Fifth Wheels and

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Fifth Wheels and Coupling Systems
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Objectives

• Describe the different types of fifth wheels used
  on tractors.
• Outline the operating principles of the Holland,
  Fontaine, and JOST fifth wheels.
• Understand the importance of correctly locating
  the fifth wheel on the tractor.
• Describe the locking principles of each type of
  fifth wheel.

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(Objectives cont.)

• Outline the procedure required to couple and
  uncouple a fifth wheel.
• Service the common types of fifth wheels.
• Describe the procedure required to overhaul a
  fifth wheel.
• Identify the overhaul procedure required of some
  common fifth wheels.

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(Objectives cont.)

• Define high hitch and outline what is required to
  avoid it.
• Describe the operating principle of a pintle hook
  and draw bar.
• Outline the function of the kingpin and upper
  coupler assembly.

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INTRODUCTION

• The fifth wheel is a coupling device. Its
  purpose is to connect a tractive unit to a towed
  unit. The tractive unit is normally a tractor,
  but in the case of multiple trailer train, a
  fifth wheel also can be located on a lead
  trailer. The fifth wheel permits articulation
  between the tractive and the towed units.

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FIFTH WHEEL TERMINOLOGY

• A fifth wheel consists of a wheel-shaped deck
  plate usually designed to tilt or oscillate on
  mounting pins. The assembly is bolted to the
  frame of the tractive unit. A sector is cut away
  in the fifth wheel plate (sometimes called a
  throat) to permit a trailer kingpin to engage
  with locking jaws in the center of the fifth
  wheel. The trailer kingpin is mounted in the
  trailer upper coupler assembly. The upper coupler
  consists of the kingpin and bolster plate.

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PINTLE HOOKS

• Another method of attaching a trailer to
  either a truck or lead trailer is by using a
  pintle hook. A drawbar eye engages the pintle
  hook assembly. The drawbar extends from the
  converter dolly (integral axle, frame, fifth
  wheel, coupling unit) in all cases in which this
  coupling method is used, the unit being towed
  would be classified as a full-trailer.

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Shop Talk

• Most truck and trailer coupling mechanisms are
  simple in design and operating principles.
  However, because of the extreme consequences of a
  trailer breakaway, care must be practiced when
  doing any work on coupling devices. Always
  consult original equipment manufacturer (OEM)
  service literature and ask questions when you are
  unsure of a procedure.

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SEMI-OSCILLATING FIFTH WHEELS
Cast steel, Forged steel, Pressed steel, or
Aluminum alloy
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COMPENSATING AND FULLYOSCILLATING
Fully oscillating gooseneck
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Cradle viewand lockout mechanism
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SPECIALTY FIFTH WHEELS

• Air-actuated elevating fifth wheel

• Hydraulically actuated elevating

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• Rigid-type fifth wheel

• Turntable-type fifth wheel

Frame-less dump with oscillating
bolster Turntable used in some converter dollies
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FIFTH WHEEL HEIGHT AND LOCATION

• Most trailers are designed with an intended
  47-inch (1.19 meters) bolster plate height. This,
  plus the fact that any trailers operated on North
  American roads cannot exceed a height of 13 feet
  6 inches (4.11 meters), determines the plate
  height of fifth wheels.

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TYPES OF FIFTH WHEELS

• SAF Holland
• Fontaine
• JOST

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HOLLAND A-TYPE
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HOLLAND B-TYPE
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Holland B-Lock Coupling
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HOLLAND SIMPLEX FIFTH WHEELS
Newer Version of A-Type
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• SAF Holland FWSI (formerly Simplex I) fifth wheel

• SAF Holland FWSI (formerly Simplex
  I) fifth wheel dimensions

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FONTAINE NO-SLACK II FIFTH WHEEL
Self Adjusting
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• Fontaine 5092 air release fifth wheel

• Fontaine No-Slack II

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JOST FIFTH WHEELS

• JOST fifth wheels have been used in Europe for
  a number of years and have recently been made
  available as an option on North American trucks.
  This family of fifth wheels uses a simple locking
  mechanism consisting of just four moving
  components.

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Locking Mechanism Used on a JOST Fifth Wheel
Self Adjusting
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Electronic Lock Indicator
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MAINTENANCE INTERVAL
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FIFTH WHEEL SERVICE TOOLS
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HOLLAND FIFTH WHEEL ADJUSTMENT

• Before attempting to adjust any fifth wheel
  mechanism, ensure that you have correctly
  identified it. Apart from the four locking
  mechanisms cited in this chapter, there are a
  number of others you will encounter, especially
  if you are working on older equipment.

