Rumpujarrut

Rumpujarrut are the Finnish term for drum brakes. They are a braking system in which brake shoes press outward against the inner surface of a rotating drum attached to the wheel. Force is typically produced hydraulically by a wheel cylinder, and return springs pull the shoes back when braking stops. An adjustment mechanism maintains a clearance as shoes and drums wear.

Rumpujarrut consist of a rotating drum, two or more brake shoes, a wheel cylinder, return springs, and an adjuster. The shoes are forced to contact the drum from inside, creating friction that slows the wheel. There are leading–trailing and duo-servo designs, which differ in how the shoes gain mechanical advantage.

Operation relies on friction and a self‑energizing effect: as the drum rotates, contact forces amplify braking torque. Hydraulic pressure from the brake pedal expands the wheel cylinder, pushing the shoes outward. On release, springs retract the shoes and the adjuster compensates for wear.

Applications and history: rumpujarrut were common on the rear axle of many older passenger cars and light trucks. They have been largely replaced by disc brakes in new vehicles for improved cooling and fade resistance, but are still used on some vehicles and as secondary braking systems or on trailers.

Advantages and disadvantages: they are inexpensive to manufacture, provide an enclosed environment that tolerates road spray and dirt, and can deliver strong initial bite with simple hardware. Disadvantages include greater heat buildup and fade during heavy braking, slower cooling, more complex service if wear or leaks occur, and the need to replace drums and shoes as a set.

Maintenance considerations: inspect for wear in the drums and shoes, check for leaks in the wheel cylinder, ensure the drum surface is smooth, and verify correct clearance with the adjuster. Regular inspection helps prevent brake imbalance and failure.