Hydraulic Brake System, Bendix 42.26

Hydraulic Brake System, Bendix 42.26 WARNING WARNING: Before starting the procedure below, read the information in "Safety Precautions, 100." Failure to be aware of the dangers of brake fluid exposure could result in serious and permanent health damage. Disassembly (Refer to Fig. 1 ) 1. Apply the parking brake, chock the tires, and tilt the hood. 2. Remove the master cylinder and reservoir assembly from the vehicle, following the instructions under "Master Cylinder Removal and Installation, 170." 3. Remove the reservoir from the master cylinder. 3.1 Remove the four flanged hexbolts that attach the reservoir to the top of the master cylinder. See Fig. 2. Note that one of the bolts has an L-bracket on it. 3.2 Lift the reservoir off the master cylinder. Turn the reservoir over, then remove the two compensating valve seals from the bottom of it. See Fig. 3. 4. Remove the small O-ring, then the two compensating valves and their springs from the top of the master cylinder housing. See Fig. 4 and Fig. 5. CAUTION CAUTION: Don t remove the piston stop at this time, or you may damage it and the piston bore in the master cylinder housing. 5. Remove the differential pressure indicator assembly from the front of the housing. 5.1 Unscrew the aluminum plug at the front end of the housing. See Fig. 6. 5.2 Using an allen wrench, remove the nylon insert underneath the aluminum plug. See Fig. 7. 5.3 Remove the differential pressure switch from the side of the housing. See Fig. 8. 5.4 Put a compressed air hose into the port on top of the housing where the primary compensating valve was. Put a shop towel over the hole at the front end of the housing, then place the housing so that the front end is facing down toward a padded surface; keep your hands away from the front of the master cylinder housing. WARNING WARNING: Be careful when using compressed air to remove the differential pressure indicator assembly from the master cylinder housing. It may come out of the housing with considerable force, which could cause personal injury or damage to the part. 5.5 Plug the primary circuit outlet ( Fig. 1, Ref. 27), then release just enough air pressure to force out the brass spool, O-ring, and collar (Refs. 5, 6, and 7). Discard the O-ring. Remove and discard the small O-ring (Ref. 8) from the brass spool. 6. Remove the primary piston assembly from the master cylinder bore. 6.1 Put the master cylinder in a vise. 6.2 Using a crossbar puller, a C-clamp, or other suitable tool, push the primary piston about 13 mm (1/2 inch) into the bore. See Fig. 9. 6.3 With the primary piston pushed in, remove the lock ring from the open end of the bore. See Fig. 9. Then remove the small piston stop from the top of the master cylinder housing. See Fig. 10. 6.4 Carefully release the tension on the primary piston, and ease it and its return spring out of the bore. See Fig. 11. 6.5 Remove and discard the pressure seal and back-up ring ( Fig. 1, Refs. 18 and 19) from the primary piston. Business Class Trucks Service Manual, Supplement 0, June 1991 172 /1

42.26 Hydraulic Brake System, Bendix 2 3 4 9 5 6 7 8 12 11a 13 10 14 12 11b 10 15 16 17 19 18 20 1 21 22 28 27 25 24 26 23 1. Secondary Outlet Port 2. Aluminum Plug 3. O Ring 4. Nylon Insert 5. Large O Ring 6. Brass Collar 7. Brass Spool 8. Small O Ring 9. Pressure Differential Indicator 10. Compensating Valve Spring (2 qty.) 11a. Secondary Compensating Valve 11b. Primary Compensating Valve 12. Compensating Valve Seal (2 qty.) 13. O Ring 26 14. Piston Stop 15. Reservoir 16. Primary Piston Return Spring 17. Primary Piston 18. Primary Pressure Seal 19. Primary Back Up Ring 20. Lock Ring 21. Secondary Pressure Seal (2 qty.) 22. Secondary Back Up Ring (2 qty.) 23. Secondary Piston 24. Secondary Return Spring 25. Master Cylinder Housing 26. Flanged Hexbolts (4 qty.) 27. Primary Outlet Port 28. Pressure Differential Switch 08/04/93 f420501 Fig. 1 172 /2 Business Class Trucks Service Manual, Supplement 0, June 1991

Hydraulic Brake System, Bendix 42.26 f420507 f420509 Fig. 2 Fig. 5 COMPENSATING VALVE SEALS f420534 Fig. 3 PISTON STOP f420522 Fig. 6 SMALL O RING Fig. 4 f420508 WARNING WARNING: Be careful when using compressed air to remove the secondary piston and actuator assembly from the master cylinder bore. Make sure the open end of the bore is pointed down toward a padded surface. Keep your hands away from the open end of the bore to prevent injury. Business Class Trucks Service Manual, Supplement 0, June 1991 172 /3

42.26 Hydraulic Brake System, Bendix LOCK RING f420537 Fig. 9 Fig. 7 f420531 7.1 Connect a compressed air hose to the front compensating valve port (Fig. 12 ) on top of the housing. 7.2 Plug the secondary outlet port ( Fig. 1, Ref. 1) and the hole where the pressure differential indicator (Ref. 9) was on the housing. 7.3 With the open end of the housing bore facing down, and about an inch away from a padded surface, carefully apply just enough air pressure to remove the secondary piston assembly and its return spring from the bore (see Fig. 13 ); don t pop it out. 7.4 Remove and discard the pressure seal and back-up ring from the secondary piston. Inspection Fig. 8 f420532 7. Using compressed air, remove the secondary piston assembly from the master cylinder bore. 1. Check the master cylinder bore for scoring or corrosion. If the master cylinder housing is pitted, rough, or corroded, replace the entire master cylinder assembly. 2. If needed, polish any discolored or stained areas in the bore with a crocus cloth. Don t use emery 172 /4 Business Class Trucks Service Manual, Supplement 0, June 1991

