This service manual, PV776-TSP194811, published in August 2003 by Volvo Trucks North America, Inc., details the specifications, tools, design, function, troubleshooting, service procedures, and maintenance for the Volvo fifth wheel, including its slider mechanism, for VN and VHD truck models. The manual emphasizes that products manufactured after August 2003 may have different specifications and repair methods, with supplementary service bulletins issued to cover changes.
Function Description
The Volvo fifth wheel serves as the critical coupling mechanism between a tractor and a semi-trailer. It is designed to securely connect the trailer's kingpin to the tractor, allowing for safe towing and articulation. The fifth wheel's locking mechanism ensures a secure connection, while the optional air-operated slider allows for easy adjustment of the fifth wheel's position on the chassis. This adjustment is crucial for distributing the load on the axles to comply with legal weight limits and optimizing vehicle handling. The top plate is designed with a large grease pattern reservoir, enabling lubrication even when the trailer is connected.
The fifth wheel locking mechanism is designed for simplicity and reliability, comprising only 12 parts, with 5 of them being moving components. It features an eccentric jaw pin that allows for three adjustment positions to maintain a tight fit with the kingpin, a process that can be completed in minutes using pliers. A built-in safety latch must be rotated rearward before the operating rod can be pulled to unlock the fifth wheel, providing a visual confirmation of the lock status. The operating rod is also designed to require less effort to pull.
The fifth wheel operates in three positions:
- Locked: The position when a trailer is hooked up, with the operating rod retracted and the safety latch swinging freely.
- Lockset: The position for uncoupling, achieved by pulling the operating rod out with a slight upward motion until its shoulder catches on the plate casting, and the safety latch is rotated rearward.
- Open: The position after uncoupling, where the jaw is open, the operating rod is dropped and moves freely, and the safety latch is rotated rearward. This is the required position for coupling to a trailer.
The fifth wheel plate is attached to the slider or stationary mounting bracket using a trunnion arrangement. This design ensures that the fifth wheel plate rests directly on top of the trunnions, transferring vertical load to the trunnions rather than the bracket pins. The bracket pin holes are oblong to accommodate this, minimizing wear between the plate and brackets.
Important Technical Specifications
- Fifth Wheel Static Vertical Load Capacity:
- Minimum: 18,144 kg (40,000 lb)
- Maximum: 31,751 kg (70,000 lb)
- Trailing Load Capacity:
- Minimum: 68,039 kg (150,000 lb)
- Maximum: 90,718 kg (200,000 lb)
- Slider Widths Available: 845 to 865 mm (33 1/4 to 34 in.)
- Slider Travel Available:
- Standard: 305 mm (12 in.), 610 mm (24 in.)
- Optional: 405 mm (16 in.), 915 mm (36 in.), 1220 mm (48 in.)
- Maximum Allowable Wear Tolerances:
- Plate casting vertical lift: 7.9 mm (5/16 in.)
- Fifth wheel jaw longitudinal movement: 3.2 mm (1/8 in.)
- Slide plate lateral movement: 9.5 mm (3/8 in.)
- Slide plate longitudinal movement: 9.5 mm (3/8 in.)
- Slide plate vertical movement: 6.4 mm (1/4 in.)
- Slide plate combined vertical and lateral movement: 9.5 to 6.4 mm (3/8 to 1/4 in.)
- Torques:
- Mounting Bolts 5/8 in.: 270 ± 27 Nm (200 ± 20 ft-lb)
- Mounting Bolts M14: 271 ± 41 Nm (200 ± 30 ft-lb)
- Mounting Bolts M16: 320 ± 50 Nm (236 ± 37 ft-lb)
- Removable Front Stops: 75 Nm (55 ft-lb)
- Fifth Wheel Height: 170 mm (6.69 in.), 175 mm (6.88 in.), 195 mm (7.67 in.), 220 mm (8.66 in.)
