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Home >> Porsche >> 2019 >> Cayenne Turbo >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 52 (46 Brakes - Brake Mechanism E-Hybrid -- 9YA - Cayenne (9YA)) >> WM, 465302 Checking Rear Brake Discs (Grey Cast Iron) >> Checking >> Checking Rear Brake Disc (Minimum Thickness)

Checking Rear Brake Disc (Minimum Thickness)

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

Information 

Normally, brake discs are used until the maximum wear dimension is reached.

> Refer to Technical data/brake wear limits in the appropriate service information.

Only in a few exceptional cases is it advisable to skim the brake discs (if there is deep scoring or corrosion of the friction surface). Only the brake disc dressing machines approved by Porsche AG may be used.

As the pressure force of a brake piston on the brake pad varies in magnitude, different areas of wear arise on the friction surface. The brake disc can basically be divided into two areas of wear:

-A-  Outer and inner wear area.

-B-  Central wear area.

G15290107Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Wear areas A and B

The central wear area -B-  is the area with the highest degree of wear.

G15290108Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Wear area B

Measure the brake discs using a suitable micrometer screw at at least 3 different places (-A, B, C-  ), offset by 120°.

G15290109Courtesy of PORSCHE CARS NORTH AMERICA, INC.

Measurement points for brake disc thickness

Checking lateral runout (brake disc/wheel hub) and thickness tolerance 

Information 

Secure dial gauge set with ball joint arm to wheel bearing housing.

Two adapters are used for checking lateral runout. The brake disc and wheel hub can be measured with these.

Brake disc lateral runout

  1. Removing wheel.

    > 440519 REMOVING AND INSTALLING WHEEL - section on "Removing"

  2. Tighten > 9510/1 - adapter plate  to tightening torque 160 Nm (118 ftlb.). > Adapter plate on wheel hub 
    G15290110Courtesy of PORSCHE CARS NORTH AMERICA, INC.

    Adapter plate on wheel hub

  3. Fit adapter > Nr.147-1 - dial gauge set with ball joint arm  at a suitable position on the wheel bearing housing. > Dial gauge on brake disc 
    G15290111Courtesy of PORSCHE CARS NORTH AMERICA, INC.

    Dial gauge on brake disc

  4. Fit dial gauge with slight pretension and measure the lateral runout at the greatest external diameter of the brake disc.

Wheel hub lateral runout

Information 

The front face of the wheel hub must not be corroded and must be cleaned if necessary using a polishing cloth.

Measure the wheel hub lateral runout at the front face of the wheel hub. Take measurements in each case at the external and internal diameter of the wheel bolt area.

  1. Removing rear brake disc.

    > 465319 REMOVING AND INSTALL THE BRAKE DISC REAR - section on "Removing"

  2. Fit adapter > Nr.147-1 - dial gauge set with ball joint arm  at a suitable position on the wheel bearing housing. Secure the dial gauge with slight preload. > Dial gauge on wheel hub 
    G15290112Courtesy of PORSCHE CARS NORTH AMERICA, INC.

    Dial gauge on wheel hub

    Brake disc thickness tolerance

    For details of brake disc thickness tolerance, see Technical data/brake wear limits.

    > 4600TW TECHNICAL VALUES - GREY CAST-IRON BRAKES

    Measure the thickness tolerance using a suitable micrometer screw at 8 places within the braking surface.

  3. Depending on the measured result, re-install the brake discs or replace them on both sides of the axle.

    > 465319 REMOVING AND INSTALLING THE BRAKE DISC REAR - section on "Installing"

  4. Install wheels.

    > 440519 REMOVING AND INSTALLING WHEEL - section on "Installing"

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