Tappet and Boot Assembly Inspection .
19

Then use 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 0.047 in. (1.2 mm). If
the gap is within the range given, the test is complete.

3.0 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

3.0.1 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.

3.1 RUNNING CLEARANCE TEST
CAUTION: Follow all safe maintenance practices.

Check the clearance at
both tappets simultaneously:
0.024 in. to 0.047 in.
(0.6 mm to 1.2 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 3.2 and check the adjuster mechanism. Where
there is no gap to measure or no movement at all, go to
Section 3.5 “Guide Pin Inspection.”

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. Ensure
that the air system pressure is at least 90psi but not greater
than the vehicle governor cut-out pressure.
11

3.2 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 Running Clearance Test (3.1) finds that the
running clearance is too small or too large.
3.2.1 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.
In cases where a second failure of the shear adapter
confirms that the adjustment mechanism is seized, the
caliper must be replaced.

Adjuster Cap
Location

Figure 17 – Adjuster Cap Location
37
Cap

23 Adjuster
61 Shear 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.
3.2.2 Using a 10 mm six-point box-end wrench, turn the
Shear Adapter (61) counterclockwise and listen for
the sound of 3 clicks as the mechanism backs-off
(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.
12

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

3.2.3 Where the adjuster mechanism is able to be backed
off normally, position a box-end wrench on the shear
adapter so that it can turn freely clockwise 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.

Flat Style Backing Plate “Stamped”
Bendix® BA236™/BX275™/BX283™
A

B

D

C

NOTE: As the number of applications increases,
the turning movement will decrease (as the brake
reaches its normal calibration point).
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 grease the outer
sealing edge using white, lithium-based grease to improve
sealing of air in future cap removal) when returning the
brake to service. Ensure that the tab is in the position
shown in Figure 19.

A

3.3- 3.4 BRAKE PADS AND ROTORS

B

New pad thickness 1.181 in. (30 mm)
BX276/BX277: Refer to image below for measurement locations
BX275/BX283: Measure anywhere on the backing plate surface
New rotor thickness 1.77 in. (45 mm)

CAUTION: Follow all safe maintenance practices.
If electronic wear sensors are present, see Section 4.2.

Minimum rotor thickness 1.46 in. (37 mm)
C

Minimum friction material thickness 0.125 in.
(3.2 mm) - approximately the thickness of a nickel

If dust covers are present, see Section 4.1.
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 4.0).

Non-Flat Style Backing Plate
“Cast” Bendix® BX276™/BX277™
Minimum thickness of BX276 Backing Plate is 0.276 in. (7 mm),
therefore the overall minimum thickness is 0.402 in. (10.2 mm)
Minimum thickness of BX277 Backing Plate is 0.354 in. (9 mm),
therefore the overall minimum thickness is 0.480 in. (12.2 mm)
0% Remaining Life

Follow the steps in Section 3.2 for backing-off the adjuster
mechanism. Slide the caliper inboard then outboard to
permit easy removal of the brake pads.
New
Friction
100% Life

Measurement locations for BX276/BX277 brake pads.
Do not measure on raised surfaces.

D

A

E
F

B
C

NOTE: The illustration shows a BX276 brake pad.
The measurement locations are the same for BX277.

A

BX276: .91 in. (23 mm)
BX277: .83 in. (21 mm)

D

BX276: .28 in. (7 mm)
BX277: .35 in. (9 mm)

B

1.18 in. (30 mm)

E

.13 in. (3.2 mm)

C

1.26 in. (32 mm)

F

BX276: .40 in. (10.2 mm)
BX277: .48 in. (12.2 mm)

Figure 22 – Pad and Rotor Dimensions
13

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

3.3 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.
3.3.1

See Figure 22. If the thickness of the friction
material – dimension “C” – is less than 0.125 in.
(3.2 mm), the pads must be replaced.

Bendix® ADB22X®, ADB22X®-V, and ADB22X®-LT air disc
brakes use both 0.276 in. (7 mm) and 0.354 in. (9 mm)
backing plates. The combined minimum thickness of
the pad and backing plate is dependent on the backing
plate thickness. The BX276 and BX277 use cast backing
plates of different thicknesses. The BX276 backing plate
is 0.276 in. (7 mm) thick; the BX277 backing plate is
0.354 in. (9 mm) thick. See Figure 22. The thickness of
the BA236, BX275, and BX283 stamped backing plates is
0.354 in. (9 mm).
3.3.2 Check for uneven end-to-end pad wear. Measure
the thickness of the total pad in at least two (2)
places at the top and two (2) places at the bottom,
at least 1/2 in. (12.7 mm) from the edge. Refer to the
Troubleshooting Guide (Section 6) for more details.
3.3.3 Compare the thickness of the inboard and outboard
pads of each set. Refer to Inspection C of the Disc
Brake Pad Inspections in the Troubleshooting Guide
(Section 5). 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. Refer to the Troubleshooting Guide
(Section 6) for more details.
If the results of the pad inspections are within the acceptable
range, inspect the pad surface. See Figure 24.

14

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 4.1 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 excessive
wear on brake components; can increase the risk of rotor
cracking; may reduce levels of safety; and invalidate the
brake warranty.

