Interpretation ID: aiam3198
Chief Engineer
Air Brakes Transportation Division
BF Goodrich Company
P.O. Box 340
Troy
OH 45373;
Dear Mr. Rainbolt: This responds to your October 29, 1979, letter asking about brak 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 197 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 submitte another request for interpretation. To support this request, you have provided information in you 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 brak 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, Frank Berndt, Chief Counsel