Tightness not due to
air disc brake. See
vehicle manual.

Replace guide pins
(5.6) OR replace
caliper/carrier
assembly (5.3)

Figure 14 – Troubleshooting Bendix Air Disc Brakes

10

Replace components
as needed
with genuine
Bendix® parts.

Disc brake OK

BENDIX® ADB22X™ TROUBLESHOOTING GUIDE
Component
(Item / Condition)

Investigation

Specs

Procedure

What To Replace

Guide Pins

Boots & Seals

Disc Brake Pads

Consumable Items: These are considered to be normal wear items and should be repaired as part of regular preventive maintenance.
Measure the thickness of the total pad
(friction material and backing plate).

Pads must be replaced when they
reach 0.433 in. (11 mm).

Section 4.3

B

Uneven wear
on single pad

Measure the thickness of the total pad in
at least two (2) places at top and two (2)
places at bottom, at least 1/2 inch from
the edge.

The average difference of top vs.
bottom, or left vs. right, should be
no greater than 0.080 in. (2 mm).

Section 4.3.2

C

Uneven wear
on inboard vs.
outboard

Measure the pad thickness as described
for Item B, but also check guide pin wear
and slide-ability.

Average difference inboard to
outboard should be no greater
than 0.138 in (3.5 mm).

Section 4.3.3

D

Surface
damage

Inspect for minor chips near the edge
and cracks on face (permitted) vs. major
sections damaged or missing.

See Figure 24 in SD-23-7541.

Section 4.3.3

E

Tears & cuts

Inspect the tappet and guide pin boots for
cuts, cracks, and tears.

Any damage must be repaired.

Sections
4.5.4 & 4.6.2

F

Melting

Inspect as Item E, but also check the
running clearance before removing the
brake pads.

Any damage must be repaired.

See Calipers
Item L

G

Binding

With the pads removed, the caliper should
move freely by hand. Re-torque the
carrier to torque plate bolts per the OE
spec and procedure, if binding.

See Figure 26 (slide) and Table 4
(torque) in SD-23-7541.

H

Excessive play

A

Worn

Worn

Measure the rotor thickness with a long
jaw caliper.

J

Surface
damage

Replace the pads on both
sides of the worn axle.

Replace the damaged boots
and replace the resultant
internal corroded guide pins
as needed.
Replace the worn guide pins as
needed and replace the torque
plate if the re-torque procedure
does not resolve the issue.

Section 4.5.2

Replace the worn guide pins
as needed.

Section 4.4
Minor cracks and grooves are acceptable,
but check for cracks over the outside
edge.

Replace the pads on both
sides of the worn axle and
replace the guide pins as
needed.

Sections
4.5.1 & 5.3

Thickness must be greater than
1.46 in. (37 mm).

Rotors

I

Feel for excessive play between the caliper
See Figure 27 in SD-23-7541.
and the carrier.

Replace the pads on both
sides of the worn axle.

See Figure 25 in SD-23-7541 for
surface details.

Refer to the OEM
recommendations for nonBendix® rotors. For Bendix
rotors, replace the rotors on
both sides of the axle.
Refer to the OEM
recommendations for nonBendix rotors. For Bendix
rotors only, replace the rotor
that is damaged.

Calipers

Non-Serviceable: These are non-serviceable items and pending warranty terms; these issues may be covered under warranty.
K

L

Adjuster
not rotating

If the 2nd sheer adapter breaks while
turning the 10mm box-end wrench
counterclockwise, the adjuster is seized.

Adjuster
With the brakes released, check the
too tight,
running clearance between the tappet
dragging brake and the inboard pad.

Adjuster must turn in both
directions with a hand wrench.

Section 4.4

The gap should be between
0.024 in. (0.6 mm) and
0.043 in. (1.1 mm).

Section 4.1

Caliper only must be replaced
with malfunctioning adjuster.

11

SECTION FOUR: WHEEL-OFF MAINTENANCE INSPECTIONS
Section Four
Section

4.0
4.1
4.2
4.3-4.4
4.3
4.4
4.4.3
4.5
4.6

Page

Wheel-Off Inspections . . . . . . 12
Caliper Movement Test . . . . . . 12
Adjuster Mechanism Inspection . . . 13
Brake Pads and Rotors . . . . . 14–16
Inspect the Brake Pads . . . . . . 15
Inspect the Rotor . . . . . . . . 16
Machining (Grinding or Turning) Rotors
16
Guide Pin Bearing Inspection . . . 17–18
Tappet & Boot Assembly Inspection . . 18

two long-blade feeler gauges to measure – over the whole
tappet surface – the gap between them and the inboard pad
backplate. (See Figure 16.) The gap should be between
0.024 in. (0.6 mm) and 0.043 in. (1.1 mm). If the gap is
within the range given, the test is complete.