3.4 INSPECT THE ROTOR
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.
3.4.1 Measure the thickness of the brake rotor at the
thinnest point (Dimension “B” 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.

3.4.2 Inspect the rotor surface. See Figure 12. The type
of rotor, and also the size, depth, and direction of
the imperfections, must all be considered.

NOTE: If surface wear conditions F through J are in the
permitted range, the rotor is still usable until it reaches the
minimum acceptable thickness for the rotor manufacturer’s
guidelines.

15

3.4.3 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.
Machining of BENDIX® SPLINED DISC® rotors is not
permitted.

1
Caliper

9
Inner
Boot

7
Brass
Bushing

5
Guide Pin

10
Cap
LONG
BEARING
SIDE

CAUTION: Always maintain air disc brake pads and
rotors within specifications. Excessive pad or rotor
wear will degrade braking performance.
Periodic inspection of the Bendix Splined Disc attachment
hardware is recommended to ensure optimum braking
performance. Bendix recommends verifying the torque on
the spring element fasteners whenever a brake inspection
is performed.
SHORT
BEARING
SIDE

A F TER M ACHI NI NG/ TURNI NG, THE M I NI MUM
ROTOR THICKNESS FOR CONVENTIONAL BENDIX®
BRAND ROTORS MUST BE AT LEAST 1.535 - 1.575 IN.
(39 - 40 MM). FOR OTHER BRANDS, CONSULT THE
MANUFACTURER’S GUIDELINES. ALSO, CHECK THE
VEHICLE MANUFACTURER’S RECOMMENDATIONS.
FAILURE TO COMPLY MAY RESULT IN BR AKE
FAILURE AND IN SERIOUS INJURY OR DEATH.
MACHINING OF BENDIX SPLINED DISC ROTORS IS
NOT PERMITTED.

6 Guide Sleeve

Outboard

Inboard

68
Cap

39
Caliper Bolt

3.4.4 Rotor Replacement
An axle is permitted to have only all Bendix Splined
Disc or all conventional rotors.

Caliper
Movement

9 Inner Boot

4 Guide Pin

Figure 25 – Guide Pins

When replacing rotors, be sure to adhere to the vehicle
manufacturer’s recommendations, including bolt tightening
torques. It is recommended to install only Bendix brand
rotors, and also that the pads should be replaced (as an
axle set) at the same time.

12 Pad
Assembly

1
Carrier

Non-Bendix brand rotors. If a non-Bendix brand rotor is
used, confirm that it complies to the vehicle manufacturer’s
recommendations.
CAUTION: The use of non-approved brake rotors may
reduce levels of safety and invalidate the warranty.
See Section 4.7 for reinstallation procedures.

Magnetic
Dial‑Gauge
Measures
Range Here

2
Caliper

3.5 GUIDE PIN BEARING INSPECTION

Figure 26 – Magnetic Dial-Gauge In Use

CAUTION: Follow all safe maintenance practices.

3.5.1 Remove the Pads (See Section 4.3). The caliper
should slide using no more than 200 N (45 lbs)
of force along the whole length of the guide pins.
A force gage may be used to help measure this
more accurately. This movement should be at least
0.95 in. (25 mm) when the pads are not present. If
the movement is less than this amount, replace the
caliper/carrier assembly.

This guide pin inspection should be carried out if the
technician cannot move the caliper. See Section 3.1.
Measure the range of travel along the guide pin
bearings:

16

Measure the “play” (range of movement) in the guide
pin bearings:
3.5.2 See Figures 25 and 26. With the wheel removed,
remove the pad retainer (11). Temporarily replace
the pads with two new pads (12). Attach a magnetic
dial-gauge holder to the carrier (2) on the short
bearing side of the caliper (1). Use the measuring
point on the caliper (1) – see the callout in Figure
26. Press the caliper in the direction of the carrier
(2) and set the dial-gauge to zero.
3.5.3 Place a suitable tool (e.g. a large flat-blade
screwdriver) between the carrier (2) and the caliper (1)
and use light hand force to move the caliper away
from the carrier, until the movement stops. Read the
maximum value on the dial-gauge. See Figure 26.
If the value is greater than 0.039 in. (1.0 mm), replace
the guide pin bushings (See Section 4.6) OR replace the
caliper/carrier assembly (See Section 4.3).
Inspect the guide pin inner boots:
3.5.4 See Figures 27 and 28. With the pads removed,
slide the carrier by hand to the inboard position
(See Figure 27). By looking through the opening
where the pads are installed – and also from
below – inspect the inner boot (9) for each of
the guide pins. I N S P E C T F O R D A M A G E,
CUTS, AND CRACKS. Replace damaged boots
immediately to prevent dirt and/or moisture affecting
the movement of the guide pins (See Section 4.4).
Damaged or corroded guide pins will impair the
operation of the brake.
In addition, during installation, the boots are
compressed to minimize the amount of air trapped
within them. Observe as you move the carrier back
towards the outboard position; the boots should only
expand outwards a small amount due to trapped
air. The boots should normally (due to their ribbed
construction) contract back into place as the caliper