Pontiac FIREBIRD 1972 Service Manual page 841

7B-2 1972 PONTIAC SERVICE MANUAL
And power train encompasses engine, propeller shaft,
universal joint angle, rear axle, differential, extension
bearing, etc.
a. Improved highways encourage sustained high
speed. Engines and entire power trains now cruis-
ing at high rpm can introduce vibration frequen-
cies that weren't critical in the past. At slower
speeds these items would get by unnoticed or only
pass through brief critical periods while accelerat-
ing or decelerating through the gears.
b. In the past, drive line vibrations such as bent
tubes, joints out-of- alignment, clutch out-of-bal-
ance, or gears and shafts in transmission out- of-
balance were fairly obvious. These items are more
critical in vehicles running at sustained high
speeds.
c. Critical vibrations associated with higher speed
are high frequency vibrations that could cause
gear seizures, damaged synchronizers, bearing
failure due to retainer bolt failures, promote bri-
nelling, etc.
Gear whine
-
is usually caused by lack of backlash
between mating gears.
Metallic rattles
-
from within transmission are usu-
ally caused by engine torsional vibrations being trans-
mitted to the transmission through the clutch.
Growl, humming or grinding noise
-
are caused by
worn, chipped, rough or cracked gears. As gears con-
tinue to wear, grinding noise is more evident, espe-
cially in the gear position that throws the greatest
load on the worn gear.
Hissing, thumping or bumping noise
-
hissing noises
could be caused by bad bearings. As bearings wear
and retainers start to break up, etc., the noise could
change to a thumping or bumping noise.
7. Excessive back lash or unmatched constant mesh
gears.
8. Sprung, worn or excessive end play in countershaft.
9. Excessive end play in reverse idler gear.
NOISE IN FORWARD SPEEDS
1. Noisy speedometer drive and/or driven gears.
2. Worn or rough mainshaft rear bearing.
3. Excessive end play of mainshaft gears.
WALKING OR SLIPPING OUT OF GEAR
1. If transmission is walking out of gear, it could be
caused by:
a. Shift linkage out of adjustment, worn or loose to
prevent full engagement of the synchronizer
sleeve.
b. Interference or resistance in side cover shift
mechanism to prevent full engagement of the syn-
chronizer sleeve, such as bent or worn shift fork,
lever and/or shaft, damaged detent cams, spring,
etc.
c. If synchronizer sleeve is engaging fully, look for
some other malfunction which could move sleeve
out of engagement, such as worn clutching teeth
on gears, synchronizer sleeve, blocker ring, etc.
2. Items which could also cause gear walk-out are:
a. Worn pads on shift fork or sleeve worn exces-
sively.
NOISE IN NEUTRAL
b. Worn taper on clutch gear teeth or gears.
1. Improper lubricant or lack of lubrication.
2. Incorrect clutch linkage adjustment.
3. Misalignment of transmission.
4. Worn or scored main drive gear and/or countershaft
bearing rollers.
c. Transmission and engine misaligned vertically or
horizontally.
3. Other items which could cause gear walk-out, espe-
cially on rough roads, are:
a. Detent cam spring in side cover broken.
b. Detent cam notches worn.
5. Worn mainshaft pilot bearings.
6. Scuffed gear tooth contact surfaces on gears; worn or
rough reverse idler gear.
c. If holding gearshift lever will prevent jump-out,
detent cam modification or replacement will often
correct it. However, when a gear has been allowed