ALTRACO ELECTRONIC DISC BRAKE CALIPER Manual de Serviço descarregar pdf (Página 6)

Checking Rotor Condition

Before removing the rotor from the vehicle, check it

for damage, warping, and proper thickness. Normal rotor

wear patterns consist of small scratches and a slight pol-

ishing of the braking surfaces. They do not greatly affect

braking and can usually be removed by light sanding

instead of machining.

Chapter 13 Disc Brake Service 219

Figure 13-21.

A—Installing new brake pads on ball and ramp calipers requires the piston be screwed back into its bore. A special

tool is needed for this procedure. Position the tool and rotate the handle counterclockwise while holding the shaft. Continue until the

tool is seated against the piston. Loosen the tool handle about one-quarter of a turn. Now hold the tool handle and turn the shaft

until the piston is completely bottomed. Even though the inward travel of the piston has stopped, it will continue to rotate after bot-

toming. B—Make sure the tabs on the pad are installed in the alignment notches in the piston. (Wagner)

Caliper

Drive

axle

Special

tool

Wrench

Turn this direction

to seat tool

against piston

Check

valve

Cone

Boot

Alignment notch

Rotate clockwise

to bottom piston

Figure 13-22.

Retracting the piston by turning in a clockwise

direction with a special locknut wrench. This will provide the

necessary clearance for installing the new brake pads. (Honda)

Extension

bar

Locknut

wrench

Piston

boot

Piston

Caliper

Figure 13-23.

After installation, the rear caliper piston must be

adjusted so the pads rest just against the rotor. This is a special

adjustment procedure that can be used to adjust rear brake

calipers. (Chevrolet)

Screwdriver

Boot

groove

Boot

Shim

Rotor

Lining

Piston

Pad

Visually inspect the rotor for scoring or grooving on

the braking surface, Figure 13-24. Scoring and grooving

are deep cuts in the rotor surface. They always follow the

rotor’s curve of rotation. If the pads have worn to the rivets

or the metal shoe surface, the rotor will be badly scored.

Sometimes, a rotor will be lightly scored by long usage,

especially in sandy or dusty areas. Do not assume the

inboard rotor surface is good if the outboard surface shows

no damage. Scoring can exist on one or both braking sur-

faces of the same rotor. Machining (turning) the surfaces is

required if the rotor shows any scoring or grooves.

Excessive brake heat can cause heat-checking (tiny

surface cracks) or bluing. There can be a combination of

heat-checking and bluing or just one condition by itself.

These patterns can also form on one or both sides of the

rotor, Figure 13-25. Bluing can sometimes be removed by

machining. If heat-checking is present or bluing cannot be

removed without excessively reducing rotor thickness, the

rotor should be replaced.

Rotors will sometimes crack. Cracks usually develop

at the wheel stud openings, although they can occur at any

spot on the rotor. Replace a cracked rotor no matter how

small the crack.

Checking Rotor Thickness and Runout

To check for rotor thickness (parallelism), you will

need a micrometer, Figure 13-26. Before checking thick-

ness, calibrate the micrometer. Then install the micrometer

on the rotor. If the rotor is grooved, place the point of the

micrometer in the deepest groove. Then read the thickness

on the micrometer and compare it to the specified mini-

mum thickness. The thickness should be more than the

minimum if the rotor will not be turned. If the rotor must be

turned, there should be enough metal remaining to be at or

above the minimum thickness after the turning process.

Turn the rotor about one-quarter turn and repeat the

thickness measurement procedure. Measure at least four

places on the rotor. If the thickness variation between parts

of the rotor is more than about .01” (.254 mm), the rotor

should be turned to prevent brake pulsation.

To check for excessive runout (warping), a dial indi-

cator should be used. Before checking runout, eliminate

any looseness in the rotor and hub assembly. If the rotor is

separate from the hub, install at least three of the wheel

bolts onto the lugs. If possible, the flat (non-tapered) side

of the nuts should contact the rotor. Lightly tighten the nuts

until there is no play between the rotor and hub. If the

rotor is integral with the hub, make sure there is no play in

the wheel bearings. If play is evident, tighten the wheel

bearings until all play is removed. Then proceed with the

runout checking procedure.

Place the dial indicator over the rotor so that the

pointer is contacting the rotor about two-thirds of the way

to the edge of the braking surface. The pointer should be

on a flat spot, not over any grooves. Then tighten the

mounting clamp. A typical dial indicator installation is

shown in Figure 13-27. Then set the micrometer dial to

zero. Turn the rotor slowly and observe the movement of

the dial indicator needle. If the needle indicates runout of

more than .01” (.254 mm), the rotor should be turned or

replaced.

220 Auto Brakes

Caution: Never attempt to machine a

heat-checked or cracked rotor. Replace any

rotor that appears to be heat-checked or

cracked.

Note: Mark the point of maximum runout

for later reference.

Figure 13-24.

Scoring or grooving on the braking surface is

caused by dirt, exposed rivets, etc. Rotor machining will be

needed to reestablish the proper brake surface. Some minor

scoring is considered normal.

Figure 13-25.

This illustrates heat-checking and bluing caused

by heavy braking, severe service, etc. A heat-checked rotor

should be replaced. (EIS)

Rotor

Heat

checking

Braking

surface

Bluing (heat

discoloration)

Groove in

rotor surface

1 2 3 4 5 6 7 8 9 10 11

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