BENDIX BW1601 User's Manual
Contents
1. 1 Place the expander unit in a bench vise with padded jaws 2 Compress the wedge return spring and remove the pin Figure 16 Slowly release the spring pressure and remove spring along with the ferrule 3 Use snap ring pliers to compress and remove the circlip snap ring Figure 17 4 Remove the dust boots from both ends of the expander housing and discard Note The dust boots should not be reused and must be replaced 5 Remove the abutment tappet input tappet piston and stop pin from the housing 6 Remove the wedge assembly wedge seal retaining ring assembly and washer 7 Push the roller tappet piston from the housing in the direction of the input tappet piston Figure 17 Note Do not slide the roller tappet piston past the wedge turret 8 Remove the bleed screw 9 Using a small screwdriver with the end rounded and polished pry the seals and o ring from the input and roller tappet piston taking care not to score the seal grooves or piston surface CLEANING AND INSPECTION Discard all of the old parts that are to be replaced with parts furnished in the repairs kits Clean all of the metal parts with unused DOT 4 brake fluid or suitable solvent Do not use gasoline or hot water solution on metal parts Clean all rubber parts that are to be reused with clean DOT 4 heavy duty brake fluid Place on clean sheet of paper to dry Inspect all of the parts that are to be reused as outlined below Replace tho2. Replace brake shoes in axle sets 10 Parking brake will 1 Defective expander unit 1 Repair or replace expander unit not engage 2 Binding wedge assembly 2 Repair or replace wedge 3 Parking brake actuator not 3 Refer to vehicle service manual working 16 BW1601 2004 Bendix Commercial Vehicle Systems LLC All rights reserved 6 2004 Printed in U S A
3. expander parts abutment tappet roller tappet piston and the wedge and roller assembly This packaged grease or an approved substitute synthetic based grease must be used and an adequate amount must be applied Refer to Figure 18 for identification of those parts being lubricated with either the synthetic based grease or DOT 4 brake fluid during assembly Use all of the parts supplied in the Bendix repair kit to replace the old parts removed from the cylinders 1 Clamp the expander housing in a bench vise with padded jaws 2 Thoroughly smear the wedge cage wedge seal and roller assembly with the greased supplied Fit the wedge seal and retaining ring assembly as close to the cage as possible 3 Insert the wedge assembly into the expander housing and retain with a new circlip 4 Turn the expander housing in the vise to enable the abutment tappet to be installed Fit the dust boot to the abutment tappet Grease the inside of the dust boot and the outside diameter and ramp face of the abutment tappet with the grease supplied 5 Insert the abutment tappet assembly into the housing bore until it engages with the wedge cage and roller Figure 19 Install the dust boot to the end of the housing 6 Smear the o ring with the grease supplied and fit onto the roller tappet piston Lubricate the piston seal with new DOT 4 brake fluid and install the seal as shown in Figure 20 with the lip of the seal facing outward toward the p
4. cylinder piston REMEDY Refinish or replace drums in axle sets Refer to vehicle service manual Refer to vehicle service manual Refer to vehicle service manual Replace with correct shoes in axle sets Replace with correct shoes in axle sets Replace grease seal wheel cylinder or expander as necessary Replace brake shoes in axle sets Adjust steady post Tighten or replace backing plate dirtshield Refinish or replace drums in axle sets Apply brakes several times to dry linings Replace or repair wheel cylinder Refer to vehicle service manual Replace with correct shoes in axle sets Replace with correct shoes in axle sets Replace shoe return springs Smooth shoe abutment surfaces and steady post with emery cloth and lubricate with brake lubricant Replace drums in axle sets Refinish or replace drums in axle sets Refer to vehicle service manual Refer to vehicle service manual Refer to vehicle service manual Adjust brake shoes and repair automatic adjuster if necessary Replace shoe return springs Repair or replace defective wheel cylinder 15 DRUM BRAKE TROUBLESHOOTING SYMPTOM CAUSE REMEDY 9 One brake drags 1 Weak or broken shoe return 1 Replace shoe return springs spring 2 Improper brake shoe 2 Adjust brake shoes and repair adjustment automatic adjuster if necessary 3 Defective wheel cylinder 3 Repair or replace wheel cylinder 4 Bentor distorted brake shoe 4
