General Information 00 COE Cab Tilting, FLA/FLB: 00–11 5 6 4 7 8 9 2 3 10 11 1 A 12 03/02/98 f310359a A. Air supply connects here. 1. Shift-Disconnect Cylinder 2. Tilt Strut 3. Right Tilt Cylinder 4. Air Motor Assembly and Button 5. Reservoir 6. Manual Pump Lever 7. Pump Control Lever 8. "Push" Port 9. "Pull" Port 10. Right Hydraulic Cab Latch 11. Left Hydraulic Cab Latch 12. Left Tilt Cylinder Fig. 2, Optional Air/Hydraulic System, Equipped With Hydraulic Cab Latches and Cab Air Suspension On FLBs, cab latches are hydraulic, and are plumbed into the cab-tilt system. over center, it falls at a controlled rate to the full-tilt position, automatically relieving hydraulic system pressure.
The tilt cylinders are connected to the pump by flex- ible high-pressure lines. Velocity fuses are built into the tilt cylinder ports. They act as check valves to prevent the cab from free-falling in case of hydraulic system damage, such as a ruptured line. When the control lever is placed in the "Lower" posi- tion, the pull circuit in the hydraulic system opens. When the pump is operated, hydraulic pressure forces the cab back up and over center. The cab then falls at a controlled rate until it settles onto the rear mounts. There are two hydraulic circuits in the Power-Packer system:
the pushcircuit raises the cab from the low- ered position to the desired tilt position, and the pull circuit brings the cab from a tilted position up and over center. See Fig. 3 . NOTE: Whenever raising or lowering the cab, stop working the pump once the cab goes over center. The cab falls at a controlled rate, and continued pumping could cause hydraulic lock-up of the tilt cylinders. Placing the control lever in the "Raise" position opens the push circuit in the hydraulic system. When the mechanical cab-hold-down latches are released and the pump is operated, hydraulic pressure builds in the tilt cylinders and the shift-disconnect cylinder.
If equipped with hydraulic cab latches, hydraulic pres- sure releases the latches. As pressure increases, the shift-disconnect cylinder releases to allow the shift tube to telescope out. Then the tilt cylinder piston rods extend, raising the cab. When the cab goes Hydraulic lock-up of the tilt cylinders can occur dur- ing very cold weather. It can also occur when the wrong hydraulic fluid is used, when there is air in the system, when there is sudden cab movement, or when a hydraulic line is ruptured. Any of these situa- tions will cause the velocity fuses to function as safety check valves, and lock up the tilt cylinders. IMPORTANT:
If the tilt cylinders lock up, check for a major problem (such as a ruptured line or Heavy-Duty Trucks Maintenance Manual, October 2009 00/19