Hydraulic Brake System, Bendix 42.26 f420519 Fig. 10 Fig. 11 f420516 f420518 cloth or sandpaper; they could scratch the bore, which could cause leakage. Connect the compressed air hose here. Fig. 12 f420517 Fig. 13 (Refer to Fig. 1 ) IMPORTANT: When assembling the master cylinder, use new seals and rings. Don t reuse old ones. 1. Wash all the parts and the cylinder bore in clean, new DOT 3 approved brake fluid. Discard the brake fluid afterward. 2. Install the secondary piston assembly in the master cylinder bore. 2.1 Install two new pressure seals and back-up rings ( Fig. 1, Refs. 21 and 22) on the secondary piston. 2.2 Lubricate the piston assembly, the seals, and the cylinder bore (see Fig. 14 ) with clean DOT 3 approved brake fluid. 2.3 Put the secondary return spring ( Fig. 1, Ref. 24) on the actuator (flanged) end of the secondary piston assembly, then insert the piston assembly, spring end first, into the cylinder bore. See Fig. 15. Push it all the way to the bottom of the bore. 3. Install the primary piston assembly in the master cylinder bore. 3.1 Install a new pressure seal and back-up ring ( Fig. 1, Refs. 18 and 19) on the primary cylinder. 3.2 Lubricate the piston assembly and the seal with new DOT 3 approved brake fluid. Business Class Trucks Service Manual, Supplement 0, June 1991 172 /5

42.26 Hydraulic Brake System, Bendix f420518 Fig. 14 f420520 3.3 Insert the small end of the primary return spring ( Fig. 1, Ref. 16) into the master cylinder bore. 3.4 Insert the primary piston assembly into the master cylinder bore, actuator (flanged) end first. See Fig. 16. 4. Put the master cylinder housing into a vise, then using a crossbar puller or a C-clamp, push the pistons far enough into the master cylinder bore to install the lock ring in its groove. See Fig. 17. 5. Install the compensating valve seals on the bottom of the reservoir. See Fig. 18. Make sure the seals are completely seated. Also install the piston stop and the O-ring. See Fig. 20. 8. With the primary piston still pushed in, install the reservoir onto the top of the master cylinder, using the four mounting hexbolts. See Fig. 21. Make sure the L-bracket goes on the front inboard (when the master LOCK RING Fig. 16 f420537 Fig. 15 f420519 6. Using a crossbar puller or a C-clamp, push the primary piston 25 mm (1 inch) into the bore. See Fig. 19. 7. Install the compensating valve poppets and their springs in the top of the master cylinder housing. Fig. 17 9. cylinder is installed on the vehicle) mounting hexbolt. Tighten the bolts 20 N m (15 lbf ft). 10. Assemble the pressure differential indicator (refer to Fig. 22 ). 172 /6 Business Class Trucks Service Manual, Supplement 0, June 1991

Hydraulic Brake System, Bendix 42.26 COMPENSATING VALVE SEALS f420534 f420507 Fig. 18 Fig. 21 10.1 Install a new small O-ring (Ref. 3) in the groove on the end of the brass spool (Ref. 4). 10.2 Install the collar (Ref. 2) on the brass spool. 10.3 Install a new large O-ring (Ref. 1) onto other end of the brass spool, and push it down onto the collar, as shown in Fig. 22. Fig. 19 f420536 11. Install the spool and collar assembly with the collar end up into the hole at the front of the master cylinder housing, as shown in Fig. 23. Using a small piece of wood, seat the assembly at the bottom of its hole. 12. Using an allen wrench, install the nylon insert on top of the brass spool. See Fig. 24. 13. Install a new O-ring on the aluminum plug ( Fig. 1, Refs. 3 and 2), then install the plug into the hole at the front of the master cylinder housing. Tighten the plug firmly. 14. Install the pressure differential switch in the side of the master cylinder housing, as shown in Fig. 25. Tighten it finger-tight. Fig. 20 f420587 15. Check the operation of the compensating valves by poking a wire through the hole in the bottom of each reservoir section. The compensating valves should depress easily, about 1.5 mm (1/16 inch), then spring back. If not, remove the reservoir and install it again. Check the valves again. Business Class Trucks Service Manual, Supplement 0, June 1991 172 /7

42.26 Hydraulic Brake System, Bendix 1 2 3 1. Large O Ring 2. Brass Collar 3. Small O Ring 4. Brass Spool 4 f420521 Fig. 22 f420531 Fig. 24 f420533 Fig. 23 16. Remove the cross-bar puller or C-clamp installed to push the primary piston into the bore. 17. Bench bleed, then install the master cylinder on the booster, following the instructions under "Master Cylinder Removal and Installation, 170." 18. Lower the hood, then remove the chocks. Fig. 25 f420535 172 /8 Business Class Trucks Service Manual, Supplement 0, June 1991