Main.TrailIndexPage | Brake System | Drum Brakes

Drum Brakes

This component is part of Brake System.

Definition

The 230 SL has rear drum brakes, unlike the later models which have disc brakes front and rear. The drums are the Alfin type with cooling fins around the outside. The drum brakes are the simplex type with one wheel cylinder and two brake shoes per wheel. The 250/280 SL's have a smaller brake drum system on the outside of the rear rotor for the hand brake. See ____ for more information.

Function

Hydraulic pressure from the master cylinder expands the wheel cylinder at the top of the backing plate. The wheel cylinder is attached to the top end of the two semi circular brake shoes which are pressed into the inside of the brake drum by the expansion of the wheel cylinder. Friction between the brake shoe lining and the brake drum slows the car. Springs pull the shoes away from the drum when the hydraulic pressure is released. The brake shoe lining wears down over time and the brakes must be adjusted to minimize the distance the shoes (and brake pedal) need to travel before they contact the drum. The shoes must be replaced or relined when the lining wears down below the minimum allowable thickness. The hand brake expands the shoes mechanically to hold the car when parked, or in the event the hydraulic system fails.

Specifications & Data

  • Drums
    • Type: Alfin
    • Diameter: 230 mm
    • Maximum reconditioned Diameter 232 mm
  • Shoes
    • Type: malleable iron
    • Width: 65 mm
    • Minimum lining thickness 1.5 mm

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Old Yahoo content

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Joe Alexander writes: Don't forget that the 230-SL models have rear drum brakes which do need adjusted from time to time. This is the most common cause of a low pedal. First try pumping the brakes. If the pedal gets significantly higher after a few strokes, air in the system is the most likely problem. If the pedal still stays low; adjust the rear brakes. Also new pads will seat themselves and the pedal will get slightly better after a little driving. As last resort check and adjust the eccentric booster bolt. This is usually not a problem unless it has been tampered with previously. Booster problems should not normally cause a low brake pedal.


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