BENDIX BW1426 User Manual

When the brake chamber is used to actuate cam-type 

foundation brake assemblies, the yoke is connected to 

a slack adjuster, which in turn is connected to the brake 

cam shaft. This forward motion of the push rod rotates the 

slack adjuster, and cam shaft, applying the vehicle brakes.

The greater the air pressure admitted to the brake chamber, 

the greater the force applied by the push rod.  Conversely, 

the less pressure applied to the brake chamber, the less 

force will be applied by the push rod. Push rod force is 

determined by multiplying the delivered air pressure by the 

effective diaphragm area. For example, if 60 psi is admitted 

to a type 30 brake chamber, the lineal force on the end of 

the push rod is approximately 1800 lbs.

When air pressure is released from the brake chamber, 

the push rod return spring — in combination with the brake 

shoe return spring — returns the diaphragm, push plate 

and rod assembly, slack adjuster, and brake cam to their 

released positions, releasing the brakes.

A.  Each month, every 8,000 miles or every 300 operating 

hours, depending on type of operation:

  1.  Check the push rod to slack adjuster alignment 

from release to the full stroke position to be sure 

the push rod moves out and returns properly without 

binding at the non-pressure plate hole or with other 

structures. 

    Also check the angle formed by the slack adjuster 

arm and push rod. It should be greater than 90

0

 

when the chamber is in the released position and 

approach 90

0

 at maximum re-adjustment stroke.

 

2.  Check tightness of mounting nuts. Check cotter pins 

to make sure they are in place.

  3.  Check all hoses and lines. They should be secure 

and in good condition.

B.  Every year, or after each 100,000 miles/3600 oper ating 

hours, depending on the type of operation:

  1.  Disassemble and clean all parts.
 

2.  Install a new diaphragm or any other parts if they are 

worn or deteriorated. When the diaphragm, spring, 

or both are replaced, they should be replaced in the 

corresponding chamber on the same axle.

A.  OPERATING TEST
 

1.  Apply the brakes and observe the push rods move 

out promptly and without binding.

 

2.  Release the brakes and observe that the push rods 

return to the released position promptly and without 

binding.

Type

Effective 

Area 

(Sq. In.)

Outside 

Diameter*

Max. 

Stroke

Max. 

Stroke 

With 

Brakes 

Adjusted

Max. Stroke 

at Which 

Brakes 

Should Be 

Readjusted

6

6

4-1/2

1-5/8

Should 

be as 

short as 

possible 

without 

brakes 

dragging

1-1/4

9

9

5-1/4

1-3/4

1-3/8

12

12

5-11/16

1-3/4

1-3/8

16

16

6-3/8

2-1/4

1-3/4

20

20

6-25/32

2-1/4

1-3/4

24

24

7-7/32

2-1/4

1-3/4

30

30

8-3/32

2-1/2

2

36

36

9-5/16

3

2-1/4

*Dimensions listed do not include capscrew head 

projections for rotochambers and bolt projections for 

clamp-type brake chambers.

B.  LEAKAGE TEST
  1.  Make and hold a full brake application.
  2.  Using a soap solution, coat the clamping ring(s). If 

leakage is detected, tighten the clamping ring only 

enough to stop leakage.  DO NOT OVERTIGHTEN 

as this can distort the sealing surface or clamping 

ring. Coat the area around the push rod hole (loosen 

the boot if necessary). No leakage is permitted. 

If leakage is detected, the diaphragm must be 

replaced.

A.   REMOVING
 

1. Block the vehicle wheels.

 

2. Release the air pressure in all reservoirs.

 

3. Disconnect the line to the chamber.

 

4. Remove the yoke pin.

 

5. Remove the brake chamber.

B. INSTALLING
 

1.  Mount the brake chamber to the mounting bracket.

  2.  Install the yoke (if removed) and yoke pin.
 

3.  Check the angle formed by the centerline of the push 

rod and slack adjuster. Consult the slack adjuster 

manufacturer for proper installation angle(s).

  4.  Connect the line to the chamber. Check to be sure 

that the hoses are properly supported and clamped, 

if necessary, to provide proper clearance.

 

5.  Adjust the brakes to the slack adjuster manufacturer’s 

recommendations.