5. SHOOTING CAUSE Excessive clearance between drums and linings Automatic adjusters not working Bent or distorted brake shoes Leak in hydraulic system Air in hydraulic system Low brake fluid Weak brake hoses Bent or distorted brake shoes Shoes not centered in drums Cracked or thin drums Air in hydraulic systems Weak brake hoses Drums out of round Grease or brake fluid on linings Glazed linings Damaged or distorted shoes Scored barrel shaped or bell mounted drums Defective master cylinder or other brake system components Incorrect or distorted shoes Incorrect linings or lining loose on shoes Grease or brake fluid on linings Shoes not centered in drums Loose or distorted backing plate dirtshield a REMEDY Adjust brakes Make several forward and reverse stops if pedal does not come up repair automatic adjusters Replace shoes and linings in axle sets Refer to vehicle service manual Bleed system refer to vehicle service manual Fill master cylinder If necessary bleed system Refer to vehicle service manual Refer to vehicle service manual Replace shoes and linings in axle sets Make certain shoe webs are seated in tappet or piston slots Replace drums in axle sets Bleed system refer to vehicle service manual Refer to vehicle service manual Refinish or replace if wear exceeds limits Replace grease seal wheel cylinder or expander as neces
6. WHEEL CYLINDER END SHOE RETURN SPRING EXPANDER END SHOE RETURN SPRING WHEELCYLINDER GASKET 5 EXPANDER SD 20 6608 CROSS OVER PIPE RETAINING SPRING A CROSS OVER PIPE SHOE HOLD DOWN CLIP NOT FITTED TO EARLY BRAKES FIGURE 1 A2LS AUTOMATIC ADJUSTING TWO LEADING SHOE DRUM BRAKE DESCRIPTION The A2LS drum brake is a hydraulically operated duo duplex brake with an automatic adjustment and parking brake feature The A2LS drum brake automatic adjust two leading shoes provides two leading shoes in either direction of drum rotation and an automatic adjustment of the brake shoes to compensate for lining wear Both the wheel cylinder unit and expander unit have cast integral brake mounting lugs each taking the brake torque load The wheel cylinder unit contains two single acting hydraulic cylinders with automatic adjusters The expander unit contains a double acting hydraulic cylinder with a park brake wedge expander Wheel cylinder and expander units have either a 1 5 8 inch 41 3mm or 1 3 4 inch 44 5mm diameter bore depending upon vehicle brake requirements The units are hydraulically connected together with a bridge pipe or crossover tube The single web brake shoes are located by slots in the wheel cylinder tappet head the expander input tappet piston and abutment tappet and are retained by the shoe return springs As with all Bendix automatic adjusting brakes provision is made for manual overri
7. YN eh BW 1257R WHEEL CYLINDER DISASSEMBLY Before proceeding clean the exterior of the wheel cylinder and make sure the work area tools and hands are clean Place a clean sheet of paper on the work bench surface 1 Clamp the wheel cylinder unit in a bench vise with padded jaws INPUT TAPPET PISTON RETURN SPRING PRING amp LOCATOR ocr FERRULE HYDRAULIC SEALS on W f ROLLER TAPPET CIRCLIP SNAP RING PISTON i rf WEDGE SEAL amp RETAINING RING TAPPET SEAL ASSEMBLY HOUSING 5 STOP PIN GASKET ABUTMENT TAPPET DUST BOOT FIGURE 17 EXPANDER UNIT 8 2 Remove the tappet head and manual override assembly from the wheel cylinder body Figure 15 Separate the tappet head from the manual override wheel 3 Using a blunt screwdriver pry the dust boots from the housing and discard 4 Carefully blow out both piston assemblies from the cylinder housing using low pressure shop air Remove the small spring and locator assembly 5 Unscrew the adjuster shaft assembly from the piston Note Do not dismantle the adjuster shaft assembly 6 Using a small screwdriver with the end rounded and polished pry the seal from the piston taking care not to score the seal groove or piston surface EXPANDER DISASSEMBLY Before proceeding clean the exterior of the expander unit and make sure the work area tools and hands are clean Place a clean sheet of paper on the work bench surface
8. age 6 Housings Examine the cylinder bores for signs of corrosion ridges or score marks Note Provided the cylinder bore surfaces are in perfect condition new seals and if necessary new pistons may be used to rebuild the existing housings If there is any doubt as to the condition of the cylinders new wheel cylinder and expander units must be installed INPUT TAPPET PISTON EI a o ip Ue SEAL POSITION ggm E w oe Ti O RING l e Yh A ROLLER TAPPET A PISTON er ABUTMENT TAPPET FIGURE 20 EXPANDER WEDGE 10 7 Backing Plate dirtshield Clean the backing plate with a damp cloth and wire brush to remove any dirt or corrosion from the surface of the backing plate IMPORTANT PLEASE READ Do not use an air hose to blow dust out of the backing plate dirtshield Never inhale dust from asbestos brake lining Asbestos dust when inhaled can be dangerous to your health Use a vacuum with a filter to remove dust carefully from the backing plate and drum 8 Brake Drum Inspect the drum for scores and cracks Refer to the vehicle service manual for inspection and resurfacing procedures Wipe drum clean with a cloth dampened in Bendix Metal Clene Do not contaminate the braking surface of the drum with grease or brake fluid REASSEMBLY ASSEMBLE EXPANDER UNIT Each Bendix drum brake repair kit contains a tube of synthetic based grease that is recommended for all internal
