MACK PI, CHU, AN, CXU, GR Repair Manual

BODY BUILDER INSTRUCTIONS

Mack Trucks

Bodybuilder; Brakes and Air Systems

PI / CHU, AN / CXU, GR / GU, TD

Introduction

This information provides design and function, specification and procedure details for
Brake and Air Systems for MACK vehicles.

Note: We have attempted to cover as much information as possible. However, this
information does not cover all the unique variations that a vehicle chassis may present.
Note that illustrations are typical but may not reflect all the variations of assembly.

All data provided is based on information that was current at time of release. However,
this information is subject to change without notice.

LR, TE / MRU

Section 5

Please note that no part of this information may be reproduced, stored, or transmitted by
any means without the express written permission of MACK Trucks, Inc.

Contents:

• “Air Brake System”, page 2

• “Air Solenoid Valves”, page 4

• “Liftable Axle Air System Requirements”, page 7

• “Air Lines Joystick Control”, page 15

• “Air Line Hose Installation”, page 16

• “Air Lines Routing”, page 23

• “Air Brake Routing Schematics”, page 34

• “Air Line Numbers and Description”, page 46

• “Air Tank Fittings”, page 52

• “Brake Literature”, page 53

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Air Brake System

Air Brake System MVSS Requirements

MVSS Compliance

As manufactured by MACK Trucks, Inc., the air brake system on MACK chassis (both incomplete and complete) comply with
the applicable requirements of U.S. Federal and Canada Motor Vehicle Safety Standards (MVSS) 106, Brake Hoses, and
121, Air Brake Systems. Any change or addition to the system may cause the vehicle to no longer be in compliance with
these MVSS.

MVSS 121 requirements cover (but are not limited to) the following:

• Air compressor build-up time

• Air reservoir volume

• Service brake stopping distance

• Brake actuation time

• Brake release time

• Parking brake hold on grades

• Emergency brake stopping distance

For a complete list of certification requirements, refer to U.S. Federal MVSS 121 or Canada MVSS 121. These motor vehicle
safety standards can be accessed at the following web addresses:

• Federal Motor Vehicle Safety Standards https://www.gpo.gov/

• Canada Motor Vehicle Safety Standards http://www.tc.gc.ca/eng/acts-regulations/regulations-crc-c1038.htm

It is the responsibility of the body/equipment installer/alterer to ensure that the MACK vehicle remains in compliance with ap­plicable MVSS. It is also the responsibility of the body/equipment installer/alterer to comply with applicable vehicle certifica­tion regulations.

Air Brake System Truck Tractor

There are basic differences between straight truck and truck tractor air systems. On a straight truck, a spring brake control
valve is added to the emergency brake air circuit. This gives the driver modulated control of the spring brakes through the
treadle valve in the event of a primary system air loss. Additionally, spring brake chambers are installed on both axles of a
tandem rear axle unit so that if there is a partial air system pressure loss, the emergency brake system will stop the vehicle
within the required stopping distance, and also to meet parking brake system requirements.

A truck air system is designed to be operated as that of a truck, and a truck tractor air system is designed to be operated as
that of a truck tractor. When converting chassis for use other than as originally intended (e.g., converting a truck tractor to a
truck), the air system must also be changed to ensure that the vehicle remains in compliance with MVSS. Contact MACK
Trucks, Inc. Product Support for more information.

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Air-Operated Equipment

Additional air system capacity may be required for air-powered accessories to operate properly without jeopardizing the in­tegrity of the air brake system. Motor Vehicle Safety Standards (MVSS) 121 requires an air capacity 12 times the total vol­ume of all air brake chambers on the vehicle. For additional information on calculating total air volume and brake chamber
rated air volumes, refer to Liftable Axle Air System Requirements section in this bulletin.

If additional air capacity is required, an expansion reservoir should be installed. The reservoir and piping must comply with
MVSS.

Note: When making any modifications to the vehicle that involves the addition of air springs (i.e., liftable tag or pusher axles
having air suspensions), the air springs should be supplied by a pressure protected air source so that the air brake system is
protected (to the setting of the pressure protection valve) against air loss should a leak develop in the auxiliary system.