Usage Features
- Kingpin Air Release Switch: For tractors with air ride suspension, this switch releases the kingpin lock. It's crucial to follow safety procedures, including chocking trailer wheels, placing the transmission in neutral, and applying parking brakes before operation. The chassis may drop quickly when suspension air is released.
- Coupling Procedures: Requires visual inspection to ensure proper coupling, as sound is not reliable. The fifth wheel must be properly lubricated and the jaw in the open position. The trailer kingpin must be centered in the throat, and the trailer plate tilted downward at the rear. After backing firmly into the kingpin, a slight forward pull tests the coupling. The operating rod must be fully retracted, and the safety latch must swing freely.
- Uncoupling Procedures: Involves setting tractor and trailer brakes, chocking wheels, placing transmission in neutral, lowering landing gear until it touches the ground (plus a few extra turns), disconnecting air and electrical lines, and unlocking the fifth wheel. For air ride suspensions, the "UNCOUPLE" position on the suspension control switch deflates air bags, allowing the tractor to pull away.
- Slider Operation: Requires stopping the tractor and trailer straight on level ground with trailer brakes locked. The slide locking plungers are released by moving a cab switch to "UNLOCK." The tractor is then slowly driven forward or backward to position the fifth wheel, and the plungers are engaged by moving the switch to "LOCK." Visual verification of plunger engagement is essential.
Maintenance Features
- Regular Inspection: Recommended every 3 months or 48,000 km (30,000 miles) for maximum life and safety. Inspections include checking for cracked, broken, or missing parts, ensuring cotter pins are adequately spread, verifying mounting bolt torques, and checking for sharp edges on the top plate (grind off to a 3 to 6 mm radius).
- Safety Latch and Operating Rod Check: Ensure the safety latch swings freely when the fifth wheel is locked and the operating rod is fully retracted. Check the lever bar and operating rod for proper alignment; replace if bent or misaligned.
- Jaw to Kingpin Clearance Check: New units have approximately 1.5 mm (1/16 in.) clearance. If clearance exceeds 3 mm (1/8 in.), adjustment is required using the eccentric pin. A SAE kingpin gauge (ASF40-2-00171) is recommended for this.
- Horizontal Movement Check (Upper and Lower Half): Measure movement between the trailer connection and the fifth wheel. It must not exceed 12.7 mm (0.5 in.).
- Horizontal Movement Check (Pivot Bracket Pin and Bracket): Measure movement between the saddle plate bracket and the bracket. It must not exceed 9.5 mm (0.375 in.); if it does, replace the saddle plate.
- Top Plate Vertical Movement Check: Measure vertical movement of the top plate. Maximum allowable movement is 8 mm (5/16 in.). If the tractor has a sliding fifth wheel mount, it must be locked down with clamps for accurate measurement.
- Slider Longitudinal Slack Check: Measure slack between the saddle plate and base plate lock pockets. If wear is significant, weld repair and addition of new lock pins can reduce slack.
- Slider Lateral Slack Check: Measure lateral movement between the saddle plate bracket and the base plate rail. If the difference between measurements exceeds 9.5 mm (3/8 in.), repairs are needed.
- Slider Vertical Slack Check: Measure the gap between the saddle plate bracket and the plate rail. If the gap exceeds 6 mm (0.25 in.), repairs are needed.
- Slider Lateral and Vertical Combined Slack Check: If lateral slack exceeds 9.5 mm (0.38 in.) and vertical slack exceeds 6.5 mm (0.25 in.) simultaneously, repairs are needed.
- Cleaning: Steam clean the entire fifth wheel periodically to remove grease contaminated with dirt.
- Lubrication: Always relubricate after steam cleaning. Otherwise, lubricate at least every 24,000 km (15,000 miles). Chassis or multipurpose grease is recommended. Maintain a heavy coating of grease on the fifth wheel plate, grease support bracket trunnions, and fittings at the saddle plate and saddle plate lock pockets.
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