Table of Contents
Advertisement
3 - 8
REAR AXLES
•
R E A R A X L E ALIGNMENT
MEASUREMENT
The following procedure for measuring rear axle
a l i g n m e n t can be used to determine i f a complaint of
abnormal rear t i r e wear is the result of a " b e n t " or
deformed rear axle shaft.
(1) Raise both rear wheels o f f the surface w i t h a
frame contact hoist.
(2) A t t a c h a one-inch long piece o f m a s k i n g tape a t
the center of each t i r e t r e a d for use as "reference
m a r k s " .
(3) Rotate t h e rear wheels u n t i l both
"reference
m a r k s " face the f r o n t o f the vehicle and measure the
distance between the outside edges of the two pieces
of tape. Record t h i s measurement as t h e " f r o n t of
t i r e " (FTR) measurement.
(4) Rotate t h e rear wheels u n t i l b o t h
"reference
m a r k s " face the rear of the vehicle and measure the
distance between the outside edges o f the t w o pieces
of tape. Record t h i s measurement as t h e "rear of
t i r e " (RTR)
measurement.
(5) Subtract the " r e a r o f t i r e " (RTR) measurement
from the "front o f t i r e " (FTR) measurement to obtain
the a m o u n t of wheel "toe". The acceptable rear wheel
"toe" position is 1/16 i n c h (1.6 mm) " t o e - i n " to 3/16
inch (4.8 mm) "toe-out".
(6) Rotate t h e rear wheels u n t i l t h e "reference
m a r k s " are facing d o w n w a r d and measure t h e dis-
tance between t h e outside edges of the two pieces of
tape. Record t h i s measurement as t h e "bottom of
t i r e " (BTR) measurement.
(7) Average t h e " f r o n t o f t i r e " (FTR) and the "rear
of t i r e " (RTR) distance measurements. Subtract t h e
"bottom of t i r e " (BTR) measurement f r o m t h i s aver-
age distance t o o b t a i n t h e camber. The acceptable
amount of camber is 1/16 i n c h to 3/32 i n c h (1.6 to 2.4
mm).
( F T R
+ R T R ) / 2 - B T R =
C A M B E R
I f t h e " b o t t o m o f t i r e " ( B T R ) d i s t a n c e m e a s u r e -
m e n t i s less t h a n t h e a v e r a g e F T R a n d R T R dis-
t a n c e m e a s u r e m e n t , t h e c a m b e r w i l l b e p o s i t i v e
(" + " ) . I f t h e " b o t t o m o f t i r e " ( B T R ) d i s t a n c e
m e a s u r e m e n t i s g r e a t e r t h a n t h e a v e r a g e F T R
a n d R T R d i s t a n c e m e a s u r e m e n t , t h e c a m b e r w i l l
b e n e g a t i v e ("-").
I f t h e "toe" position and/or the amount of camber
is/are not acceptable i n conjunction w i t h t h e abnor-
m a l t i r e wear, a " b e n t " or deformed rear axle shaft is
most l i k e l y the cause.
T I R E / W H E E L B A L A N C E
INDEX
Page
General Information
8
GENERAL INFORMATION
The "off-vehicle" (static) rear tire/wheel balancing
method is preferred for R a m R W D v a n and wagon
vehicles. I f the "on-vehicle" (dynamic) rear t i r e bal-
ancing method is employed, b o t h front wheels m u s t
be securely blocked to prevent a n y vehicle
move-
ment. For vehicles equipped w i t h a standard type dif-
ferential (i.e., not equipped w i t h a S u r e - G r i p or a
T r a c - L o k differential), only t h e rear wheel/tire t h a t
is to be balanced should be l i f t e d off t h e surface.
W h e n i n v o l v e d i n " o n - v e h i c l e "
( d y n a m i c )
r e a r
w h e e l / t i r e b a l a n c i n g , b e a w a r e t h a t a 35 m p h (56
km/h) s p e e d o m e t e r
i n d i c a t i o n r e p r e s e n t s
a 70
m p h (113 km/h) r e a r w h e e l speed. A speed of 35
m p h (56 km/h) is t h e m a x i m u m necessary for dy-
namic wheel/tire balance.
I f
t h e v e h i c l e
i s e q u i p p e d
w i t h
d u a l
r e a r
Page
Sure-Grip/Trac-Loc Differentials
9
w h e e l s , i t i s a b s o l u t e l y n e c e s s a r y t h a t t h e wheel/
t i r e b e r e m o v e d f r o m t h e v e h i c l e w h e n b a l a n c -
i n g i s n e c e s s a r y .
B a l a n c i n g a wheel/tire w i t h t h e "on-vehicle" (dy-
namic) method essentially balances
t h e t i r e , t h e
wheel and the b r a k e d r u m . The "balanced" condition
is lost w h e n the wheels/tires are rotated to equalize
t i r e t r e a d wear, or w h e n t h e wheels/tires are re-
moved f r o m the vehicle for any reason and then not
installed a t the o r i g i n a l location on t h e brake drum/
hub (i.e., before removal, t h e wheel and a stud are
indexed/marked for i n s t a l l a t i o n reference and t h e n
the wheel/tire are i n s t a l l e d a t the o r i g i n a l location).
WARNING: WITH NO LOAD ON THE ENGINE, IT IS
POSSIBLE TO ATTAIN A TIRE ROTATIONAL SPEED
(ANGULAR VELOCITY) THAT IS SUFFICIENT TO
CAUSE VIOLENT TIRE FAILURE AND CREATE A
HAZARDOUS SITUATION.
Advertisement
Table of Contents
