Chevrolet 10 Series 1968, Руководство по обслуживанию

Страница: 489 / 713

CLUTCHES AND TRANSMISSIONS 7-26
DIAGNOSIS
MECHANICAL
Any one of the following general complaints may be due
to non-standard mechanical conditions in the overdrive
unit:
1. Does not drive unless locked up manually.
2. Does not engage, or lock-up does not release.
3. Engages with a severe jolt, or noise.
These troubles may be diagnosed and remedied as de­
scribed in the following paragraphs.
1. Does not drive unless locked up manually.
a. Occasionally, the unit may not drive the car fo r­
ward in direct drive, unless locked up by pulling
the dash control. This may be caused by one or
more broken rollers in the roller clutch, the
remedy for which is the replacement of the entire
set of rollers.
b. This may also be caused by sticking of the roller
retainer upon the cam. This retainer must move
freely to push the rollers into engaging position,
under the pressure of the two actuating springs.
c. Sometimes this is due to slight indentations, worn
in the cam faces by the rollers spinning, reme­
died by replacement of the cam.
2. Does not engage, or lock-up does not release
a. Dash control improperly connected--Unless the
overdrive dash control wire is connected to the
lock-up lever on the left side of the overdrive
housing in such a manner as to move the lever all
the way back when the dash control knob is pushed
in, it may hold the shift rail in such a position as
to interlock the pawl against full engagement re ­
sulting in a buzzing noise when overdrive engage­
ment is attempted.
To correctly make this connection, loosen bind­
ing post at lever, pull dash control knob out 1/4",
move lever all the way to the rear, and tighten
binding post.
b. Transmission and overdrive improperly align—
The same symptoms as above may also result
from misalignment, at assembly, of the overdrive
housing to the transmission case, resulting in
binding of the overdrive shift rail, so that the r e ­
tractor spring cannot move the rail fully forward,
when the dash control knob is pushed in, and the
transmission is not in reverse. Under such con­
ditions, the unit may remain fully locked up.
To test for this, be sure that the transmission
is not in reverse; disconnect the dash control
wire from the lock-up lever, and feel the lever
for free forward movement. If the lever can be
moved forward more than 1/4", it indicates that
misalignment probably exists. To correct this,
loosen the capscrews between the overdrive hous­
ing and transmission case, and tap the adapter
plate and overdrive housing until a position is
found where th e rail s h i f t s freely; tighten
capscrews.
c. Kickdown switch improperly adjusted— The posi­
tion of the kickdown switch should be adjusted, by
means of the two large nuts which clamp the
switch shank, so the switch plunger travels 3/16"
before the throttle lever touches its stop.
Occasionally the large nuts which clamp the
OVERDRIVE
switch through the switch bracket are tightened
sufficiently to bend the switch shank, thus p re­
venting free motion of the switch stem. This may
usually be remedied by loosening the upper of the
two nuts.
d. Improper installation of solenoid--If car cannot
be rolled backward under any circumstances and
there is no relay click when the ignition is turned
on, it probably indicates that the solenoid has
been installed directly, without twisting into the
bayonet lock between solenoid stem and pawl,
thus jamming the pawl permanently into over­
drive engagement. If the car will occasionally
roll backwards, but not always, (and there is no
relay click when the ignition switch is turned on)
it may indicate that, upon installation, the bayonet
lock was caught, and the solenoid forcibly twisted
into alignment with the attaching flange, thus
shearing off the internal keying of the solenoid.
Under these circumstances, the end of the sole­
noid stem may not catch in the pawl, and upon
release of the solenoid, the pawl will not be with­
drawn promptly from engagement, but simply
drift out. If the solenoid stem end has its two
flats exactly facing the two solenoid flange holes,
it will not withdraw the pawl properly. If the
stem can be rotated when grasped by a pair of
pliers, it indicates that the internal keying has
been sheared.
e. Improper positioning of blocker ring--Occasion-
ally, either in assembly at the factory, or in
service operations in the field, the internal parts
of the overdrive unit may have been rotated with
the solenoid pawl removed, causing the blocker
ring to rotate, so that its two lugs are not proper­
ly located with respect to the pawl.
In other words, the solid portion of the blocker
ring may be in alignment with the pawl, which
will prevent full engagement of the pawl with the
sun gear control plate.
To test for this condition, remove solenoid
cover, pull dash control knob out, roll car 2 ft.
forward. Push dash control in, turn ignition
switch on. Then ground the “ KD” terminal of
relay, and watch movement of center stem of
solenoid. It should not move more than 1/8" when
the solenoid clicks. Then, with the relay terminal
still grounded, shift into low gear, and roll car
forward by hand. Solenoid stem should then move
an additional 3/8", as the pawl engages fully.
These two tests indicate proper blocker action.
Unless both tests are met, the blocker ring is
probably not in the correct position.
3. Engages with a severe jolt or noise
Insufficient blocker ring friction may cause the ring
to lose its grip on the hub of the sun gear control
plate. Check the fit and tension of the ring as de­
scribed under “ Cleaning and Inspection” .
4. Free-wheels at speeds over 30 MPH
If cam roller retainer spring tension is weak the unit
will free wheel at all times. Check spring action as
described under “ Cleaning and Inspection” .
CHEVROLET TRUCK SERVICE MANUAL