Interpretation ID: aiam1907
Technical Representative
Toyo Kogyo Co.
Ltd. (Mazda)
Representative Office
23777 Greenfield Rd.
Suit 462
Southfield
Michigan 48075;
Dear Mr. Hirai: This responds to your April 16, 1975, question whether the tes procedure of S7, 7, 1 of Standard No. 105-75, *Hydraulic brake system*, permits reapplication of the parking brake if the vehicle fails to hold on the required grade after the first application of a force or series of forces. You also ask whether a brake warning indicator which signals a shortlived loss of pressure during a spike stop brake application would conform to S5.3.1(a) (1).; Section S7.7.1 directs (in part) application of the parking brake wit a force or series if forces, release of the service brake which has been holding the vehicle on the required grade, and indicates that in release of the service brake, 'it may be necessary to reapply *it*, if the vehicle moves slightly, to take up the parking brake system slack' (emphasis added).; The word 'it' refers to the service brake system, and not the parkin brake system. This sentence permits application of the service brake only, which has the effect of taking up parking brake system slack due to rotation of the brake shoes and drum prior to bottoming against the anchor pin. This service brake application is intended to provide the best opportunity for a static test of the parking brake.; You state that a differential pressure can occur within the Mazd master cylinder during a spike stop brake application because the piston travels beyond the outlet port to the rear wheel brake lines. This pressure differential causes momentary activation of the brake warning indicator lamp.; The NHTSA would consider in this case that, as a technicality momentary failure of the rear wheel subsystem has occurred because continued braking pressure cannot be applied to the rear wheels. you point out that the system corrects immediately and the signal lamp is extinguished.; From your description of the Mazda system, NHTSA concludes that th activation of the signal lamp conforms to the requirements of S5.3.1(a) (1) as long as it is designed to extinguish as soon as the system corrects and continued brake force could be applied to the read wheels.; Yours truly, Richard B. Dyson, Assistant Chief Counsel