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ADB Service Manual


XS5 22XLT™ / XS7 22XLT™

1. ADB Description

This manual describes the maintenance and repair of Air Disc Brakes, including the work methods and work processes required to replace the components using the available maintenance tools.
This manual is intended for service technicians trained for commercial vehicles.

  • Carefully read all safety instructions and the repair and maintenance instructions contained in this manual before beginning maintenance, repair, or replacement of parts. These instructions must be followed to prevent personal injury or material damage.
  • HDNABI™ BRAKE warrants the safety, reliability and performance of its products and systems only in compliance with all instructions, cautions and safety instructions.
  • Always follow the specifications and instructions of the axle or vehicle manufacturer.
  • Always follow corporate and national accident prevention guidelines and health and safety regulations.

Figure 1. Air DiscBrake

2. Safety Information

Be sure to observe the following safety precautions when servicing and diagnosing the brake system.

  • Set the vehicle on a flat surface, use parking brakes, and secure the wheels with a wedge shaped wheel chock.
  • When working under or around a vehicle, stop the engine and remove the ignition key.
  • Always wear personal protective equipment when servicing.
  • Always wear safety glasses when working with air pressure.
  • Do not exceed the vehicle manufacturer’s recommended air pressure.
  • Protects against rotation, leakage, heating or contact with electrically charged parts.
    It is also recommended that you make clear markings or markings nearby.
  • Never install, remove, disassemble or assemble the device until you have read and thoroughly followed the recommended procedure.
  • Some products include strong springs, which can cause injury if not properly disassembled and reassembled. Use only the right tool and be careful about disassembly.
  • Replace worn or damaged brake discs immediately.
  • Regularly check the abrasion limits of the brake pads and brake discs.
  • When disassembling, servicing or replacing a product that may affect braking performance or system, it must be checked.
  • Before servicing the vehicle, restore all components and the brake system if any abnormalities occur.

3. ADB Identification

    • Find the Lot. Number on the back of the housing.
    • The used Lot. Number. See the table below for information on Number

      Figure 2. ADB Lot. Number Position

    • The identification of ADB LH and RH can be distinguished by the length difference of the guide pin and the arrow marking on the side of the bridge.The arrow marking indicates the rotation direction of the rotor. (See FIGURE 5, 6.)

(L): Long Guide Pin
(S): Short Guide Pin

Figure 4. ADB RH/LH Identification

Figure 5. Rotation Direction Marking of ADB RH

Figure 6.Rotation Direction Marking of ADB LH

1. ADB Components

Figure 7. Parts Development of the Air Disk Brake



01. Hub

12. Tappet and Boot Assembly

23. Cap

02. Rotor

13. Piston

24. Adjuster

03. Carrier

14. Lever

25. Adjust Cap

04.Torque Plate

15. Housing

26. Pad Assembly

05.Caliper Mounting Bolt

16. Inner Boot

27. Pad Holder Spring

06. Bridge

17. Bushing(S)

28. Pad Retainer

07. Bridge Bolt

18. Bushing(L)

29. Retainer Bolt

08. Ring

19. Guide Pin(S)

30. Retainer Washer

09. Boot

20. Guide Pin(L)

31. Chamber

10. Housing Bolt

21. Guide Pin Bolt(S)

32. Chamber Nut

11. Traverse Assembly

22. Guide Pin Bolt(L)

2. ADB Section View

Figure 8. Sectional View of Air Disc Brake

3. Operation Description

When air pressure is applied, the push rod of the chamber advances and moves the lever.
The input force is transmitted to the bridge through the piston gear. The force is distributed
to the bridge and the tappet. The reaction force of the bridge is transmitted to the outer pad
Clamping force is transmitted to inner pad to generate braking force.

Figure 8. Sectional View of Air Disc Brake

After releasing the air pressure, the return spring pushes the bridge and lever back into the
starting position.
The Auto-Adjust feature maintains running clearance between Pad and Rotor.(.6 mm)

1. Preventive Maintenance

For long-life parts, it is also necessary to regularly check the general condition of some components. The following periodic inspections ensure the life of the disc brake and prevent

  • 3 Three-month cycle recommended items
    (Ex. every time tire pressure is inspected), you should visually check the pad wear (Section 3.2).
    (Pads must be replaced) Adjuster operation check (Section 3.3), Tappet and boot assembly (Section 3.5)
    Check caliper / check operation of guide pin (see Section 3.4)
  • Yearly Inspection Recommended Items: Caliper Driven Clearance (Section 3.2 and Section 3.3)
    The above cycle is minimum and may need to be checked more often depending on the application use of the vehicle. The disc must be checked according to the axle or vehicle
    manufacturer’s specifications.

