Disc Brake Inspections - Commercial Vehicle Safety Alliance

Air Disc Brakes
In-Service Inspection
Requirements
Brake Safety Symposium
December 5-7, 2006
Randy Petresh
Haldex Commercial Vehicle Systems Inc.
1

Disc Brake Models
• Currently, five Disc Brake models in service today:
• Bendix/ Dana
• Bendix SB/ SN Series
• Haldex ModulX
• Meritor WABCO EX225
• Meritor WABCO PAN22
Refer to the following illustrations for additional details
associated with each specific Disc Brake configuration.
2

Disc Brakes Configuration
Although there are specific differences between the
various Disc Brake models, All of them conform to
this basic configuration.
Common components include:
–Caliper
–Rotor
–Pads
–Carrier
–Chamber/ Spring Brakes
9

Disc vs. Drum Inspection “Challenges”
• Obviously, Disc Brakes will require completely
different inspection procedures and requirements
than currently practiced for Drum Brakes. The
challenges will be:
– Cannot view/ inspect braking surfaces.
– Cannot view/ inspect disc pads.
– Cannot view/ inspect brake actuation.
– Cannot view/ measure push rod stroke/ brake adjustment.
10

Actuation/ Adjuster
mechanism totally
enclosed in Caliper
housing
Chamber/ Spring Brake
mounted directly to the
back of the caliper
Caliper Assembly
permanently lubricated
and sealed
11

Disc Brake Inspections
• Disc Brake Inspections which can be performed:
– Loose, damaged, missing components.
– Cracked, damaged brake hoses.
– Oil, grease, dirt buildup contamination.
– Chamber/ Spring Brake breather holes are clear and not
obstructed by contamination.
– All of these inspection points are similar to current Drum
Brakes.
– Can be performed with “wheels on”.
– Reference Out-of-Service- Appendix A/ Part II
12

Disc Brake Inspections
• Additional Disc Brake inspection points:
– Presence of manual adjuster access plug, and slide pin
boots and caps (back of caliper).
– Rotor inboard plate and outer circumference, if no dust
shields are present.
– And finally, Visual Pad Wear Indicators, if the Disc Brake is
so equipped.
• Unique indicator for each Disc Brake model.
13

Visual Wear Inspection- Bendix
• Slide pin relative to rubber bushing is in
direct relationship to pad and rotor wear.
• New pads/ new rotor- pin exposed.
• Pads worn- pin below edge of rubber
bushing.
• Length of rolling boot is in direct
relationship to pad and rotor wear.
• New pads/ new rotor- rolling boot
extended.
• Pads worn- rolling boot extension
significantly reduced.
14

Visual Wear Inspection- Meritor WABCO EX225
• Indicator is located on the inboard side of
caliper next to short or long slide pin
• Spring loaded pin is an indicator of total
pad and rotor wear.
• New pads/ new rotor- pin exposed.
• Pads / rotor worn- pin flush with or below
caliper casting.
• Pin position is an approximate indicator of
pad and rotor conditions and does not
account for all tolerances.
• Automatically resets when pads / rotor are
replaced.
Indicator
Visual Wear
Indicator
15

Visual Wear Inspection- Meritor WABCO
PAN22
• Indication based on Caliper (edge A)
to Carrier (edge B) relationship.
• Edge A and edge B visible through
wheel rim.
• New pads
– Edge A in front of edge B.
– Edge B not visible.
• Worn pads
– Edge A position moves until same position
as edge B.
16

Visual Wear Inspection- Haldex
• Indications based on Caliper projection
to carrier indicator pin relationship.
• New pads
– Indicator pin extended past projection.
• Worn pads
– Indicator pin flush to Caliper projection.
• Without carrier indicator pin:
– Measure distance from Caliper projection
to carrier mounting face.
17

Additional Disc Brake inspections may be possible
depending on installation/ orientation of the Disc
Brake.
• Oil soaked/ contaminated pads.
• Missing or loose/ detached friction material (pads) from
backing plate.
• Brake Caliper movement.
• Caliper should move freely on slide pins in the axial (inboard/
outboard) direction..
• No movement indicative of non-sliding Caliper.
• Rotor cracking/ heat checking.
18

Rotor Cracking/ Heat Checking
• Heat Checks: Short, thin radial
indications on the rotor braking
surfaces. Heat checks will wear
away and reform. May develop into
braking surface cracks.
• Cracks: Heat checks similar in
appearance to cracks. Cracking is
defined as a “surface split” radiating
into or from an edge of the rotor or
over 75% in length.
Light Heat Checking
Heavy Cracking
19

Rotor Inspection Guide
20

Brake Adjustment Inspection
• Check adjustment by sliding Caliper back and forth.
– If Caliper slides more than .080 in., Disc Brake is out of
adjustment.
• Or, measure running clearance between pad and
braking surface; normal operating clearance should
be between .020 in. and .040 in.
• Or, perform an adjuster functional check.
21

Adjuster Functional Check
• Remove rubber access plug.
• Attach box end wrench to adjuster shaft.
• Deadjust brake.
• Actuate brake several times.
• If wrench rotates when brake is
actuated, adjuster mechanism is
working properly.
• If wrench does not rotate, adjuster
mechanism is not working, and caliper
may need to be replaced.
22

Service Chambers/ Spring Brakes
• Identical size on both wheelends/
each axle.
• Disc Brake compatible chambers.
– NOT the same as Drum Brakes.
– External Seal to Caliper housing.
– Internal Boot.
External Seal
Internal Boot
23

Additional Information and Inspection Details
• Refer to TMC RP-652
• Manufactures Maintenance Manuals
24

Thank You
25