Air Compressor Capacity

If increased air system volume is necessary, it is also necessary to determine if the air compressor has the capacity to supply
the air system without having to run in the loaded mode (compressing) for long periods of time. Motor Vehicle Safety Stand­ards (MVSS) 121 requires that the air compressor must be able to increase pressure in the supply and service (primary and
secondary) reservoirs from 586 – 690 kPa (85 –100 psi), with the engine running at maximum governed RPM, in a specific
amount of time, depending on required and actual reservoir capacity. If the existing compressor cannot accomplish this, a
larger compressor must be used. First, however, make sure that an air compressor malfunction or other type of problem with
the air system is not causing the slow build-up time.

Build-up time may be calculated as shown.

W5032562

Calculating Air System Build-up Time

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Air Solenoid Valves

MACK chassis now incorporate electrically operated air solenoid valves to direct air pressure to the various accessory air cir­cuits such as air suspension control, fifth wheel slide, inter-axle lockout, power takeoff (PTO), etc. Additional air solenoid
valves can be added to the air solenoid valve pack which is located on the right-hand frame rail, mounted behind the inter­mediate crossmember.

W5032563

Fig. 1 Air Solenoid Valve Pack Location

To add an air solenoid to the solenoid valve pack, disconnect the valve pack connector from the chassis harness, and then
remove the valve pack from the mounting bracket. Remove the end cap from the valve back by twisting the cap counterclock­wise. Engage the new solenoid into the locking ring of the last solenoid in the pack, and then twist the solenoid clockwise to
lock the solenoids together. Reinstall the end cap in the same manner.

W0113594

Fig. 2 Assembling Solenoid Valve

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Run the wires for the new solenoid(s) along the existing valve pack harness, and then connect the terminal ends for the sole­noid(s) into the appropriate cavities (pins D and S for the PTO control solenoid and pins K and N for neutral control) of the
valve pack connector body. The following table lists the solenoid valve pack pin assignments:

W5032565

Fig. 3 Air Solenoid Valve Pack Connector Pin Assignments

Pin + Pin Description

B L Inter-Wheel Lock

C R Air Suspension Control (dump valve)

D R PTO Control

E S Inter-Axle Lock

F R Inside/Outside Air

G M Fifth Wheel Release

H A Fifth Wheel Slide

K N Air Horn or Neutral Control

J R Auxiliary Axle 1

J R

First Lift Axle

G M Second Lift Axle

J R First Lift Axle

G M Second Lift Axle

P M Third Lift Axle

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Air Solenoid Valve Pack Connector and Pin Part Numbers

Should replacement of the valve pack connector body, pins, seals and plugs be necessary, refer to the following illustration
for the applicable part numbers.

Fig. 4 Connector Component Part Numbers

Key Part No. Description

1 20739620 Seal

2 20739618 Terminal

3 20388120 Plug (for unused connector

4 20387692 Connector body

W5032566

cavities)

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Liftable Axle Air System Requirements

Installation of a liftable axle(s) may require additional air capacity for operation of the service brakes, up/down air bags and
suspension air bags.

Note: The addition of a liftable axle increases the load carrying capacity of the vehicle, which may affect the ability of the
parking brake system to hold the vehicle on a hill. Motor Vehicle Safety Standard (MVSS) 121 requires that the parking brake
system be capable of holding the vehicle under specified conditions. To ensure continued compliance with MVSS 121 when
a liftable axle is added, it may be necessary for the installer to increase the capacity of the parking brake system to account
for the increase in the gross vehicle weight rating (GVWR).

Liftable Axle Air Capacity

U.S. Federal and Canada Motor Vehicle Safety Standard (MVSS) 121 requires that total air capacity for the vehicle must be
12 times the total volume of all air chambers (front and rear chambers and liftable axle air brake chambers). As an example,
a standard chassis having four type-30 service brake chambers on the rear axles and two type-24 service brake chambers
on the front axle would require a total air system capacity of 5,880 cubic inches, excluding air requirements for the liftable
axle brake chambers.

W5032567

Fig. 5 Calculating Air System Capacity

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The addition of two type-24 brake chambers for the liftable axle installation would require an additional 1,608 cubic inches of
air system capacity.

W5032570

Fig. 6 Calculating Air System Capacity with Additional Chambers for Liftable Axle

Total air system capacity for the chassis, including the additional capacities for the two type-24 brake chambers, would be
7,488 cubic inches.

The following table from MVSS 121 lists the brake chamber rated volumes at 689.5 kPa (100 psi) for the length of stroke for
each chamber type.

