Interpretation ID: aiam1743
Fontaine Truck Equipment Co.
9051 Sorenson Avenue
Santa Fe Springs
CA 90670;
Dear Mr. Massey: Mr. S. G. Holder of the Fontaine Truck Equipment Company asked th National Highway Traffic Safety Administration to explain for your benefit the requirements of Standard No. 121, *Air brake systems*, for alteration of wheelbase and installation of a liftable axle on incomplete or complete vehicles by a dealer like yourself.; I have enclosed a copy of the standard as requested. It lists severa requirements which would be affected by the addition of an additional axle. These changes can be complex, and we believe that some assistance from the manufacturer of the axle may be necessary to assist a final-stage manufacturer or vehicle alterer like yourself in meeting the certification requirements. I enclose a letter to a liftable axle manufacturer which explains the responsibilities of the various parties to each other.; Standard No. 121 was issued in February 1971 in part to reduce th incompatibility in brake performance between the larger air-braked vehicles on the highway and other highway users. Its provisions substantially improve the stopping distance performance and other braking characteristics of air-braked vehicles. To meet these requirements, chassis-cab and other vehicle manufacturers have limited the modifications which may be made to their brake system design so that a vehicle will remain in compliance.; It is for this reason that final-stage manufacturers and vehicl alterers are more limited than previously in the modifications which they can undertake. Wheelbase alteration is an example of the type of modification which seriously affects brake system performance. We expect experience with Standard No. 121 will justify greater freedom in the future for such modifications as wheel base alteration.; Yours truly, Richard B. Dyson, Acting Chief Counsel