Interpretation ID: nht74-2.43

DATE: 05/24/74

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

TO: Dorsey Trailers

TITLE: FMVSS INTERPRETATION

TEXT: This responds to your May 3, 1974, question concerning the certification responsibility of a manufacturer of trailers that must conform to Standard No. 121, Air brake systems. You ask if the substitution of parts not specified by an axle manufacturer will affect certification if the parts are nearly identical in their specifications and performance to the recommended parts.

In the case of substitution of parts, you must simply satisfy yourself that your vehicles are capable of meeting the requirements of the standard in a test by the NHTSA. If you are satisfied that the supplier's recommended package will meet the requirements, and you determine that a substitution would not adversely affect the vehicle's performance to the point where it no longer would meet the requirements, you are free to make the substitution. It would be advisable to make some record of your calculations of the effect of such substitutions.

Yours truly,

ATTACH.

May 3, 1974

James B. Gregory, Administrator -- National Highway Traffic Safety Administration

Dear Sir:

Dorsey Trailers, Inc. has selected Wagner Electric Corporation and The Berg Manufacturing Company to supply the air actuation and anti-skid equipment for all trailers manufactured by this company. Other companies have been reviewed as suppliers on special customer request but our Engineering and Production techniques are only developed for the above two suppliers at this time. Both of the suppliers have assured us of adequate inventory of the required material to start shipping trailers by September 1, 1974 with the F.M.V.S.S. 121 specifications.

The two major axle suppliers which we use, Kershaw Axle Division of C. & M. Spring Company and Standard Forg and Axle Company, have both promised axles with brakes to meet the 121 specifications by September 1, 1974.

The problem that concerns us is the dynamometer brake rating. We have just been given a new interpretation of the requirements for the dynamometer rating, stating that if any portion of the combinations of components such as air chambers, slack adjusters, brake drums, etc. is changed from the exact specified part number and brand name used in certifying an axle with a given brake lining, the certification is voided and not acceptable. If this is true, then there does not seem to be enough dynamometer time available to meet a deadline even by January 1, 1975 for all combinations of parts available to the trailer industry.

As a smaller manufacturer of trailers we do not enjoy the luxury of telling our customers that certain parts are our standard materials and we won't furnish other components. Our customers usually have their own part specifications to simplify their maintenance.

If we had an axle certified with B-W slack adjusters, 6" long and B-W type 30 spring brake chambers, but our customer specified his axles must have Berg 6" slack adjusters and Berg Type 30 spring brake chambers, would this affect the certified axle? The substitution would be of equal parts and performance but different brand names.

Another example would be an axle certified with a Webb #66518 drum weighing 96 pounds and the customer specifying a Webb #67518 drum which weighs 106 pounds. The addition of the 10 pounds of weight would increase the fade-away characteristics by better heat dissipation but would this change require another dynamometer test?

Some customers specify cast brake shoes while others prefer fabricated brake shoes. With all other components being the same, would the change in brake shoes require a new certification?

If our suppliers meet their commitments, we could offer certain of our options to meet "121" specs on September 1, 1974. To certify all of the options that we are required to furnish, there could possibly not be enough dynamometer time available by January 1, 1975. Please give us an interpretation on varying the components and how this would effect the certifications.

Due to material shortages, the privilege of switching suppliers of certain assemblies is almost prohibitive since allocation of material is very common. This problem will only multiply the above problem of dynamometer testing time. If your regular supplier does not have his own dynamometer, it will be very difficult to secure time on an independent test machine and impossible to get the service of your competitors' equipment.

Yours very truly,

DORSEY TRAILERS; Roy C. Belcer - Vice President -- Manufacturing and Engineering

CC: G. L. Collier