Freightliner Cargo Maintenance Instruction - page 19

42–06 Brake Chamber

Inspection (All Models)

DANGER

Do not loosen or remove the parking brake clamp
ring for any purpose at any time. The
parking/emergency brake section is not intended
to be serviced. Serious injury or death may result
from sudden release of the power spring.

Before doing any repairs or adjustments on a
service/parking brake chamber, read the appli-
cable warnings and instructions in the applicable
brake chamber section in Group 42 of the

Cargo

Workshop Manual

.

WARNING

Do not operate the vehicle with the front brakes
backed off or disconnected. Backing off or discon-
necting the front brakes will not improve vehicle
handling and may lead to loss of vehicle control
resulting in property damage or personal injury.

NOTE: Vehicles operating under severe or ad-
verse conditions should be checked more fre-
quently. If the brake chamber requires disas-
sembly, see Group 42 of the

Cargo Workshop

Manual for instructions.

1.

With the slack adjuster properly adjusted, check
the angle formed by the centerline of the piston
rod and slack adjuster. This angle should be
greater than 90 degrees in the released position
and approach 90 degrees in the applied position.
See

Fig. 1

.

At angles less than 90 degrees, brake chamber
force is reduced, which reduces braking
efficiency.

2.

Check each brake chamber for correct installa-
tion.

2.1

Check each mounting stud for the pres-
ence of prevailing torque locknuts and
hardened flatwashers. Make sure that the
hardened flatwashers are installed be-
tween the mounting bracket and the lock-
nuts. Do not install flatwashers touching
the service (non-pressure) chamber.

2.2

If the locknuts are loose, tighten them.
For correct torque values, see the appli-
cable brake chamber section in Group 42
of the

Cargo Workshop Manual

.

3.

Observe the piston rod engagement with the cle-
vis. Engagement of at least 7 threads is required;
there should be 1 inch (25 mm) clearance from
the centerline of the clevis pin hole to the end of
the piston rod. See

Fig. 2

. Adjust if needed.

4.

Check the tightness of the piston rod nut. Tighten
if needed.

5.

See if the chamber piston rod is in line with the
slack adjuster. Misalignment can cause the pis-
ton rod to rub on the non-pressure chamber and
cause a dragging brake. Reposition the brake
chamber on the mounting bracket, if necessary.

6.

Inspect the condition of the hose(s) to the brake
chamber. Check carefully for chafing, restrictions
such as kinking or bending, and make sure the
hoses are properly supported. Replace a dam-
aged hose with the same size hose. With the
service brakes applied, check for leaks at the
hose-to-chamber connections. Any leaks are
probably caused by loose connections or by a
damaged hose fitting. Eliminate all leaks.

On chambers equipped with an external breather
tube, make sure that the flexible elbows are in
place and that the connector tube is inserted into
each elbow 1/2 inch (13 mm).

f420009a

07/27/94

1

3

2

C

B

A

A. Brakes Released
B. Brakes Applied

C. Greater than 90

degree angle

1.

Brake Chamber

2.

Piston Rod

3.

Slack Adjuster

Fig. 1, Angle Between Piston Rod and Slack Adjuster

Brakes

42

Cargo Maintenance Manual, January 2000

42/2

DANGER

Read and follow all applicable warnings and in-
structions in Group 42 of the

Cargo Workshop

Manual

for repairs to the service/parking brake

chambers. These chambers contain a power
spring, which if released, could cause serious in-
jury or death.

7.

Inspect the exterior surfaces of the chamber for
damage. Make sure the breather holes in the
non-pressure section(s) are open and free of de-
bris. Using the instructions in Group 42 of the

Cargo Workshop Manual

, replace any damaged

parts.

8.

On parking brake chambers equipped with inte-
gral release bolts, lubricate the bolt with thread
anti-seize compound. Check the tightness of the
bolt. For torque values, see the applicable brake
chamber section in Group 42 of the

Cargo

Workshop Manual

.

CAUTION

If the external breather tube is missing or incor-
rectly installed, road dirt and debris can adversely
affect the operation of the brake chamber. Once
inside the chamber, dirt and debris cause the in-
ternal parts to deteriorate and shorten their lives.

9.

On brake chambers equipped with an external
breather tube, make sure the flexible elbows are
in place and the connector tube is inserted into
each elbow 1/2 inch (13 mm).

10. On all parking brake installations, check for pres-

ence of an end cover cap or dust plug and make
sure the cap or plug is securely snapped into
place.

Service Brake Operation and
Leakage Check

DANGER

Do not loosen or remove the parking brake clamp
ring for any purpose at any time. The
parking/emergency brake section is not intended
to be serviced. Serious injury or death may result
from sudden release of the power spring.

Before doing any repairs or adjustments on a
service/parking brake chamber, read the appli-
cable warnings and instructions in the applicable
brake chamber section in Group 42 of the

Cargo

Workshop Manual

.

1.

Apply the service brakes and check that the pis-
ton rods move out promptly, without binding.

2.

Release the service brakes and check that the
piston rods return to the released positions
promptly, without binding.

DANGER

Read and follow all applicable warnings and in-
structions in Group 42 of the

Cargo Workshop

Manual

for repairs to the service/parking brake

chambers. These chambers contain a power
spring, which if released, could cause serious in-
jury or death.

3.

Check the service brake chambers for leakage.

f420225a

1

2

3

B

A

08/20/93

4

5

A. Minimum of 1 inch (25 mm) clearance between

centerline of clevis pin hole and piston rod end.

B. Minimum of 7 threads engagement.
1.

Piston Rod

2.

Piston Rod Nut

3.

Clevis

4.

Cotter Pin

5.