Brake Chamber Rated Volumes

Brake Chamber (Nominal Area of Piston

or Diaphragm Square in)

Full Stroke (in) Rated Volume (Cubic in)

Type 9 1.75/2.10 25

Type 12 1.75/2.10 30

Type 14 2.25/2.70 40

Type 16 2.25/2.70 46

Type 18 2.25/2.70 50

Type 20 2.25/2.70 54

Type 24 2.50/3.20 67

Type 30 2.50/3.20 89

Type 36 3.00/3.60 135

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MVSS 121 requires that the combined volume of all service reservoirs and supply reservoirs be at least 12 times the com­bined volume of all service brake chambers. For each brake chamber type having a full stroke at least as great as the first
number in Column 1 of the table above, but no more than the second number in Column 1 of the table above, the volume of
each brake chamber for purposes of calculating the required combined service and supply reservoir volume shall be either
that specified in Column 2 of the table above or the actual volume of the brake chamber at maximum travel of the brake pis­ton or push rod, whichever is lower. The volume of a brake chamber not listed in the table above, is the volume of the brake
chamber at maximum travel of the brake piston or push rod. The reservoirs of the truck portion of an auto transporter need
not meet this requirement for reservoir volume.

An expansion reservoir must be added to the air system to supply air pressure for the braking and up/down functions of a lift­able axle(s). The expansion reservoir for the liftable axle brake function must be supplied by the primary air system, and sup­ply to the expansion reservoir should include a one-way check valve to protect the liftable axle air system should a leak
develop in the primary air system. Additionally, supply to the liftable axle(s) control valves for suspension function should be
supplied by the secondary air system and should also include a pressure protection valve. A pressure protection valve pre­vents a total loss of pressure should a leak develop in any part of the lift axle system.

It must also be determined if the air compressor capacity is sufficient to handle the increase in air volume. For additional in­formation, refer to Air Compressor Capacity section in this bulletin..

Liftable Axle Air Piping

• Relay Valve

A liftable axle must have its own service brake relay valve. A standard R-12 relay valve (part No. 8235–RKN28067 or 745-

103009N) can be used.

Note: It is the responsibility of the body/equipment installer/alterer to ensure that the chassis remains in compliance with
U.S. Federal and Canada Motor Vehicle Safety Standards (MVSS) 106 and 121 when modifications are made to the air
brake system. With respect to brake timing, a quick release valve (such as part No. 8235-RKN32011) may be necessary
in the control circuit when a liftable axle is added. Do not use a pressure differential-type quick release valve for this type
of application.

Note: One relay valve is capable of supplying pressure to four brake chambers. For multiple axle installations, additional
relay valves must be installed according to the number of additional brake chambers being added to the system (i.e., one
relay valve is required for one or two additional axles [four brake chambers], two relay valves are required for three or four
additional axles [eight brake chambers], etc.).

• Air Line Tubing

It is recommended that 12.7 mm (1/2 in) plastic air line tubing be used from the expansion air reservoir to the supply port of a

lift axle service brake relay valve. On liftable axles equipped with Type 20, 24 or 30 brake chambers, 12.7 mm (1/2 in) air
line hose is recommended for the line from the relay valve delivery ports to the brake chambers. A 9.5 mm (3/8 in) air line
hose is recommended for Type 12 and 16 brake chambers. If air pressure is being delivered from a liftable axle relay valve
to a bulkhead fitting, 12.7 mm (1/2 in) air line hose is recommended for the line to the bulkhead fitting. It is recommended
that the guidelines listed above be used for the lines from the bulkhead fitting to the brake chambers.
It is recommended that 9.5 mm (3/8 in) plastic air line tubing be used for control pressure lines. Control pressure for a lift­able axle brake circuit must be supplied from the primary side of the brake treadle valve. On chassis NOT equipped with
automatic traction control (ATC), a T-fitting should be installed into the control port of the rear axle service brake relay
valve to supply control pressure to a liftable axle service brake relay valve. On chassis equipped with ATC, control pres­sure must be plumbed into the rear axle relay control circuit ahead of the ATC valve.
Air pressure for the liftable axle suspension and lift bags should be supplied from the secondary air system.

The following piping diagrams illustrate the recommended brake, suspension and lift air piping for liftable axles.

