Eaton 74318 Owner's manual

Model 74318 and 74348 Piston Motors
Fixed Displacement, Valve Plate Design
Eaton®
Medium Duty Piston Pump
Repair Information

13
14 15
17
16
18 19 20
21
19
12345654
8
7
10
9
11
22
24
23
26
12
25
7
8A
26
24
28A
27
28
25
26
28B
29 30
Include :
Housing Assy., 9
Camplate Insert, 11
Rotating Kit Assy., 12
Valve Plate, 22
O-ring, 23
28A
28B
24
Date Code and
Assembly Number
Location
Parts Drawing
© Copyright 1991 Eaton Corporation
Thru Shaft Backplate Assembly
Same Side Porting Backplate
Assembly
Rear or Opposite side Porting
Backplate Assembly

+ Parts included in 74418-904 and 74448-900 seal repair kits.
++ Parts included in 74448-900 thru shaft backplate seal repair kit.
Dimensions are in Metric [U.S.].
Parts List - 74318 and 74348 Piston Motor
Item
No. Descri
p
tion Quantit
y
+
1Retaining Ring 1
+
2Shaft Seal 1
3Washer 1
+
4Retaining Ring 2
5Thrust Race 2
6Thrust Bearing 1
7Drive Shaft 1
8Key 1
8A Key (Used on thru shaft only) 1
9Housing Assembly (Includes item #10) 1
10 Needle Bearing 1
11 Camplate Insert 1
12 Rotating Kit Assembly (Includes item # 13 thru #21) 1
13 Piston Assemby 9
14 Spider 1
15 Spider Pivot 1
16 Pin Keeper 1
17 Piston Block 1
18 Pins 3
19 Washer 2
20 Spring 1
21 Retaining Ring 1
22 Valve Plate 1
+
23 O - ring, 2.38 mm x 101.6 mm [3/32 in. x 4 in.] 1
24 Backplate Assembly (Includes item #25 thru # 27) 1
25 Needle Bearing 1
26 Roll Pin 2
27 Roll Pin 1
28 Cap Screws 6
28A Cap Screws (Use with same side porting) 3
28B Cap 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) 1

