Vehicle construction

1. Chapter 9
Vehicle Construction

2. Objectives
• Define the most important parts of a vehicle
• Explain body design and frame variations
• Compare unibody and body-over-frame
construction
• Identify the major structural parts, sections, and
assemblies of body-over-frame vehicles

3. Objectives (continued)
• Identify the major structural parts, sections and
assemblies of unibody vehicles
• Summarize how to classify vehicles by body,
engine, and drivetrain configurations

4. Introduction
• Vehicle construction refers to how a vehicle is
made
• Vehicles are a maze of interacting mechanical-
electrical systems
• Over 15,000 parts are used in a typical vehicle
• Damage to one part can affect the operation of
another seemingly unrelated part
• Different types of construction require different
methods repair frame/unibody damage

5. Crash Testing
• Vehicles must be light, aerodynamic, and yet
strong and safe
• Computer-simulated crash testing is used before
building a prototype to find weak structural areas
• Critical that passenger compartment is strong
enough to prevent injury
• Certified crash tests are done with a real vehicle
and sensor equipped-dummies
• Crush zones are built into the frame or body to
absorb some of the energy of a collision

6. Vehicle Classifications
• Vehicle classification relates to the construction,
size, shape, number of doors, type of roof, and
other criteria of a motor vehicle
• To communicate properly in collision repair, you
must understand these basic terms

7. Vehicle Construction
• Part or component refers to the smallest units on
a vehicle
• An assembly is several parts that fit together
• Panel refers to a large removable body part
• Pan refers to a floor-related component
• Chassis includes everything under the body,
consisting of the mechanical systems that
support and power the car

8. (B) With body-over-frame construction, a thick gauge steel frame provides the foundation for
holding other parts. This type of construction is commonly used on large trucks and SUVs.
Figure 9-4. Two very different methods used to construct modern vehicles: unibody and
body-over-frame construction
(A) Unibody construction welds major body panels together to form the frame for attaching
the engine, drivetrain, suspension, and other parts. This type of construction is commonly
used on cars.

9. Full Frames
• Body-over-frame vehicles have separate body
and chassis parts bolted to the frame
• Full frame vehicle is heavier - high amounts of
energy are absorbed by the frame in a collision
• Torque boxes allow some twisting to absorb
road shock and collision impact
• Crossmembers extend sideways across frame
rails to support the engine, suspension, chassis
• Full- or partial-frame construction is used on
most full-size and some small pickup trucks

10. Full Frames (continued)
• Frame is an independent separate part
• Perimeter frame has a frame rail near the
outside of the vehicle, and is the most common
• Ladder frame has long frame rails with a series
of straight crossmembers, and is seldom used
• Partial frame is a cross between a solid frame
and a unibody
– Sub-frame assemblies are used at the front and
rear while the unibody supports the middle area

11. Unibody Construction
• Unibody construction uses body parts welded
and bolted together
– Uses lighter, thinner, high-strength steel alloys
• Body shell is formed by welding sheet metal into
a box- or egg-like configuration
– Strength is achieved through shape and design
instead of mass and weight
• Stressed hull structure disperses force over the
entire body shell

12. Space Frame
• Space frame vehicle has a metal body structure
covered with an outer skin of plastic or
composite panels
• Roof and quarter panels may be attached with
mechanical fasteners or adhesives
• After a collision a space frame is more likely to
have hidden damage, or hidden corrosion
• Support members are bolted to unibody bottom
– Needed in high-stress areas to reduce body flex

13. Figure 9-7. The suspension and braking systems bolt
directly to the body on a vehicle with unitized construction.

14. Joining Parts
• Fastened parts are held together with fasteners
• Welded parts are permanently joined by welding
• Press-fit or snap-fit parts use clips or an
interface to fit parts together
• Adhesive-bonded parts use high-strength epoxy
or special glue to hold parts together
• Composite unibody is made of plastics and other
materials
– Keeping metal parts to a minimum cuts weight
while increasing strength and performance

15. Figure 9-8. Note the space frame construction. Composite (plastic) panels fasten to
a metal inner body structure. Composite panels can be made flexible to resist door
dings and small dents.

16. Major Body Sections
• Vehicle is divided into three sections
– Front, center and rear
• Front section includes everything between front
bumper and fire wall
– Also called nose section, front clip, “doghouse”
• Center section or midsection includes body parts
that form passenger compartment
– Also called a “greenhouse”
• Rear section also called tail section, rear clip,
“cathouse”

17. Panel and Assembly Nomenclature
• Panel is a stamped steel or molded plastic sheet
that forms a body part
• When panels are joined with other components,
the result is an assembly
• Vehicles built for American roads
– Left side is steering wheel side
– Right side is passenger side

18. Front Section Parts
• Cowl is near rear of front section, right in front of
the windshield
• Shock towers or strut towers are reinforced body
areas for holding upper parts of suspension
• Dash panel, firewall, or front bulkhead is panel
dividing front and center sections
• Bumper assembly bolts to front frame horns or
rails to absorb minor impacts

19. Figure 9-12. This top view of unibody construction shows how
structural members are added to support the engine suspension
and other mechanical systems.