2. Pad and Disc Wear Test

– The thickness of the pad should be checked periodically according to the operation of the vehicle.
– You can visually check the wear of the brake pads and rotor without detaching the wheel. (See Figure 10)
① You can position the top and rotor on top of the brake to see
② You can check the wear of the pad through Visual Wear Sensor. (See Figure 11)
– Notch mismatch: pad wear limit not reached
– Notch match: worn pad need to check the pad and rotor.

Figure 10. Wear Inspection Location

– Compare the relative positions of the two notches marked on the Carrier and Bridge, and you should inspect the pads and rotor when the two notches are aligned.

Figure 11. Visual Wear Indicator, to Notify when to Check the Rotor & Pad

The rotor should be measured at its thinnest point. Do not measure near the rotor edge as burrs may exist.
The friction material should be replaced if the thickness at the thinnest point is less than 2 mm.
Pad and Rotor information (See Figure 12)

Figure 12. Pad and Rotor Information

A = Rotor thickness
New = 45mm, Wear Condition = Max 37mm
(Rotor replacement required)
C1 = Overall pad thickness (New) 30 mm
C2 = Overall pad thickness (New) 30 mm
D1 = Back Plate 9 mm
D2 = Back Plate 9 mm
E = Minimum thickness of friction material 4 mm
F1 = Wear of backplate and friction material
Minimum allowable thickness 13 mm
(Replacement of pads required)
F2 = Minimum allowable thickness in abrasion of backplate and friction material 13 mm Replacement of pads required).
If the thickness (A) at the thinnest point of the rotor is less than 37 mm, the rotor must be replaced.
Pads should be replaced immediately if: (See Figure 13)
– When the friction material cracks
– Grease and oil contaminated
– Part of the friction material is damaged.
– When the friction material is removed
– When the pad reaches the wear limit

Figure 13. Examples of Pads that need to be replaced

The rotor must be replaced immediately if: (See Figure 14)
– When the disk surface is cracked.
– If the surface roughness of the disc is not uniform

Figure 14. Examples of Rotors requiring Replacement

In the event of a problem with the above mentioned pads and rotors, it is necessary to replace the parts immediately to ensure normal brake performance.

3. Adjuster Inspection

[Caution] Follow all safety procedures during operation.

[Reference] Refer to Annex Table for necessary tools for Adjuster inspection. (Annex A)

– Pads must be assembled to check the Adjuster.
– Check that the brake is released before checking the Adjuster.

[Caution] If the vehicle is stationary and parked, take appropriate measures to prevent the vehicle from moving.

Remove the wheel first and disassemble the Pad Retainer. Retainer Bolt (M14) must be disassembled using hexagon socket wrench 14 mm. (See Figure 22)

[Caution] When disassembling Pad Retainer, Pad Retainer may suddenly pop out by Pad Holder Spring.

Press the caliper towards the wheel and check the gap between the outer pad and the bridge using the feeler gauge. (See Figure 15). This gap should be between 0.6 mm and 1.0 mm.

[Caution] If the gap is too wide, there is a risk of brake failure. If the gap is too narrow, there is a risk of overheating, which may result in damage to the brake.

Figure 15. Measuring Pad Clearance

Remove the cap and check the direction of operation of the Tappet (Piston) by rotating the Adjuster to check that the mechanism of the Adjuster is working properly. (See Figures 17 and 18)
– Clockwise: Tappet (Piston) appears.
– Counterclockwise: Tappet (Piston) enters

Figure 17. Tappet Direction (Adjuster Clockwise Rotation) To Adjust brake (Tighten)

Figure 18. Tappet Incoming Direction (Adjuster Clockwise Rotation)

[Caution] Excessive operation of the adjuster can damage the adjuster.
Do not exceed 9.4 lb-ft( clockwise rotation torque.

[Caution] Be careful not to lose the cap.

If there is no cap, foreign matter may get into the inside of the caliper, which may cause problems in function.

If the spacing is too small or too large, the Adjuster may not work well and the pads must be reoriented. Adjust the gap between the pad and the rotor to 0.6~0.8 mm using a feeler gauge, assemble the pad, and turn the Adjuster counterclockwise 1 times (90 degrees at a time) while the gap is “0”. (See Figure 16)

Figure 16. Pad Gap Adjustment Meathod

4. Caliper Inspection

Follow all safety procedures during operation.
check the brake release status.