4.0 WHEEL-OFF INSPECTIONS
CAUTION: During these inspections, follow all safe
maintenance practices, including those on page 2 of this
service manual. Also, follow the vehicle manufacturer’s
recommendations. When working on foundation
brakes, be sure that the vehicle is on level ground, that
the vehicle is parked by other means than the foundation
brakes, and that the wheels are chocked.

Pull
Caliper
Inboard

Figure 15 – Pull Caliper Inboard

4.0.1 Wheel Removal and Re-Installation
Refer to the vehicle manufacturer’s recommendations for
removing the wheel.
Note: When removing the wheel, inspect first to see that
there is no contact between the caliper and axle, vehicle,
chassis sections or carrier, etc. that may be impeding the
free movement of the caliper.

Not all wheels and valve stems are compatible with
Bendix® Air Disc Brakes. Use only wheels and valve
stems approved by the vehicle manufacturer to avoid
risk of valve stem shear and other compatibility
issues. After re-installing a wheel according to the vehicle
manufacturer’s recommendations, ensure that there is
sufficient clearance between the tire inflation valve stem,
the caliper, and the wheel rim, to avoid damage.

4.1 CALIPER MOVEMENT TEST
CAUTION: Follow all safe maintenance practices.
Remove the wheel. With the spring brakes released or
caged, push the caliper assembly inboard on its guide
pins. Note: To fully release the spring brakes, ensure that
the air system pressure is at least 90 psi. Using a suitable
tool (for example a large flat-blade screwdriver), press the
inboard pad (12) away from the tappets. Check that there
is no dirt, etc. in the gap, and clean if necessary. Then use

12

Check the clearance at
both tappets simultaneously:
0.024 in. to 0.043 in.
(0.6 mm. to 1.1 mm.)
Figure 16 – Running Clearance Check
CAUTION: If the clearance is too wide, there is a
danger of brake failure. If the clearance is too small,
or if there is no gap at all, there is a danger of the brake
overheating. These conditions must be corrected
before returning the vehicle to service.
For further investigation, where there is some gap, go to
Section 4.2 and check the adjuster mechanism. Where
there is no movement at all (and so no gap to measure),
go to Section 4.5 “Guide Pin Inspection.”

4.2 ADJUSTER MECHANISM INSPECTION
CAUTION: Follow all safe maintenance practices.
Aside from the normal maintenance schedule, the
adjuster mechanism inspection that follows is also
carried out when the Caliper Movement Test (4.1) finds
that the running clearance is too small or too large.
4.2.1 With the spring brake released (or caged), remove
the adjuster cap (37) using the tab, taking care not
to move the shear adapter (61). Note: One of two
styles of adjuster cap (stamped metal or plastic
adjuster cap) may be used.

Figure 20 – Backing-Off (Increasing) the Running
Clearance
If the shear adapter fails, you may attempt a second time
with a new (unused) shear adapter.
Note: Always double-check that the spring brake is released
(where applicable) if a shear adapter fails; if this step was
missed, the shear adapter will break off, and it may appear
that the caliper is seized.

Adjuster Cap
Location

In cases where a second failure of the shear adapter
confirms that the adjustment mechanism is seized, the
caliper must be replaced.

Figure 17 – Adjuster Cap Location
37
Cap

Figure 21 – Applying Moderate Applications of the
Brakes: The Wrench Moves Clockwise as the Running
Clearance is Diminished

23 Adjuster
61 Adapter
Tab

37
Cap

Figure 18 – Exploded
View of Adjuster and
Adapter

Tab

Figure 19 – Cap Installed:
Tab Location

For illustration purposes, the exploded view (Figure 18)
shows the adjuster (23) and shear adapter (61) separated.
When using the adjuster mechanism, always have the
shear adapter installed on the adjuster.
4.2.2 Using a 10 mm. six-point box wrench, turn the
Shear Adapter (61) counterclockwise and listen
for the sound of 3 clicks as the mechanism backsoff (increases) the running clearance. Note: Do not
use an open-ended wrench as this may damage the
adapter. See Figure 20.
CAUTION:
Never turn the adjuster (23) without the shear adapter
(61) installed. The shear adapter is a safety feature and
is designed to prevent excessive torque from being
applied to the adjuster. The shear adapter will fail (by
breaking) if too much torque is applied.
13

4.2.3 Where the adjuster mechanism is able to be backedoff normally, position a box-end wrench on the shear
adapter so that it can turn clockwise freely without
coming into contact with parts of the vehicle (See
Figure 21). Make five to ten moderate applications
of the brakes [at about 30 psi (2 Bar)], and observe
that the box-end wrench or socket should turn
clockwise in small increments.

A

B

NOTE: As the number of applications increases,
the turning movement will decrease (as the brake
reaches its normal calibration point).

C

If the box-end wrench does not: (a) turn at all; (b) turns only
with the first application; or (c) turns forward and backward
with every application, the automatic adjuster has failed and
the caliper/carrier assembly must be replaced.
After completing these wheel-off tests, Bendix recommends
installing a new adjuster cap (lightly greased using white,
lithium-based grease) when returning the brake to service.
Ensure that the tab is in the position shown in Figure 19.

