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CTA November, 2015 Pasadena, California
Bus Technical, Maintenance Workshop By: Frank Forde
Maintenance Instructor LA Metro
Los Angeles County Metropolitan Transportation Authority
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.
Meritor EX225 caliper visual brake pad wear indicator
Visual Wear Indicator
KNORR SN7 caliper visual brake pad wear indicator
Visual Wear Indicator
Rubber boot type with axial ribbing indicator . This bushing if fully extended showing a
new pad condition
This bushing is almost fully
retracted indicating a
worn pad and / or rotor
• 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.
Metro General Service Recommendation
Q & A