9. and parking brakes finally road test FINAL CHECK IMPORTANT PLEASE READ Before test driving any vehicle first check the hydraulic fluid level in the master cylinder 1 Check the hydraulic fluid level of the brake master cylinder If the fluid level is more than 1 4 inch 6 35 mm from the top of the reservoirs fill the reservoirs with DOT 4 heavy duty hydraulic brake fluid 2 Depress the brake pedal several times to seat the brake shoes against the drums Recheck the fluid level of the master cylinder reservoirs 3 Check the brake pedal travel by pushing the brake pedal as far down as possible If the brake pedal free play exceeds recommended dimensions or brake warning light is lit refer to the vehicle service manual 4 With the vehicle on a level surface in a parking or service area start the engine and apply the parking brake test for operation 5 With the vehicle moving at slow speed make a series of light snubs and follow with a series of normal service stops before making a panic stop Make sure the service brakes stop the vehicle in an even and straight line without any pulling to either side 6 Accelerate the vehicle to a speed of 20 mph 32 km h then apply the service brakes A 30 ft 92 4 m stop with the service brake from 20 mph 32 km h is recognized as being satisfactory 13 SYMPTOM 1 Low Pedal 2 Springy or spongy pedal 3 Hard pedal 4 Grabby brakes 14 DRUM BRAKE TROUBLE
10. aulic brake hose 7 Install the brake shoes following procedures under Brake Shoe Installation in this manual Refer to the vehicle service manual for procedures to bleed the air from the brake system After bleeding manually readjust the brake shoe to drum clearance as necessary Refer to Brake Shoe Adjustment in this manual BRAKE SHOE INSTALLATION High temperature grease should be used on those external parts that require lubrication slots on the pistons and tappets and on the steady posts FIGURE 24 POSITION OF BRAKE SHOE RETURN SPRINGS 2 Lubricate the adjuster shaft with DOT 4 brake fluid and screw the adjuster shaft fully into the piston assembly then unscrew one full turn Figure 22 3 Install the spring and locator assembly into the adjuster Always install new brake shoes in axle sets When installing shaft assembly Lubricate the piston assembly with new new brake shoes also install new shoe return springs DOT 4 brake fluid and install the piston assembly into the cylinder housing Fit the dust boot onto the housing 4 Install a new retainer into the override wheel and install the override wheel and tappet head onto the piston On old style A2LS drum brakes the override wheel had an internal retainer ring which also locates in a groove in the neck of the piston Figure 23 The latest override Note The color of the spring identifies its position in the wheel still uses the retainer ring but it is positioned furt
11. cle manufacturer s maintenance manual 3 Un adjust the vehicle brake shoes as follows A Remove the rubber grommets from the manual override access holes marked ADJ in the backing DO NOT ALLOW SPRING END plate dirtshield and insert a blunt screwdriver or TO ENGAGE INSIDE HOLE adjusting tool until it engages the manual override wheel Refer to Figure 10 l l FIGURE 12 SHOE RETURN SPRING REMOVAL B Using the backing plate dirtshield as a fulcrum Figure 11 turn the override wheel in a CLOCKWISE direction as viewed from the override wheel end until the lining clears the lip in the drum Watch the lining through the lining inspection hole Figure 26 SPRING REMOVAL TOOL MADE C Repeat this procedure with the other brake shoe and eR SON r eae lek remove the drum IMPORTANT Do not apply service or park brake after drums have been removed m g O w gt Hou i ue ul 1 8 IN THK 3 8 IN DIA COUNTER CLOCKWISE TO ADJUST UP CLOCKWISE TO DE ADJ UST FIGURE 11 ADJUSTINGADJUSTER MECHANISM FIGURE 13 6 CLOCKWISE TO DE ADJ UST FIGURE 14 DE ADJUSTING ADJUSTER MECHANISM 4 Place the recessed end of a 3 8 inch 9 53 mm square drive socket extension over the end of the wheel cylinder end shoe return spring Figure 12 Tap the end of the socket extension until the hook end of the spring passes through the brake shoe web 5 Shape a length of drill rob or equivalent tool steel into a to