[Caution] If the vehicle is stationary and parked, take appropriate measures to prevent the vehicle from moving.

Caliper drive test (Sliding force of guide pin)

Remove the Pad Retainer and pull the calipers by hand while the pads are assembled and check if the movement of 0.6 mm to 1 mm is smooth. (See Figure 19)

Remove the next pad and make sure that the minimum movement is 25 mm when the calipers are moved by hand, At this time, the calipers should be smooth in motion with low force. If the caliper does not move after applying a high force, replace the caliper assembly. Also, if the movement of the caliper is less than 25 mm, replace the caliper assembly.

Inspect inner boot of guide pin

With the pad removed, slide the caliper inward to expose the booting of the guide pin. Inspect the guide pin boot for, damage, cut, cracked, torn, or boots. Replace any damaged boots immediately to prevent entry of dust and moisture, which will affect the movement of the guide pins.

[Caution] When inspecting the boot, if excessive air enters the boot, it should be removed as much as possible.

Once the boot is extended, it should be shrunk, without swelling of the boot when it returns to its original position.

5. Tappet and Boot Assembly Inspection

To inspect the tappet and boot assembly, remove the pad and adjusting hex bolt the Adjuster to extend the tappet.

[Caution] Do not extend the tappet beyond 40 mm. (See Figure 21)

Figure 21. Tappet Boot Assembly Checks

Inspect the tappet and boot assembly for damage, cuts, cracks, tears, and corrosion. Damaged boots can lead to penetration of dust and moisture, can cause corrosion and interfere with the operation of the brakes. Replace the damaged boot immediately.

Once the tappet and boot have been inspected, return the tappet to its initial position. At the time of installation, the boot is assembled in a compressed state to minimize the inflow of air inside.

[Caution] If excessive air is introduced into the boot, remove the chamber with the Tappet folded and re-install the chamber.

6. Pad Replacement

[Caution] Follow all safety procedures during operation. Check the brake release status. If fitted to the vehicle, take appropriate measures to prevent the vehicle from moving. Cage chamber parking brake.

[Important] It is recommended that you check the operation of the Adjuster mechanism before removing the pads.

(See Section 3.3)

Removing the Pad

Remove the wheel first and disassemble the Pad Retainer. Retainer Bolt (M14) must be disassembled using hexagon socket wrench 14 mm. (See Figure 22)

Figure 22. Disassembly of Pad Retainer

Figure 23. Pad Removal

[Caution] When disassembling the Pad Retainer, the Pad Retainer may pop out suddenly by Pad Holder Spring. Press the Pad Retainer by hand and disassemble.

[Caution] If the Pad Retainer and the bolt are corroded or damaged, they must be replaced.

Disassemble the Pad Retainer and remove the Outer Pad and Inner Pad. When removing the pad, slide the caliper slightly by hand to make it easier to pull out the pad.

[Caution] If the pad does not fit smoothly, use the rotate Adjuster clockwise to push the piston in.
(See Adjustment 3.3)

6-1. Assembly of Pad

Figure 24. Inner Pad Assembly

Figure 25. Outer Pad Assembly

Figure 26. Pad Retainer Assembly

[Important] Pads must be used only with OEM genuine manufacturers approved pad.
Failure to do so will invalidate the brake’s warranty, vehicle manufacturer’s warranty may be voided by the vehicle manufacturer, axle manufacturer and disc brake manufacturer, and may affect the vehicle’s operating license.

[Caution] Do not operate Adjuster excessively. It can cause damage to the Adjuster. Use Adjuster to completely restore Tappet.
Not to exceed in pound torque.

Push the next caliper inward to assemble the Inner Pad, and then slide the caliper outward to attach the Outer Pad.
Attach the Pad and adjust the gap between the Pad and the rotor.Use a filler gauge to adjust the gap between the pad and the rotor to 0.6 mm, assemble the pad, and turn the Adjuster counterclockwise 1 time (90 degrees at a time) while the gap is “0”.
(See Figure 16)

Assemble the Pad Retainer with the gap adjustment completed. After attaching the Pad Retainer to the groove of the caliper, you must press the Pad Retainer by hand so that it can be tightened with a bolt.
When fastening with bolts, be sure to fasten the washer together.

[Caution] If the bolt is tightened beyond the specified torque, the washer and bolt may be damaged.
Observe the specified torque. (See Appendix A)
Be careful not to contaminate the friction material with grease or grease during assembly of the Pad.

