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REAR AXLES
•
PRE-DISASSEMBLY INSPECTION
A close inspection o f t h e rear axle differential p r i o r
to disassembly can often reveal valuable i n f o r m a t i o n
concerning t h e extent and type o f repairs or adjust-
ments t h a t are necessary. T h i s i n f o r m a t i o n combined
w i t h t h e road test results w i l l provide a basis for de-
t e r m i n i n g t h e degree of disassembly required.
Because t h e most frequent causes of axle differen-
t i a l noise a r e incorrect r i n g gear " b a c k l a s h " and/or
differential bearing "preload" torque, a few r o u t i n e
adjustments could be a l l t h a t is necessary t o correct
the problem. Therefore, before axle differential disas-
sembly, t h e following measurements should be made:
• r i n g gear "backlash", and
• drive p i n i o n gear shaft bearing "preload" torque.
Record a n d analyze the results. The r e s u l t o f these
measurements w i l l a i d i n d e t e r m i n i n g t h e extent the
required axle differential service.
AXLE SHAFT BEARING NOISE
Defective or damaged axle shaft bearings produce a
v i b r a t i o n o r " g r o w l " noise t h a t w i l l continue after
the transmission is shifted t o " N E U T R A L " and t h e
vehicle is coasting. A " b r i n e l l e d " axle shaft bearing
causes a " w h i r r i n g " noise. "Spalled" axle shaft bear-
ings n o r m a l l y produce a noise s i m i l a r to a " g r o w l "
t h a t is caused by either flaked or p i t t e d bearing r o l l -
ers or b e a r i n g races. Unless t h e damage is severe,
axle shaft bearing noise is seldom noticed a t vehicle
speeds exceeding 30 m p h (48 km/h).
To differentiate between axle shaft bearing noise
and differential gear noise, road test the vehicle on a
smooth road (black-top) a t m e d i u m a n d l o w speed.
W i t h traffic p e r m i t t i n g , "swerve" the vehicle sharply
right-to-left. I f the noise i s caused b y axle shaft bear-
ings, i t w i l l usually increase i n loudness w h e n t h e
vehicle is "swerved"
a n d i t w i l l probably be more
pronounced a t the "loaded" bearing side o f the axle
shaft ( w i t h tapered roller bearings only).
I f the source o f the noise can not be determined, a n
inspection o f the bearings w i l l be necessary.
"KNOCK" AT LOW SPEEDS
Low speed " k n o c k " is u s u a l l y caused b y either a
" b r i n e l l e d " U-joint spider or excessive differential
side gear hub-to-counterbore clearance. Inspect a n d
replace t h e U-joint or t h e differential case and side
gear, as applicable.
BACKLASH "CLUNK"
A loud " c l u n k " noise upon vehicle acceleration and
deceleration can be caused by excessive clearance i n -
v o l v i n g any of the following components (or i n com-
bination):
• d i f f e r e n t i a l p i n i o n mate gear shaft-to-differential
case bore,
• axle shaft splines-to-differential side gear splines,
• d i f f e r e n t i a l side gear hub-to-differential case coun-
terbore,
• d i f f e r e n t i a l side gears-to-pinion gears,
• w o r n t h r u s t washers, and
• excessive r i n g gear "backlash".
Measure
t h e clearances,
inspect t h e components
and replace as required (or, i f applicable, adjust t o
specifications).
DRIVELINE "SNAP"
A d r i v e l i n e "snap" noise r e s u l t i n g f r o m sudden ve-
hicle s t a r t f r o m stop, either forward or reverse, c a n
be caused b y a loose drive p i n i o n gear shaft (axle)
yoke. Remove the drive shaft and the yoke, and i n -
s t a l l t h e yoke 180 degrees f r o m its o r i g i n a l position.
The d r i v e p i n i o n gear shaft bearing "preload" torque
and t h e shaft n u t torque m u s t be adjusted t o t h e
specified values after i n s t a l l a t i o n .
ENGINE AND TRANSMISSION NOISE
Occasionally noise t h a t appears t o originate i n t h e
rear axle is actually caused b y t h e engine or t h e
transmission. To identify the t r u e source o f the noise,
note t h e approximate vehicle speed a n d t h e condi-
tions w h e n t h e noise occurs or when i t is t h e most
pronounced. Stop t h e vehicle i n a quiet place (to
avoid a n y i n t e r f e r i n g noise) and, w i t h the t r a n s m i s -
sion i n " N E U T R A L " , accelerate the engine slowly u p
t h r o u g h and t h e n decelerate down t h r o u g h t h e en-
gine speed t h a t approximately corresponds to the ve-
hicle speed noted when the noise occurred or was t h e
most pronounced. I f a s i m i l a r noise is produced b y
t h i s method, i t w i l l usually indicate t h a t the noise i s
being caused b y the engine or the transmission and
not t h e rear axle.
DRIVE SHAFT VIBRATION
Objectional
v i b r a t i o n , w h i l e t r a v e l i n g o n roads/
streets w i t h a "good" surface, can be caused by t h e
wheels/tires, t h e engine or the drive shaft.
A systematic method o f i d e n t i f y i n g t h e source o f
the v i b r a t i o n w i l l a i d i n a fast and correct repair.
The order of analysis should be:
•
wheels/tires,
• engine, and
• d r i v e shaft.
Tires t h a t are "out-of-round" (i.e., r a d i a l " r u n o u t " )
or wheels/tires t h a t are excessively unbalanced w i l l
cause a l o w frequency
v i b r a t i o n t h a t w i l l
induce
p r o m i n e n t m i r r o r a n d door
"shake".
Tire
and/or
wheel
faults m u s t be corrected before
proceeding
w i t h t h e analysis.
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