Chevrolet 70 1969 Series, Shop Manual

Page: 826 / 913

TRANSM ISSIO N AND CLUTCH 7-80
auxiliary must be made. T he remote units and lin k ­
age must be in good w orkin g order if the transm is­
sion and auxiliary are expected to shift satisfactorily.
M a n y times the answer to the trouble is apparent
when the unit is inspected prior to disassembly, but
this evidence is often lost when the parts are sepa­
rated. If possible, check the unit prior to disassem­
bly. Bear in mind that a careful inspection of the unit
should be made as each disassembly step is per­
formed.
It is poor practice to disassemble a unit or com ­
plete transm ission as quickly as possible without
bothering to examine the parts as they came down.
It happens m any times that a mechanic has com ­
pletely disassembled a unit and failed to find the
cause of the trouble because he did not bother to ex­
amine the parts as they came apart. After the trans­
mission is disassembled, check the lubricant for for­
eign particles which often reveal sources of trouble
that are overlooked during the disassembly.
N O ISY OPERATION
N o ise is usually very elusive and generally not the
fault of the transm ission; therefore, mechanics should
road test to determine if the driver’s complaint of
noise is actually in the transmission.
N O IS E A R IS IN G O U T SID E T R A N S M IS S IO N
In num erous instances, drivers have insisted that
the noise was in the transm ission; however, investiga­
tions revealed the noise to be caused by one of the
following conditions:
1. Fan out of balance or blades were bent.
2. Defective vibration damper.
3. C rankshaft out of balance.
4.
Flywheel out of balance.
5. Flywheel m ounting bolts loose.
6. Engine rough at idle producing rattle in gear
train.
7. Clutch assembly out of balance.
8. Engine mounts loose or broken.
9. Power take-off engaged.
10. Universal joints worn out.
11. Propeller shifts out of balance.
12. Universal joint angles out of phase or at exces­
sive angle.
13. Center bearings in drive line dry - not m ou n t­
ed properly, etc.
14.
W heels out of balance.
15.
Tire treads hum m ing or vibrating at certain
speeds.
16.
A ir leaks on suction side of induction system
-especially with turbo-chargers (if used).
N O IS E A R IS IN G IN T R A N S M IS S IO N
M echanics should try to locate and eliminate noise by
m eans other than transm ission removal, or overhaul.
However, if the noise appears to be in the transm ission
try to break it down into the following classifications. If
possible, determ ine w hat position the gear shift lever is in
when the noise occurs. If the noise is evident in only one
gear position, the cause of the noise is generally traceable
to the gears in operation.
1. Growl and H um m ing, or m ore serious, a grinding
noise. These noises are caused by worn, chipped, rough or
cracked gears. As gears continue to wear, the grinding
noise will be noticeable, particularly in the gear position
that throws the greatest load on the worn gear.
2. Hissing, or m ore serious, a thum ping or bum ping-
type noise. Hissing noises could be caused by bad bear­
ings. A s bearings w ear and retainers start to break up,
etc., the noise could change to a thum ping or bum ping.
3. M etallic Rattles within the transm ission usually result
from a variety of conditions. Engine torsional vibrations
are transm itted to the transm ission through the clutch. A
characteristic of the two-plate clutch is a rattling noise,
due to oscillation of the interm ediate plate drive lugs
within the flywheel openings when the clutch is released.
In general, engine speeds should be 600 rpm or above to
elim inate objectionable rattles and vibration during the
idle. A defective or faulty injector would cause a rough or
lower idle speed and a rattle in the transm ission. R attle
could also be caused by excessive backlash in power
take-off unit m ounting.
4. Im proper L ubricants, or lack of lubricant, can pro­
duce noises. Transm issions with low oil levels som etim es
run hotter than norm al, as there is insufficient lubricant
to cool and cover the gears.
5. Squealing, particularly when the transm ission is oper-
ating at higher speeds, could be caused by one of the
free-running gears seizing on the thrust face or fluted di­
am eter tem porarily and then letting go. In general, a mild
seizure will clear itself up and the transm ission will con­
tinue to operate very satisfactorily w ithout this defect
being known. See Step 7 following:
6. G ear Seizure at high speed usually accom panied with
loud squaling noise. This type of seizure is readily a p p ar­
ent to the driver since the truck will suddenly slow down
as if the brakes were being applied. If the truck continues
to move ahead, even though the gearshift lever is placed in
neutral, it would indicate the floating gear on the m ain ­
shaft had seized. Depressing the clutch should interrupt
the driving torque. T he seized gear could e checked quite
readily by depressing the clutch and checking the action
with the gearshift lever progressively in all shift positions.
If releasing the clutch tends to kill the engine, then this
rear position has not seized. In other words, the transm is­
sion would be in two gears at the sam e time. By a process
of elim ination, the gear at fault can be readily identified.
See Step 7 following:
7. Vibration: G ear seizures on thrust faces or fluted di­
am eters are usually caused by vibrations in the power
train - this could be engine, propeller shafts, joint angle,
rear axle, differentials, etc.
a. Im proved highways perm it sustained high speeds. The
fact that engines and entire power trains can now cruise
CHEVROLET SERIES 70-80 H E A V Y DUTY TRUCK SH O P M A N U A L