Los Angeles County Metropolitan Transportation Authority CTA November, 2015 Pasadena, California Bus Technical, Maintenance Workshop By: Frank Forde Maintenance Instructor LA Metro
Los Angeles Metro Facts FY15 Metro Bus Operations Statistics • 327 million boarding's • 85 million revenue service miles • 2,252 buses in active revenue service • Extreme Duty Cycle • 35,000 to 45,000 yearly bus miles • 11 mph average system speed Los Angeles Metro serves one of North America’s largest and most heavily congested counties, with over 10 million residents and a service area of over 1,433 square miles.
Los Angeles Metro Facts • 2,252 buses on property – 1849 buses in daily peak service • 1,750 disc brake equipped buses – 650 45’ transit buses – 700 40’ transit buses – 391 60’ articulated buses – 7,770 wheel ends • 502 S-cam drum brake buses
Disc Brakes • LA Metro has two manufacturers of air disc brake on it’s fleet . • Air disc brakes have been in operation at LA Metro since 2004 – Meritor EX225 air disc brake 2004 – KNORR SN7 air disc brake 2014
Why Disc Brakes? • Reduced Maintenance Cost • Reduced number of part numbers equal less parts to stock • Reduced drag and rolling resistance resulting in faster acceleration. • No loss of brake power due to overheating • Higher residual brake force after repeated braking. • Brake disks can withstand extremely high temperatures. • Brake fading is almost completely eliminated. • Simply a more efficient way of braking.
Disc Brakes Service Intervals • Disc Brake Average Mileage: – 45’ transit bus = 40,000 miles – 40’ transit bus = 40,000 miles – 60’ articulated bus = 35,000 miles • Pad Replacement: 4 labor hours per axle • Pad and Rotor Replacement: 8 labor hours per axle • Mileage average same for all axles • Brake reline mileage is enhanced by the transmission retarder – Aggressive retarder-longer brake life. – Allison Gen 4 / 5 transmission retarder is medium capacity, resulting in lower brake life .
System Operation • Air caliper actuated pads. The application force is amplified by the design of the caliper shaft. • Floating caliper design; the inboard is applied by the caliper force; the outboard pad is applied by the floating housing pulling against the rotor.
System Operation • The automatic adjuster makes an adjustment to the operation of the brake pads to compensate for pad wear. • Each time the brake is applied, the system senses whether adjustment is required or whether the disc-to-pad running clearance is still within the built-in tolerance.
Visual Wear Indicator Meritor EX225 caliper visual brake pad wear indicator
Visual Wear Indicator KNORR SN7 caliper visual brake pad wear indicator This bushing is almost fully retracted Rubber boot type with axial ribbing indicator indicating a . This bushing if fully extended showing a worn pad and / new pad condition or rotor
Metro General Service Recommendation • For service procedures – consult service manual • Use only OEM spare parts • Do not open caliper assembly, as this voids the warranty. • Never actuate the brake while pads and/or rotor are removed from the assembly. • Do not re-surface the rotor when replacing brake pads. • Remove rubber plug located on the bottom of the actuator service brake. • Do not use any tool on the brake adjuster screw other than a closed box wrench or 1/4” drive ratchet. • Do not lay the caliper on the outer boot when servicing the caliper off the axle.
Q & A
Contact: Frank Forde 213-922-5928 fordef@metro.net
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