4.3- 4.4 BRAKE PADS AND ROTORS
CAUTION: Follow all safe maintenance practices.

A

New pad thickness (1.181 in.) (30 mm.)
BX276: Refer to diagram below for measurement
locations BX275/BX283+: Measure anywhere on
the backing plate surface.

B

New rotor thickness (1.77 in.) (45 mm.)
Minimum rotor thickness (1.46 in.) (37 mm)

If electronic wear sensors are present, see Section 5.2.
If dust covers are present, see Section 5.1.
See Figure 23. While pressing down against the pad
retaining bar (11), remove and retain the clip (26),
washer (45) and pin (44). Remove the pad retainer bar
(11). Bendix recommends that these items be replaced with
new (See available kits and parts, Section 5.0).
Follow the steps in Section 4.2 for backing-off the adjuster
mechanism. Slide the caliper inboard then outboard to
permit easy removal of the brake pads.

C Minimum friction material thickness (0.080 in.)
(2 mm.) - approximately the thickness of a nickel.
Measurement locations for BX276 brake pads.
Do not measure on raised surfaces.

Figure 22 – Pad and Rotor Dimensions

14

See Figure 22 for initial brake pad and rotor dimensions,
as well as minimum acceptable dimensions.
Minor Damage Is Acceptable

Where a
small amount
of brake
material is
chipped from
the edge

44
Pin
11 Pad Retainer Bar
45 Washer
26 Spring Clip

Figure 23 – Retainer Bar Removal

4.3 INSPECT THE BRAKE PADS
Regular inspection of the brake pads (even for vehicles
that use an electronic wear indicator) is an important part
of vehicle maintenance.
4.3.1 See Figure 22. If the thickness of the friction
material – dimension “C” – is less than 0.080 in.
(2 mm.), the pads must be replaced.
Bendix® ADB22X™, ADB22X-V™ and ADB22X™-LT air disc
brakes use 0.35 in. (9 mm.) backing plates, so dimension
“D” (the combined pad and backing plate thickness) must
be a minimum of 0.43 in. (11 mm.).
4.3.2 Check for uneven end-to-end pad wear. If the
difference in wear is greater than 0.080 in. (2 mm.),
replace the brake pads and also inspect the guide
pins. (See Section 4.5.)
4.3.3 Compare the thickness of the inboard and outboard
pads of each set. If the difference between the
inboard and outboard pad thickness is greater than
0.138 in. (3.5 mm.), replace the brake pads and
inspect the guide pins (See Section 4.5).
If the results of the pad inspections are within the acceptable
range, inspect the pad surface. (See Figure 24.)

Major Damage Is Not Acceptable

Section
damaged or
missing

Figure 24 – Brake Pad Surface Inspection
Minor damage at the edges is permitted, but replace the
pads if major damage on the surface of the pad is found.
When replacing brake pads, Bendix strongly recommends
that all the brake pads on an axle be replaced at one time.
See Section 5.1 for the pad replacement procedure. Also,
see the vehicle manufacturer’s recommendations found in
the operator’s manual.
Bendix air disc brakes are precision-engineered braking
mechanisms. The “friction couple” braking characteristics
have been carefully optimized – and the rotor design and
materials have been matched with special formulation
brake pads for optimal performance. In all cases, use
brake pads with the type of backing plate and lining material
originally supplied by the vehicle manufacturer.
CAUTION: When replacing brake pads and rotors,
use only Bendix® brand replacement pads and rotors
and/or those approved by the OEM. Non-approved
replacement disc pads or rotors can cause excess
wear to brake components, and can increase the risk
of rotors cracking, etc.

15

4.4 INSPECT THE ROTOR

NOTE: If surface wear conditions F through J are

CAUTION: Follow all safe maintenance practices.
Identify if the rotor is a Bendix® Splined Disc®, or Bendix®
brand conventional rotor (See Section 1.03). Rotors should
be inspected regularly (See Section 2.0 for recommended
inspection schedule) and at each pad change.
4.4.1 Measure the thickness of the brake rotor at the
thinnest point (Dimension “E” in Figure 22). Avoid
measuring near the edge of the rotor as minor burrs
may result in an inaccurate measurement. For
Bendix brand rotors, replace the rotor when
the minimum thickness of 1.46 in. (37 mm.) is
reached. For other brands of rotors, refer to the
rotor manufacturer’s guidelines.

in the permitted range, the rotor is still usable until
it reaches the minimum acceptable thickness for the
rotor manufacturer’s guidelines.

4.4.3 Machining (Grinding or Turning) Rotors
Bendix brand rotors are normally service-free. In the case
of severe grooving of the entire friction surface, however,
CONVENTIONAL ROTORS may be turned when changing
pads, to increase the load-bearing surface.