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Issue 1 en
Checking Wheel Brakes Wear
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Scania CV AB 2006, Sweden
Contents
Disc Brakes .................................................................................. 3
Removing the wheels ............................................... 4
Checking the Brake Pads.......................................... 5
Check brake disc thickness....................................... 7
Checking brake disc for cracks................................. 8
Drum Brakes .................................................................................. 9
Measurement of brake lining thickness.................. 10
Removal.................................................................. 11
Fitting ..................................................................... 13
Checking brake drum ............................................. 14
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2 Scania CV AB 2006, Sweden
Disc Brakes
! WARNING!
Work on the brake system is only to be
carried out by personnel with sufficient
training and knowledge. If problems
arise, contact your supervisor for
assistance.
When working on the brake system, it is
important to follow the instructions to
avoid accidents and injury.
It is also important to use the correct
components when carrying out work on
the brakes. A brake system which fails
due to faulty components can have
disastrous consequences on the road.
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Scania CV AB 2006, Sweden 3
Removing the wheels
In most instances, the wheels must be removed
whilst work is carried out on the disc brakes.
1 Support the axle on stands.
! WARNING!
Never work under a vehicle supported
by jacks only. Always use stands. If the
axle is air suspended, the air bellows
must be emptied.
2 Release the parking brake.
3 Remove the wheels. Use wheel hoist
trolley 587 121.
07:0253
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Checking the brake pads
Specifications
Brake disc, thickness Minimum permissible brake pad lining thick-
ness
> 40 mm 2 mm
37-40 mm 4 mm
Instructions
General
The brake caliper position indicates the
wear of the brake disc and the brake pads.
DU bushing with wear indicator
Brake caliper position when the brake pads are Brake caliper position when 1 mm remains of
new. brake pad wear surface.
Brake caliper position when the brake pads are
moderately worn. Remove the wheel and visu-
ally check whether the brake pads are unevenly
worn.
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Rubber bushings with wear indicators
Rubber bushing position for new brake pads. Rubber bushing position at maximum brake
pad wear.
1 Measure the brake pad lining thickness
between the brake disc and the brake pad
backing plate using a vernier caliper.
Note: Look carefully for signs of uneven wear.
2 Measure any wear edge on the disc and add
it to the brake pad thickness.
3 Renew the pads if you think that they may
wear out before the next inspection.
103 678
103 680
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Checking brake disc thickness
Specifications
Control measurements
New brake disc 45 mm
Minimum permissible brake disc thickness 37 mm
General
Drive the vehicle until normal operating tem-
perature for the brakes is achieved.
Thickness
• A wear edge may have formed on the outer
circumference of the disc. Measure on the
inside using spacers, e.g. two nuts.
• Renew the brake disc if there is a risk that
it will wear down to 37 mm before the next
inspection.
Example: Two 10 mm thick nuts. Brake
disc + nuts = 64 mm. The thickness of the
disc is therefore 64 - (2x10) mm = 44 mm.
103 074
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Checking brake discs for cracks
Specifications
Control measurements
Maximum permissible length of cracks 40 mm
Maximum permissible width of cracks 1.5 mm
Instructions
• Check that cracks on the brake disc do not
exceed permitted levels. Cracks up to a
maximum of 40 mm in length are permit-
ted, provided that they do not reach the
edge. If the cracks are wider than 1.5 mm,
the disc must be ground or replaced. After
grinding, the thickness of the disc must not
fall below 40 mm.
IMPORTANT! Brake discs with a prohibited
crack formation must be replaced.
Permitted crack formation
Prohibited crack formation
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Brake drums
! WARNING!
Work on the brake system is only to be
carried out by personnel with sufficient
training and knowledge. If problems
arise, contact your supervisor for
assistance.
When working on the brake system, it is
important to follow the instructions to
avoid accidents and injury.
It is also important to use the correct
components when carrying out work on
the brakes. A brake system which fails
due to faulty components can have
disastrous consequences on the road.
