Three-Point Retractable Seat Belt Cinching{7327} Caterpillar

Off-Highway Truck/Tractor:

769D (S/N: BBB475-UP)

770 (S/N: BZZ1-UP)

771D (S/N: BCA1-UP)

772 (S/N: RLB1-UP)

773E (S/N: BDA728-UP)

773F (S/N: EED1-UP)

775E (S/N: BEC468-UP)

775F (S/N: DLS1-UP)

776D (S/N: AFS1-UP)

777D (S/N: AGC1639-UP; FKR1-UP; 2YW1-UP)

777F (S/N: JRP1-UP)

784C (S/N: 2PZ1-UP)

785C (S/N: 1HW1-UP; APX1-UP; 5AZ1-UP)

789C (S/N: 2BW1-UP)

793B (S/N: 4AR1-UP)

793C (S/N: CBR1-UP; ATY1-UP; 4GZ1-UP)

793D (S/N: FDB1-UP)

797B (S/N: JSM1-UP)

Introduction

Reference Systems Operation, Testing and Adjusting, Disassembly and Assembly, RENR2165, "Comfort Series Seat For Caterpillar Machines".

Reference Systems Operation, Testing and Adjusting, Disassembly and Assembly, PEVD5717, "Comfort Series Seat For Caterpillar Machines DVD".

Reference Special Instruction, REHS2761

The problem that is identified below does not have a known permanent solution. Until a permanent solution is known, use the interim solution that is identified below.

Problem

The seat belt is tightening against the operator's shoulder.

The excessive movement and excessive bounce of the machine during operation will cause the shoulder strap to continually lock. The locking of the seat belt may restrict the movement of the operator.

The 280-8111 Seat Belt Gp replaces the former 220-0131 Seat Belt Gp . The 280-8111 Seat Belt Group is part of the 220-0120 Seat Group .

Solution

The locking of the seat belt may be reduced or eliminated by completing one or more of the actions in the following steps:

1. Replace the bottom seat cushion that is standard with a 218-0861 Pan Assembly if the operator is slipping forward in the seat while operating the machine.

2. Add the 192-7848 Shock Absorber Kit if the operator is concerned of the following:
   • The seat bounces excessively when the suspension is properly adjusted.

   • The seat is bottoming out or topping out

   The seat should be adjusted from the mid-height to the 3/4 height position.

   Refer to Special Instruction, REHS2761 for additional information on the 192-7848 Shock Absorber Kit .

   Inspect the original adjustable shock and ensure that the shock is functioning correctly. Ensure that there are no oil leaks and that there is definite difference in firmness between the light and heavy shock dampening settings.

3. Ensure that the operator knows the location of all of the controls for the seat. Ensure that the operator knows the proper way to use all of the controls for the seat.

   Note: For most operators the suspension should be adjusted from the mid-height to the 3/4 height position. Most importantly, the operator should not bottom out or top out when the shock (damper) control lever is properly set for the operator and the operating conditions.

   The shoulder belt retractor senses the following:

   • angle of the seat back

   • angle of the vehicle

   • deceleration of the vehicle

   • acceleration of the web

   The retractor is designed to provide unrestricted movement under normal operating conditions.

   The shoulder belt retractor will lock when the retractor senses a change in the angle of the vehicle greater than approximately 15 degrees from normal, this includes the seat recline adjustment. The retractor for the shoulder belt will also lock when the retractor senses rapid vehicle deceleration and/or acceleration. The sensing device that controls the lock conditions is also sensitive to external inputs such as rough roading conditions or excessive bouncing.

   The retractor is also designed to sense a rapid change in web acceleration. The retractor will lock if the upper body of the operator moves quickly or if the operator experiences upper body movement due to a sudden change in the motion of the machine.

   Various conditions can affect the sensitivity of the seat belt cinching unit. Example, if the vehicle angle is approaching 15 degrees and the operator turns quickly, the retractor will lock more quickly due to web acceleration than if the machine was at a neutral angle. If the retractor does lock under sensitive conditions, the retractor will remain locked until conditions are neutralized (minimize vehicle angle, vehicle bounce, seat recline, and web acceleration) and pressure is relieved from the belt. In order to relieve pressure from the belt, feed 25.4 ± 50.8 mm (1.0 ± 2.0 inch) of webbing into the retractor while holding the belt at the upper retractor. Operators should anticipate and attempt to control upper body movement, neutralize lock conditions and relieve pressure on the web in order to minimize lock conditions.

   The Series C and Series D Large Off-Highway Trucks/Tractors and most replacement Large Off-Highway Truck/Tractor cabs have two sets of holes for mounting the seat riser. Use the front set of holes for medium to short operators. Use the rear set of holes for medium to tall operators.