Subaru XT 1988 Service Manual page 528

3-2 AUTOMATIC TRANSMISSION AND DIFFERENTIAL
(3) Band brake
• Construction
i"
ci
Rev, . c, lutch drum
_~__
_
~"
Lock nut
~- ~::..:::",
' W h
~"~' ~,"
-- , as er
~.,
" ' i
''\: M -
a-ring
\W~
\;;t ' , . . , -------
Brake band adjusting screw
'~""
\\0- ' "
, \\\--,------
\w", ',(
Brake band ASSY
',p, ', ..
------~.!,~
',',-
~Strut
/?~~~~""
' , _ ' , ___
Band servo piston stem
/ / .... of'
.l' ' , : " " ' "
I", ""
.~./~,
Return piston spring
/#"l / \', ",
:;;;;;/,/.. .~j
"",0,,;-:=-
,;-~
Band servo piston (1-2)
'-"'~'" .~~
r:
=-,
Retainer
~.-\lL~;lf
.1-
--'-"""1"1,",,'" --- "
~I
_
_~~O_O~'~"~iO"
Retainer
Band servo piston a.D. return spri ng
0.0. (3-4)
L3-600
Fig. 20
The band brake consists of a flex type brake band, a band
One end of the brake band is secured to the transmission case
via the brake band adjusting screw.
When no hydraulic pressure is applied to the servo piston from
the hydraulic pressure controller, the servo piston and band
servo piston 0.0. are forced downward by the return spring,
as shown in (A) of the Figure.
When hydraulic pressure 2A is applied to the servo chamber
(II), it causes the band servo piston to come into contact with
the stepped portion of the band servo piston stem, thereby
pushing the band servo piston stem upward to state (B). Under
this condition, the brake band slowly tightens the reverse
clutch drum and fixes the front sun gear of the front planetary
gear. (2nd speed state)
Next, when the release pressure 3R to the servo chamber
(I)
and the hydraulic operating pressure 2A to the servo chamber
(II) are applied simultaneously, the band servo piston is
pushed downward by the force of the return spring and the
pressure difference between chamber
(I)
and chamber (II),
caused by the difference in operating areas of the band servo
pistons. Under this condition, state (A) is resumed, and the
brake band loosens and releases the reverse clutch drum.
(3rd speed state)
(A) (e)
L3-602
brake adjusting mechanism, two servo pistons, two retainers,
Fig. 22
two return springs, a stem, a strut, and others. The band brake
can be adjusted as installed on the vehicle .
• Function
Band servo piston
Drain
-r"t;ii;t, ............
t1
Fig. 21
~,~:::r::=zt-
Release pressure
3R
Hydraulic operating
pressure 2A
14
When hydraulic pressure 4A is applied to the servo chamber
(III) under the 3rd speed condition, the band servo piston
0.0. is brought into contact with the retainer installed at the
lower end of the band servo piston stem. Hence, the stem is
pushed upward. As a result, state (e) is ach ieved where the
brake band slowly tightens the reverse clutch drum and fixes
the front sun gear of the front planetary gear. (4th speed state)
The accumulator is built into the transmission case as shown
in the Figure. When hydraulic pressures 2A, 3R, and 4A are
applied from the hydraulic control unit to the respective
servo chambers, the hydraulic shock loads are absorbed by the
accumulator. This is because the accumulator piston moves
slowly, and the brake band is tightened or released slowly.
This results in smooth gearshift operation.
t,
I ,
r