4
Repair Information - Model 74318 and 74348 Piston Motors
Cleanliness is extremely important when repairing these motors.
Work in a clean area. Before disconnecting the lines, clean port
area of motor. Disconnect hydraulic lines, removing motor
assembly from vehicle and plug ports. Thoroughly clean the
outside of the motor. After cleaning, remove port plugs and
drain oil.
Tools Required for Disassembly and Reassembly
1/2 in. Socket
Ratchet Wrench
Torque Wrench, 68 N•m [50 lbs. ft.]
Soft Face Hammer
Internal Retaining Ring Pliers
(Straight 2.3mm[.090 in.] Tip)
External Retaining Ring Pliers
(Straight 1.8mm[.070 in.] Tip)
Seal Driver or Similar Tool
Petroleum Jelly (Such as Vaseline)
Disassembly
1Clamp the drive shaft end of the piston motor in a protected
jaw vise with the cap screws up. Remove the six cap screws (28,
or 28A and 28B) from the motor assembly.
2Use a mallet and tap the backplate (24) to loosen and
remove from housing.
3Remove valve plate (22) and O-ring (23) from backplate. It
is not necessary to remove roll pins in backplate.
4Remove motor from vise and remove rotating assembly
(12) from motor housing.
5If pistons (13) did not come out with piston block remove
them along with spider (14) and spider pivot (15).
6The disassembly of the piston block assembly (12) is not
required unless the pins (18) or spring (20) are possibly
damaged.
Caution
The following procedure should be used if the spring is to be
removed from the piston block. The spring (20) is highly
compressed and the retaining ring (21) should not be removed
without compressing the spring (20).
The following parts will be needed to disassemble the piston
block:
2 ea. 3/8 in. I.D. x 1-1/8 in. O.D. flat washers
1 ea. 3/8 in. x 3-1/4 in. N.C. cap screw, and
1 ea. 3/8 in. N.C. nut
Place one of the flat washers over the 3/8 in. x 3-1/4 in. cap
screw and place this through the center of the piston block.
Place the other washer over the cap screw and let it rest on the
three pins. Screw the nut on and compress the spring inside the
piston block. Use a pair of retaining ring pliers and remove the
internal retaining ring (21). Remove the nut, bolt, and the two
washers. Remove the washer (19), spring (20), washer (19),
and three pins (18), and the pin keeper (16).
7Remove the camplate insert (11) from housing (9). Caution
not to mar the finish that makes contact with pistons.
8Remove retaining ring (1) from housing. Press shaft (8)
from housing (9) and remove shaft seal (2), and washer (3).
9Remove retaining ring (4) from shaft and remove thrust
washers (5) and thrust bearing (6).
10 On through shaft assembly, remove snap ring (30) and
shaft seal (29) from backplate.
11 Discard the shaft seals, and o-ring and replace with new
items upon reassembly.
Inspection
1Check the condition of the needle bearing (25) in backplate
(24) and replace if necessary.
2Inspect valve plate (22) on the bronze side next to the
piston block for wear. A smooth surface is required. Do not lap
valve plate bronze surface. Replace valve plate if any wear
exists.
3Inspect the piston block (17) surface that makes contact
with valve plate. This surface should be smooth and free of
deep scratches. Do not lap piston block.
4The pistons (13) should move freely in the piston block
bore. If they are sticky in the bore, examine the bore for scoring
or contamination.
5Examine the O.D. of the pistons for finish condition. They
should not show wear or deep scratches. Inspect the shoes for a
snug fit on the ball end of the pistons and a flat smooth surface
that comes in contact with the camplate. Do not lap piston
shoes.
6Examine the spider (14) for wear in the pivot area.
7Examine the pivot (15) to insure smoothness and no signs
of wear.

5
8The polished finish on the shoe surface of the
camplate insert (11) should show no signs of scoring.
9Inspect the shaft (7) for wear in the seal, bearing and
spline areas.
10 Inspect thrust bearing (6) and washers (5) for wear.
11 Check the condition of the needle bearing (10) in housing
(9) and replace if necessary.
Reassembly
1Clean all parts in suitable solvent and lubricate all
critical moving parts before reassembly.
2If necessary, install new needle bearing (10) in
housing (9) with numbered end of the bearing outward.
3Install retaining ring (4) on shaft (8). Install thrust
washer (5), thrust bearing (6), and second thrust washer
(5). Secure with second retaining ring (4).
4Install shaft in housing. Install washer (3), new shaft
seal (2), and retain with retaining ring (1).
5Install camplate insert (11) with the lettering side of
insert to the front of the housing. Use petroleum jelly to
hold in place during assembly.
6If piston block assembly was disassembled complete
the following: Compress the pin keeper (16) and install in
the spline of piston block. Install the three pins (18) with
head end to the inside of the block and placed in the
special grooves of the piston block spline.
7Install the washer (19), spring (20), and second
washer (19) in the piston block. Use the two 3/8 in. I.D.
washers, nut, and 3/8 in. x 3-1/4 in. cap screw to
compress the spring and retain with retaining ring (21).
Remove the nut, cap screw and the two washers.
8Install the pivot (15), spider (14), and the piston
assemblies (13) on the piston block (17). Install rotating
assembly (12) in to housing assembly over shaft. The
piston shoes must make contact with the camplate insert.
Be sure all parts are in their proper position before
proceeding.
9Clamp motor assembly in a protected jaw vise with
the open end of the housing up.
10 If roll pins were removed install to dimension shown
and with opening of roll pin oriented away from bearing
within 5 degrees of bearing center line.
11 To replace bearing (25) in backplate (24). Press
bearing down to the dimension shown protruding from
backplate with number end of bearing facing up next to
valve plate.
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Bearing
Roll Pin (26)
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Roll Pin and Bearing
Installation
12 Apply small amount of petroleum jelly to the steel
side of valve plate (22) to hold in place for installation.
Place the valve plate (22) in position onto the backplate
(24), with steel side against backplate, bronze colored
side against piston block.
13 Placing new o-ring (23) onto backplate, install
backplate assembly (24) onto housing assembly (9).
Make sure valve plate stays in position.
14 Insert the cap screws (28) and torque 20.3 to 24.4
N•m [15 to 18 lbs. ft.] in a criss-cross pattern.
15 If assembling a motor with a thru shaft install new
shaft seal (29) into backplate and retain with retaining
ring (30).
16 Fill case half full of hydraulic oil and install on vehicle.

