Chevrolet 10 Series 1970, Service Manual

Page: 484 / 671

CLUTCHES AND TRANSMISSIONS 7-54
W hile road testing with the tran sm ission o il p r e s - connected, the tran sm ission p ressu res should check
sure gauge attached and the vacuum m odulator tube approxim ately as shown on chart.
Minimum Maximum
L2-2nd G ear - Steady road load at approxim ately 25 mph 145 psi 155 psi
Gear
Selector L e v e r P osition
Minimum Maximum
1st
D riv e
2nd
3rd
( “ Z e r o ” throttle to fu ll th rottle) 60 150
3rd D riv e Range, Z e ro T h rottle at 30 mph
60
R e v e rs e R ev. (Z e r o to fu ll throttle) 95 260
T ran 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
A ltitude of Check
(Ft. above sea l le v e l)
D riv e
Neutral
Park
L I
or
L2 R e v e rs e
0 150 150 244
2,000 150 150 233
4,000 145 150
222
6,000 138 150 212
8,000 132 150
203
10,000 126 150
194
12,000 121
150 186
14,000 116 150
178
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.
D riv e , Neutral, P a rk L I o r L2 R e v e rs e
60 150 107
TURBO H Y D R A -M A T IC 4 0 0 M O D ULA TO R
ASSEMBLY D IA G N O SIS
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. F o r this reason, the
fo llo w in g procedu re is recom m ended fo r checking Turbo
H yd ra-M atic 400 modulator assem b lies in the fie ld b efore
replacem en t is accom plished.
1. Vacuum D iaph rag m Leak Check
In sert a pipe clean er into the vacuum connector pipe
as fa r as p ossib le and check fo r the p resen ce o f tra n s­
m ission oil.
If o il is found, rep lace the modulator.
NOTE: Gasoline o r w ater vapor m ay settle
in the vacuum side of the m odulator. If this is
found without the p resen ce 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 p ed upper to low er
housing seam , and the threaded sc re w s e a l (F ig . 5T).
CHEVROLET TRUCK SERVICE MANUAL