GMC 1976 ZEO 6083 Maintenance Manual page 470

7- 2 2 TRANSMISSION
stuck.
a. Pressure regulator and/or boost valve
b. Incorrect pressure regulator spring .
c. Too many pressure regulator valve spacers.
d. Pump casting bad.
e. Pressure boost valve installed backwards or
defective.
ting .
f. Wrong type pressure regulator valve.
IMPORTANT :
Use only pressure regulator valve
which has an orifice cup plug in it .
g . Pressure boost bushing broken or other-
wise defective.
5. Control Valve Assembly .
a. Spacer plate-to-case gasket off location .
b. Wrong spacer plate-to-case gasket, or gas-
kets installed in reverse order.
CAUSES OF IMPROPER VACUUM AT
MODULATOR
1 . Engine .
a. Requires tune up .
b. Loose vacuum fittings .
c . Vacuum operated accessory leak (hoses,
vacuum advance, etc.)
d. Engine exhaust system restricted .
2 . Vacuum Line to Modulator.
a. Leak .
b. Loose fitting.
c. Restricted orifice, or incorrect orifice size .
d. Carbon build up at modulator vacuum fit-
e. Pinched line.
f. Grease or varnish material is pipe (no or
delayed up-shift-cold) .
CONTROL VALVE ASSEMBLY--
GOVERNOR LINE PRESSURE CHECK
3 . With vehicle on hoist (front wheels off
ground), foot off brake, in drive, check line pressure
at 1000 rpm .
4. Slowly increase engine rpm to 3000 rpm and
determine if a line drop occurs (7 psi or more).
5. If pressure drop occurs, disassemble, clean and
inspect control valve assembly .
4. Check governor valve entry and ex-
haust ( .020" min.) .
1 . Check screen in governor feed pipe hole
in case assembly .
holes.
1 . Install line pressure gage .
2. Disconnect vacuum line to modulator.
6. If no pressure drop occurs :
a. Inspect governor .
1 . Stuck valve.
2. Weight freeness .
3. Restricted orifice in governor valve.
b. Governor feed system .
2. Check for restrictions in governor pipe .
3. Check for fit of governor pipes in cast
CAUSES OF BURNED CLUTCH PLATES
NOTE:
Burned clutch plates can be caused by
incorrect usage of clutch plates . Also, anti-freeze
in transmission fluid can cause severe damage,
such as large pieces of composition clutch
material peeling off.
1 . Forward Clutch .
a. Check ball in clutch housing damaged,
stuck or missing.
b. Clutch piston cracked, seals damaged or
missing.
c. Low line pressure .
d. Manual valve mispositioned .