Components Drum brake

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1 components

1.1 backing plate
1.2 brake drum
1.3 wheel cylinder
1.4 brake shoe





components

drum brake components include backing plate, brake drum, shoe, wheel cylinder, , various springs , pins.


backing plate

the backing plate provides base other components. plate increases rigidity of whole set-up, supports housing, , protects foreign materials dust , other road debris. absorbs torque braking action, , why plate called torque plate . since braking operations exert pressure on backing plate, must strong , wear-resistant. levers emergency or parking brakes, , automatic brake-shoe adjuster added in recent years.



back plate made in pressing shop.


brake drum

the brake drum made of special type of cast iron heat-conductive , wear-resistant. rotates wheel , axle. when driver applies brakes, lining pushes radially against inner surface of drum, , ensuing friction slows or stops rotation of wheel , axle, , vehicle. friction generates substantial heat.


wheel cylinder

cut-away section of wheel cylinder.


one wheel cylinder operates brake on each wheel. 2 pistons operate shoes, 1 @ each end of wheel cylinder. leading shoe (closest front of vehicle) known primary shoe. trailing shoe known secondary shoe. hydraulic pressure master cylinder acts on piston cup, pushing pistons toward shoes, forcing them against drum. when driver releases brakes, brake shoe springs restore shoes original (disengaged) position. parts of wheel cylinder shown right.


brake shoe

brake shoes typically made of 2 pieces of steel welded together. friction material either riveted lining table or attached adhesive. crescent-shaped piece called web , contains holes , slots in different shapes return springs, hold-down hardware, parking brake linkage , self-adjusting components. application force of wheel cylinder applied through web lining table , brake lining. edge of lining table has 3 “v -shaped notches or tabs on each side called nibs. nibs rest against support pads of backing plate shoes installed. each brake assembly has 2 shoes, primary , secondary. primary shoe located toward front of vehicle , has lining positioned differently secondary shoe. quite often, 2 shoes interchangeable, close inspection variation important.



brake shoe assembly


linings must resistant heat , wear , have high friction coefficient unaffected fluctuations in temperature , humidity. materials make brake shoe include, friction modifiers (which can include graphite , cashew nut shells), powdered metal such lead, zinc, brass, aluminium , other metals resist heat fade, binders, curing agents , fillers such rubber chips reduce brake noise.


in uk 2 common grades of brake shoe material used available. don 202 high friction material did not require brake power servo. disadvantage lining prone fading on steep hills (calculate kilowatts dissipated one-ton car descending 15% hill @ constant 60 mph) harder lining, famous vg95 produced required brake servo. other snag parking brake fail annual mot test unless high friction linings installed test.







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