20. Center Section Parts
• Floor pan is main structural section in bottom of
passenger compartment
• Tunnel is formed in floor pan for transmission
and drive shaft
• Pillars are vertical body members that hold roof
panel in place and protect in case of rollover
• Front pillars extend next to windshield edges
– Must be strong; also called A-pillars
• Center pillars or B-pillars, are roof supports
between front and rear doors

21. Center Section Parts (continued)
• Rear pillars, or C-pillars, extend up from quarter
panels to hold rear of roof
• Rocker panels or door sills are strong beams
that fit at bottom of door openings
• Rear shelf, or package tray, is a thin panel
behind rear seat in front of back glass
• Window regulator is a gear mechanism that
allows you to raise and lower door glass
• Side impact beams are metal bars or corrugated
panels that bolt or weld inside door assemblies

22. Figure 9-15. Doors normally have strong steel beams under the door
skin to protect people during side impact collisions.

23. Rear Section Parts
• Rear hatch is a larger panel and glass assembly
hinged for more access to the rear
• Quarter panels are large side body sections that
extend from side doors back to rear bumper
• Lower rear panel fits between trunk
compartment and rear bumper
• Rear shock towers hold rear suspension
• Inner wheel housings surround rear wheels

24. Gaskets and Seals
• Various gaskets and rubber seals prevent air
and water leakage between body parts
• Seals or weatherstripping are often used around
doors and the rear deck lid
• Rubber seal is partially compressed when door
or lid is closed to form a leakproof connection
• Rubber gasket often seals stationary glass
where it fits into body

25. Anticorrosion Materials
• Anticorrosion materials prevent rusting of metal
parts
• Undercoating is often a thick tar or synthetic
rubber-based material sprayed onto underbody
• After performing repairs, you must restore all
corrosion protection

26. Sound-Deadening Materials
• Sound-deadening materials help quiet
passenger compartment
– Insulation that prevents engine and road noise
from entering passenger area

27. Engine Locations, Drivelines
• Longitudinal engine mounts to crankshaft
centerline front-to-rear
– Used by front-engine RWD vehicles
• Transverse engine mounts sideways in engine
compartment, its crankshaft centerline extends
toward right and left
• Front-engine, front-wheel drive (FWD) has both
engine and transaxle in front
– Constant velocity (CV) axles extend out from
transaxle to power front wheels

28. Engine Locations, Drivelines
(continued)
• Front-engine, rear-wheel drive (RWD) has engine in
front and drive axel in rear
• Rear-engine, rear-wheel drive (RRD) has engine in
back
– Transaxle transfers power to rear drive wheels
• Mid-engine, rear-wheel drive (MRD) has engine
behind front seat
• All-wheel drive uses two differentials for all wheels
• Four-wheel drive uses a transfer case to send
power to two differentials and all wheels

29. Vehicle Sizes
• Compact car is smallest body classification
– Normally uses a 4-cynlinder engine
– Lightweight, gets the highest gas mileage
• Intermediate car is medium in size
– Uses a 4-, 6- or 8-cylinder engine
– Usually has a unibody construction
• Full-size car is large, heavy and often has a high
performance V8 engine
– Either unibody or body-over-frame construction

30. Roof Designs
• Sedan is a body design with a center pillar that
supports roof
• Hardtop does not have a center pillar to support
roof
• Hatchback has a large third door at back,
commonly found on small compact cars
• Convertible has a retractable canvas roof with a
steel tube framework, or a removable hardtop
• Station wagon extends roof straight back to rear
of body with a rear hatch or tailgate

31. Vans and Trucks
• Van has a large box-shaped body to increase
interior volume or space
• Full-size van normally is front-engine, RWD
• Minivan is smaller and often uses front-engine
FWD with unibody construction
• Pickup truck normally has a separate cab and
bed, typically with front-engine, RWD

32. Summary
• Vehicle classification relates to construction, size,
shape, number of doors, type of roof, etc.
• Three main types of frame construction
– Body-over-frame, unibody, and space frame
• Vehicle commonly divided into 3 body sections
– Front section, or nose section
– Center section, or midsection
– Rear section, tail section, or rear clip
• Vehicle sizes: compact, intermediate, full size