MCI SERVICE INFORMATION

 

Tag Axle Steering - 102DL3 / D4500

Since the beginning of MCI 102DL3 production, tag axle steering has been a basic feature. The coach has a shorter turning radius and is more maneuverable at low speeds in both forward and reverse gears. The tag axle is a modified front axle assembly, with spindles, king pins, a tie rod assembly, etc., and mounted on the tag axle support structure are two air cylinders that control the steerability of the axle assembly. The normal operation is explained below:

Bolted to the lower portion of the axle assembly is a small air cylinder. Attached to this cylinder is a pin that fits into a slotted plate clamped to the tie rod assembly. Air pressure is supplied to one port of the cylinder to lift the pin up and out of the slotted locking plate, allowing the tag axle to caster freely. When the air pressure is switched to the other port on the cylinder it locks the axle in the straight position once the pin engages the plate.

On the upper portion of the tag axle support structure is a second air cylinder, which is much larger than the lock cylinder at the tie rod assembly. When the coach is shifted into reverse, air pressure supplied to one port of this cylinder forces it to extend, pushing the top of the tag axle structure forward. This action reverses the caster angle of the tag axle wheels, allowing the tag axle to caster while the coach is driven in reverse. When the transmission is shifted out of reverse, air pressure is switched to the other port on the cylinder causing the top of the axle structure to shift rearward, restoring the caster angle for forward movement of the coach.

When the road speed of the coach exceeds 18-20 mph, air pressure to the lock cylinder is switched to extend the pin, allowing it to engage the plate. A speed switch located in the front junction box reads the transmission speed signal and controls the switching function at 18-20 mph.

Positioned on each cylinder are two reed switches which sense the movement of a magnet attached to the piston inside the cylinders. These switches operate the dash tell tales.

Listed below are the most common failures reported with this system and the cause of that failure:

  1. The "Tag Lock" tell tale light stays on and the axle is unlocking/locking properly:
    1. Interference between the lock pin and locking plate is preventing full extension of the cylinder
    2. The harness connecting the reed switches on the cylinder to the main tag axle electrical harness is unplugged or damaged.
    3. The reed switches have slipped out of the proper positioning. If the switch is positioned improperly so the internal magnetic is not in proximity to the switch, the light stays on (Also applies to note "b".)
    4. Defective reed switch(es) on the cylinder.
  2. The "Tag Lock" tell tale light stays on and the axle is not unlocking/locking properly:
    1. The Tag Lock switch on the LH console is in the wrong position. When the Tag Lock switch is "ON", the Tag Lock tell tale light is illuminated and the tag axle stays locked.
    2. Low or no air pressure to activate the cylinder.
    3. Speed switch failed.
    4. Solenoid valve in engine compartment has failed.
  3. The "Tag Steer" tell tale light stays on and the axle is shifting forward/rearward properly:
    1. The harness connecting the reed switches on the cylinder to the main tag axle electrical harness is unplugged or damaged.
    2. Defective reed switch on the cylinder.
    3. The reed switches have slipped out of the proper positioning. If the switch is positioned improperly so the internal magnetic is not in proximity to the switch, the light stays on.
  4. The "Tag Steer" tell tale light stays on and the axle is not shifting forward/rearward properly:
    1. Low or no air pressure to activate the cylinder.
    2. Mechanical failure in the tag axle support structure preventing the tag steer cylinder from shifting the axle forward and back.
    3. Solenoid valve in engine compartment failed.
  5. Tag axle does not lock up at speeds greater than 18-20 mph:
    1. Speed switch failed.
    2. Solenoid valve in engine compartment failed.
  6. The tag axle wheels won't steer in reverse:
    1. Low or no air pressure to activate the cylinder.
    2. Mechanical failure in the tag axle support structure preventing the tag steer cylinder from shifting the axle forward or backward.
    3. Solenoid valve in engine compartment failed.
  7. While driving around a curve and increasing the vehicle speed above 18-20 mph, the Tag Lock tell tale light comes on until the vehicle is driven in a straight line:
    • The system is working properly.
      • The tag axle cannot lock until the coach is driven in a straight line. When the coach is driven around a curve, the slot in the tie rod locking plate doesn't match up with the slots in the lock cylinder mounting plate, which prevents the pin from engaging the locking plate. The axle is still unlocked and the tell tale light will be on because the cylinder is not in the proper position. As soon as the coach is driven in a straight line the slots line up and the axle locks. This item needs to be addressed during the drivers training prior to operating the coach.

If you need further assistance, contact the MCI Customer Support Center at (800) 241-2947.

Motor Coach Industries - A New Flyer company: Corporate Address 200 East Oakton Street, Des Plaines, Illinois 60018 | Phone: 866-MCICOACH

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