Chevrolet Light Duty Truck 1973, Service Manual

Page: 612 / 979

7 M - 2 2 CLUTCHES & M A N U A L T R A N S M IS S IO N S
the synchronizer ring can rotate a small amount relative
to the hub.
The internally splined mainshaft 1st and reverse
synchronizer sleeve (1, Fig. 14) slides along the external
splines of the hub (9, Fig. 14). The 1st speed gear clutch
sleeve splines are recessed to form a shallow annular
groove (2, Fig. 14) in which rest the raised portion of the
keys (8, Fig. 14), when in neutral position. Each spline of
the 1st and reverse speed gear clutch sleeve and each
tooth of the synchronizer ring has on both sides a wedge
angle (9 and 4, Fig. 14). Through the press of these
wedge angles, the engagement of the gears is prevented
until the synchronizer ring (7, Fig. 14) has brought the
mainshaft 1st speed gear (5, Fig. 14) to the speed of the
hub (3, Fig. 14).
SYNCHRONIZING OPERATION
When shifting into 1st speed, the 1st and reverse
synchronizer sleeve (1, Fig. 17) is moved toward the 1st
speed gear. As the three keys (2, Fig. 17) are spring-
loaded, they are moved along at first until they contact
the synchronizer ring (3, Fig. 17) which is also moved
toward the 1st speed gear (4, Fig. 17). The synchronizer
ring pressing against the 1st speed gear cone causes
friction and starts pre-synchronization. The friction
instantly causes the synchronizer ring to turn in relation
to the hub to the amount of the clearance between the
keys and the sides of the synchronizer ring slots (Fig.
17). This small turning action of the syncrhonizer ring
relative to the hub causes the wedge angles (4, Fig. 14) of
the 1st and reverse synchronizer gear to press against the
wedge angles (9, Fig. 14) of the syncrhonizer ring.
Through the movement of the 1st and reverse
synchronizer sleeve to the point where the wedge angle
contact is made, the keys are pressed out of the 1st and
reverse synchronizer sleeve annular groove, and the
action of pre-synchronization by means of the keys is
ended. The necessary additional pressure for the friction
clutch is now directly applied by the pressure of the
wedge angles of the 1st and reverse synchronizer sleeve
onto the wedge angles of the synchronizer ring. The
pressure caused by this friction prevents a further
engagement of the 1st and reverse synchronizer sleeve as
the wedge angles of the synchronizer ring lock the wedge
angles of the 1st and reverse synchronizer sleeve.
Only when the friction of the syncrhonizing clutch has
equalized the speeds of the 1st speed gear and the hub -
synchronization - friction and pressure on the synchro­
nizer ring wedge angles are relieved.
The wedge angles of the 1st and reverse synchronizer
sleeve now can push aside the synchronizer ring wedge
angles allowing the 1st and reverse synchronizer sleeve
splines to engage the 1st speed gear teeth (Fig. 17). The
keys are now again located in the middle of the
synchronizer cover slots. According to the relative speeds
of the roating hub and the gear to be synchronized
either the right or the left wedge angles of the hub apply
pressure onto the right or left wedge angles of the
synchronizer ring.
Fig. 1 6 — S y n c h r o n iz e r H u b a n d R in g
LIGHT DUTY TRUCK SERVICE MANUAL