GMC 1989 Light Duty Truck, Repair Manual, Page: 953 / 998

SECTION 7D2
NEW PROCESS 241 TRANSFER CASE
CONTENTS
SUBJECT PAGE
New Process 241 Transfer C a s e ...........................................................................................................................................7D2- 1
D escrip tio n ............................................................................................................................................................................... 7D2- 1
Disassembly of Transfer C a s e ............................................................................................................................................... 7D2- 4
External C o m p o n e n ts ...........................................................................................................................................................7D2- 4
Mainshaft Extension and Oil Pump H ousing........................................... ...................................................................... 7D2- 4
Internal C om ponents............................................................................................................................................................. 7D2- 4
Cleaning and In spectio n ........................................................................................................................................................... 7D2- 7
Assembly . . . ................................................................................................................................................................................7D2- 8
Bearing and Seal Replacem ent........................................................................................................................................... 7D2- 8
Internal C om ponents............................................................................................................................................................. 7D2- 9
External C o m p o n e n ts ........................................................................................................................................................... 7D2-10
Specifications ..............................................................................................................................................................................7D2-14
Special T o o ls ................................................................................................................................................................................7D2-14
NEW PROCESS 241 TRANSFER CASE
DESCRIPTION
The Model 241 transfer case is an aluminum case,
chain drive, four position unit providing four-wheel drive
high and low ranges, a two-wheel high range, and a
neutral position. The model 241 is a part-time four-wheel
drive unit. Torque input in four-wheel high and low ranges
is undifferentiated. The range positions on the Model 241
are selected by a floor mounted gearshift lever.
The case is a two-piece aluminum case containing front
and rear outp ut shafts, two drive sprockets, a shift
mechanism and a planetary gear assembly. The drive
sprockets are connected and operated by the drive chain.
The planetary assembly which consists of a six pinion
carrier and an annulus gear provide the four-wheel drive
low range when engaged. Reduction ratio is 2.72:1 in this
range (figures 1 and 2).
IDENTIFICATION
An identification tag is attached to the rear half of the
transfer case (figure 3). This tag provides the transfer
case m odel number, low range reduction ratio, and
a sse m b ly num ber. The in fo rm a tio n on th is tag is
necessary for servicing information. If the tag is removed
or becomes dislodged during service operations, it should
be reattached using an adhesive sealant such as Loctite
242, or equivalent.
POWER FLOW
In all drive range positions input torque is transm itted to
the transfer case gear train through the transfer case
input gear.
In 2H range, torque flows from the input gear to the
range shift hub and main shaft. Torque flow continues
through the slip yoke which is splined to the mainshaft,
and finally to the rear propeller shaft and axle. In 2H
range, the mode synchronizer remains in the neutral
position and does not lock the drive sprocket to the
mainshaft. As a result, torque is not transferred to the
driven sprocket.
In 4H range, input torque from the input gear is
transmitted to the mainshaft in exactly the same fashion
as in 2H range. However, in 4H position, the mode
synchronizer sleeve is shifted into engagem ent with the
clutch teeth of the drive sprocket. This locks the drive
sprocket to the m ainshaft through the synchronizer.
Torque is transm itted through the drive sprocket to the
driven sprocket by the connecting drive chain. Since the
front output shaft is splined to the driven sprocket, torque
flows through the front output shaft to the front propeller
shaft and axle resulting in high range four-wheel drive.
In 4L range, the path of torque through the transfer
case is exactly the same as in 4H range but with one
major difference. In 4L range the range shift hub is shifted
into engagem ent with the planetary carrier. This causes
the input gear to rotate the planetary pinions inside the
annulus gear, causing the planetary carrier, range shift
hub and mainshaft to rotate at a gear reduction ration of
2.72:1.