[Note] It is recommended to clean the friction material dust, etc. around the pad mounting area of Carrier after removing the pad.

7. Tappet and Boot Assembly Replacement

Figure 27. Tappet and Boot Assembly Development Diagram

[Caution] Follow all safety procedures during operation.
Check the brake release status. If fitted to the vehicle, take appropriate measures to prevent the vehicle from moving.

You can remove the caliper if required. However, when reinstalling the caliper, replace the caliper mounting bolt with a new one. It is recommended replacing with new mounting bolts. (See section 3.8)

[Information] This maintenance procedure uses special tools.
Cage spring brake with caging bolt.

Remove the air hose from the brake chamber. (See Section 3.10)

Remove the pad from the brake. (See Section 3.6)

Inspect the rotor of the brake. (See Section 3.2)

Tappet and boot assembly removal Adjust the Adjuster to expand the Tappet to 40 mm or less, as shown in Figure 21.
Space between the tool and Tappet must be ensured.

Tappet and boot assemblies can be separated using wedge-shaped fork(ST006).
Remove boot from Tappet and remove Tappet. Orient the fork(ST006) so that the tapered section faces the Tappet.(See Figure 28)

Figure 28. Tappet and Boot Assembly Removal

Carefully remove the boot using A Flat-head screwdriver(S8).
At this time, do not insert the tool so deeply that it contacts the piston. (See Figure 29)

Figure 29. Removing the Boot Assembly from the Cover Plate

Remove the boot from the cover plate.
[Caution] Be careful not to let foreign substances into the cover plate.
Assembling tappet and boot assembly when the caliper is mounted on the vehicle
Make sure that the new Tappet and boot assembly are not damaged before assembly.
Use special tools (ST001 & ST003) for this operation. (Figure 30).
Insert the piston as much as possible into the tappet. Next insert the Nylon Disc into the tool(ST001 & ST003) and turn the upside down to face the disc rotor.
Rotate the nut on tool(ST003) to fully seat the Tappet in the piston as shown in (Figure 31).

[Caution] Damage to the rotor can prevented, it is necessary to assemble Black Nylon Disc (S7) in the rotor direction.

Figure 30. Boot Assembly when Mounted on Vehicle

Figure 31. Tappet Assembly when Mounted in Vehicle

Assembling tappet and boot assembly when the caliper is removed from the vehicle
Make sure that the new Tappet and boot assembly are not damaged before assembly.
The method of operation is the same as when the caliper is mounted on the vehicle.(See Figures 32 and 33)
Make sure that the Tappet is solidly assembled. Assemble the pad to the brake. (See Section 3.6) If the caliper is removed from the vehicle, assemble it. (See section 3.8)

Figure 32. Boot Assembly when Disconnected from Vehicle

Figure 33. Tappet when Disconnected from Vehicle Assembly

8. Caliper Replacement

[Caution] Follow all safety procedures during operation. Check the brake release status.
If fitted to the vehicle, take appropriate measures to prevent the vehicle from moving.

[Caution] When lifting the brake using a hoist, do not move the brake (or chain) on the Pad Retainer.
Pad Retainer is not designed to support the weight of the brake. Wrap the entire brake with a brace (or chain) and connect it to the hoist.

Caliper Removal Cage Spring Parking Brake

Need Cage Spring Brake procedure prior to removal or repair.

Remove the air hose from the brake chamber. (See Section 3.10)
Remove the pad from the brake.(See Section 3.6)
Properly support the brake, remove the mounting bolts (6EA) fastened to the toque plate, and remove the caliper assembly from the vehicle.
[Note] It is recommended to clean the contact area with the axle after Caliper decomposition.

Reassembling the calipers When reassembling the caliper, observe the specified tightening torque values for the mounting bolt.
Tightening torque: 369-427 ft lbs

[Reference] When reassembling the Caliper Assembly,
we recommend replacing the Mounting Bolts (6EA) with a new one.

Figure 34. Disassembling the Caliper Assembly

9. Replacing the guide pin and boot assembly

Figure 27. Tappet and Boot Assembly Development Diagram

Deactivate Spring Brake

[Caution] Follow all safety procedures during operation.
Check the brake release status.
If fitted to the vehicle, take appropriate
measures to prevent the vehicle from moving.

Remove the wheel. Refer to the vehicle manufacturer’s recommendations for removal.
Cage chamber parking brake.

