34 21 200 Removing and installing/replacing both rear disc brakes

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

Special tools required:

34 1 280
34 6 306
34 6 307
34 6 308
34 6 309

IMPORTANT: The brake pad wear sensor must be replaced once it has been removed (brake pad wear sensor loses its retention capability in the brake pad).

Necessary preliminary tasks:

Remove WHEELS .
Remove BRAKE PAD WEAR SENSOR

Detach locking clip (1) in direction of arrow.

Disengage parking brake Bowden cable (2) from actuating lever (3) at brake caliper.

Feed out parking brake Bowden cable (2) downwards.

Fig 1: Identifying Parking Brake Bowden Cable And Locking Clip

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IMPORTANT: Both guide bolts must be released and then the brake caliper detached towards the rear!
The springs may be bent when only one bolt is released and the brake caliper is folded up!

Unscrew guide bolts (1).

If necessary, grip at hexagon head (2).

Installation:

Replace guide screws.

Tightening torque 34 21 3AZ

Fig 2: Identifying Guide Bolts And Hexagon Head

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IMPORTANT: Mark any worn brake pads.
In the event of one-sided brake pad wear, do not change brake pads round.

Remove brake pads (1) in direction of arrow from brake console.

Observe MINIMUM THICKNESS OF BRAKE PADS .

Clean brake pads.

Do not apply grease to brake pad backplate.

Fig 3: Identifying Brake Pads

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Check minimum brake disc thickness:

Position special tool 34 1 280 at three measuring points in area (1) and measure.
Compare measurement result and lowest value with SETPOINT VALUE

New brake pads may only be installed if the brake disc thickness is greater than or equal to the MINIMUM BRAKE DISC THICKNESS (MIN TH).

Fig 4: Identifying Three Measuring Points

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NOTE: The minimum thickness of the brake disc is designed so that it holds over the service life of a further set of brake pads if it is greater than or equal to the MINIMUM BRAKE DISC THICKNESS (MIN TH).

IMPORTANT: When pressing piston back, note brake fluid level in expansion tank.
Overflowing brake fluid will damage the paintwork.

Insert brake piston into brake caliper with special tools 34 6 309, 34 6 306, 34 6 307, 34 6 308.

Fig 5: Inserting Brake Piston Into Brake Caliper With Special Tools

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IMPORTANT: Dust boot must not come into contact with brake pad paste as this may cause the dust boot to swell.

Check dust boot for damage and renew if necessary.

Clean contact surface (1) of brake piston with brake cleaner and apply a thin coating of brake pad paste.

Fig 6: Identifying Contact Surface Of Brake Piston

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Clean contact surface (1) of brake caliper with brake cleaner and apply a thin coating of brake pad paste.

Fig 7: Identifying Contact Surface Of Brake Caliper

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So as not to damage the surface coating, if possible do not mechanically clean the guide surface (1) for the brake pads on the brake caliper mounting bracket. Clean guide surface (1) with brake cleaner and apply a thin coating of brake pad paste.

Fig 8: Identifying Guide Surface For Brake Pads

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Apply a thin coating of brake pad paste to both sides of T-head of brake pad in area (1).

Fig 9: Identifying Paste Application Area

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IMPORTANT: Brake pad with bulge (1) is intended for accommodating the brake pad wear sensor and must be fitted on the piston side.

Fig 10: Identifying Brake Pad

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After completing work:

When installing new brake pads at front and rear axles, brake fluid level must be brought up to "MAX" marking.
Read and comply with notes on BREAKING IN NEW BRAKE DISCS/BRAKE PADS .
Fully depress brake pedal several times so that brake pads contact brake discs.
If necessary, when replacing pads, reset CBS display in accordance with factory specification.

Replacement:

Remove lining springs (1) and replace.

Installation note:

So as not to damage the surface coating, if possible do not mechanically clean the guide surfaces (1) for the brake pads on the brake caliper mounting bracket. Instead, clean with brake cleaner and apply a thin coating of brake pad paste.

Fig 11: Identifying Lining Retaining Springs

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