GMC 1989 Light Duty Truck, Repair Manual, Page: 925 / 998

BORG WARNER TRANSMISSIONS 7B 4-1
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SECTION 7B4
BORG WARNER TRANSMISSIONS
CONTENTS
SUBJECT PAGE
D e s c rip tio n .................................................................................................................................................................................... 7B4- 1
Disassembly of the 77 mm T ra n s m is s io n ..............................................................................................................................7B4- 2
Disassembly and Assem bly of Sub-A ssem blies.................................................................................................................. 7B4- 7
Main Drive G e a r......................................................................................................................................................................... 7B4- 7
M ainshaft.................................................................................................................................................................................... 7B4- 7
Extension H o u s in g .................................................................................................................................................................. 7B4-10
Main Drive Gear Bearing R e t a in e r .......................................................................................................................................7B4-10
Shift C o ver.................................................................................................................................................................................. 7B4-11
Transmission Assembly (Installation of Sub-A ssem blies)................................................................................................ 7B4-12
Specifications................................................................................................................................................................................ 7B4-14
Fastener T o r q u e .......................................................................................................................................................................7B4-14
L u b ric a tio n ................................................................................................................................................................................ 7B4-14
Special Tools.................................................................................................................................................................................. 7B4-15
DESCRIPTION
The
77 mm
5 speed is a constant mesh transmission,
synchronized in all speeds except reverse.
The main components are:
1. Main drive gear.
• An integral shaft is splined to engage with the
clutch driven plate.
• The gear drives the countergear.
• A tapered bearing supports the shaft in the
case.
2. Countergear.
• The countergear is one unit for constant rota­
tion with the main drive gear.
• Bearings support the countergear in the case.
• Thrust washers limit the play of the counter­
gear.
• An extra gear is mounted to the countergear
for 5th speed.
3. Mainshaft.
• The drive gears rotate freely on the mainshaft
and are in constant mesh with the counter­
gear.
• Key type synchronizers engage the gears.
• The 1st and 2nd synchronizer hub is ma­
chined in place.
• A tapered bearing supports the mainshaft in
the rear of the case.
• Roller bearings support the mainshaft inde­
pendently in the main drive gear.
• The main drive gear and mainshaft are engaged by
a synchronizer for direct drive in top gear.
• Thrust washers limit the play of the mainshaft.
4.
Reverse idler gear.
• The idler gear drives the mainshaft in reverse.
• The idler gear is supported on it’s own shaft.
5.
Shift lever.
• The shift lever is mounted on the extension
housing and holds the shift lever.
• The shift lever moves the shafts which are
mounted in the transmission top cover.
• Shift forks mounted on shafts move the syn­
chronizers to engage the gears.
• A pin-type interlock blocks the other shafts
when one is moved.
Certain precautions should be followed when repairing
the transmission. Unless proper care is taken, the compo­
nents may be damaged.
• Repair of a transmission should be done in a clean
work area. The outside of the case should be clean
to keep dirt out of the transmission. On transmis­
sions with a standard gearshift lever, install the lever
before cleaning the outside of the transmission.
• During transmission repair, all the parts should be
cleaned in cleaning solvent and then air dried. Wip­
ing cloths or rags should not be used to dry the
parts as lint may get on the parts and cause trouble
later. All the parts, except those being worked on,
should be kept covered with clean paper.