Service Brakes Service Brakes, Hydraulic Service Brakes, Hydraulic:Foundation Components Service Brakes, Hydraulic:Foundation Components:Master Cylinder
On May 20, 2014, ODI opened PE14-014 based on eight complaints alleging incidents of excessive brake pedal travel in model year (MY) 2013 through 2014 Nissan Sentra, Versa Sedan and Versa Note passenger cars (Figure 1) and information in Early Warning Reporting field reports indicating issues with master cylinder internal seals.In response to an information request letter sent by ODI, Nissan identified a condition with the master cylinder in early production subject vehicles that could result in a slow internal leak past one of the recuperating seals to the brake reservoir when the brake pedal is depressed very slowly or lightly (Figure 2).The subject vehicles are equipped with fixed seal master cylinders supplied by TRW.To address concerns with water hammer noise with the standard seal design, the master cylinders in the early production subject vehicles used AWH (anti-water hammer) seals.The AWH seals are sensitive to contamination from assembly plant cleanliness issues, which can produce the internal leak condition during slow or light brake applies but perform as designed with normal or emergency brake applications.TRW indicated that the risk of contamination interacting with the subject seals is greatest after the evacuation and pressure fill process used to fill the brake system during the manufacturing process (early life issue).TRW developed a new master cylinder seal design (EVO seal) that addresses the noise concern and eliminates the internal leak concern associated with contamination by providing a secondary seal (Figure 3).Nissan implemented the new master cylinder design in vehicle production on September 23, 2013.ODI's analysis shows that the master cylinder warranty claim rate is much higher in vehicles produced before the change (Figure 4).Statistical analysis showed that the condition is an early-life problem with relatively low failure rates projected through 100,000 miles and approximately 58 percent of the failures projected to occur by that mileage have already occurred (Table 1).Warranty claims are highest (78% of claims) in vehicles with less than 10,000 miles (Figure 5) and 50 percent of claims involved vehicles with less than 90 days in service (Figure 6).ODI evaluated 22 crash claims that included allegations of master cylinder failure, sinking brake pedal or pedal to the floor (Table 2).The analysis identified only three crashes in which a brake performance issue related to the master cylinder was duplicated by post-incident inspection, including one with a different problem than the seal leak issue (a broken plunger).The two crash complaints related to a possible master cylinder concern involved 1 vehicle with the AWH seal and 1 with the EVO seal.Both were minor crashes.The remaining crashes do not appear to be related to any issues with the master cylinder or other brake system fault.In the 4 crashes with Event Data Recorderinformation available, the data indicated that the brakes were applied too late to avoid the collisions.These include 2 crashes with less than a half second of braking before impact and 2 in which brake applications lasting 1.0 to 2.5 seconds resulted in high decelerations consistent with fully functioning brake systems, but too late to avoid the collision.Overall, the rates of crashes adjusted for vehicle exposure (total vehicle years in service) do not show any correlation to the high warranty rates associated with the AWH seal leak concern (Table 3 & Figure 7).Given these circumstances, further use of the agency resources in this matter does not appear to be warranted.Accordingly, this investigation is closed. The closing o