12. de of the automatic adjuster This should only be needed for initial adjustment of the shoes to a specific drum clearance or to back off shoes to enable a lipped drum to be removed The brake assembly incorporates an integral backing plate dirtshield to protect the brake from excessive water and dirt intrusion The backing plate dirtshield contains a steady post for each brake shoe to insure that lining material is kept parallel to the drum braking surface Both brake shoes are free to slide on their abutment faces against the backing plate dirtshield and are therefore able to centralize themselves to the drum Lining material is 3 4 inch 19 11 mm thick in the center of the shoe tapering to approximately 5 8 inch 15 9 mm at each end Lining inspection holes and 1 manual override access holes are covered by rubber grommets INPUT TAPPET PISTON WHEEL CYLINDER Ee N f WHEEL CYLINDER PISTONS ROLLER TAPPET PISTON ABUTMENT TAPPET FIGURE 2 SERVICE BRAKE APPLICATION OPERATION On brake pedal application hydraulic fluid pressure is delivered to the wheel cylinder and expander unit This hydraulic pressure forces the wheel cylinder pistons outwards Figure 2 moving the brake shoes against the drum At the same time hydraulic pressure also forces the input tappet piston and abutment tappet in the expander unit outward moving the opposite end of the brake shoes toward the drum The expander input tappet pist
13. e work has been performed requiring the removal of the brake drum This adjustment is necessary to avoid excessive movement of the wheel cylinder pistons and to achieve a correct and stabilized running clearance The manual override is also used to un adjust the brakes when removing the drum when a lipped drum condition exists IMPORTANT PLEASE READ The manual override should not be used as an alternative to the auto adjuster It is essential that the auto adjust mechanism be kept in good operating condition to insure safe and reliable brake operation PREVENTIVE MAINTENANCE The A2LS drum brakes normally do not require any service except when new linings are being installed The automatic adjusters eliminate the need for any periodic adjustment of the brakes To insure safe operation of the brakes the following service checks should be performed The following is a recommended time table the actual times may vary depending upon the use of the vehicle and the type of operation and condition the vehicle is exposed to LINE HAUL VEHICLES Every 50 000 miles 80 000 km six months or 900 operating hours whichever occurs first perform the service checks outlined in this manual CITY DELIVERY Every 15 000 miles 24 000 km two months or 300 operating hours whichever occurs first perform the service checks outlined in this manual SERVICE CHECKS With the vehicle on a level surface block the wheels to prevent m
14. ge in the wheel cylinder unit or expander unit install new dust boots if necessary Refit the tappet head and manual override assembly to the wheel cylinder Temporarily install an elastic band around the wheel cylinder adjuster pistons to prevent them form becoming displaced WHEEL CYLINDER AND EXPANDER UNIT REMOVAL 1 TAPPET HEAD AND Disconnect the hydraulic inlet hose and bridge pipe from the wheel cylinder and expander unit lf the expander unit is being removed at this time remove the parking brake chamber from the expander body and backing plate dirtshield Refer to the vehicle service manual Remove the fixing bolts that secure the wheel cylinder and expander to the backing plate dirtshield and remove the units Move the wheel cylinder and expander to a clean work bench for service TAPPET HEAD MANUALOVERRIDE E aS WHEELASSEMBLY FIGURE 15 WHEEL CYLINDER fy fie 4 AR J DUST BOOT MANUAL OVERRIDE a WHEEL PISTON ADJUSTER SHAFT ASSEMBLY SPRING amp LOCATOR ASSEMBLY GASKET DISASSEMBLY BRAKE SHOES Bendix brake shoes and linings are available as sets with new factory lining installed If the brake shoes are in good condition neither worn nor bent new lining may be installed on the old brake shoes For lining installation procedures and brake shoe inspection procedures refer to Bendix se publication The Brake Block Manual Part 11 Form No FERRULE
