Interpretation ID: aiam1637
Engineering Department
Todco Division
2195 Alpine Way
Hayward
CA 94545;
Dear Mr. Wigand: This responds to Todco's September 27, 1974, question whether Standar No. 121, *Air brake systems*, 49 CFR 575.121, requires a spring brake system on Todco's 'Jifflox converter dolly.' You describe the Jifflox dolly as a trailer converter dolly which may also be used as a 'third axle attachment' on a two-axle truck.; Standard No. 121 applies to vehicles, and specifies separat requirements for trucks, buses, and trailers. It appears that the Jifflox is subject to separate requirements under the standard depending on its use.; If Todco manufactures and sells the Jifflox for use as a 'traile converter dolly' (defined in 49 CFR 571.3 as a trailer equipped with one or more axles, a lower half of a fifth wheel, and a drawbar), it constitutes a vehicle subject to Standard No. 121. As such it is exempted from the parking brake system requirements (S5.6) and its emergency braking capability is not required to be applied by an emergency source, such as a spring brake, that is not affected by loss of air pressure or brake fluid pressure in the service brake system.; If a truck manufacturer utilizes the Jifflox as an additional axle i the suspension of its vehicle, the truck manufacturer must assure that the truck meets the requirements applicable to it with the Jifflox incorporated in it. This means that, if the truck is manufactured to accept the Jifflox dolly and the truck is rated for a gross vehicle weight rating that depends on inclusion of the axle, the truck must comply with all applicable requirements of the standard with the Jifflox attached. If the truck manufacturer determines that parking brakes are required on the Jifflox axle to meet S5.6.1 or S5.6.2, those parking brakes would have to be applied by an energy source that is not affected by loss of air pressure or brake fluid pressure in the service brake system.; Yours truly, Richard B. Dyson, Acting Chief Counsel