Fault Code Guide

General Information
Meritor Q Plus brakes are standard for both front and
rear axles. These Cam-Master
®
brakes are air-
actuated, cam-operated, foundation brakes. The
main components in each brake assembly (wheel
end) include the following:
• an S-head camshaft
• a brake spider
• a camshaft-and-chamber bracket
• two brake shoe and lining assemblies
• two retaining springs
• a return spring
• two anchor pins
The S-head camshaft transfers braking force from
the slack adjuster to the brake shoe assemblies. The
camshaft passes through the brake spider and
camshaft-and-chamber bracket before connecting to
the slack adjuster. See Fig. 1.
Each brake shoe is mounted on an anchor pin on the
brake spider and is controlled (moved) by either the
outward braking force of the S-head camshaft or the
inward restoring force of the return spring.
The heavy-duty, double-web brake shoes have
notches on one end of the webs that fit on the an-
chor pins. Two retaining springs secure the brake
shoes to each other near the anchor pins, creating a
hinge for brake-shoe movement. This design makes
quick-change brake service possible.
Meritor steer axles have seven 0.656-inch-diameter
holes for attaching the spider to the axle flange. An
oversized eighth hole (0.687-inch diameter) in the
axle flange is for an antilock brake system (ABS)
wheel speed sensor bushing. See Fig. 2. The eighth
hole is in the 10 or 2 o’clock position, depending on
which side of the axle is viewed.
Q Plus MX500 brakes are extended maintenance
brakes. These brakes can be identified by an identifi-
cation tag affixed to the brake shoe. An additional
identification tag is affixed to the brake camshaft-
and-chamber bracket (on top of the plugged grease
hole). MX500 brakes and Meritor automatic slack
adjusters do not have grease fittings.
Principles of Operation
When the brake pedal is depressed, compressed air
enters the brake chamber, causing the diaphragm to
move a pushrod assembly.
The pushrod turns the slack adjuster and brake cam-
shaft. As the camshaft turns, the S-type cam head
forces the brake shoes against the brake drum and
braking occurs.
When the brakes are released and air is exhausted
from the brake chamber, the actuator return spring
(within the brake chamber) and the brake shoe return
spring return the camshaft, brake shoes, slack ad-
juster, and pushrod to their released positions.
Meritor Cam-Master Q Plus Brakes 42.01
General Information
Business Class M2 Workshop Manual, Supplement 0, January 2002 050/1