MG Magnette KA Instruction Manual page 95

I
I
A U T O M A T I C
ADJUSTER
N U T S
A N D SPRINGS
l
\
O P E R A T I N G
B&
B P
ENGAGED
S T R U T S
3RD SPEED
A D J U S T E R
F N G A G E D
/SET S C R E W
Illustration G.-The left-hand illustration w i l l make the action o f the busbar and operating
struts quite clear.
I t w i l l be seen that the second strut from the left is engaged by the busbar and
is forced upwards, while the other struts are free of the busbar and do not engage w i t h i t at all. The
action of the busbar rising can be seen by referring t o the right-hand illustration. It w i l l be noted
that the adjuster set screws on the bands are all free of the adjuster nut, except the third gear, which
has been forced up against the adjuster set screw by the action of the busbar.
A
side view of t h e bands and operating mechanism can be examined after t h e
gearbox casing has been removed from the base plate. In Illustration
G
the busbar,
through the action of the spring, is in the up position, and
it
will be noted that the
3rd speed actuating strut has been engaged with the groove in the busbar, and
has been forced upwards while t h e other operating struts are entirely free of the
busbar's action. The whole action of the busbar is t o spring load the brake
band contracting levers o r linkages so as t o cause the bands t o grip the drum.
The first question that was asked was, W h a t was the action o f the camshaft?
This action will now be made clear when it i s realised that the flat springs inside the
box, which are allowed t o move forward when they drop into a notch in the cam,
come in contact w i t h the operating struts, w i t h the result that when the
pedal is pushed o u t and the busbar i s allowed t o fall, t h e spring will force the
operating strut sufficiently far forward t o engage w i t h the groove in the busbar
and allow the particular pre-selected gear t o come i n t o operation. Carrying this
further, the t r u e understanding of the pre-selector gearbox w i l l be grasped.
Suppose, for example, that the car is running in 3rd gear, the busbar will be up
and the 3rd speed brake bands w i l l be contracted. The action o f rotating the cam-
shaft by moving the selector lever w i l l have no other effect than causing t h e springs
t o move forward and backward, w i t h the result that they w i l l simply press up
against the operating struts which are lying idly in the box. These operating
struts cannot engage with the busbar because, on referring t o Illustration
G,
it
will be seen that
it
is necessary for the busbar t o d r o p considerably first.
W h e n
the busbar does, however, drop through being forced down by the pedal,
and another gear has been pre-selected, the small spring contained in the linkages
o f the operating struts w i l l t h r o w the strut that has previously been in operation
outwards free of the busbar, and then the action of t h e flat selector springs on the
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