“What I Learned Today” With Jeff Smith: Hydraulic Clutch Effort

There’s a widely believed automotive myth that maintains that converting a mechanical clutch linkage to a hydraulic release system will reduce the pedal effort. In nearly every case, this is not true. Generally, a hydraulic system will duplicate the effort of a mechanical-release system in terms of pedal effort. The load felt at the pedal is created by the pressure plate and the mechanical advantage (or leverage) of the hydraulics is almost always very close to the leverage created by mechanical systems.

This is why most street clutches are designed to use the diaphragm-style pressure plate. Diaphragm clutches are designed to drastically reduce the effort required to hold the pedal down once the spring reaches its center point. This differentiates the diaphragm from the other coil spring-style pressure plates. A Borg & Beck or three-finger long-style clutch uses simple coil springs. As the springs are compressed, load (pedal effort) increases and remains high with the pedal pushed to the floor. This requires more effort than a diaphragm. Adding a hydraulic release bearing system will not reduce the effort created by the pressure plate.

If you are looking for a way to reduce the load on the clutch pedal, a hydraulic release system will not do the job. The best way to reduce clutch-pedal effort is to lower the pressure-plate load. Hydraulics do not offer a major improvement over the leverage provided by a mechanical system.

This is not to infer that there are no advantages to a hydraulic clutch release system. The most obvious is that a small hydraulic hose takes the place of all that clumsy mechanical linkage that makes fitting headers and exhaust systems so difficult. Most hydraulic systems now use an internal hydraulic piston that presses directly on the release bearing to release the load on the pressure plate.

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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