Transmission brake
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A transmission brake or driveline parking brake is an inboard vehicle brake that is applied to the drivetrain rather than to the wheels.
Historically, some early cars used transmission brakes as the normal driving brake and often had wheel brakes on only one axle, if that.[citation needed] In current vehicles, these brakes are now rare. They are found in some makes, notably Land Rover, usually for light off-road vehicles. Simple transmission brakes could be found in large vehicles too, such as the 16 inch single disc parking brake used in the M19 Tank Transporter of World War II.[1] Such a system was also used on the HMMWV.[2]
The transmission brake is provided solely as a parking brake or handbrake. Normal wheel brakes are still provided for use when driving. Driver's manuals usually caution against using the transmission brake when driving, as it is neither powerful enough nor robust enough and so will not work effectively and may even be damaged by trying to stop a moving vehicle.[3]
Transmission brakes use
As the transmission brake is mounted inboard of the
One advantage of a transmission brake is that it locks the entire drivetrain, including all four wheels of a
Automatic transmissions
A form of transmission brake is commonly fitted to automatic transmissions. These brakes use a dog clutch or pawl system, rather than friction linings. They thus provide a simple and positive lock when stationary, but cannot (or at least, should not) be engaged when moving.
In the US, this is the conventional form of parking brake and leads to the handbrake being almost entirely ignored and thought of only as the 'emergency' brake.
See also
References
- ^ Inboard brakes generally place extra torque on the drive shafts, which must be adequately specified to cope with it, but not the final drive.
- ^ TM 9-768 45-ton Tank Transporter Truck-trailer M19. US Dept. Of the Army. 25 Oct 1944. pp. 329–334. Retrieved 17 Sep 2015.
- ^ "PARKING BRAKE ADJUSTMENT AND CLEANING". hummer-hmmwv.tpub.com. Retrieved 2018-10-18.
- ^ TM 9-768, p. 329