15. her brake assembly up the override wheel The groove in the piston neck has been deleted 1 Lightly smear the abutment ends of the brake shoes and steady posts with high temperature grease Keep the grease away from all hydraulic components and the shoe linings Refer to Figure 24 for correct position of the replacement brake shoes and shoe return springs LINING INSPECTION HOLE SPRING TOOL REFER FIGURE 13 BRAKE LINING FIGURE 25 USING TOOL TO ATTACH SPRING FIGURE 26 BRAKE SHOE INSPECTION HOLE 12 RED Park brake expander end on both LH and RH brakes GREEN Wheel cylinder end on LH brakes YELLOW Wheel cylinder end on RH brakes 2 Remove the elastic bands from around the wheel cylinder used to retain the pistons for assembly 3 Push the abutment ends of the brake shoes into the slots on the piston and tappets 4 Attach the swan neck end end opposite the loop in the spring of each return spring to the brake shoe web as shown in Figure 25 Using the tool Figure 13 hook the other end of the return spring into the shoe web Install the brake drums Repeat with opposite wheel Ensure that the wedge stem is centralized ON DO Fit spring brake chambers to brakes per vehicle service manual 9 If new wheel cylinders or expander units were installed or the brake system drained refer to the vehicle service manual and bleed the brake system BRAKE SHOE ADJUSTMENT 1 Manually adjust both wheel cy
16. ive ring spring The brake shoe tip engaging in the piston tappet head and a spring between the adjuster shaft assembly and the face of the adjuster bore insure that a back lash is maintained on the mating threads of the adjuster shaft and piston When the brake pedal is applied hydraulic fluid pressure causes the piston to move outwards lifting the adjuster shaft AT REST NORMAL APPLICATION NO ADJUSTMENT REQUIRED SHOE RETURN SPRING LOAD PISTON AND ADJUSTER SCREW MOVE OUT FIGURE 7 ADJUSTER OPERATION BRAKE APPLICATION ADJUSTMENT REQUIRED DRIVE RING LIFTED OFF SEATING ROTATES RIDES DOWN HELIX AND RE SEATS BRAKES HELD ON DRIVE RING ALREADY SETTLED IN NEW POSITION DRIVE RING RE SEATED FIGURE 8 ADJUSTER OPERATION off its seat in the cylinder body If the movement of the adjuster shaft helix through the adjuster drive ring is less than the axial clearance back lash no rotation of the adjuster shaft takes place Figure 7 When the movement of the adjuster shaft helix through the adjuster drive ring is greater than the axial clearance rotation of the drive ring relative to the adjuster shaft will occur Figure 8 As the adjuster shaft helix passes through the drive ring the drive ring lightly loaded by the drive ring spring will rotate in its seat in the cylinder body As the brake pedal is released the brake shoe return springs cause the brake shoe to push the piston and adjuster shaft assembly bac
17. k through the cylinder BRAKES HELD ON DRIVE RING ALREADY SETTLED IN NEW POSITION RETURN STROKE ADJUSTMENT COMPLETED SHOE RETURN SPRING LOAD DRIVE RING DRIVE RING SEATED RE SEATED FIGURE 9 ADJUSTER OPERATION 4 As the axial tolerance between the adjuster shaft helix and adjuster drive ring is taken up the load on the drive ring helix forces it onto its seat The resultant friction keeps it from further rotation As the piston and adjuster continue through the cylinder the adjuster shaft helix is forced to rotate through the drive ring Figure 9 This rotation of the adjuster shaft relative to the piston unscrews the adjuster shaft from the piston increasing the overall length of the adjuster and piston assembly This in turn reduces the brake shoe lining to drum clearance The automatic adjustment rate is variable each application of the brake takes up only a percentage of the excess shoe to drum clearance This avoids over adjustment when the drums get hot and expand Note Due to manufacturing tolerances it is unlikely that all brake shoes will run at the same clearances No detrimental effect will result and no attempt should be made to standardize these clearances MANUAL OVERRIDE MECHANISM The manual override mechanism is used to override the automatic adjuster to set the initial shoe to drum clearance This initial adjustment is made after new brake shoes have been installed or other maintenanc
18. leed the air from the brake system After bleeding manually readjust the brake shoe to drum clearance as necessary Refer to Brake Shoe Adjustment in this manual ASSEMBLE WHEEL CYLINDER UNIT Use all of the parts supplied in the Bendix repair kit to replace the old parts removed from the cylinder 1 Lubricate the piston seal Figure 15 with new DOT 4 brake fluid and install the seal onto the piston with the lip facing inwards Figure 21 Install the dust boot to the piston and smear the inside of the dust boot with the grease furnished in the kit OVERRIDE RETAINER RING GROOVE IN PISTON RETAINER RING GROOVE IN PISTON HAS BEENELIMINATED FIGURE 23 NEW AND OLD STYLE PISTON AND OVERRIDE WHEEL 11 a Note A new design piston may be used to replace the piston pp ee fee Ly in older style brakes but the override wheel must also tE be changed Although it would be permissible to fit an eiin old style piston into a new style brake it would be a RED ON LH amp 5 j BRAKE YELLOW RH BRAKES retro grade step and is not recommended Ensure that ON RH BRAKE the tappet head assemblies are located securely on l the piston necks IMPORTANT Do not turn the manual override wheel 5 Repeat the above procedure for the other wheel cylinder 6 Install the wheel cylinder unit to the backing plate dirtshield using a new gasket Figure 1 and secure in place with fixing bolts Install the bridge pipe and hydr
