Interpretation ID: nht75-5.47

DATE: 05/05/75

FROM: AUTHOR UNAVAILABLE; R. B. Dyson; NHTSA

TO: Oshkosh Truck Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This will acknowledge receipt of your request for reconsideration of the NHTSA determination of February 18, 1975, to Oshkosh Truck Corporation that Standard No. 121, Air brake systems, permits the installation of a handoperated service brake control that meets the requirements of the standard.

We will advise you of our determination as soon as possible.

YOURS TRULY,

OSHKOSH TRUCK CORPORATION

April 10, 1975

Richard Dyson Chief Council Office NHTSA

This responds to NHTSA approval of a hand-operated service brake control. Previous correspondence on this subject is attached for your reference.

Oshkosh trucks are equipped with service, emergency and parking brake systems which meet the requirements of FMVSS 121. As an additional parking brake, to be used in lieu of the standard parking brake supplied, a customer has requested a hand-operated control to activate the service brake system. Oshkosh Truck is concerned that installation of this control will circumvent certain FMVSS 121 parking brake and service brake requirements.

Parking brakes must be applied by an energy source not affected by an air pressure loss in the service brake system, as stated in FMVSS 121, Section 5.6.3. The parking brake control must be separate from the service brake control as stated in FMVSS 121, Section 5.6.4. If a truck is equipped with a hand-operated control which activates the service brake system and if this system, rather than the parking brake system, is used to park the truck, then Sections 5.6.3 and 5.6.4 are circumvented.

The service brake system must stop the truck in distances specified by FMVSS 121, Section 5.3.1. The hand-operated service brake control only applies air pressure to the front brakes. If a truck is equipped with a hand-operated control which applies only the front service brakes and if this system, rather than the normal dual service braking system (operating on front and rear brakes) is used to stop the truck, then stopping distances will be exceeded and Section 5.3.1 will be circumvented.

The NHTSA with the advent of FMVSS 121 specifies performance requirements for air brake systems. Oshkosh Truck has taken extraordinary measures to comply with these requirements and we are reluctant to add a component which circumvents any of those requirements, or by-passes any of our carefully engineered systems.

The NHTSA has determined that installation of a hand-operated control lever is acceptable. We are concerned that if this system is used to park a truck or stop a moving truck that it will not meet the requirements of FMVSS 121. Therefore, please reconsider the previous NHTSA determination and reply as soon as possible.

Thank you.

Danny J. Lanzdorf

Supervising Engineer