Auto Mechanics playlist:
more at
Drum brakes: “A CLEAR EXPLANATION OF HYDRAULIC BRAKES AND OF THEIR USE ON THE MODERN MOTORCAR.”
also see: Drum Brakes, Principles of Operation, US Army, 1983
NEW VERSION with improved video & sound:
Public domain film from the Prelinger Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).
A drum brake is a brake that uses friction caused by a set of shoes or pads that press against a rotating drum-shaped part called a brake drum.
The term drum brake usually means a brake in which shoes press on the inner surface of the drum. When shoes press on the outside of the drum, it is usually called a clasp brake. Where the drum is pinched between two shoes, similar to a conventional disc brake, it is sometimes called a pinch drum brake, though such brakes are relatively rare. A related type called a band brake uses a flexible belt or “band” wrapping around the outside of a drum…
History
The modern automobile drum brake was invented in 1902 by Louis Renault. He used woven asbestos lining for the drum brakes lining, as no alternative dissipated heat like the asbestos lining, though Maybach has used a less sophisticated drum brake. In the first drum brakes, levers and rods or cables operated the shoes mechanically. From the mid-1930s, oil pressure in a small wheel cylinder and pistons (as in the picture) operated the brakes, though some vehicles continued with purely mechanical systems for decades. Some designs have two wheel cylinders.
The shoes in drum brakes wear thinner, and brakes required regular adjustment until the introduction of self-adjusting drum brakes in the 1950s. In the 1960s and 1970s, disc brakes gradually replaced drum brakes on the front wheels of cars. Now practically all cars use disc brakes on the front wheels, and many use disc brakes on all wheels. However, drum brakes are still often used for handbrakes, as it has proven very difficult to design a disc brake suitable for holding a parked car. Moreover, it is very easy to fit a drum handbrake inside a disc brake so that one unit serves as both service brake and handbrake.
Early brake shoes contained asbestos. When working on brake systems of older cars, care must be taken not to inhale any dust present in the brake assembly. The United States Federal Government began to regulate asbestos production, and brake manufacturers had to switch to non-asbestos linings. Owners initially complained of poor braking with the replacements; however, technology eventually advanced to compensate. A majority of daily-driven older vehicles have been fitted with asbestos-free linings. Many other countries also limit the use of asbestos in brakes.
Components
Drum brake components include the backing plate, brake drum, shoe, wheel cylinder, and various springs and pins.
Backing plate
The backing plate provides a base for the other components. It attaches to the axle sleeve and provides a non-rotating rigid mounting surface for the wheel cylinder, brake shoes, and assorted hardware…
Brake drum
The brake drum is generally made of a special type of cast iron that is heat-conductive and wear-resistant. It rotates with the wheel and axle. When a driver applies the brakes, the lining pushes radially against the inner surface of the drum, and the ensuing friction slows or stops rotation of the wheel and axle, and thus the vehicle. This friction generates substantial heat.
Wheel cylinder
One wheel cylinder operates the brake on each wheel. Two pistons operate the shoes, one at each end of the wheel cylinder. Hydraulic pressure from the master cylinder acts on the piston cup, pushing the pistons toward the shoes, forcing them against the drum. When the driver releases the brakes, the brake shoe springs restore the shoes to their original (disengaged) position…
Brake shoe
Brake shoes are typically made of two pieces of sheet steel welded together. The friction material is either riveted to the lining table or attached with adhesive. The crescent-shaped piece is called the Web and contains holes and slots in different shapes for return springs, hold-down hardware, parking brake linkage and self-adjusting components. All the application force of the wheel cylinder is applied through the web to the lining table and brake lining…