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Scania CV AB 2006, Sweden 9
Measuring brake lining thickness
Specifications
Minimum thickness
Standard lining (drum diameters up to 417 mm) 8 mm
Oversize lining 10 mm
Description
There are inspection covers at the top and the
bottom of the brake shield.
1 Apply the parking brake.
2 Move the inspection cover to one side and
lift out and pull away the cover at the other
end.
3 Brake lining thickness must not be below
8 mm (10 mm for oversize linings).
4 Check the thickness against the indicator
line.
Wear indicator
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Removal
Special tools
No. Designation Illustration Tool board
87 368 Puller bolt 87 368
AM1, D3, B1,
AD1
00 1805
Other tools
No. Designation Illustration Tool board
587 121 Wheel hoist trolley - -
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Description
! WARNING!
Danger when working under vehicle!
Use a lifting device when lifting off the
brake drum.
1 Remove the wheel. Use wheel hoist trolley
587 121.
2 Wheels with spring brake chambers:
Unscrew the release bolt in the spring
brake chamber so that the brake drum can
be rotated manually.
3 Adjust the slack adjuster so that there is
maximum clearance between the brake
shoes and the brake drum.
07:0253
4 If present, remove the fixing bolts between
the brake drum and hub.
5 Fit three release bolts 87 368 and pull off
the brake drum. Use a lifting device on the
brake drum.
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Fitting
Specifications
Tightening torque
Wheel nut 600 Nm
Fixing bolts, brake drum - hub 10 -20 Nm
Special tools
No. Designation Illustration Tool board
98 661 Torque socket 98661 AD1, MT1
00_1535
Description
1 Fit the brake drum, use a lifting device.
2 Fit the fixing bolts between the brake drum
and hub. Use copper paste and tighten to
10 - 20 Nm. If there are no fixing bolts
present, see Fitting brake drum bolts.
3 Fit the wheel and tighten the lubricated
nuts to 600 Nm. Use a torque wrench or
nut runner with torque socket 98 661.
4 Set the slack adjuster.
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Checking brake drum
Wear
Specifications
General
Nominal diameter 412.75 mm
Diameter for oversize liners 417 mm
Max. diameter when machining 419 mm
Scrapping limit 421 mm
Surface quality during machining Ra 2.5
Max. crack width 1.5 mm
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Wear patterns
The considerable heat release generated during
braking may cause certain changes in the wear
surface of the brake drum.
A wear pattern featuring measurably deep
scratches, a fine meshed network of evenly
spread thermal cracks (cracking) such as single
minor hard spots, is not justification for
replacing the brake drum.
Figure A shows a wear pattern with measurable
scratches and minor hard spots due to
overheating. Figure A. Brake drum with hard spots due to
overheating.
Figure B shows the same brake drum after an
additional 700 instances of normal braking
from 70 to 0 km/h with a fully laden vehicle.
The figures show that braking without
overheating causes the hard spots to partially
disappear and that brake drum wear pattern
improves.
Figure B. The same brake drum after a further
700 instances of braking.
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Careful attention must be paid to a wear pattern
with considerable crack formation, particularly
in the hard spots (see figure C). Heat tension in
the material rapidly deepens crack formation.
In the hard spots, the material has become
martensite and, as a result of this change, has
lost its material strength and expanded. A hard
spot is an elevation in the wear surface of the
brake drum.
During braking, the hard spots in the brake
drum become considerably overloaded and
overheated and the resulting shrinking stresses
give rise to rapid crack growth.
Figure C.
Figure D shows brake drum wear surface after
an additional 700 normal braking instances.
Crack formation is now so deep that there is
considerable danger of drum failure.
Figure D.
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When assessing whether it is appropriate to
replace brake drums, see wear pattern E which
is a borderline case. This drum is acceptable
provided it is ground.
Figure E.
Replace and scrap brake drums with wear
patterns as shown in figures F and G. Do not
turn or grind these brake drums.
Figure G.
Turn or grind worn or oval brake drums and
drums with hard spots that do not have worse
crack formation.
Check brake drum ovality either with the drum
fixed on the hub or in a brake drum lathe.
Figure F.
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