brakes were machined. To correct the problem, follow the steps below.
Review safety procedures in ALLDATA Repair S3000 before beginning.
Remove the wheels and separate the brake calipers from the carrier using factory and/or industry standard practices.
Brake Disc Inspection
A detailed brake disc inspection is needed to determine if the brake disc should be machined or replaced. Inspect brake disc friction surfaces on both sides of the brake disc for:
• Severe discoloration (bluing);
• High heat surface damage (raised hard spots); or
• Visible cracks.
Brake discs showing any of the described conditions must be replaced.
Measuring Disc Thickness
Each brake disc has the minimum allowed thickness cast, stamped or laser-etched into the disc hub (see Fig. 1).
Measure the brake disc thickness in four locations using factory and/or industry standard practices. Measurements must be taken the same distance from the brake disc outer circumference to ensure consistency (see Fig. 2).
Note: The brake disc must exceed the minimum thickness after the machining process is completed in order for it to be reused.
Brake Disc Machining
Tip: Brake discs must be machined in pairs (front axle and/or rear axle).
Note: To ensure that a high- quality brake disc finish is produced, brake lathe cutting tools must be maintained as directed by the lathe manufacturer.
• Follow the brake lathe manufacturer’s instructions for setup and machining.
• Wash the brake disc with a soap and water solution upon completion of resurfacing to remove all machining particles (see Fig. 3).
• Re-measure brake disc thickness in four locations to verify that minimum thickness is still exceeded. If the recorded brake disc measurement is less than the minimum thickness, the brake disc must be replaced (see Fig. 4).
Note: Always replace brake discs in pairs (front axle and/or back axle).
• Measure brake disc lateral runout. Runout must not exceed 0.1 mm (see Fig. 5).
Andrew Markel is the director of content for Brake & Front End magazine. He has been with Babcox Media for 20 years. He is a technician and former service writer and holds several automotive certifications from ASE and aftermarket manufacturers. He can be reached at [email protected].
You might be seeing more blues, reds and various other colors on the threads of bolts when working on drivetrain, suspension and brake components. OEMs put these threadlocking compounds there for a reason, and not servicing them could get you into trouble. To get the most out of these “liquid” tools, you first need to know how they work.