Front Axle/Steering

Question 1

% of GVW carried by front axle

Answer 1

25-37%

Question 2

Key contributors to amount of weight carried by front axle

Answer 2

SFFA or SBFA,
5th wheel position (tractor)
body load location (truck)

Question 3

what is axle center called

Answer 3

beam

Question 4

what is beam usually made from

Answer 4

forged steel I-beam (most common)

round tubular tempered seamless steel (heavy loads)

Question 5

2 types of front axles

Answer 5

Driving

non-driving

Question 6

when would front axle be driving axle

Answer 6

off-road

extreme heavy duty

Question 7

In phrase 6x4, what does 6 mean

Answer 7

truck has 3 axles

Question 8

in phrase 6x4, what does 4 men

Answer 8

truck has 2 axles driven by engine

Question 9

what axle config is most common for class 8 tractors

Answer 9

6x4

Question 10

2 common examples of measurement from front bumper to centerline of front axle

Answer 10

SFFA

SBFA

Question 11

Which type of front axle carries more load on the front axle

Answer 11

SBFA

Question 12

when would you want a SFFA

Answer 12

• distribute loads where possibility of overloading front axle exists
• where Federal bridge law requirements are enforced

Question 13

what rating range does PB offer for non-steer front axles

Answer 13

10-22k pounds

Question 14

what rating range does PB offer for steer front axles

Answer 14

12-23k pounds

Question 15

what is gawr

Answer 15

gross axle weight rating

Question 16

what are the components that determine gawr

Answer 16

axle
suspension
wheels
tires
steering gear

Question 17

what is usually used to drive a front drive axle

Answer 17

transfer case mounted behind the transmission

Question 18

what option other than transfer case can be used for powering front drive axle

Answer 18

AWD system - divider often called transfer case

Question 19

what is used to ensure front and rear wheels receive the torque in same proportion for front drive axle

Answer 19

differential

Question 20

what is normal size of power steering reservoir

Answer 20

2 quarts

Question 21

what is happens to steering reservoir for GAWR 16-20k pounds?

Answer 21

larger reservoir required

Question 22

what are key factors for steering geometry (alignment)

Answer 22

• caster
• camber
• ackermann geometry
• toe-in/toe-out

Question 23

what is caster

Answer 23

fore/aft tilt of top of steering knuckle pin

Question 24

what is a positive caster

Answer 24

knuckle pin toward rear of vehicle

Question 25

what caster angle does peterbilt use?

why?

Answer 25

+4 degrees
-maintain steering stability and steering return to center
more positive increases effort

Question 26

how can caster angle be adjusted

Answer 26

-inserting wedge-shaped shims between front suspension springs and front axle beam (or spacer block if installed)

Question 27

what is camber

Answer 27

vertical tilt as seen from front or rear of truck

Question 28

what is positive camber

Answer 28

top of wheel away from axle

Question 29

What is Toe

Answer 29

relationship of distance between front and rear of front tires

Question 30

What is toe-in

Answer 30

distance between tires at front is smaller than distance of rear of front tire

Question 31

which wheel cut angle is normally quoted

Answer 31

Inside is normally quoted (and has larger angle)

Question 32

what factors influence wheel cut angle

Answer 32

• tire size
• wheel size
• width of front axle

Question 33

what are the 2 turning radius measurements

Answer 33

• curb to curb - arc desribed by front wheel

- wall to wall - described by outside edge of bumper or fender