Repair Information - Eaton

1 Model 74318 and 74348 Piston MotorsFixed Displacement, Valve Plate DesignEaton Medium Duty Piston PumpRepair Information13141517161819202119123456548 71091122242326122578A262428A2728252628B2 930 Include :Housing Assy., 9 Camplate Insert, 11 Rotating Kit Assy., 12 Valve Plate, 22O-ring, 2328A28B24 Date Code andAssembly NumberLocationParts Drawing Copyright 1991 Eaton CorporationThru Shaft Backplate AssemblySame Side Porting BackplateAssemblyRear or Opposite side PortingBackplate Assembly +Parts included in 74418-904 and 74448-900 seal Repair kits.++Parts included in 74448-900 thru shaft backplate seal Repair are in Metric [ ].

2 Parts List - 74318 and 74348 Piston +1 Retaining Ring1+2 Shaft Seal13 Washer1+4 Retaining Ring25 Thrust Race26 Thrust Bearing17 Drive Shaft18 Key18 AKey (Used on thru shaft only)19 Housing Assembly (Includes item #10)110 Needle Bearing111 Camplate Insert112 Rotating Kit Assembly (Includes item # 13 thru #21)113 Piston Assemby914 Spider115 Spider Pivot116 Pin Keeper117 Piston Block118 Pins319 Washer220 Spring121 Retaining Ring122 Valve Plate1+23O - ring, mm x mm [3/32 in. x 4 in.]124 Backplate Assembly (Includes item #25 thru # 27)125 Needle Bearing126 Roll Pin227 Roll Pin128 Cap Screws628 ACap Screws (Use with same side porting)328 BCap Screws (Use with same side porting)3++29 Shaft Seal (In thru shaft backplate) 1++30 Retaining Ring (In thru shaft backplate) 1 Seal Repair Kit (74418-904)1 Seal Repair Kit (74448-900) (Used w/ thru shaft backplate)14 Repair Information - Model 74318 and 74348 Piston MotorsCleanliness is extremely important when repairing these in a clean area.

3 Before disconnecting the lines, clean portarea of motor. Disconnect hydraulic lines, removing motorassembly from vehicle and plug ports. Thoroughly clean theoutside of the motor. After cleaning, remove port plugs anddrain Required for Disassembly and Reassembly1/2 in. SocketRatchet WrenchTorque Wrench, 68 N m [50 lbs. ft.]Soft Face HammerInternal Retaining Ring Pliers(Straight [.090 in.] Tip)External Retaining Ring Pliers(Straight [.070 in.] Tip)Seal Driver or Similar ToolPetroleum Jelly (Such as Vaseline)Disassembly1 Clamp the drive shaft end of the piston motor in a protectedjaw vise with the cap screws up. Remove the six cap screws (28,or 28A and 28B) from the motor a mallet and tap the backplate (24) to loosen andremove from valve plate (22) and O-ring (23) from backplate.

4 Itis not necessary to remove roll pins in motor from vise and remove rotating assembly(12) from motor pistons (13) did not come out with piston block removethem along with spider (14) and spider pivot (15).6 The disassembly of the piston block assembly (12) is notrequired unless the pins (18) or spring (20) are following procedure should be used if the spring is to beremoved from the piston block. The spring (20) is highlycompressed and the retaining ring (21) should not be removedwithout compressing the spring (20).The following parts will be needed to disassemble the pistonblock:2 in. x 1-1/8 in. flat washers1 in.

5 X 3-1/4 in. cap screw, and1 in. nutPlace one of the flat washers over the 3/8 in. x 3-1/4 in. capscrew and place this through the center of the piston the other washer over the cap screw and let it rest on thethree pins. Screw the nut on and compress the spring inside thepiston block. Use a pair of retaining ring pliers and remove theinternal retaining ring (21). Remove the nut, bolt, and the twowashers. Remove the washer (19), spring (20), washer (19),and three pins (18), and the pin keeper (16).7 Remove the camplate insert (11) from housing (9). Cautionnot to mar the finish that makes contact with retaining ring (1) from housing.

6 Press shaft (8)from housing (9) and remove shaft seal (2), and washer (3).9 Remove retaining ring (4) from shaft and remove thrustwashers (5) and thrust bearing (6).10On through shaft assembly, remove snap ring (30) andshaft seal (29) from the shaft seals, and o-ring and replace with newitems upon the condition of the needle bearing (25) in backplate(24) and replace if valve plate (22) on the bronze side next to thepiston block for wear. A smooth surface is required. Do not lapvalve plate bronze surface. Replace valve plate if any the piston block (17) surface that makes contactwith valve plate. This surface should be smooth and free ofdeep scratches.

7 Do not lap piston pistons (13) should move freely in the piston blockbore. If they are sticky in the bore, examine the bore for scoringor the of the pistons for finish condition. Theyshould not show wear or deep scratches. Inspect the shoes for asnug fit on the ball end of the pistons and a flat smooth surfacethat comes in contact with the camplate. Do not lap the spider (14) for wear in the pivot the pivot (15) to insure smoothness and no signsof polished finish on the shoe surface of thecamplate insert (11) should show no signs of the shaft (7) for wear in the seal, bearing andspline thrust bearing (6) and washers (5) for the condition of the needle bearing (10) in housing(9) and replace if all parts in suitable solvent and lubricate allcritical moving parts before necessary, install new needle bearing (10) inhousing (9) with numbered end of the bearing retaining ring (4) on shaft (8).

8 Install thrustwasher (5), thrust bearing (6), and second thrust washer(5). Secure with second retaining ring (4).4 Install shaft in housing. Install washer (3), new shaftseal (2), and retain with retaining ring (1).5 Install camplate insert (11) with the lettering side ofinsert to the front of the housing. Use petroleum jelly tohold in place during piston block assembly was disassembled completethe following: Compress the pin keeper (16) and install inthe spline of piston block. Install the three pins (18) withhead end to the inside of the block and placed in thespecial grooves of the piston block the washer (19), spring (20), and secondwasher (19) in the piston block.

9 Use the two 3/8 in. , nut, and 3/8 in. x 3-1/4 in. cap screw tocompress the spring and retain with retaining ring (21).Remove the nut, cap screw and the two the pivot (15), spider (14), and the pistonassemblies (13) on the piston block (17). Install rotatingassembly (12) in to housing assembly over shaft. Thepiston shoes must make contact with the camplate sure all parts are in their proper position motor assembly in a protected jaw vise withthe open end of the housing roll pins were removed install to dimension shownand with opening of roll pin oriented away from bearingwithin 5 degrees of bearing center replace bearing (25) in backplate (24).

10 Pressbearing down to the dimension shown protruding frombackplate with number end of bearing facing up next tovalve plate. @@@@@@@@@@ @@@@@@@@@@@@@@@ @@ @@@@ [.173] [.09]BearingRoll Pin (26) @@@@@@@@@@@@@@@@@@@@ Roll Pin and BearingInstallation12 Apply small amount of petroleum jelly to the steelside of valve plate (22) to hold in place for the valve plate (22) in position onto the backplate(24), with steel side against backplate, bronze coloredside against piston new o-ring (23) onto backplate, installbackplate assembly (24) onto housing assembly (9).Make sure valve plate stays in the cap screws (28) and torque to m [15 to 18 lbs.]