19. lers force the expander abutment tappet and roller tappet piston apart Figure 5 and directly or through the expander input tappet piston the brake shoes are forced against the drum In parking brake operation the brake assembly is a one leading and one trailing shoe brake in either forward or reverse drum rotation AUTOMATIC ADJUSTMENT OF BRAKE SHOES In the A2LS drum brakes automatic adjustment is controlled by the wheel cylinder units Adjuster assemblies within the wheel cylinder units control the clearance between the drum and brake shoe by the back lash built into each adjuster mechanism During braking application when no adjustment is required brake shoe travel takes place within the back lash available As the linings wear and the distance between the lining and drum exceeds the predetermined clearance travel of the piston exceeds the back lash available and adjustment of the brake shoe is automatically made Each wheel cylinder piston has an adjuster mechanism screwed into it Figure 6 The rotation of this adjuster relative to the piston adjusts the brake shoes according to the amount of lining wear The adjuster shaft has a fast helix thread onto this is mounted a drive ring having a corresponding thread with an axial clearance back lash built in AD USTER S EM ADJUSTER SHAFT HELIX DRIVE RING MANUALOVERRIDE WHEEL The adjuster drive ring is held in light contact with its seat in the cylinder body by the dr
20. linders through the adjusting holes Figure 10 until the shoe to drum clearance is less than 76 mm 030 Check the shoe to drum clearance by using a feeler gauge through the lining inspection holes Figure 26 2 Apply the foot brake pedal to centralize the brake shoes and release Recheck the shoe to drum clearance if not 0 51 to 0 76 mm 0 020 to 0 030 manually adjust the wheel cylinder until those dimensions are reached 3 Replace all rubber grommets previously removed from the backing plate dirtshield Note Due to manufacturing tolerances it is unlikely that all shoes on an axle will run at the same drum clearances No detrimental effects will result from this condition and no attempt should be made to standardize the clearance 4 Correct and full adjustment will only occur with the drum rotating i e with the vehicle moving Pumping the brake pedal with the vehicle stationary will not achieve proper adjustment 5 Refit road wheels IMPORTANT Run engine and release park brake Wind the park brake chamber spring release bolts in place until they bottom firmly in the unit They should be torqued to the vehicle manufacturer s recommendations 6 Rotate each wheel to insure that the hydraulicsystem has fully released parking brakes 7 Apply parking brake and check that the wheels cannot be rotated by hand 8 Jack down vehicle Run engine and release parking brakes Drive vehicle slowly and check service
21. ol as shown in Figure 13 6 Insert the end of the tool into the loop on the end of the shoe return spring Using the expander unit body as a fulcrum unhook the spring from the brake shoe web Figure 25 Be careful not to damage the rubber dust boot Note The brake shoe return spring is hooked into the back side of the shoe web 7 Ease the shoes from under the shoe hold down clips where fitted and remove the back shoes 8 Remove the tappet head and manual override assemblies from the wheel cylinder units 9 Torapidly un adjust the adjusters fit a piece of 3 4 inch 19 05 mm heater hose inside a suitable 12 point socket Figure 14 on either a speedbrace or ratchet drive Place the heater hose over the piston neck and fully wind back the adjusters as shown in Figure 14 A load must be applied to the wheel cylinder piston while winding back the adjusters Note To avoid locking the auto adjuster mechanism in the fully un adjusted position wind out each wheel cylinder piston one complete turn after fully un adjusting the pistons 10 Inspect the wheel cylinder unit and expander unit for 11 leaks Lift the dust boots at their inner diameters from the tappets and pistons If fluid escapes when the dust boots are lifted the wheel cylinder or expander must be removed for service Follow the instructions in this manual for wheel cylinder unit and expander unit removal and service lf there is no evidence of brake fluid leaka
