Chevrolet 10 Series 1968, Service Manual

Page: 161 / 713

FOUR WHEEL DRIVE 3-22
FOUR WHEEL DRIVE
(SERIES K IO AND K 20 )
INDEX
Page
In tro d u ctio n ............................................................................. 3-22
General D e s c r ip t io n ............................................................. 3 -2 2
Front A x l e ..........................................................................
3_22
Steering Knuckle and “ U” Joint .................................... 3-22
Tran sfer C a s e .................................................................... 3-22
Adapter A s s e m b l y ............................................................. 3_22
F ree-w heeling H u b s .......................................................... 3-23
Pow er T ak e-off ................................................................. 3-23
Other C o m p o n e n ts ............................................................. 3-23
Maintenance and A d ju s tm e n ts ............................................. 3-23
King Pin Trunnion Check and A d ju s t m e n t ................... 3-23
Component P arts R e p la c e m e n t .......................................... 3-25
Free-w heeling H u b s .......................................................... 3-25
Front A xle Assem bly ....................................................... 3-27
R e m o v a l............................................................................. 3-27
Page
I n s t a lla t io n ....................................................................... 3-27
Front Axle Shaft A s s e m b l y .............................................
3-27
R e m o v a l.............................................................................
3-27
R e p a i r s .............................................................................
3-2 7
I n s t a lla t io n ....................................................................... 3-27
Steering K n u c k le .................................................................
3-28
R e m o v a l............................................................................. 3-28
Bearing Cup R e p la c e m e n t............................................. 3-28
Seal R ep la cem en t.............................................................
3-28
In s t a lla t io n .......................................................................
3-28
Tran sfer C a s e ....................................................................
3-28
R e m o v a l.............................................................................
3-28
Adapter A s s e m b l y .......................................................
3-28
R e m o v a l.......................................................................
3-28
I n s t a lla t io n ................................................................
3-28
I n s t a lla t io n ................ ......................................................
3-29
INTRODUCTION
The four-wheel drive models are essentially conven­
tional vehicles which have been modified to include a
driving front axle, a transfer case to distribute power
to front and rear axles with the required propeller shafts
and controls (fig. 1). Service information on these com­
ponents is included in this section.
Refer to the applicable section of this manual for
service information on components which are common
to four-wheel drive and conventional vehicles.
Disassembly and repairs to the Front Axle Differen­
tial is outlined in Section 3 “ Front Suspension’ * 1968
Truck Overhaul Manual. The Adapter and Transfer Case
assemblies are covered in Section 7 “ Transmission” ,
1968 Truck Overhaul Manual.
GENERAL DESCRIPTION
Primary purpose of four wheel drive is to provide
additional tractive effort in off-the-road driving in order
to overcome such obstacles as sand, deep mud or snow,
hilly terrain with steep grades, etc.
With four wheels capable of driving, all the vehicle
and payload weight is utilized to give maximum tire
traction.
The power unit is driven through a Muncie three-speed
or Chevrolet four-speed transmission and consists of an
adapter and a two-speed transfer case with a steering
and driving front axle. A single control lever (fig. 1) is
used to shift the transfer case from direct drive to low
four wheel drive at a ratio of 1.94 to 1, thus eight for­
ward speeds and two in reverse as provided.
Front wheel drive may be engaged or disengaged at any
time without clutching when the transfer case is in direct
drive; however, in returning to 2 wheel from 4 wheel the
accelerator may have to be varied as steady pressure is
applied on lever. This releases gear tooth pressure dur­
ing shifting.
A yoke and trunnion universal joint permits continuous
power flow to each front wheel, regardless of the turning
angle.
Provisions for Power Take-off have been incorporated
in the transfer case.
FRONT AXLE
The front axle is a Spicer hypoid gear axle unit
equipped with steering knuckles. Axle assembly number
and production date are stamped on left tube of assembly.
Refer to Specifications for Spicer Model application.
Conventional truck service brakes are provided on all
4-wheel drive units.
STEERING KNUCKLE AND UNIVERSAL JOINT
To permit the front wheels to be driven as well as
turned, the axle is equipped with steering knuckles and
the axle shafts are equipped with yoke and trunnion type
universal joints.
TRANSFER CASE
The transfer case, also known as a drop gear box, is
the unit which transmits power from the transmission to
the rear and/or front axles and power take-off (fig. 2).
Engagement of front wheel drive, power take-off or speed
range is accomplished through control levers in the cab.
The case is mounted to an adapter at the rear of the
transmission.
Model number, ratio and production date are stamped
on a plate located on top of the transfer case.
ADAPTER ASSEMBLY
An adapter assembly has been designed to locate the
transfer case directly behind the transmission (fig. 2).
Presently there are two adapters available, one for use
with the Muncie three-speed transmission, and one for
use with the Chevrolet truck four-speed. This adapter
assembly design will allow the vehicle body to be lowered
approximately 3 inches and will also eliminate the need
for an intermediate propeller shaft.
The two adapters are similar in that they both contain
a splined drive sleeve. The one for the three-speed
Muncie takes the place of the transmission extension and
has a straight spline input to match the transmission
output shaft spline. The output spline is involute to
CHEVROLET TRUCK SERVICE MANUAL