All dimensions are for reference only.

Measure and record the “X” and “Y” dimensions (Figure 1).
“X” Dimension - The dimension from bottom of actuator to end of push-rod.
“Y” Dimension - The dimension from bottom of actuator to centerline of yoke pin.

Figure 1

Figure 2

Y
X

NOTE: If for some reason the spring chamber power spring cannot be caged and fully released, then the “X” and “Y” dimensions will need to be measured
from another actuator of the exact type from the same vehicle provided it is retracted to its zero stroke position (brake fully released) and was operating correctly.
(d)

Before marking push-rod to be cut on a new unit, be sure the spring chamber and push-rod are fully retracted to the zero position.
(This may be done with the manual caging bolt or by applying 90-100 psi (6.2 - 6.9 bar) air pressure to the spring chamber air inlet
port.)

(e)

Take measured “X” dimension from the removed unit and mark push-rod of new unit from the bottom of the actuator.

(f)

Thread jam nut past mark on push-rod. Align bottom edge of nut with mark.

(g)

Use a sharp hack-saw and cut push-rod on the mark (Figure 2).

(h)

After cutting rod, thread jam nut off to clean up the thread.

(i)

Thread jam nut then yoke onto the push-rod. Yoke from removed unit may be reused provided yoke pin hole is not worn. Adjust
yoke to the same “Y” dimension as measured from the removed unit.

(j)

Hold yoke to prevent it from turning and tighten jam nut against yoke 25-35 lb-ft (33.9 - 47.5 N-m) torque.

TO INSTALL NEW UNIT ON VEHICLE: Refer to MGM Brakes Service Manual for the model that is being installed.

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144

Note: Product information and specifications subject to change without notice.

PROPER BRAKE ADJUSTMENT
NOTE: The last half of an air chamber stroke is less efficient than the first half. Therefore, the following adjustments are recommended for maximum
efficiency when using manually adjusted slack adjusters.

PROPERLY - ADJUSTED BRAKES “ON” - APPLIED

BRAKES “OFF” - NOT APPLIED

Stroke should be as short as possible with no lining
to drum contact.

Type

IMPROPERLY ADJUSTED BRAKES “ON” - APPLIED

Effective
Area
(SQ. IN.)

Approx.
Diaphragm
O.D.

Rated Stroke
of Chamber

Inches mm

Inches

mm

Inches

1.75

45

1.35

35

1.35

35

1.75

45

2.00

51

1.75

45

2.00

51

Maximum recommended readjustment stroke has been exceeded)
MGM Brake “Stroke Alert” (Excessive Stroke Warning)

5.00

125

Maximum
Stroke
with Brakes
Adjusted

“B” MV/MA
Recommended
Readjustment
Stroke
mm

9

9

12

12

5.50

140

1.75

45

16

16

6.00

150

2.25

57

16L

16

6.00

150

2.50

64

20

20

6.50

165

2.25

57

20L

20

6.50

165

2.50

64

24

24

7.00

175

2.25

57

1.75

45

SHOULD
BE AS
SHORT AS
POSSIBLE
WITHOUT
LINING
TO DRUM
CONTACT

24L

24

7.00

175

2.50

64

2.00

51

24L3

24

7.00

175

3.00

76

2.50

64

30

30

8.00

200

2.50

64

2.00

51

30L3

30

8.00

200

3.00

76

2.50

64

36

36

9.00

230

3.00

76

2.25

57

See chart for recommended readjustment stroke
SOURCE: MVMA (Motor Vehicle Manufacturers Association)
Note: The push-rod must remain perpendicular to the bottom
surface of the non-pressure chamber (NPC) within ±3° zero to full stroke.

• IMPORTANT•

!

RECOMMENDED SPRING BRAKE ACTUATOR DISARMING PROCEDURE
Warning: This procedure must be strictly adhered to. Never attempt to remove the spring chamber clamp ring from a double diaphragm actuator or
the spring chamber retaining ring from a piston actuator. Both actuators employ a high energy power spring that could cause serious bodily injury
if the spring were suddenly released due to improper disassembly.

All retired spring brake actuators must be safely disarmed before they are disposed of to prevent serious personal injury from accidental sudden release of the high energy
spring (as much as 2700 lbs of force -12.0 kN) in the parking chamber. To disarm the unit, remove it from the vehicle following the instructions in the MGM Brakes Service
Manual. Be sure to release the brake per Section (2) of the MGM Brakes Service Manual. Never attempt to remove the head which contains the power spring. Observe all
safety precautions. Place the unit in a steel *container and use an acetylene torch to cut a hole through the head housing the power spring. Cut completely through at least
two spring coils. The steel container must have openings to expose the head where it is to be cut with the acetylene torch and it must be strong enough to prevent parts
from hurtling out should the unit suddenly separate before it is safely disarmed. It is the users responsibility to ensure the steel container is safe.
*Information concerning a suitable container is available through your MGM Brakes Representative.