Remove the air hose from the brake chamber. (See Section 3.10)

Remove the pad from the brake.(See Section 3.6)
Guide pin and boot disassembly

In most cases, the caliper should be removed from the vehicle to replace the guide pin and boot. Remove the mounting bolt and remove the caliper from the vehicle. (See section 3.8)

Place the brake on the workbench and fasten with a vise. (See Figure 36)

Figure 36. Example of Brake Fixing Position

Use a “-” shaped screwdriver or similar tool and hammer to lightly tip the end of the cap and remove the cap. All caps removed should be discarded. (See Figure 37)
[Caution] The cap is not reusable. Disassemble the cap once, and replace it with a new cap.

Figure 37. Cap Schematics Blown-Up

Loosen the housing bolts and disassemble the bridge from the caliper to facilitate replacement of the guide pins.
The housing bolt (M14) can be disassembled using a 12 mm hexagon wrench.(See Figure 38)

Figure 38. Removal of Bridge

[Caution] When disassembling the bridge, be careful not to drop the bridge.

Loosen the guide pin bolts on both sides and remove the guide pin and guide pin ring.
Guide pin bolts (M16) can be disassembled using a 14 mm hexagon wrench.
All disassembled guide pins should be discarded. (See Figure 39)

Figure 39. Guide Pin Bolt and Guide Pin Disassembly

[Caution] When disassembling the guide pin bolt, the housing will be detached from the carry, so be careful not to drop the housing.
Remove the guide pin boot from the housing while twisting the ring assembly of the boot with a “-” type screwdriver. Be sure to discard the removed boot. (See Figure 40)

Figure 40. Guide Pin Boot Removal

Clean the surface of the housing from which the guide pin boot has been removed and the surface of the carrier from which the guide ring has been removed.

To replace the guide pin and guide pin boot, lay the carrier on the vise.

Bush Removal

Figure 41. Bushing Removal Tool T1

Clean top and bottom of housing surface around bushing. Fixed the bridge to makes mounting section is vertical.
Apply grease to the inside of the Long Adaptor (ST010) and the Bolt_210 mm(ST007) Tap before disassembling.

Apply grease to the Long Bolt_200 mm (ST007), and then gently assemble the Long Nut (ST011).
Before remove the Bushing, make sure that Bushing Nut is correctly installed. (See FIGURE 42)

Figure 42. Bushing Removal Tool Assembly

Turning the top of the bolt head will pull the brass Long Nut(ST011) up and the bush will disassemble. Disassemble by visually checking that the bush comes up.
Discard the disassembled bush. (See FIGURE 43)

Figure 43. Bushing Removal

[Caution] Disassemble the bushing by keeping the removal tool exactly aligned with the guide pin center. (See FIGURE 44)

Figure 44. Keep Accurate Alignment

Discard the disassembled bushing, wipe the insert, and make sure it is clean.

Bushing Assembly
Clean the top and bottom surfaces of the housing around the bushing.
Fixed the bridge to makes mounting section is vertical.
Apply grease to outside of Bush, Housing mounting part, and the Bolt_210 mm(ST007)
Tap part before assembling.

Connect the bolt and washer to the short adapter(ST009). (See FIGURE 45)

Figure 45. Bushing Install Tool T2

Put the new Bushing into the Short Nut (ST012) and assemble it to the mounting.
Rotate the bolt until the bushing contacts the Short Adaptor(ST009).

Assemble and secure the bushing in the correct position. (See Figure 46.)

Figure 46. Assembly and Fixing Bushing

Remove the installation tool and check that the bushing position and metal sheath remain

Guide Pin and Boot Assembly

Apply grease to the bush inside the guide pin assembly hole of the housing.

First, assemble the guide pin boot into the housing and check that the boot is securely in place and that no damage has occurred during installation.

Assemble the new guide pin inside the BUSHING, assemble the boot into the groove
of the guide pin as shown in Fig. 48, and assemble the guide pin ring. (See Figure 47)

Figure 47. Guide Pin Assembly

Figure 48. Guide Pin and Boot Assembly

Figure 49. The shape in which the Guide Pin is assembled to the Carrier

Align the guide pin ring on one side of the carrier and tighten the guide pin bolts to secure the guide pins to the carrier. Please tighten the guide pin bolts according to the specified tightening torque.
Before tightening the guide pin bolts, loctite type the bolts to prevent loosening.

– Tightening torque: 217-253 ft lbs

Assemble the opposite guide pin with the same procedure.

[Caution] Be careful not to damage the boot when assembling the guide pin.

[Caution] When assembling the guide pin ring to the carrier, make sure that it is seated correctly in the groove.

