Interpretation ID: 19323.wkm
Mr. Michael L. Mack
Bosch Automotive Proving Grounds
Bosch Braking Systems Corporation
32104 State Road 2
New Carlisle, IN 46552-9605
Dear Mr. Mack:
Please pardon the delay in responding to your letter to this office in which you referred to paragraph S5.6.2 of Federal Motor Vehicle Safety Standard (Standard) No. 121, Air brake systems, and asked whether, after activating the parking brake and releasing the service brake, the vehicle would be allowed to "roll a bit" before the parking brake takes hold. The answer is a qualified yes.
Paragraph S5.6.2 of Standard No. 121 provides:
Grade holding. With all parking brakes applied, the vehicle shall remain stationary facing uphill and facing downhill on a smooth, dry portland cement concrete roadway with a 20-percent grade, both
(a) When loaded to its GVWR, and
(b) At its unloaded vehicle weight plus 500 pounds (including driver and instrumentation).
We assume that Bosch is referring to the distance traveled during brake "wrap-up" (partial revolution of the braked wheels to enable the brake shoes to reach peak torque). Although the standard is silent on this issue, the agency discussed it in a February 8, 1990 Federal Register notice (55 FR 4447-4453, copy attached), stating that some small amount of movement, on the order of several inches, can result during the transition from the service brake application to the parking brake application. Therefore, we would not consider such small amount of movement during brake wrap-up to be in violation of the grade holding requirements of Standard No. 121.
I hope this information is helpful to you. Should you have any questions or need additional information, you may contact Walter Myers of my staff at this address or by telephone at (202) 366-2992 or by fax at (202) 366-3820.
Sincerely,
Frank Seales, Jr.
Chief Counsel
ref:121
d.7/2/99