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Fig. 7 One Tag Axle or One Pusher Axle

W0113590

1. Primary Supply Pressure (from Primary Reservoir)

2. Primary Expansion Reservoir

3. One Way Check Valve (MACK Part No. 745–800376)

4. Rear Axle Service Brake Relay Valve

5. Primary Supply Pressure

6. ATC Valve (if Equipped)

7. Primary Control Pressure (from Treadle Valve)

8. Quick Release Valve (if Required)

9. Liftable Axle Service Brake Relay Valve R-12 (Part No.
8235-RKN28067 or 745-103009N)

10. Tag or Pusher Axle Brake Chamber

11. Secondary Reservoir

12. Supply Pressure to Secondary Reservoir
(from Supply Reservoir)

13. Up/Down Solenoid Valve

14. Pressure Regulator

15. Pressure Gauge

16. Pressure Protection Valve (MACK Part No.

25168652)

17. Lift Control Valve (Normally Open)

18. Liftable Axle Air Suspension Relay Valve

19. Liftable Axle Suspension Air Bag

20. Liftable Axle Lift Air Bag

21. Quick Release Valve

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Fig. 8 Two Pusher Axles

W0113591

1. Primary Supply Pressure (from Primary Reservoir)

2. Primary Expansion Reservoir

3. One Way Check Valve (MACK Part No. 745–800376)

4. Rear Axle Service Brake Relay Valve

5. Primary Supply Pressure

6. ATC Valve (if Equipped)

7. Quick Release Valve (if Required)

8. Primary Control Pressure (from Treadle Valve)

9. Pusher Axle Service Brake Relay Valve R-12 (Part No.
8235-RKN28067 or 745-103009N)

10. Pusher Axle Brake Chamber

11. Secondary Reservoir

12. Supply Pressure to Secondary Reservoir
(from Supply Reservoir)

13. Up/Down Solenoid Valve

14. Pressure Regulator

15. Pressure Gauge

16. Pressure Protection Valve (MACK Part
No. 25168652)

17. Pusher Axle Air Suspension Relay Valve

18. Pusher Axle Suspension Air Bag

19. Lift Control Valve (Normally Open)

20. Quick Release Valve

21. Pusher Axle Lift Air Bag

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Fig. 9 One Tag Axle and One Pusher Axle

W0113592

1. Primary Supply Pressure (from Primary Reservoir)

2. Primary Expansion Reservoir

3. One Way Check Valve (MACK Part No. 745–800376)

4. Service Brake Relay Valve

5. ATC Valve (if Equipped)

6. Primary Control Pressure (from Treadle Valve)

7. Quick Release Valve (if Required)

8. Pusher Axle Service Brake Relay Valve R-12 (Part No.
8235-RKN28067 or 745-103009N)

9. Pusher Axle Brake Chamber

10. Tag Axle Service Brake Relay Valve R-12 (Part No.
8235–RKN28067 or 745-103009N)

11. Tag Axle Brake Chamber

12. Secondary Reservoir

13. Supply Pressure to Secondary Reservoir (from
Supply Reservoir)

14. Up/Down Solenoid Valve (Tag and Pusher
Circuits)

15. Pressure Regulator (Tag and Pusher Circuits)

16. Pressure Gauge (Tag and Pusher Circuits)

17. Pressure Protection Valve for Tag and Pusher Cir­cuits (MACK Part No. 25168652)

18. Lift Control Valve (Normally Open)

19. Tag and Pusher Suspension Air Bag Relay Valve

20. Quick Release Valve

21. Axle Lift Air Bags (Tag and Pusher Axles)

22. Axle Air Suspension Air Bags (Tag and Pusher
Axles)

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Fig. 10 Two Pusher Axles and One Tag Axle

W0113593

1. Primary Supply Pressure (from Primary Reservoir)

2. Primary Expansion Reservoir

3. One Way Check Valve (MACK Part No. 745–800376)

4. Rear Axle Service Brake Relay Valve

5. Delivery Pressure to Rear

6. Primary Supply Pressure

7. ATC Valve (if Equipped)

8. Quick Release Valve (if Required)

9. Primary Control Pressure (from Treadle Valve)

10. Pusher Axle Brake Chambers

11. Pusher Axle Service Brake Relay Valve R-12 (Part
No. 8235-RKN28067 or 745-103009N)

12. Tag Axle Service Brake Relay Valve R-12 (Part No.

13. Tag Axle Brake Chamber

14. Secondary Reservoir

15. Supply Pressure (from Supply Reservoir)

16. Up/Down Solenoid Valve

17. Pressure Regulator

18. Pressure Gauge

19. Pressure Protection Valve (MACK Part No.

25168652)

20. Lift Control Valve (Normally Open)

21. Liftable Axle Air Suspension Relay Valve

22. Quick Release Valve

23. Liftable Axle Lift Air Bag

24. Liftable Axle Suspension Air Bag

8235-RKN28067 or 745-103009N)

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Liftable Axle Anti-Lock Brakes

CAUTION

If liftable axles (tags or pushers) are being added to a chassis equipped with the MACK Road Stability Advantage (RSA)
system, and it is desired to keep the RSA system active, the liftable axle(s) must be self-steer type axles. The self-steer lift­able axle(s) service brakes MUST NOT be activated by modulated air pressure from the anti-lock brake system. Currently,
the only chassis having the RSA system approved for adding self-steer liftable axles are chassis used in concrete mixer
and heavy-haul tractor applications.

Anti-lock brakes are not specifically required for liftable axles. Should anti-lock brakes be desired, however, the following pip­ing diagrams illustrate how liftable axles can be included in the anti-lock brake system.

W5032574

Fig. 11 6S/6M Anti-Lock Brakes with Single Tag and Single Pusher and One Relay Valve for Tag and Pusher Axles

1. ABS Sensor

2. ABS Modulator Valve

3. T-Fitting or Quick Release Valve (If Required)

4. Automatic Traction Control (ATC) Valve (If Equipped)

5. Service Brake Relay Valve R-14

6. Lift Axle Service Brake Relay R-12 (Part No. 8235 –
RKN28067 or 745 –103009N)

7. Brake Chamber

8. Tag Axle

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9. Spring Brake Chamber

10. Drive Axles

11. Expansion Reservoir (Primary Air)

12. Primary Reservoir

13. Supply Reservoir

14. Steer Axle

15. Secondary Reservoir

16. Front Axle Quick Release Valve

17. Treadle Valve

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Air Lines Joystick Control

TE / MRU and LR models include a bundle of seven 6.4 mm (1/4 in) air lines routed from the joystick area inside the cab to
the outside of the cab. These air lines provide a convenient means of connecting a joystick to the chassis air system and to
the different systems that the joystick will control. Refer to the following illustration for the location of the air line bundle.

W5032577

Fig. 12 Joystick Air Line Bundle TE / MRU Models

1. Joystick Air Line Bundle

2. Joystick Mounting Area

Fig. 13 Joystick Air Line Bundle LR Models

1. Joystick Air Line Bundle 2. Air Line Bundle Pass-Through Grommet

3. Air Line Bundle Pass-Through Grommet

W5032578

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Air Line Hose Installation

Flexible air line hose may eventually fail. However, by following proper installation, clamping and routing procedures, hose
life can be maximized. Also, when selecting an air line hose, make sure that the hose is the same diameter as the hose being
replaced. Replacing an air line hose with a different size hose may affect brake timing.

Avoid Twisting Hoses are imprinted with a layline along the length of the hose to help determine if the hose is twisted. The
hose is twisted if the layline spirals around the hose. Swivel fittings make it possible to install a hose without a twist. When in­stalling a hose, install one fitting so that the layline is visible when the fitting is tight. While the other fitting is still loose, the
hose may be rotated as needed until the layline follows the hose routing without spiraling around the hose. Similarly, elbow
fittings can be aligned to avoid hose twist.

W5032579

Fig. 14 Twisted and Straight Laylines

Notes

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Avoid Excessive Torque on Fittings Unlike pipe threads, swivel fittings do not depend on thread compression to seal. DO
NOT overtighten a swivel fitting, as this will damage the fitting or sealing surfaces.

An air line should be installed as follows:

1 Tighten male pipe ends of hose assemblies first, then tighten the swivel fittings.

2 Whenever possible, install any adapters needed in accessories (as a bench procedure) first.

3 Use an adjustable or open end wrench to install air hose assemblies. DO NOT use pipe wrenches as they will mar the fit-

tings and damage the plating material.

4 DO NOT use pipe thread-sealing compound on swivel-nut hose fittings. Thread sealant should only be used on pipe

threads.

5 When installing male-end fittings, use the nipple hex, not the socket hex, to tighten the fitting.

W5032580

Fig. 15 Tightening Male-End Fittings

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