Pontiac FIREBIRD 1972 Service Manual page 965

7E-76 1972 PONTIAC SERVICE MANUAL
ROLL MODCLIIOR ON r1.l s r s f ~ c t 1 0 D ~ T ~ R M u t
f THE
S.ttVI SCOhCtklR C T O l k t MODJulOR CAN
I T H E SLttVt lSBtNl.RCNOC1 W l l l Bt VlSlBLt
I
Fig. 7 E - 1 5 0 Checking Concentricity of Sleeve
MODULATOR AND VALVE
INSPECT
1. Inspect modulator assembly for any signs of bending
or distortion (Fig. 7E- 150):
a. Roll main body of modulator on a flat surface and
observe the sleeve for concentricity to the body.
b. If sleeve is concentric and the modulator valve is
free within the sleeve,the modulator is acceptable.
2. Check modulator for atmospheric leakage as follows
(Fig. 7E- 15 1):
a. Apply a liberal coating of soap bubble solution
(available at 5 & 10 cent store) to vacuum connec-
tor pipe seam, crimped upper-to-lower housing
seam and to the threaded screw seal.
b. Using a short piece of rubber tubing, apply air
pressure to the vacuum pipe b y blowing into tub-
ing and observe for leak bubbles.
c. If bubbles appear, replace the modulator.
RIREADED S C R E W S E A L
VACUUM CONNECTOR SEAM ' U PPER TO LOWER HOUSING SEA^
Fig. 7E-151 Vacuum Modulator Seams and Seals
BELLOWS
DIAPHRAGM
Fig. 7E-152 Cross Section of Vacuum Modulator
CAUTION: Do not use any method other than
human lung po wer for applying air pressure as
pressures over 6 psi may damage the modula-
tor.
3. Inspect O-ring seal seat for damage.
4. Check for vacuum diaphragm leakage as follows
(Fig. 7E- 152):
a. Insert a pipe cleaner into vacuum connector pipe
as far as possible and check for presence of trans-
mission fluid.
b. If transmission fluid is found on pipe cleaner,
replace the modulator.
NOTE: Gasoline or water vapor may settle in
vacuum side of diaphragm. If this is foundwith-
out presence of transmission fluid, modulator
should not be changed.
5. Make a bellows comparison check by using a com-
parison gauge (Fig. 7E- 153) and compare the load of
a known good modulator of the same part number
with the modulator in question, as follows:
I
ENDS TO B E SQUARE
WITHIN
U4"
-
SCRIBED LINE
'
'%Y"
TO %'
,
ROUND OR
FLAT STOCK
Fig. 7E-153 Comparison Gauge