Chevrolet 10 1971 Series Chassis Service Manual page 302

CLUTCHES AND TRANSMISSIONS 7-26
Approximate Altitude
of Check (Ft. Above
Sea Level)
2000
4000
6000
8000
10000
12000
14000
Fig. 6— Vacuum Modulator Assembly
V ACU U M MODULATOR ASSEMBLY
1. V acuum D iap hrag m Leak Check
Insert a pipe cleaner into the vacuum connector pipe
as far as possible and check for the presence of trans­
mission oil. If oil is found, replace the modulator.
Gasoline or water vapor may settle in
NOTE:
the vacuum side of the modulator. If this is
found without the presence of oil, the modulator
should not be changed.
2. Atm ospheric Leak Check
Apply a liberal coating of soap bubble solution to the
vacuum connector pipe seam, the crimped upper to lower
housing seam (Fig. 6). Using a short piece of rubber
tubing, apply air pressure to the vacuum pipe by blowing
into the tube and observe for leak bubbles. If bubbles
appear, replace the modulator.
Do not use any method other than human
NOTE:
lung power for applying air pressure, as pres­
sures over 6 psi may damage the modulator.
Absolute
Manifold
Pressure
("Hg)
0 16
16
16
16
16
16
16
16
Relative
Drive
Engine
Neutral
Vacuum
Park
("Hg)
12 86
12
89
12
91
12
94
12 97
12 99
12
101
12
103
ENDS TO BE SQUARE
SCRIBED LINE
Fig. 7—-Bellows Comparison Gauge
3. Bellows Com parison Check
Using a comparison gauge, as shown in Fig. 7, com­
pare the load of a know good Turbo Hydra-Matic 350 mod­
ulator with the assembly in question.
A. Install the modulator that is known to be acceptable
on either end of the gauge
B. Install the modulator in question on the opposite end
of the gauge.
Holding the modulators in a horizontal position,
C.
bring them together under pressure until either
modulator sleeve end just touches the line in the
center of the gauge. The gap between the opposite
modulator sleeve end and the gauge line should then
be 1/16" or less. If the distance is greater than
this amount, the modulator in question should be
replaced.
4. Sleeve A lignm ent Check
Roll the main body of the modulator on a flat surface
and observe the sleeve for concentricity to the cam. If
the sleeve is concentric and the plunger is free, the mod­
ulator is acceptable.
Once the modulator assembly passes all of the above
tests, it is an acceptable part and should be re-used.
L-6 and
V-8 Reverse
LI or L2
106 130
108 134
110 139
112
143
114 147
116 150
117
154
119 157
1 3 /3 2 " TO 3 / 8 "
ROUND OR FLAT STOCK
10-30 CHEVROLET TRUCK SERVICE MANUAL