Chevrolet 10 Series 1970 Service Manual page 484

CLUTCHES AND TRANSMISSIONS 7-54
W hile road testing with the transm ission o il p re s -
sure gauge attached and the vacuum m odulator tube
L2-2nd G ear - Steady road load at approxim ately 25 mph
Gear
1st
2nd
3rd
3rd
R e v e rs e
Tran sm ission o il p re s s u re gauge and engine tachom e­
te r should be connected and the o il p re ssu res should
check as follow s:
2. P re s s u re s indicated below are 0 output speed with
the vacuum m odulator tube disconnected and with
engine at 1200 rpm.
Approxim ate
Altitude of Check Neutral
(Ft. above sea l le v e l)
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
3o P re s s u re s indicated below are with the vacuum tube
connected fo r n orm al m odulator operation, and with
su fficient engine speed to s ta b ilize pump p ressu re
(approx. 1000 rpm ).
NOTE: P r e s s u re s are not sign ifican tly affected
by altitude o r b a ro m e tric p ressu re when the
vacuum tube is connected.
Selector L e v e r Position
D rive
( " Z e r o " throttle to fu ll th rottle)
D rive Range, Z e ro T h rottle at 30 mph
R ev. (Z e ro to fu ll throttle)
D rive L I
or
Park L2 R e v e rs e
150 150 244
150 150 233
150 222
145
212
138 150
132 150 203
194
126 150
186
121 150
116 150 178
connected, the transm ission p ressu res should check
approxim ately as shown on chart.
Minimum
145 psi
Minimum
60
60
95
D riv e , Neutral, Park
60
TURBO H Y D R A -M A TIC 4 0 0 M ODULATOR
ASSEMBLY DIAGNOSIS
A fte r thorough investigation of fie ld returned modulator
a ssem b lies, it has been found that o v e r 50% of the parts
returned as d efective w ere good.
follow in g procedu re is recom m ended fo r checking Turbo
H ydra-M atic 400 modulator assem blies in the fie ld b efore
replacem ent is accom plished.
1. Vacuum D iaphragm Leak Check
Insert a pipe clean er into the vacuum connector pipe
as fa r as p ossib le and check fo r the presen ce o f tran s­
m ission oil. If o il is found, replace the modulator.
NOTE: Gasoline o r
in the vacuum side of the modulator. If this is
found without the presence of oil, the m odulator
should not be changed.
2. Atmospheric Leak Check
Apply a lib e ra l coating of soap bubble solution to the
vacuum connector pipe seam , the crim ped upper to low er
housing seam, and the threaded screw sea l (F ig . 5T).
Maximum
155 psi
Maximum
150
260
L I or L2 R everse
150 107
F o r this reason, the
w ater vapor may settle
CHEVROLET TRUCK SERVICE MANUAL