OOSC, Part II, Item 1. Brake Systems - Parking Brake Power Springs Included in the 20 Percent Rule

Besides their impact on parking and emergency brake performance, broken spring brake chamber power springs can impact service brake performance by interfering with automatic adjuster operation and leading to a misleading chamber pushrod stroke measurement due to failure of the pushrod to fully retract when the brake is released. Consideration should be given to adding a broken spring brake chamber power spring to the list of brake defects that count toward the 20 percent rule.

NTSB Safety Recommendation HS-02-20 states that CVSA should "include spring brake caging port covers as an inspection item." In its recent response to NTSB on this recommendation, CVSA declined to accept the recommendation for several reasons, but did agree to have the "Vehicle Committee consider adding defective parking brake springs to the 20 percent rule during the next scheduled CVSA meeting in March 2008 in Denver CO." CVSA felt that this change would, in part, address the problem of broken spring brakes that NTSB found in its accident investigation that precipitated recommendation HS-02-20.

Change item 1.a.(2) of the OOSC to add the phrase "parking brake power springs". This section already mentions "springs" but the assumption is that these are shoe return springs. (Perhaps the words "shoe return" should also be added to the existing "springs" to clarify and discriminate between the two different types of springs). Suggested final wording: 1.a.(2) Missing or broken mechanical components including shoes, linings, pads, shoe return springs, parking brake power springs, anchor pins, cam rollers, pushrods and air chamber mounting bolts. (393.48(a))