Brake Interlock (M970A1 including M970 SN TC-
operating and brakes are properly adjusted. If clearance is
not between .040- and .060-inch, proceed to step (5).
0843, TC-0844, and TC-103 thru TC-178). The brake interlock
system is activated when the door on the hose reel cabinet is
open. When actuated, the interlock valve sends air from the
rear reservoir into the service air line. This gives a service
If adjusting bolt starwheel will not turn using
signal to the emergency brake relay valve. The relay valve
hand pressure, lightly tap the tool with a
releases air from the rear reservoir to the brake air chambers to
apply the brakes. Figures 4-56 and 4-58 show how the
interlock system connects into the air brake system
(5) Insert brake adjusting spoon or long thin
Slack Adjusters. These convert linear motion of
screwdriver into slot to meet the starwheel on the
the brake chamber to rotating motion of the camshaft.
adjusting bolt. The adjusting bolt has right hand threads.
The slack adjuster consists of a housing, two gears, and
Turn the starwheel counterclockwise to reduce brake
two gear covers. Brake adjustments are made through the
(6) Back off the starwheel until you get a very
Service Brake Shoe Assemblies, M967,
slight drag on the drum. Check brake lining clearance
M969, and M970 except M970 SN TC-0843,
again (step (4)).
TC-0844, andTC-103 thru TC-178.
(7) Repeat steps (4) through (6) above for the
Test and Adjustment.
other shoe on brake.
(1) Jack up the semitrailer and lift all wheels off
(8) Repeat steps (1) through (6) for all brake
the ground. Block the frame securely.
Inspection and Replacement.
(2) Release the fail-safe units (pars 2-4).
and drum assembly
(1) Remove wheel
(3) Remove dust plugs from access slots at top
and bottom of dust shield (fig. 4-59).
(2) Inspect brake linings for damage and wear.
New lining has approximately -inch of stock above
center rivets and approximately -inch of stock above end
rivets. Replace brake shoe if lining is damaged or is worn
within .030-inch of rivet heads. By recording lining wear
between scheduled annual brake maintenance periods,
expected wear can be calculated. Shoes with linings that
will not last until the next scheduled maintenance internal
should be replaced.
(1) Remove hub, drum, and wheels (para 4-49).
(2) Turn the automatic adjusters with a brake
adjusting spoon or a long thin screwdriver clockwise until
the wedge brake plungers are fully contracted.
(3) Remove brake shoe return springs using
brake spring pliers.
(a) Unhook top hook of both return springs.
Figure 4-59. Adjusting Brake Lining-to-Drum Clearance.
(b) Remove springs.
(4) Insert a feeler gage into the access slots and
(4) Remove brake shoes being careful not to
check brake drum to brake lining clearance. If clearance is
disturb the position of the wedge brake parts.
between .040- and .060-inch, automatic adjusters are