No braking surface shall be capable of being disconnected from the wheels. Nevertheless, such disconnection shall be permitted in the case of some of the braking surfaces, on condition:
(a) That it is only momentary, as for example, during a change of gear;
(b) That so far as concerns the parking brake, it can be effected only by the action of the driver; and
(c) That so far as concerns the service or secondary (emergency) brake, braking remains possible with the efficiency prescribed in the paragraph 5 of this Annex.