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Shop Talk

• Do not attempt to inspect a fifth wheel
  without removing the grease. The best way to do
  this is to first scrape off as much as possible,
  and then apply some solvent before hot pressure
  washing. Check the turntable plate, throat, and
  saddle/pivot assembly for cracks. Check the
  dynamic action of the locking mechanism and the
  secondary lock integrity. Check all the mounting
  fasteners and welds. Do not weld and cracks in
  deck! 1/8 in wear max on coupler.

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MOUNTING FIFTH WHEELS

• A properly mounted fifth wheel

• (A) Single-angle outboard mount and (B)
  double-angle inboard-outboard mount.

A with mounting plate, B less torsional rigidity
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WEIGHT-OVER-AXLE VARIABLES

• The further forward a fifth wheel is
  positioned on the tractor frame, the higher the
  percentage of weight on the tractor front axle.
  As the fifth wheel is moved rearward, weight is
  shifted off the front axle and on to the rear
  tractor axles.

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SLIDING FIFTH WHEELS
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CAUTION!

• The trailer must be stationary with its
  parking brakes applied to prevent damage to the
  tractor or trailer by uncontrolled sliding of the
  fifth wheel.

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Air slide release plunger position
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Manual slide release plunger position
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SLIDING MECHANISM INSPECTION AND ADJUSTMENT

• When adjusting the locking plungers
• Loosen the locknut and turn adjusting bolt out
  (counterclockwise).
• Disengage and engage the locking plungers. Check
  that the plungers are securely seated without
  binding.
• Turn adjusting bolt in (clockwise) until it
  contacts the rack. Turn adjusting bolt an
  additional one-half turn and then tighten the
  locknut securely.

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KINGPINS AND UPPERCOUPLERS

• The kingpin stub is mounted on the trailer
  upper coupler assembly. It is designed to
  securely engage with the fifth wheel locking
  mechanism and to permit articulation so that a
  tractor/trailer or tractor/train combination can
  turn corners. There are two SAE standard kingpin
  sizes, 2 inches and 3.5 inches. Do not weld worn
  kingpins!

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CAUTION!

• Always consult the manufacturer for the
  correct procedure when welding kingpins to upper
  coupler assemblies. Welding diagrams often are
  provided with replacement kingpins.

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UPPER COUPLERS
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Welding Upper Couplers
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Bowed Upper Coupler
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PINTLE HOOKS
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Two methods of mounting a drawbar to a tongue
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COUPLING DEVICE CVSA OOS

• Commercial Vehicle Safety Alliance (CVSA)
  out-of service (OOS) are not maintenance
  standards. They define the point at which highway
  equipment becomes dangerous to operate. OOS are
  used to issue citations during safety inspections.

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Summary

• The semi-oscillating fifth wheel is the most
  common highway tractor fifth wheel.
• A semi-oscillating fifth wheel articulates or
  oscillates about an axis perpendicular to the
  vehicle centerline that is, on a fore-aft plane.

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Summary (cont.)

• Compensating fifth wheels are designed to
  provide both front-to-rear and side-to-side
  oscillation between the tractor and semi-trailer.
  Side to- side oscillation occurs below the fifth
  wheel plate surface and lessens the effect of
  trailer torque or twist acting on the frame of
  the tractor or lead trailer.

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Summary (cont.)

• Fully-oscillating fifth wheels articulate on
  all planes and are used with gooseneck, low-bed
  trailers, especially those operated on rough, off
  highway terrain.
• Elevating fifth wheels are used on yard shunt
  tractors. They may be equipped with either air or
  hydraulic lift mechanisms.

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Summary (cont.)

• Many fifth wheels are built with a sliding
  mechanism that permits longitudinal adjustment
  placement of the fifth wheel on the tractor
  frame. This allows the point at which the weight
  of the trailer is supported by the tractor to be
  altered according to load and legislative
  requirements.

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Summary (cont.)

• Some OEMs offer in-cab, pneumatic coupling and
  uncoupling. Electronic lock indicators display on
  the dash the coupling status of the fifth wheel.
• Fifth wheel mountings may be plate mounted or
  angle-on-frame mounted.
• The fifth wheel should be inspected every
  30,000 miles (48,000 km) or 3 months, whichever
  comes first.

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Summary (cont.)

• Proper lubrication of the fifth wheel includes
  keeping water-resistant, lithium-based grease
  applied to the fifth wheel plate, lubricating all
  moving parts with light oil, and applying chassis
  grease to the grease zerks at the pivot points
  and the cam.
• Kingpins are usually welded to the trailer
  upper coupler unit and are used to couple a
  trailer to the fifth wheel.