Chevrolet 1977 light duty truck, Service Manual

Page: 719 / 861

M i n i m u m M a x i m u m
L 2 - 2 n d G e a r - S t e a d y r o a d l o a d a t a p p r o x i m a t e l y 2 5 m p h
1 4 5 p s i 1 5 5 p s i
G e a r
S e l e c t o r L e v e r P o s i t i o n
M i n i m u m
M a x i m u m
1s t D r i v e
2 n d
3 rd
( “ Z e r o ” t h r o t t l e t o f u l l t h r o t t l e ......................................
.................. 6 0 1 5 0
3 r d D r i v e R a n g e , Z e r o T h r o t t l e a t 3 0 m p h .................
.................. 6 0
R e v e r s e
R e v . ( Z e r o t o f u l l t h r o t t l e ............................................. .................. 9 5
2 6 0
Fig . 7A-6C--OM P r e s s u r e C h e c k
7. R o a d test a n d c h e c k f o r leaks.
VACUUM MODULATOR DIAGNOSIS
A d e f e c t i v e v a c u u m m o d u l a t o r c a n be d e t e r m i n e d
b y p e r f o r m i n g the f o l l o w i n g p r o c e d u r e s .
Vacuum Diaphragm Leak Check
In sert a p i p e c l e a n e r i n to the v a c u u m c o n n e c t o r p ip e
as f a r as p o s s i b le a n d c h e c k f o r the p re se n c e o f
tra n s m i s s i o n oil. I f o il is f o u n d , r e p l a c e the m o d u l a t o r .
G a s o l i n e o r w a t e r v a p o r m a y settle in the v a c u u m
A p p r o x i m a t e
A l t i t u d e o f C h e c k
( F t . a b o v e s e a l e v e l )
D r i v e
N e u t r a l
P a r k
L I
o r
L 2
R e v e r s e
0 1 5 0
1 5 0 2 4 4
2 , 0 0 0 1 5 0
1 5 0 2 3 3
4 , 0 0 0 1 4 5
1 5 0 2 2 2
6 , 0 0 0 1 3 8
1 5 0 2 1 2
8 , 0 0 0 1 3 2
1 5 0 2 0 3
1 0 , 0 0 0
1 2 6 1 5 0
1 9 4
1 2 , 0 0 0 1 2 1
1 5 0 1 8 6
1 4 , 0 0 0
1 1 6 1 5 0
1 7 8
R o a d o r N o r m a l O p e r a t in g C o n d it io n s
sid e o f the m o d u l a t o r . I f this is f o u n d w i t h o u t the
p r e se n c e o f oil, the m o d u l a t o r s h o u l d not be c h a n g e d .
Atmospheric Leak Check
A p p l y a l i b e r a l c o a t i n g o f s o a p b u b b l e s o lu tion to
the v a c u u m c o n n e c t o r p i p e se a m , the c r i m p e d u p p e r to
lo w e r h o u s i n g s e a m , a n d the t h r e a d e d scre w seal ( F i g .
7 A - 9 C ) . U s i n g a s h o r t p ie c e o f r u b b e r t u b i n g a p p l y a ir
p re ssu re to the v a c u u m p i p e b y b l o w i n g in to the tu b e
a nd o b s e r v e f o r le a k b u b b le s . I f b u b b l e s a p p e a r , re p la ce
the m o d u l a t o r .
N O T E : D o not use a n y m e t h o d o t h e r t h a n h u m a n
lu n g p o w e r f o r a p p l y i n g a i r pre ssu re , as p re ssu re s
o v e r 6 psi m a y d a m a g e the m o d u la t o r .
Bellows Comparison Check
U s i n g a c o m p a r i s o n g a u g e , as s h o w n in F i g u r e 7 A -
10 C, c o m p a r e the l o a d o f a k n o w n g o o d m o d u l a t o r w ith
the a s s e m b l y in q u e stio n .
a. In stall the m o d u l a t o r that is k n o w n to be
a c c e p t a b l e o n e it h e r e n d o f the g a u g e ( F i g . 7 A - 1 1C).
b. Install the m o d u l a t o r in q u e s tio n on the
o p p o s i t e end o f the g a u g e . ( F i g . 7 A - 1 2 C ) .
Fig . 7 A - 7 C - O il P r e s s u r e C h e c k - V e h ic le S t a t io n a r y ,
V a c u u m T u b e D is c o n n e c t e d
Drive, N eutral, Park L I o r L2
Reverse
60 150 107
F ig . 7 A - 8 C - O il P r e s s u r e C h e c k - V e h ic le S t a t io n a r y ,
V a c u u m T u b e C o n n e c t e d