Interpretation ID: nht80-1.16
DATE: 02/25/80
FROM: AUTHOR UNAVAILABLE; F. Berndt; NHTSA
TO: BF Goodrich Company
TITLE: FMVSS INTERPRETATION
TEXT: This responds to your October 29, 1979, letter asking about brake adjustments prior to testing for compliance with Standard No. 121, Air Brake Systems. In your letter, you ask that the agency permit up to three adjustments during the burnish for dynamometer testing.
By letter of interpretation and by preamble to our November 1974 Federal Register Notice (39 FR 39880), adjustments were permitted during the burnish procedures in S6.1.8 and S6.2.6 for the purpose of controlling brake temperature. According to agency information at the time of those interpretations, controlling brake temperature was the only reason that would require the use of brake adjustments during burnish. In a subsequent letter to the agency, you requested that we modify that position in light of your experience with disc brakes and their need for adjustment during burnish for dynamometer testing for reasons other than temperature control. The agency denied that request in April of 1979 while suggesting that the NHTSA would reconsider if more supporting data were supplied.
In response to the agency's request for more data, you have submitted another request for interpretation. To support this request, you have provided information in your letter and have also provided other information directly to our technical staff. As a result of this information, the agency agrees that adjustments during the burnish procedures may be necessary for reasons other than temperature control. Accordingly, the agency will permit adjustments during the burnish procedures for the sections cited above for any reason.
The standard presently is silent on the issue of how many brake adjustments may be made during burnish. As discussed with you and your staff we are considering limiting the number of adjustments to three during the burnish tests. However, no limitation is in effect at this time. The agency will undertake rulemaking shortly to limit the number of adjustments during burnish and encourages manufacturers to limit adjustments to three in the interim.
Sincerely,
ATTACH.
October 29, 1979 FRANK BERNDT -- CHIEF COUNSEL, Department of Transportation
Dear Mr. Berndt:
This letter comments on and is in regard to your correspondence of April 27, 1979 to Mr. D.L. Haines; the Mr. Joseph J. Levin, Jr. letter dated January 24, 1979 also to Mr. D.L. Haines; the BFGoodrich letter of January 15, 1979 to Mr. Tad Herlihy; and the BFGoodrich letter of November 8, 1978 to Mr. Joseph J. Levin, Jr.
BFGoodrich reviewed your interpretation of FMVSS 121, Paragraph S5.3, S5.4, and S6.1.8 and S6.2.2 regarding brake adjustment during burnish. In summary, you state that brake adjustments may be made during burnish, but only to control brake temperature.
In reference to that interpretation, BFGoodrich submits the following observations and comments.
1. The intent of our original inquiry, dated November 8, 1978, was to ensure that the BFGoodrich interpretation of FMVSS 121 with regard to adjustment during burnish was correct.
2. Mr. Levin's response of January 24, 1979, which postdated our letters of November 8, 1978 and January 15, 1979, was originally thought to be a reply to BFGoodrich correspondence and was interpreted as supporting our position that adjustment during the burnish sequence is not restricted.
3. Your letter of April 27, 1979 declined to support our position but suggested that NHTSA would consider data and information that would indicate that the NHTSA position on this matter might be too narrow.
4. Your letter of April 27, 1979 also stated that "The National Highway Traffic Safety Administration is unaware of a reason other than control of brake temperature which would justify adjustments during burnish." BFGoodrich establishes that reason for adjustment by means of the information presented in the following paragraphs.
A. A review of our Vehicle testing in compliance with procedures detailed in FMVSS 121 (including sections recently deleted for trucks and trailers in response to the 9th Circuit remand) has shown that vehicles using the BFGoodrich Air Disk Brake can meet all performance criteria without brake adjustment during the burnish sequence.
B. A review of BFGoodrich Air Disk Brake dynamometer testing in compliance with procedures detailed in FMVSS 121 has shown that the dynamometer tests can be completed and meet all performance criteria. However, during burnish, as a flat and fully mated lining/disk interface is established, a maximum of three brake adjustments is required to maintain burnish decelerations.
C. The burnish procedures detailed in FMVSS 121 appear to be tailored to the needs of drum brakes equipped with organic linings. The primary need is to cure the "green" organic lining in preparation to meeting the actual performance requirements of the standard.
D. The burnishing requirements for the BFGoodrich disk brake are significantly different due to the fact that its metallic lining material requires minimal conditioning. For example, the BFGoodrich disk brake lining can be conditioned after 100 dynamometer burnish stops (and many times with as few as 50) to successfully complete the performance requirements. Such an abbreviated burnish sequence requires no brake adjustments between any burnish stops.
In presenting the foregoing data, we feel we have established a reason for an interpretation which is supportive of our position that adjustment during burnish is acceptable. In our particular case, the reason and need is limited to the dynamometer burnish in which we require a maximum of three burnish adjustments in order to complete a full burnish sequence. Parenthetically, it should be noted that an abbreviated dynamometer burnish sequence of 100 stops can be accomplished with our disk brake without brake adjustment between burnish stops. In either case, the actual performance testing following the dynamometer burnish can be successfully completed.
Listed below is a summary of the BFGoodrich viewpoints on this matter:
* There is no clear basis for the no-adjustment-during-burnish interpretation in the wording of FMVSS 121 as applied to disk brakes.
* The above position is strengthened by the interpretive precedent. established in November of 1974, which allowed adjustment during burnish to control brake temperature (reference the Joseph J. Levin, Jr. letter of January 24, 1979).
* The burnish procedure is preceived as a preparation for testing and not a performance requirement in itself.
* Technical criteria used in establishing the burnish sequences appear to be based only on drum brake experience and requirements, and that criteria is not necessarily representative of the burnish requirements of other braking technologies such as the BFGoodrich Air Disk Brake.
* No degradation of performance requirements are suffered by allowing adjustment during burnish.
In light of the above and for the reasons noted earlier, BFGoodrich requests a reconsideration or modification to the previous interpretation which would allow up to three brake adjustments during the burnish for dynamometer testing.
If the Department still feels that there is insufficient reasoning to reconsider the current interpretation and additional discussion is required, please advise me as to a date that you will be available to review this issue.
Sincerely,
THE B F GOODRICH COMPANY -- Engineered Products Group;
Jack D. Rainbolt -- Chief Engineer, Air Disk Brakes, Transportation Division
cc: K. M. Ryan