[Caution] Make sure that the entire end of the boot is seated correctly inside the guide pin
ring. If there is a protruding part outside the guide pin ring, push it in.

Assemble the bridge using the housing bolt.
Apply loctite type to prevent loosening.
Assemble the housing bolts according to the specified tightening torque.(See Figure 50)

Figure 50. Shape after Bridge Assembly

Tightening torque: 217-253 ft lbs

Assemble the pad to the brake. (See Section 3.6)

Assemble the calipers. (See section 3.8)

Install the brake chamber. (See Section 3.10)

Check that the guide pin has been replaced normally. (See Section 3.4)

Cap Assembly – Place the Brake on the working table and secure it with a vise.

Attach the cap to the tool Dumbell_Cap(ST002).

Assemble the cap by hammering the end of the ST002 using a hammer or other tool.
(See Figure 51)

Figure 51. Cap Assembly

The Cap cannot br reused.
Discard improperly disposed caps and replace with new cap.

A. Maintenance tools and tightening torque










Caliper Mounting Bolt





Bridge Bolt





Guide Pin Bolt








Retainer Bolt





CoverPlate Bolt





Chamber Nut




C. Spare Part / Kit

Spare Part/Kit




Pad Kit

(26, 27, 28, 29, 30)

Tappet and Boot Assembly



Adjuster Cap



Guide Pin, Bush & Boot Kit

(8, 9, 17, 18, 19, 20, 21, 22, 23, 25)

Guide Pin Boot Kit

(8, 9, 23, 25)

Bridge Bolt



Caliper Mounting Bolt



Chamber Assembly


(31, 32)

Air Disc Brake


(3, 6, 7, 8, 9, 10, 11, 15, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)

D. Grease specification and inlet

Specification Number

Mixing Blend (@25 C)

Red Dot

Base Oil



280 ~ 310

250 C

Mineral Oil

High Load/ High Temperature Lubrication

– Equivalent to Germany ADDINOL GRANULE HT2


260 ~290

200 C

Synthetic Oil

For Rubber and Plastic

– Equivalent HIRAX RR-S NO.2



Grease Inlet Part

Specifi- cation

Amount (mg)

Inlet Place



Between Housing and Saddle


Min. 300



Between Saddle and Bearing Seat


Min. 600





Min. 2000


Whole Front and Back


Between Saddle and Lever


Min. 250





Min. 200


All Around


Between Housing and Traverse


Min. 1300



Between Roller and Piston Gear


Min. 400



Adjust Gear


Min. 300


Teeth of Gear Part


Piston Gear


Min. 300


Teeth of Gear Part


Connecting Gear


Min. 600


Teeth of Gear Part


Between Housing and Connecting Gear


Min. 100



Caution: High Compressed spring is loaded inside of the Spring Brake.
It is VERY IMPORTANT to read all the manuals and follow the instruction. Releasing piggyback or spring chamber forcefully without proper instruction may cause death, severe personal injury and/or property damage. If Spring Brake is not caged, Mounting Nut and Clamp Nut should never be released. This may cause severe injury.

Piston Diaphragm Spring Brake

Important Notification for Installation

Prior to installation, it is mandatory that the Spring Brake is caged.
If not caged, must be done before the installation.
To maximize the life of the Spring Brakes, we highly recommend you to follow the service manual when installing the product to your vehicle.

Air Disc Brake Chamber Removal Instruction

  1.  Always block wheels when working on the brake to prevent vehicle rollaway.
  2.  After removing the parking brake, apply vehicle or shop pressure 6.2 ~ 8.3 bar
    (90~120psi/620~830 kPa minimum) to the emergency parking brake. Maintain vehicle or shop air pressure, caged the release bolt(A) counterclockwise from the top of the chamber head using 0.75(3/4)inch (19 mm) wrench. (Use caging bolt to cage the spring brake.)
    (If air leaks from the spring brake, you can manually cage the spring brake by using the caging bolt).
  3. Activate the parking brake on the vehicle to exhaust all the air from inside of the spring brake.
  4. Follow the manufacturer’s instruction precisely, using spanner wrench, release the air hose and the connector from the chamber. Marking before the separation to ensure the location of the air line and connector is highly recommended.
  5. Using a 24 mm (15/16 inch) socket wrench, unscrew the mounting nut (B) counterclockwise and cautiously remove the old chamber.

figure 1

Installation of Air Disc Brake Chamber

CAUTION:  Before installing new air disc brake chamber, the sealing s CAUTION urface must be cleaned.
Using grease recommended by the manufacturer, apply it to the cup inside of the LEVER flange surface (A) should be free from damage and impurities. Seal and Pushrod area must be in dry condition and free from impurities.