6
Motor Trouble Shooting
In trouble shooting a pump and motor system it is necessary to isolate the pump from the motor. This will determine which unit is
actually malfunctioning. A worn pump or motor will both give the same system indication. Therefore, it is advisable to first run a
pressure and flow check on the pump. Making sure it is performing at its operating specifications. The following trouble shooting
suggestions are based on the assumption that the pumps flow and pressure are found within operating specifications.
Problem Possible Causes Correction
1Motor turns while unloaded but
slows down or stops when load
is applied.
AScored Valve plate ARemove backplate and examine
bronze surface of valve plate; if
scored, replace valve plate.
BScored or worn piston shoes. BDisassemble motor, examine
condition of shoes on pistons;
replace rotating kit assembly as
a complete set. Do Not Lap
pistons.
CLow pressure. CCheck relief valve for proper
pressure setting; adjust or
replace relief valve.
2
Motor will not turn. ASeverely scored internal parts ADisassemble motor completely.
Inspect all parts, clean all parts,
replace all worn parts and flush
hydraulic system.
3
Motor will not hold load when
system is in neutral position. ANo make up fluid from charge pump. ACheck charge pressure.
BScored valve plate or piston
shoes. BDisassemble motor and examine valve plate and piston shoes,
replace as required.
4
Excessive case drain flow. AExcessive internal wear in
motor. ADisassemble motor, inspect parts and replace as necessary.
Case drain flow should not
exceed 7.6 L/m [2 gal/m] at full
pressure.

7

Order parts from number 6-142 Parts Information booklet.
Each order must include the following information.
1. Assembly Number and/or Part Number
2. Date Code
3. Part Name
5. Quantity
Identification Number
Stamped on each units mounting flange.
Engineering change code
Last number of year built
00 00 00 = Data Code
74318 - DAV = Assembly Number
Week of year 0 thru 52
Testers initials
Example ot numbers
on flange.
Identifies type of product
74 = Fixed Axial Piston Motor
Sequential Identification
Rotation
D = Dual
Identifies Displacement
3 = 41 mL [2.48 cu. in.]
Valve Plate Design
Identifies Backplate and Displacement
18 = Plain Backplate, 41 mL [2,48 cu. in.]
48 = Thru Shaft Backplate, 41 mL [2,48 cu. in.]

© 2008 Eaton Corporation
All Rights Reserved
Printed in USA
Document No. E-PUPI-TS014-E
Supersedes 07-141
December 2008
Eaton
Fluid Power Group
Hydraulics Business USA
14615 Lone Oak Road
Eden Prairie, MN 55344
USA
Tel: [phone]
Fax: [phone]
www.eaton.com/hydraulics
Eaton
Fluid Power Group
Hydraulics Business Europe
Route de la Longeraie 7
1110 Morges
Switzerland
Tel: [phone]
Fax: [phone]
Eaton
Fluid Power Group
Hydraulics Business Asia Pacific
11th Floor Hong Kong New World Tower
300 Huaihai Zhong Road
Shanghai 200021
China
Tel: [phone]
Fax: [phone]