22. on pushes against one shoe and the roller tappet piston pushes on the expander abutment tappet and through this to the other shoe ARROW INDICATES DIRECTION OF DRUM ROTATION FIGURE 3 FORWARD DRUM ROTATION 2 ARROW INDICATES DIRECTION OF DRUM ROTATION TORQUE TORQUE LOAD ont LOAD FIGURE 4 REVERSE DRUM ROTATION When the brake shoe lining contacts the drum the shoes are forced around sliding on the abutmenis in the direction Of drum rotation In the forward direction Figure 3 the torque load from one shoe is taken by the wheel cylinder piston bottoming in its bore in the wheel cylinder and from the opposite shoe by the expander abutment tappet resting against the expander unit body In the reverse direction Figure 4 the torque load from one shoe is taken by the other wheel cylinder piston bottoming in its bore in the wheel cylinder and from the opposite shoe by the expander input tappet piston head resting against the expander body In this way regardless of forward or reverse drum rotation the brake will always be a two leading shoe brake PARKING BRAKE APPLICATION On application of the parking brake the spring actuator screwed into the back of the expander unit housing pushes the wedge assembly forward As the wedge assembly moves WEDGE AAJ ASSEMBLY FIGURE 5 PARKING BRAKE APPLICATION PISTON DRIVE RING SEAL SPRING FIGURE 6 WHEEL CYLINDER ASSEMBLY CUT AWAY forward the wedge rol
23. ovement of the vehicle 1 Remove one or more of the lining inspection plugs Check the thickness of the brake linings 2 Activate the brake pedal Observe the brake shoes through the inspection holes and make sure that the brake shoes move against the drums smoothly and promptly Release the brake pedal and make sure the brake shoes retract promptly and smoothly 3 Apply the parking brake Observe the brake shoes through the inspection hole and make sure the brake shoes engage the drum 4 Check all hydraulic fittings and the surface of the backing plate dirtshield for any evidence of hydraulic fluid leakage 5 Refer to the vehicle manual for service checks of other brake related items WARNING When working on or around brake systems and components the following precautions must be observed WARNING PLEASE READ AND FOLLOW THESE INSTRUCTIONS TO AVOID PERSONAL INJURY OR DEATH When working on or around brake systems and components the following precautions must be observed at all times 1 Park the vehicle on a level surface apply the parking brakes and always block the wheels When working around or under the vehicle stop the engine and remove the key from the ignition Always keep hands away from chambers as they may apply as system pressure drops Always wear safety glasses 2 When working in the engine compartment the engine should be shut off and the ignition key should be removed Where circumstances
24. require that the engine be in operation extreme caution should be used to prevent personal injury resulting from contact with moving rotating leaking heated or electrically charged components 3 Do not attempt to install remove disassemble or assemble a component until you have read and thoroughly understand the recommended procedures Use only the proper tools and observe all precautions pertaining to the use of those tools 4 Following the vehicle manufacturer s recommended procedures deactivate the electrical system in a manner that safely removes all electrical power from the vehicle 5 Ifthe vehicle is equipped with an air over hydraulic brake system or any auxiliary pressurized air system make certain to drain the air pressure from all reservoirs before beginning ANY work on the vehicle If the vehicle is equipped with an AD IS air dryer system or a dryer reservoir module be sure to drain the purge reservoir 6 Never connect or disconnect a hose or line containing pressure it may whip Never remove a component or pipe plug unless you are certain all system pressure has been depleted 7 Never exceed manufacturer s recommended pressure 8 Never attempt to disassemble a component until you have read and understand all recommended procedures Some components contain powerful springs and injury can result if not properly disassembled Use only proper tools and observe all precautions pertaining to use of those
25. ressure side Liberally grease the ramp face and DUST BOOT PISTON CML SCREW ON FULLY AND UNSCREW ONE COMPLETE TURN FIGURE 22 PISTON ADJUSTER insert the assembly into the bore of the housing until it engages the wedge cage and rollers Figure 16 Install and tighten the stop pin to 16 ft lbs 23 3 N m 7 Fitthe dust boot to the input tappet piston lubricate the piston seal with new DOT 4 brake fluid and install the seal onto the piston with the lip facing inward Figure 20 Grease the inside of the dust boot with the grease supplied and install the input tappet piston assembly into the housing bore until it rests on the roller tappet piston Fit the dust boot to the end of the housing 8 Turn the expander housing in the vise to enable the wedge return spring to be installed Locate the spring ferrule on the spring and compress the spring over the wedge stem until the pin can be inserted Figure 16 Release the spring carefully Note Push in wedge assembly slightly and center it inside the housing 9 Install the bleed screw 10 Install the expander to the backing plate dirtshield using a new gasket Figure 1 and secure in place with fixing bolts 11 Refer to the vehicle service manual and stall the parking brake chamber Install bridge pipe and hydraulic hose 12 Install the brake shoes following procedures under Brake Shoe Installation in this manual Refer to the vehicle service manual for procedures to b
