Working on the drum brake

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Working on the drum brake
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Working on the drum brake

Working on the drum brake
Not only a disc brake needs care

You are completely isolated from the outside world. Their care and maintenance is often neglected. Work on drum brakes is easy to master. Our workshop sequence shows how it’s done.

10/12/2011

Drum brakes are still widespread in the late 21st century: as rear brakes on many older young timers through to more modern mid-range bikes, enduros and scooters.

function
By operating the hand or foot brake lever, either a Bowden cable or a brake linkage is operated, which acts on the wheel brake lever which is mounted on the brake shaft. The inner part of the brake shaft is a brake cam that is flattened on both sides: If the brake shaft is rotated by a certain amount during the braking process, the brake cam spreads the brake shoes, which then come into contact with the brake drum (“brake ring”) from the inside.

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Not only a disc brake needs care

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Regular checks

  • The hand and foot brake levers must move easily and return cleanly to their original position when released.
  • The “free play” at the end of the brake lever (before the brake shoes come into contact with the brake drum) must be at least 10 to 15 mm and must not exceed 25 mm.
  • The foot brake lever must not touch any parts of the vehicle when stepping through it, such as B. footrest bracket, exhaust pipe or engine side cover. If this is the case, as often after a fall: First adjust the brake lever!
  • External wear assessment: A wear indicator is attached to the anchor plate, which shows the wear on the brake linings depending on the position of the wheel brake lever. When the brake pads are almost worn out, the adjustment of the brake linkage is also exhausted.
  • At the latest when removing the wheel to change tires, the brake pads should be checked for sufficient thickness and undamaged surface.

Cleaning / braking problems / checking


Working on the drum brake


MPS photo studio

Fast pavement inspection from the outside? This is not rocket science, because there is the wear indicator on the anchor plate with pointer (left on the lever) and markings (right on the anchor plate).

Clean the drum brake
When removing the wheels, e.g. B. to change tires, the brake should be cleaned well, the brake shaft and brake shoes should be checked on their pivot points for good fit and free movement. Use brake cleaner for this purpose (oil-based sprays such as WD 40 or MoS are absolutely taboo). After careful cleaning, smear the turning and contact points with a little copper paste. Caution: Do not use grease or oil to lubricate the brake shoe pivot points!

Braking problems
Brake problems are usually announced by squeaking when the brake is applied and the wheel is not turning. They occur when the brake cam is stiff or almost seized in its bearing in the brake anchor plate – a common cause is corrosion. Equally problematic: the brake lever is difficult to operate, does not move back to its original position by itself when it is released and does not release the brake shoes.

These are typical faults in an everyday machine that is a few years old, has not seen a workshop for a long time, was only used for short trips in the big city and was exposed to all the rigors of wind and weather all year round as a lantern parker on the sidewalk.

So if there is a risk of the brakes seizing up or, in the worst case, already being seized: Stop driving a meter, but take care of correcting the error immediately. A defective brake can be repaired by disassembling it, cleaning it and reassembling it cleanly.

Check the brake drum

  1. The maximum permissible unbalance of the brake drum is 0.1 mm. An out-of-round, warped brake drum can be felt by the rhythmic flapping of the foot brake lever.
  2. In use, grooves form in the brake ring of the brake drum, which can be felt with a fingernail. This is quite normal to a certain extent. However, if you clearly stumble from scratch to scratch during the finger test, the brake drum is worn out.
  3. If the brake ring has deep steps in the transition to the surface that is not touched by the brake lining, i.e. on the outer and inner edge, the brake drum is also worn and must be replaced. Well-equipped specialist brake shops (listed in the “Yellow Pages” under “Brakes”) can turn drum brakes out and re-grind them, although the hub must be spoked out for this.
  4. Remove rust in the brake ring with emery cloth.

Change brake pads


Working on the drum brake


Schermer

Manageable workload: dismantled anchor plate with brake shaft and wheel brake lever.

Change brake pads
When the brake pads are worn out, the entire brake shoes are replaced. The old method in which the fresh brake pads were glued or riveted on practically no longer exists. However, if, contrary to expectations, there are no new brake shoes for your machine, the old ones have to be reassigned. To do this, please contact a motorcycle dealer or a specialist brake company.

  1. Remove the wheel, take off the brake anchor plate and lay it on your back.
  2. Remove the brake shoes together with the springs from the anchor plate. Simply tilt both brake shoes evenly off the brake cam and bearing point.
  3. Clean the anchor plate, springs and brake cams with a brake cleaner and compressed air. Caution, brake dust is poisonous! Only work outdoors, do not breathe dust.
    3.1.     Remove brake cam: Remove wheel brake lever, pull brake cam out of its mounting.
    3.2.     Clean bearing points with brake cleaner.
  4. Install brake cams:
    4.1.     Lubricate the bearing point in the brake anchor plate with a thin layer of copper paste.
    4.2.     Push the brake camshaft into the bearing, push on the wear indicator, place the brake lever on the toothing: Note the marking, it must be aligned with the clamping slot, screw the brake lever tight.
  5. Install new brake shoes:
    5.1.     Hang the springs in both brake shoes.
    5.2.     Put some copper paste on the bearing points of the brake shoes and the surfaces of the brake cam.
    5.3.     Place both brake shoes together on the bearing point and brake cam.
  6. Install wheel, adjust brake lever play:
    When the brake lever is pulled 10 to 15 mm, it must “drag” slightly, then the brake pads just touch the brake ring. When the brake lever is pulled between half and three quarters, the brake has to grip again powerfully.

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