Interpretation ID: nht80-1.29

DATE: 03/10/80

FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA

TO: The Bendix Corporation

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your January 22, 1980, letter asking whether sections S6.1.8.1 and S6.2.6 of Standard No. 121, Air Brake Systems, permit the adjustment, after burnishing, of brakes that are equipped with automatic brake adjusters. The answer to your question is no.

On April 28, 1977, the agency responded to a similar request that you made for an interpretation of these sections to permit brake adjustment for brakes equipped with automatic adjusters. At that time, the agency stated that the provisions of Standard No. 121 do not permit the type of a brake adjustment that you request. However, the agency noted that it would accept a petition for rulemaking to modify the standard in the manner you suggest if such a petition were supported with sufficient technical data.

In your current request for an interpretation, you merely restate your 1977 letter without offering the necessary supporting data and without petitioning the agency to amend the standard. Accordingly, we must restate the agency's interpretation that the standard does not permit the type of adjustment that you request.

SINCERELY,

Heavy Vehicle Systems Group

The Bendix Corporation

Office of Chief Counsel National Highway Traffic Safety Administration

January 22, 1980

Subject: Request for Interpretation - Federal Motor Vehicle Safety Standard 121

Gentlemen:

The Bendix Corporation, Heavy Vehicle Systems Group (Bendix) respectfully requests an interpretation from the National Highway Traffic Safety Administration (NHTSA) on the application of Section S6.1.8.1 and S6.2.6 of Federal Motor Vehicle Safety Standard 121 - Air Brake Systems (FMVSS 121) with respect to brakes equipped with automatic adjusters. These sections cover the brake burnish procedures for road and dynamometer testing and specify that after burnishing, the brakes are to be adjusted as recommended by the manufacturer. Specifically, Bendix requests concurrence from the NHTSA that FMVSS 121 Section S6.1.8.1 and S6.2.6 permits manual adjustment, after burnishing, of brakes equipped with automatic adjustment.

In considering this request, your attention is directed to the fact that on March 29, 1977 Bendix submitted a similar request, however the NHTSA's response of April 28, 1977 addressed the issue of disconnect and overadjustment, not the issue of manual adjustment.

Now, due to increased customer activity, and current governmental interest in fostering the use of automatic adjustment of brakes, Bendix again submits its request for an interpretation permitting adjustment, after burnishing, of brakes equipped with automatic adjuster. Such interpretation would allow all brakes, with or without automatic adjustment to be tested by using the same procedures.

Bendix supports the need to improve in-service brake performance and stability, which improvement can be achieved through the use of brakes equipped with automatic adjustment mechanisms, and as such Bendix feels that clarity in the applicable Standards are necessary to assure compliance. It should be noted that automatic adjusters maintain a good level of brake performance, however not to the original level of the manual adjustment of the brake. But this difference, in our estimation, is not detrimental because the total procedure of controlled conditioning of the brakes is to achieve optimum performance and repeatability, and is not necessarily representative of actual operating conditions. Under actual operating conditions, the use of automatic adjustment mechanisms insures continued good brake performance.

Bendix hereby respectfully requests concurrence of NHTSA in Bendix' interpretation that FMVSS 121 Section S6.1.8 and S6.2.6 permits the manual adjustment of brakes with or without automatic adjusters after the burnish procedures. Bendix believes that such an interpretation would greatly accelerate the voluntary usage by vehicle manufacturers of automatic adjusting brakes on air braked vehicles and alleviate the need for amended or new rulemaking in the area of brake adjustment.

We would be pleased to discuss this matter further at your convenience.

R. W. Hildebrandt Group Director Engineering