Automobile Engineering in ME
The condition that causes vapour locking in a brake system is

An excessively high engine speed on a downhill road
Overcooling of the brakes during high speed driving
Keeping the vehicle without use for an extended period
Overheating of the fluid due to frequent brake application

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Automobile Engineering in ME
In a ventilated disc brake

Disc contains radial vanes between its rubbing surfaces for optimum cooling performance
Caliper is covered with cooling fins
A duct directs air towards the caliper for cooling while the vehicle is moving
Disc contains many small holes for optimum cooling performance

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