Hydraulic drum brakes on Long John bikes
For decades the basic Long John model had only one single brake: a coaster brake in the rear hub. Somewhen in the 1980s SCO started to offer an optional Sachs drum brake for the front wheel. Unfortunately this front brake suffered from heavy performance losses due to the extra long bowden cable that operated the brake. It took until the 1990s before this problem was solved when hydraulic drum brakes became available. Hydraulic power transmission works almost lossless, and the length of the cable/pipe is negligible.
Before looking at hydraulic brakes used on Long Johns lets have a quick glance on the inner life and functionality of conventional Sachs drum brakes. The complete braking mechanism is mounted on the drum brake arm which is placed on the left side of the drum. The drum brake arm can be easily removed from the drum and is shown below. Within the 1980s and 1990s Sachs produced three different models of drum brakes, VT3000, VT4000 and VT5000, but there´s no significant difference between the drum brake arms.
Engaging the lever (1, usually by bowden wire) will rotate the cam (2). The cam has an oval profile; when rotating it forces the brake pads (3) apart and against the inner wall of the drum. The brake pads are hold together by a strong spring; disengaging the lever will let them snap back to their original position. The rotating direction of the lever and cam doesn´t matter, the mechanism works equally in both directions.
Sachs Hydro Pull
The Sachs Hydro Pull was actually an hydraulic upgrade kit to be mounted on a conventional Sachs drum brake. It became available on SCO Long Johns in the mid-nineties.
The hydraulic brake lever on the handle bar operates the hydraulic piston mounted above the drum brake. The piston pulls a short cable that is connected to the small lever at the drum. The small lever moves upwards, the brake brakes.
Hydraulic brake by Magura
When Monark took over the production of Long Johns they replaced the no longer available Hydro Pull with another system. It is based on hydraulic parts build by Magura.
A Magura piston is mounted onto the drum brake arm of a Sachs VT5000 drum brake. When being operated the piston pushes down the drum brake lever.
Drum brakes on bicycles are frequently smiled at because of their relatively high weight and their moderate brake performance compared to modern rim brakes and disk brakes. However, their advantages are often neglected: drum brakes are almost completely independent on weather conditions, they´re clean (unlike rim brakes), they´re sturdy and once adjusted they are maintenance-free. And with a hydraulic upgrade their performance gets a remarkable boost.
Thanks to Steve Hinshaw, Kai-Martin Knaak and Lars Evdokiyos for providing images of their hydraulic brakes.
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