Figure 2

  1. Prior to spring brake chamber installation, ensure that spring brake is completely caged (power spring aged), and the service brake pushrod is fully retracted to zero stroke position.
  2. Install the spring brake chamber to caliper bracket and using 24 mm(15/16 inch) mounting nut (1) socket wrench, screw the mounting nut clockwise. Recommended torque is 133~155 lbf.ft (18~21kgf.m).
  3. Using Loctite glue or Teflon tape, tighten the chamber fitting(2) at 25lbf.ft (3.6kgf.m) torque. Connect the correct air hose to each position. Air hose needs to be free from entangling and interference at all time.
  4. After charging the air tank to 90~120 psi (6.2~8.3 bar / 620~ 830 kPa, release the parking brake (parking lever off), charge the spring chamber, turn caging volt(3) to clockwise to torque at 44~58 lbf.ft (6~8Kgf.m).

Figure 3

ATTENTION! : Remove the plug from the lowest drain hole of the brake chamber after assembly. Other drain holes must be closed by plugs!

Installation Inspection

  1. After charging the air tank to 90~120 psi (6.2~8.3 bar /620 ~830kPa), release the parking brake.
    Using soapy water (NEVER ANY TYPE OF OIL) inspect air leak from airline and fitting and also from service part airline and fitting during foot brake operation.
  2. Follow your vehicle manufacturer’s recommended manual for brake adjustment.

SAFE DISCARD of Old Spring Brake

  1. All retired spring brake chamber must be safely disarmed before they are disposed of to prevent serious personal injury and property damage from the accidental sudden release of the high energy spring.
  2. To dispose of the spring chamber, place it in the steel container and close it. Use a gas torch to cut through the head housing and cut the actuator spring.

Figure 4

1. Hazard Alert Messages

Read and observe all Warning and Caution hazard alert messages in his publication. They provide information that can help prevent serious personal injury, damage to components, or both.

WARNING – To prevent serious eye injury, always wear safe eye protection when you perform vehicle maintenance or service.

Park the vehicle on a level surface. Block the wheels to prevent the vehicle from moving. Support the vehicle with safety stands. Do not work under a vehicle supported only by jacks. Jacks can slip and fall over. Serious personal injury and damage to components can result.

When raising the trailer/axle, place lifting devices and/or jack stands directly under the spring seat bracket or other area of the trailer frame. Do not place lifting devices or jack stands directly on the axle beam or damage to the axle may result.

2. Guidelines

The installation and service performance of all suspension system brackets welded to STA axles are the responsibility of the system integrator.

3. Only Use Certified Welders

The American Welding Society’s (AWS) Document D1.1 requires that you only use certified welders.

4. Methods

Four methods can be used to weld hardware to trailer axles.
– Shielded Metal Arc (Stick electrodes)
– Gas Metal Arc (MIG-Solid Wird)
– Gas Tungsten Arc (TIG)
– Flux Cored Arc (Tubular Wire)
Refer to the following table for the American Welding Society (AWS) classifications and specifications.

Method for Welding Carbon and Low Alloy Steels

AWS Electrode Classification

AWS Specification

Shielded Metal Arc


A5.1 / A5.5

Gas Metal Arc



Gas Tungsten Arc



Flux Cored Arc



The AWS requires that weld tensile strength must be 70,000 psi(4826.33 bar). Weld tensile strengths that are either higher or lower than this rating are not acceptable.

The best fusion and strength will be obtained using the voltage, current and shielding medium recommended by the electrode manufacturer.

If the Shielded Metal Arc method is used, electrodes must be clean, dry and come from stock that has been stored according to AWS specifications.

5. Axle Preparation

The area to be welded must be free of paint, grease, dirt, slag and other contaminants that can affect  weld quality.

The axle tube and the hardware to be welded to the axle must be at a temperature of at least 60°F (15°C). Welds made with the axle components at the correct temperature will perform better, since there is less of a tendency to form an area of brittle material next to the weld.

Never bring an axle into a factory or repair facility from the cold and immediately weld. Rather, the axle and brackets to be welded should be stored overnight in a correctly heated room.

If temperature requirements are not met, pre-heat the weld area to a temperature of at least 200°F (93°C) using a “rosebud.” Do not concentrate heat in one area. Rather, slowly heat a wide area around the joint to be welded. Verify the temperature with a temperature-sensitive crayon or other appropriate means.

