Chevrolet 70 Series 1970, Service Manual

Page: 612 / 841

TRANSMISSIONS AND CLUTCHES 7-13
TRUCK MODELS WITH ALLISON AUTOM ATIC TRANSMISSION
LINKAGE ADJUSTMENTS
P r io r to making any ch eck s o r adjustm ents of
tra n sm issio n manual and throttle control linkage,
check perform ance of the engine. The tr a n sm is­
sion is often blam ed for poor operation of the
v e h ic le when the engine i s not tunedto d eliver peak
p ow er. R efer to GASOLINE ENGINES (SEC.
6
A) of
th is manual fo r recom m ended tune-up p r o c ed u res.
It should be kept in mind, that to a ssu r e efficient
perform ance of pow er plant, the tra n sm issio n
should be a s carefu lly balanced with the engine as
a r e fu el and ignition s y s te m s .
The A lliso n tr a n sm issio n control linkage m ust
b e checked and p rop erly adjusted w henever any of
the follow ing events occur:
1. At tim e of "New V eh icle Inspection," after
fin al engine idle adjustm ents have been made.
2. A fter any tr a n sm issio n control linkage has
been rem oved or rep laced .
3. A fter tr a n sm issio n has been rem oved and
r e in sta lle d in v e h icle.
4. When tr a n sm issio n i s not perform ing
p ro p erly .
ACCELERATOR AND TV LINKAGE
ADJUSTMENTS
WARNING: DO NOT start engine with
shift linkage disconnected, as serious
injury could result to vehicle or personnel.
The throttle linkage to tr a n sm issio n m ust be
p rop erly adjusted so that engine and tra n sm issio n ,
a s a m atched p a ir, can give maximum perform ­
a n ce. If tr a n sm issio n th rottle linkage i s in c o r r e c t­
ly adjusted, the engine may not operate at full
governed rpm , o r the tra n sm issio n upshift and
downshift points may be in co rrect.
Throttle linkage to the tra n sm issio n should be
adjusted so that tr a n sm issio n upshift o ccu rs at
approxim ately 50 rpm below engine governed speed
during fu ll throttle operation.
A detent p osition is incorporated in throttle
linkage to provide additional control of tr a n sm is­
sio n sh ifts. If the sh ift points a re not c o r r e c t at
the to-d eten t p osition (full throttle), the linkage
re q u ires adjustm ent. If the to-detent shift points
a r e c o rrect, but the through-detent shift points
a re not c o rr ect, the TV m echanism in the tra n s­
m issio n may be stick in g . The through-detent p o s i­
tion should not allow tr a n sm issio n to upshift and
should allow downshifts at highest rpm p o ssib le .
CAUTION: The transmission should
not be operated if throttle linkage is not
adjusted correctly because insufficient
TV pressure could cause reduction of
main pressure, which in turn, might re ­
sult in clutch slippage and transmission
failure. ________________________
A c c e le ra to r and TV Linkage Adjustment
P roced u re (R efer to F ig . 14)
1. Start engine and adjust id le sp eed to 575-
600 rpm, then stop engine.
2. D iscon n ect c le v is (G) from TV le v e r (F).
P o sitio n le v e r (A) 0 .0 6 0 -in ch from stop (B ).
3. With carburetor throttle le v e r (C) at id le
p osition and le v e r (A) 0.060-in ch from stop (B),
adjust the sw iv e ls on rod (I) to provide fr e e -e n tr y
into le v e r s (A and B ).
4. With carburetor throttle le v e r (C) at id le
p osition , and TV le v e r (F) against rear stop (ro­
tated away from engine), adjust c le v is (G) on rod
(H) for fr e e -e n tr y into le v e r (F). Then turn c le v is
(G), to shorten rod, two full turns. In sta ll c le v is
pin, tighten jam nut and se c u r e c le v is (G) to TV
le v e r (F) with cotter pin.
NOTE: On tilt cab m od els, with carb u retor
throttle le v e r (C) in idle p osition, rod (J) should
c le a r radiator support by 1 /8 -in c h . Lengthen rod
(J), a s n e c e ssa r y .
IMPORTANT: A djustm ent of the detent button
(E) is accom p lish ed by relocatin g the two jam nuts
located on eith er sid e of the cab floor (se e fig . 14).
With the a cce lera to r pedal d ep ressed to the thru-
detent p osition (detent button (E) - com p ressed )
am ple clearan ce m ust e x ist betw een the pedal and
flo o r , to a ssu r e com plete m ovem ent of the TV
linkage to the thru-detent position .
5. With the a c c e le ra to r pedal (D) just touching
detent button (E), the carburetor throttle le v e r
should be in fu ll th rottle p osition . If adjustm ent is
required, shorten or lengthen rods between a c c e l­
erator pedal and carburetor throttle le v e r and, if
n e c e ssa r y , rep osition detent button (E) to obtain
above conditions.
6
. U sing a tachom eter to accu rately ch eck
engine rpm , road te s t o r dynam om eter te s t v e h ic le
to check for fu ll throttle, fu ll load upshift (5th to
6
th). Upshift should occur at approxim ately 50
rpm below the engine governed sp eed . If u p sh ifts
do not occur at sp ecified rpm , adjust a s follow s:
a. To r a is e sh ift point, shorten rod (H), by
turning c le v is (G) one turn at a tim e until the d e­
s ir e d sh ift point is obtained. Tighten jam nut s e ­
cu rely against c le v is .
b. To low er sh ift point, lengthen rod (H) by
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL