Front Axle/Steering Flashcards
% of GVW carried by front axle
25-37%
Key contributors to amount of weight carried by front axle
SFFA or SBFA,
5th wheel position (tractor)
body load location (truck)
what is axle center called
beam
what is beam usually made from
forged steel I-beam (most common)
round tubular tempered seamless steel (heavy loads)
2 types of front axles
Driving
non-driving
when would front axle be driving axle
off-road
extreme heavy duty
In phrase 6x4, what does 6 mean
truck has 3 axles
in phrase 6x4, what does 4 men
truck has 2 axles driven by engine
what axle config is most common for class 8 tractors
6x4
2 common examples of measurement from front bumper to centerline of front axle
SFFA
SBFA
Which type of front axle carries more load on the front axle
SBFA
when would you want a SFFA
- distribute loads where possibility of overloading front axle exists
- where Federal bridge law requirements are enforced
what rating range does PB offer for non-steer front axles
10-22k pounds
what rating range does PB offer for steer front axles
12-23k pounds
what is gawr
gross axle weight rating
what are the components that determine gawr
axle suspension wheels tires steering gear
what is usually used to drive a front drive axle
transfer case mounted behind the transmission
what option other than transfer case can be used for powering front drive axle
AWD system - divider often called transfer case
what is used to ensure front and rear wheels receive the torque in same proportion for front drive axle
differential
what is normal size of power steering reservoir
2 quarts
what is happens to steering reservoir for GAWR 16-20k pounds?
larger reservoir required
what are key factors for steering geometry (alignment)
- caster
- camber
- ackermann geometry
- toe-in/toe-out
what is caster
fore/aft tilt of top of steering knuckle pin
what is a positive caster
knuckle pin toward rear of vehicle
what caster angle does peterbilt use?
why?
+4 degrees
-maintain steering stability and steering return to center
more positive increases effort
how can caster angle be adjusted
-inserting wedge-shaped shims between front suspension springs and front axle beam (or spacer block if installed)
what is camber
vertical tilt as seen from front or rear of truck
what is positive camber
top of wheel away from axle
What is Toe
relationship of distance between front and rear of front tires
What is toe-in
distance between tires at front is smaller than distance of rear of front tire
which wheel cut angle is normally quoted
Inside is normally quoted (and has larger angle)
what factors influence wheel cut angle
- tire size
- wheel size
- width of front axle
what are the 2 turning radius measurements
- curb to curb - arc desribed by front wheel
- wall to wall - described by outside edge of bumper or fender