6. Hardware Fit

Refer to the axle and suspension manufacturer’s installation documentation for weld zones and locations.

7. Welding Preparation

Welding equipment should be grounded to the axle through a cable connection that is both clean and tight. The connection should be located at a point that will place a 300mm from the torque plate.
It should not be located at a point that will place a wheel bearing between the ground connection and weld area.(Figure 1.1)

Figure 1.1

A connection that places a wheel bearing between the ground cable connection and the weld area can damage the bearing by electric arcing as shown below. (Figure 1.2)

Figure 1.2

Prior to applying final welds, hardware should be tack welded to the axle following recommendations provided by the component manufacturer. This will help minimize both axle distortion and residual stresses caused by final welds. After tack welding, clean up any weld slag, then fuse the tack welds into the final welds. (Figure 1.3)

Figure 1.3

Do not locate tack welds at the ends of the bracket.
Rather, they should be located toward the center of the brackets. (Figure 1.4)

Figure 1.4

8. Location

Axles are more likely to crack at a weld location, since welds lower the strength of the axle material adjacent to the weld and set up a stress riser at the weld site. You must confine welding to areas of relatively low stress near the center or neutral axis of the beam. (Figure 1.5)

Figure 1.5

WARNING – An incorrect weld location will void the axle warranty and can result in reduced fatigue life of the trailer axle beam. Serious personal injury and damage to components can result.

The following guidelines are for welding locations on round axles.
Welding is not allowed on 5-inch (127 mm) diameter axles within 1.50-inches (38.1 mm) of the top-center of the axle. (Above Figure 1.6)

Figure 1.6

Horizontal welding is not allowed on 5-inch (127 mm)
diameter axles more than 1.50-inches (38.1 mm)
below the axle horizontal centerline. (Figure 1.7)

Figure 1.7

Vertical welding is not allowed on 5-inch (127 mm)
diameter axles more than one-inch (25.4 mm) below the axle horizontal centerline. (Figure 1.8)

Figure 1.8

The round axle welding locations are in reference to their position when installed onto the vehicle.

NOTE: Axles can be rotated up to 20 degrees.
Do not install the brackets with the correct welds, then rotate them out of the correct positions.

The following procedures are for welding locations on rectangular axles. Welding is not allowed within one-inch (25.4 mm) of the top-center of the axle. (Figure 1.9)

Horizontal welding is not allowed more than 1.50-inches (38.1 mm) below the axle horizontal centerline.
(Figure 1.10)

Figure 1.10

Vertical welding is not allowed more than one-inch (25.4 mm) below the axle horizontal centerline.(Figure 1.11)

Weld location requirements in this section apply to all welds. In some instances, axles have been found with bracket attachment welds in authorized locations, but with tack welds in unauthorized locations.
Neither tack welds nor brackets attachment welds are allowed in unauthorized locations.
This can cause a material change that can reduce axle fatigue life. (Figure 1.12)

Figure 1.12

Do not test the weld arc on the axle beam in unauthorized locations. This can cause a material change that can reduce axle fatigue life.

9. Welding Procedures

Observe the following when performing welding procedures.

Axles are more likely to crack at the end of the bracket attachment welds. It is critical to avoid welding imperfections such as craters, undercuts and poor
fusion at these locations. Some methods of avoiding these imperfections include using correct welding parameters, starting and stopping the arc a short distance away from the ends of the weld pass and maintaining correct arc position and length. (Figure 1.13)


Some brackets are attached to trailer axles with multiple welds. For example, at each of the weld locations shown in (Figure 1.14), roadside front, curbside rear, etc., three weld passes are applied.


Axle distortion can be minimized in this situation by equencing the welds. This involves alternating weld passes from the front to the rear of an individual bracket and between the brackets located on the axle roadside and curbside.
This is in contrast to applying all the welds at one bracket location prior to applying the welds at other locations.

When attaching a bracket, the first weld pass should be made on the front side of the bracket.
This will result in any distortion causing the more desirable toe-in rather than the less desirable toe-out condition.

It is good manufacturing practice to specify a welding procedure that prevents excessive distortion and o periodically check this procedure to ensure that it is understood and is being followed.


10. Bead Size

The maximum weld bead size allowed, regardless of whether the weld is achieved with a single or multiple asses, is 3/8-inch 9.5 mm) on rectangular axles and 1/2-inch (12.7 mm) on round axles.