Note: Product information and specifications subject to change without notice.

145

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TECHNICAL

To check brake adjustment, apply 90 to 100 psi (6.2 - 6.9
bars) air pressure to the service chamber. Consult the
vehicle manufacturer for the correct angle between the
slack adjuster arm and push-rod and/or the push-rod length.
This is necessary since different dimensions are required
for automatic or manual slacks, various slack lengths and
different slack adjuster manufacturers.

Angle must always be greater than 90° due to various
slack adjuster lengths and installation setups. (Refer to
axle or OEM manufacturer’s manual for recommended
angle).

FASTENER TORQUE VALUE CHART

BOLT TORQUES
Component

Bolt Size

Foot/Pounds of Torque

Newton/Meters of Torque

RELEASE BOLTS
CAGING TORQUE
TR Models

1/2 - 13 UNC

40-50

54-68

TR Models

5/8 - 11 UNC

40-50

54-68

L Models

5/8 - 11 UNC

40-50

54-68

J Models

5/8 18 UNF / 1/2 - 13 UNC

74 Max.

100 Max.

TR Models

1/2 - 13 UNC

TR Models

5/8 - 11 UNC

STORAGE TORQUE
10

14

10

14

L Models

45-50

61-68

J Models

50-60

68-81

5/16 - 24 UNF

18-23

24-31

3/8 - 16 UNC

30-35

41-47

1/2 - 20 UNF

20 - 30

27 - 41

5/8 - 18 UNF

25 - 50

34 - 68

3/4 - 16 UNF

75 - 100

102 - 136

M16 X 1.5 - 6G

25 - 50

34 - 68

CLAMP BAND NUTS & BOLTS

TECHNICAL

YOKE NUTS

MOUNTING NUTS & BOLTS
7/16 - 14 UNC

35-40

47-54

5/8 - 11 UNC

133-155

180-210

5/8 18 UNF

133-155

180-210

M16 X 1.5 - 6G

133-155

180-210

3/8 - 18 NPTF

25 - 30

34 - 40

3/8 - 24 UNF

17 - 19

23 - 26

M16 X 1.5- 6H

13 - 15

18 - 20

AIR INLET FITTINGS

!

Warning: Do not use impact wrench.

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146

Note: Product information and specifications subject to change without notice.

LENGTHEN THE EXTERNAL BREATHER TUBE
PROCEDURE TO LENGTHEN THE EXTERNAL BREATHER TUBE
1.0

Purpose:

To provide a procedure to add a tube section to lengthen a breather tube in the field when the
replacement actuator needs to be modified to replicate the breather tube, and/or port positions as per the
currently installed OEM actuator.

2.0

Scope:

All MGM Brakes models with an external breather tube.

3.0

Material required:

8081128 Rubber Extension Tube or 3/8 Inch I.D. Rubber Vacuum/Washer Hose
8052021 3/8 Inch Hose Clamp (2) or Adhesive

NOTE: If rubber extension tube and hose clamps unavailable, use appropriate length of 3/8” I.D. rubber

vacuum/washer hose and appropriate adhesive. (Recommend Loctite #414 “Superbond” or equivalent.)
4.0

Procedure:

4.1

Using a plastic tubing cutter or sharp knife, cut the 3/8” O.D. breather tube approximately half way
between the rubber elbows.. (Fig. 1)

4.2

Using the recommended procedure in the MGM Brakes Service Manual (Ref Form 5044 - J-Series,
Form 5011 – TR, Form 5042 – LTR, Form 5065 – Wedge) loosen the service chamber clamp and rotate the
spring side to the desired position. Tighten service chamber clamp.

NOTE: Units designed for air disc applications are not to be rotated. (Fig. 2)

4.3

If necessary, cut the 8081128 rubber extension tube, or the 3/8” vacuum/washer hose, to a length that
will insure a minimum of 1/2 inch engagement over both ends of the cut 3/8” O.D. nylon breather tube.

4.4

Install the 8052021 hose clamps (2) over each end of the nylon breather tube, or apply Loctite #414
“Superbond” adhesive, or equivalent, to both ends of the nylon breather tube.

4.5

Insert the section of 8081128 rubber extension tube over both ends of the cut breather tube a minimum
of ½ inch. (Fig. 3)

4.6

If hose clamps are used, compress clamp with pliers and place one over each end of the rubber extension
tube. The edge of the clamp should be approximately .050 ±.015 from the edge of the rubber tube when
installed. If adhesive is being used, wait for adhesive to dry before pro ceeding.

5.0

Using the recommended procedure in the MGM Brakes Service Manual (Ref Form 5044 – J-Series, Form
5011 – TR, Form 5042 – LTR, Form 5065 – Wedge), check the service chamber clamp for leaks.