Chapter 33

Heavy-duty Truck Trailers

Objectives (1 of 2)

• Describe what is meant by semi-trailers and full trailers.

• Identify the various different tractor/trailer and train combinations.

• Describe what is meant by full frame, unibody, and monocoque.

• Explain the various types of hitching mechanisms used and their effects on tractor/trailer or train designation.

Objectives (2 of 2)

• Describe the design characteristics of the dry van, reefer, flatbed, tanker, and other types of highway trailer.

• Explain the operating principles of a reefer trailer.

• Outline some common trailer maintenance practices.

Types of Trailers

Semi-trailer

B-Train

Full Trailer

A-Train

Converter Dolly

Gooseneck

Unibody

C-Train

Cargo Vans

Reefer (1 of 2)

Reefer (2 of 2)

Flat-Bed

Dump Trailers

Tankers

Shop Talk

• For optimum brake performance and safety, both wheel ends of each axle must have the same type of lining and drum equipment.

• If the trailer has tandem axles, both axles must also have the same type of wheel equipment.

• The vehicle brake-lining thickness must be the same on each brake shoe and on each side of the axle.

• When brake linings are 1/4 inch in thickness or less at their thinnest point, they should be replaced.

Shop Talk

• One of the weight-savers now being used as an option by some trailer OEMs is fiber composite springs

• They can save up to 50 pounds per spring, and can outlast steel springs.

• Although the initial cost is around four times that of steel springs, they can last the life of the trailer, so they are ultimately, an economical choice.

Landing Gear

Trailer Lighting (1 of 2)

Trailer Lighting (2 of 2)

• See Table 33-1 on page 1092 of textbook.

Reflective Tape

Shop Talk

• The entire body shell in a unibody van trailer is the frame. If any body component is damaged the structural integrity of the frame is at risk.

• A slightly damaged floor or out-of-square doorframe can be an indication of a much more serious problem.

Caution

• High modern power wash equipment can produce high impact water jets.

• Take care when using it on trailer panels and tanker skins because it can indent or cause abrasive damage.

Summary (1 of 6)

• A semi-trailer is a trailer in which a portion of the trailer weight is supported by the tow unit— either a tractor or a lead trailer.

• A full-trailer is any trailer in which the trailer weight is self-supported and the unit is towed by a tractor or lead trailer by means of a hook and drawbar assembly.

• A semi-trailer can be converted to a full-trailer by means of a converter dolly.

• A train is a combination of a tractor and multiple trailers.

Summary (2 of 6)

• An A-train double consists of a tractor, semi-lead trailer, and full-pup trailer.

• A B-train double consists of a tractor, semi-lead trailer, and semi-pup trailer.

• A C-train double uses a rigid double drawbar and converter dolly to attach the pup trailer.

• Many van trailers use a unibody or monocoque frame.

Summary (3 of 6)

• A unibody frame is essentially a shell in which all of the shell components play a role in the frame dynamic, including the floor, side panels, bulkhead, doors, and roof.

• The van trailer is the most common truck trailer on North American roads.

• There are two ways to obtain light weight without sacrificing strength. – One is by using lighter, more expensive materials

such as aluminum and high-strength steel in posts and crossmembers.

– The other is to use wall posts and floor cross-members that have a deeper section.

Summary (4 of 6)

• A 1-inch increase in the width of a 53-foot trailer often makes the difference between getting two pallets side by side or not.

• Freight vans are probably the most widely used trailer model in operation.

• Modern refrigerated trailers or insulated vans are dry freight vans that are completely insulated and have a reefer unit usually located at the front or nose of the trailer.

Summary (5 of 6)

• In addition to vans, there are several trailer types and designs. – One of the most common types is the platform or

flatbed trailer. • The number of axles and tires used with each trailer

design depends on the rated load it is intended to carry.

• There are two basic designs of tank trailers: liquid (wet) haulers and dry-bulk haulers.

• Landing gear damage often results from driver and yard jockey abuse especially during coupling and uncoupling.

Summary (6 of 6)

• Trailer wheel and tire designs are generally interchangeable between tractors and trailers.

• Trailer slide tandems allow the load bridge formula to be altered; they increase flexibility, maneuverability, and ability to meet weight laws.

• Trailers must be serviced on regular preventive maintenance schedules: service schedules may be based on hubdometer mileage or in applications that are used intermittently, by calendar.