26. sary Replace brake shoes in axle sets Sand lining surfaces or replace shoes and linings in axle sets Replace brake shoes in axle sets Refinish or replace drums in axle sets Refer to vehicle service manual Replace with correct shoes in axle sets Replace with correct shoes in axle sets Repair grease seal wheel cylinder or expander as necessary Replace brake shoes in axle sets Adjust steady post Tighten or replace backing plate dirtshield SYMPTOM 5 Vehicle pulls to one side 6 Noise and chatter 7 Pulsating brake pedal 8 Decreasing pedal travel DRUM BRAKE TROUBLESHOOTING CAUSE Scored hard spotted or out of round drums Rough or corroded master cylinder bore Binding brake pedal linkage Faulty power brake unit Incorrect or distorted shoes Incorrect linings or linings loose on shoes Grease or brake fluid on linings Shoes not centered in drums Loose or distorted backing plate dirtshield Scored hard spotted or out of round drums Water on linings Sticking wheel cylinder piston Faulty Suspension parts Bent damaged or incorrect shoes Worn linings Broken shoe return spring Rough grooved or dry shoe abutment surfaces or steady post on dirtshield Cracked or threaded drums Out of round drums Bent axle Worn or damaged wheel bearings Defective master cylinder Brakes overadjusting Weak or broken shoe return spring Sticking wheel
27. se parts that are damaged or excessively worn 1 Wedge assembly Check the wedge shaft and wedge surfaces for scoring Check the rollers for scoring pits cracks and flat spots Check the roller cage for fatigue cracks 2 Abutment Tappet Check the abutment tappet for any nicks burrs or corrosion Check the brake shoe web slot for any burrs or damage Smooth with a fine emery cloth or clean 3 Tappets Pistons Check the outer surfaces for scoring pits or nicks Check the seal ring and o ring grooves for any nicks burrs or corrosion Check the brake shoe web slot of the expander input tappet piston Check the inside of the piston for damaged threads Smooth witha fine emery cloth or clean as required DOT 4 FLUID DOT 4 FLUID FIGURE 18 EXPANDER LUBRICATION POINTS TAPPETS LOCATED OVER WEDGE CAGE amp ROLLER ASSY STOP PIN FIGURE 19 EXPANDER TAPPET LOCATION Note Normal wear pressure marks should not be mistaken for scoring Some discoloration of the piston diameter may be apparent this is a normal result of brake actuation over a long period of operation and should be ignored 4 Adjuster Shaft Assembly Check for damaged threads Check the helix for burrs corrosion or missing teeth Check that the adjustment shaft turns easily in the piston for the full length of the threads Smooth with a fine emery cloth or clean as required 5 Manual Override Check the teeth of the manual override for wear or dam
28. tools 9 Use only genuine Bendix replacement parts components and kits A Use only components devices and mounting and attaching hardware specifically designed for use in hydraulic brake systems B All replacement hardware tubing hose fittings etc must be of equivalent size type and strength as the original equipment 10 Components with stripped threads or damaged parts should be replaced rather than repaired Do not attempt repairs requiring machining or welding unless specifically stated and approved by the vehicle and component manufacturer 11 Prior to returning the vehicle to service make certain all components and systems are restored to their proper operating condition ADJUSTMENT OPENING FIGURE 10 REAR VIEW OF THE BACKING PLATE DIRTSHIELD REMOVAL BRAKE SHOE REMOVAL The removal disassembly cleaning and reassembly instructions presented are primarily for reference Disassembly particularly of the wheel cylinders and expanders should not be attempted without the proper maintenance kits on hand Damage to some parts may occur as a result of disassembly Maintenance kits are available from your local authorized Bendix parts outlet 1 Park the vehicle on a level surface and prevent vehicle movement by a means other than with the parking brake Shut off engine 2 Manually cage all hydraulic spring actuators raise the axle and remove the wheels and tires using the procedure recommended by the vehi
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