Clevis Pin

Fig. 2, Piston Rod Engagement With the Clevis

Brakes

42

Cargo Maintenance Manual, January 2000

42/3

3.1

Apply the service brakes and hold them
on full line pressure of at least 80 psi
(550 kPa).

CAUTION

Do not overtighten the clamp ring. This can distort
the flange sealing surface, or the clamp ring itself.

3.2

Using soapy water, coat the service
chamber clamp ring. Leakage is exces-
sive if it produces a 1-inch (25-mm)
bubble within 5 seconds.

If leakage is detected, tighten the clamp
ring; but do not exceed the maximum
torque limits in Group 42 of the

Cargo

Workshop Manual

.

3.3

If leakage persists, use the instructions in
Group 42 of the

Cargo Workshop Manual

to replace the service brake diaphragm.

3.4

Using soapy water, coat the area around
the piston-rod bore. No leakage is permit-
ted. If there is leakage, use the instruc-
tions in the applicable brake chamber
section in Group 42 of the

Cargo Work-

shop Manual

and replace the service

brake diaphragm.

Parking Brake Operation and
Leakage Check

DANGER

Do not loosen or remove the parking brake clamp
ring for any purpose at any time. The
parking/emergency brake section is not intended
to be serviced. Serious injury or death may result
from sudden release of the power spring.

Before doing any repairs or adjustments on a
service/parking brake chamber, read the appli-
cable warnings and instructions in the applicable
brake chamber section in Group 42 of the

Cargo

Workshop Manual

.

1.

Chock the tires.

2.

Build the air pressure in the system to at least
100 psi (690 kPa), and shut off the engine.

3.

Place the park control valve in the park position.
The brake should apply immediately. Then, place
the park control valve in the released position.
The brake should release immediately.

If the brakes do not apply or release as required,
see the air brake system troubleshooting guide in
the applicable brake chamber section in Group
42
of the

Cargo Workshop Manual

for possible

causes and corrections.

WARNING

Do not disconnect the pressurized parking brake
hose. If disconnected under pressure, the parking
brake hose will whip as air escapes from the line,
and the air stream can direct dirt or sludge toward
persons in the area, which could result in injury.

4.

Check the parking brake chambers for leakage.

4.1

With the park control valve released, ap-
ply soapy water around the parking brake
diaphragm clamp ring and at the drain
slots and exhaust breather on the body.
Disconnect the service brake hose at the
service port, and apply soapy water to
check for piston O-ring leakage.

DANGER

Read and follow all applicable warnings and in-
structions in the applicable brake chamber section
in Group 42 of the

Cargo Workshop Manual

for

repairs to the service/parking brake chambers.
These chambers contain a power spring, which if
released, could cause serious injury or death.

4.2

If leakage is detected at either the clamp
ring or the drain slots, replace the parking
brake section. Slight leakage is permitted
at the service port. Any other leakage is
not acceptable. Using the instructions in
the applicable brake chamber section in
Group 42 of the

Cargo Workshop

Manual

, replace the parking brake section

(

do not attempt to service the parking

brake section

).

5.

Connect the air hose to the brake chamber, mak-
ing sure that the fittings are clean and free of
debris. Finger-tighten the nut. Using a wrench,
further tighten the nut until you feel resistance.
Tighten the nut one-sixth turn more.

Brakes

42

Cargo Maintenance Manual, January 2000

42/4

6.

Repeat the above steps for each parking brake
chamber.

7.

Apply the parking brakes. Remove the chocks
from the tires.

42–07 Camshaft Bracket

Bushing Lubrication

Pump multipurpose chassis grease (NLGI grade 1 or
2) into the chamber bracket until it appears at the
slack adjuster end of the bracket. See

Fig. 3.

Use

care that no grease enters the drum cavity. If grease
leaks out under the camhead, the camshaft grease
seal is worn or damaged, or is installed backwards.

NOTE: The use of meter-type fittings, having a
maximum 40 psi (275 kPa) pressure relief at
shutoff, is recommended.

42–08 Automatic Slack

Adjuster Check

1.

Check the boot for cuts, tears, etc. (

Fig. 4

), and

replace it if necessary.

2.

Check the brake shoe lining wear to determine
the proper reline time.

3.

Check the free-stroke. If the vehicle has new
brakes or brakes with new linings, you must

check the free-stroke. If the vehicle is in for rou-
tine maintenance and the brakes or linings are
not new, go to the next step and check the brake
chamber stroke.

IMPORTANT: Do not use installation tem-
plates to check the slack adjuster angles.
Installation templates are used only when
installing a new slack adjuster or reinstalling
the existing slack adjuster.

3.1

With the brakes fully released, measure
the distance from the bottom of the brake
chamber to the center of the large clevis
pin. See

Fig. 5

, Ref. A.

3.2

Use a pry bar to move the slack adjuster,
applying the brakes. Again, measure the
distance from the bottom of the brake
chamber to the center of the large clevis
pin. See

Fig. 5

, Ref. B.

The difference between the two measure-
ments is the initial free-stroke, and sets
the clearance between the linings and the
drum. The free-stroke must be:

f420011a

05/28/93

1

2

3

A

A. Grease Exit
1.

Brake Chamber

2.

Slack Adjuster

3.

Grease Fitting

Fig. 3, Camshaft Bracket Bushing Lubrication

f420012a

10/20/93

1

2

3

4

5

6

7

1.

Brake Chamber

2.

Clevis

3.

Actuator Rod

4.

Boot

5.

Pressure-Relief Capscrew, Gasket, Pawl Spring,
and Pawl

6.

Manual Adjusting Nut

7.

Grease Fitting (or lube plug)

Fig. 4, Meritor Automatic Slack Adjuster

Brakes

42

Cargo Maintenance Manual, January 2000

42/5

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