IBM Selectric Reference Manual

1.
2.
3.
Backspace Rack - Wi th the backspace rack in the rest
position, a clearance of .005" to .015" should exist
between the working surfaces of the rack tooth and the
backspace pawl (Fig. 200). Adjust the hexagon headed
stud in the backspace bellcrank to obtain this conditi on.
Interlock Interposer
Ylill2lJITIQ~spacebar In~r J
Adjustable Stop
FIGURE
198.
.020" To -025"
Adjustable Stop
BACKSPACE MECHANISM
Be sure that pri nt escapement and op,arati ona I control
adjustments are correct before attempting backspace
adjustments.
Tab Lever Stop - The rest position of the tab lever is
controlled by a lug on the escapement bracket called
the tab lever stop (Fig. 199). The stop should be formed
front
or rear so that a clearance of .00111 to .003" exists
between the vertical lug on the tab lever and the back-
space pawl when the backspace pawl is bottomed in its
rack.
The tab lever stop may be formed by inserting the T ~
bender from the upper right side. It wi II be necessary
to force the tab torque bar to the rear in order to insert
the T -bender.
This adjustment insures that the backspace pawl wi II not
be prevented from bottoming in its rack during a back-
space operati on. The tab lever rest posi ti on a Iso di-
recty affects the adjustments of the tab mechanism.
It determines how much motion must be provided to the
tab lever to properly remove the backspace and escape-
ment pawls from their racks during a tab operation.
FIGURE 199. Tab Lever Stop Adjustment
2-67
Adjusting Stud
Backspace Be 1.1 crank --~.r-----J~
Escapement Pawl
Backspace Pawl
@~~-C-§9 c
FIGURE 200. Backspace Rack Adjustment
The adjustment minimizes lost motion in the mechanism
and insures that the backspace pawl wi II positively re-
set into the next rack tooth at the completi on of a
backspace operation. Excessive clearance can con-
tribute to escapement problems as well as backspace
fai lures by allowing the backspace pawl to hold the
carrier against a backspace rack tooth. Partial spacing
will result if the carrier alternates holding on the es-
capement pawl and the backspace pawl.
The adjustment may be gauged by feeling the motion of
the rack as it is manually moved from its rest position
into contact with the backspace pawl. The movement
should be equal to the adjustment clearance. The check
should be made at both extreme positions of the carrier
so as to include the difference in mainspring tension in
the check. Check the resetting of the pawl at both
positions by operating the backspace bellcrank manually
and releasing it slowly.
4. Intermediate Lever (Late Style - Identify by presence
of C-5 auxi liary cam follower) - With the backspace
cam manually operated to the high point, the escape-
ment pawl should just fai I to drop into the preceding
rack tooth causing the manual backspace operation to
fai I. Adjust the intermediate lever pivot screw forward
or back in its elongated mounting hole to obtain this
condition (Fig. 201).

IBM Selectric Specifications

General

Type	Electric typewriter
Introduced	1961
Keyboard Layout	QWERTY
Carriage Return	Electric
Manufacturer	IBM
Printing Technology	Typeball (golf ball)
Power Source	AC Power
Power Supply	120V AC