Parker Hydraguide HGA Series Manual

Hydraulics
Bulletin 2751-001-M1/USA
Hydraguide™
Service Procedure
Effective: July 1, 2000
HGA Series Hydrostatic
Steering System

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
2
FAILURE OR IMPROPER SELECTION OR IMPROPER USE OF THE PRODUCTS AND/OR SYSTEMS DESCRIBED HEREIN OR
RELATED ITEMS CAN CAUSE DEATH, PERSONAL INJURY AND PROPERTY DAMAGE.
This document and other information from Parker Hannifin Corporation, its subsidiaries and authorized distributors provide product and/or
system options for further investigation by users having technical expertise. It is important that you analyze all aspects of your application
and review the information concerning the product or system in the current product catalog. Due to the variety of operating conditions and
applications for these products or systems, the user, through its own analysis and testing, is solely responsible for making the final selection
of the products and systems and assuring that all performance, safety and warning requirements of the application are met.
The products described herein, including without limitation, product features, specifications, designs, availability and pricing, are subject to
change by Parker Hannifin Corporation and its subsidiaries at any time without notice.
WARNING
The items described in this document are hereby offered for sale by Parker Hannifin Corporation, its subsidiaries or its authorized distributors.
This offer and its acceptance are governed by the provisions stated in the "Offer of Sale".
ãCopyright 2000, Parker Hannifin Corporation, All Rights Reserved
Offer of Sale

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
3
Typical Oil Flow .................................................................................................................................................... 4
Hydraguide™ Steering
Model HGA ....................................................................................................................................................... 6
System Operation ............................................................................................................................................. 7
Design and Function ......................................................................................................................................... 7
Control Valve ..................................................................................................................................................... 8
Metering Section ............................................................................................................................................... 8
Rotor Operation ................................................................................................................................................ 8
Power Steering Operation ................................................................................................................................. 9
Manual Steering Operation ............................................................................................................................... 9
Exploded View.................................................................................................................................................... 10
Service Parts List ............................................................................................................................................... 11
Service Procedure.............................................................................................................................................. 13
Work Conditions.............................................................................................................................................. 13
Seal Replacement Instructions ....................................................................................................................... 14
Servicing of HGA Unit ..................................................................................................................................... 14
Disassembly Procedure ..................................................................................................................................... 15
Inspection and Replacement.............................................................................................................................. 18
Assembly Procedure .......................................................................................................................................... 19
HGA Column ...................................................................................................................................................... 23
Oil & Hydraulic Fluid
Filling and Air Bleeding System ...................................................................................................................... 24
Hydraulic Fluid ................................................................................................................................................ 24
Tips for Maintaining the System ......................................................................................................................... 25
Offer of Sale ....................................................................................................................................................... 26
Table of Contents

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
4
Typical Oil Flow
SUPPLY PRESSURE (From Power Pump)
RETURN OIL FLOW (To Reservoir)
METERED OIL FLOW (To Cylinder)

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
5
Typical Oil Flow
OILFLOW (From Recirculating Valve)
RETURN OIL (To Recirculating Valve)
METERED OIL FLOW (To Cylinder)

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
6
Hydraguide™Steering
MODEL HGA
Hydraguide™is the name given to hydrostatic steering systems. In the HGA type Hydraguide™steering system,
an engine-driven pump, relief valve, cylinder, reservoir, filter, fluid lines, and an HGA control unit are needed. An
automotive type steering wheel is attached to the HGA unit and the cylinder is connected by suitable means to
the steered wheels.
The driver has power steering control at all times, so long as system components work together, system integrity
is maintained, and adequate fluid is present. If there is a failure in the high-pressure circuit, a loss of power
steering will result. The HGA, however, is designed to have some manual steering capability, depending on the
installation. If you can’t manually steer the vehicle without using extraordinary measures, such as leaving your
seat, or pushing with your legs, don’t try it. Repair the failure in the power circuit. Some vehicles may be impos-
sible to steer manually because of their weight and size.
WARNING: ALL STEERING MECHANISMS ARE LIFE AND LIMB ITEMS. AS SUCH, IT IS IMPERATIVE
THAT THE INSTRUCTIONS IN THIS BOOKLETARE FOLLOWED TO THE LETTER. FAILURE TO OB-
SERVETHE PROCEDURES SET OUT IN THIS PAMPHLET MAY RESULT IN LOSS OF STEERING.
WARNING: EXTRAORDINARYMEASURES SHOULD NOT BE USED INATTEMPTING TO MANUALLY
STEER THE VEHICLE,AS THEY MAY GENERATE FORCES IN EXCESS OF 125 FT. LBS., THEREBY
DAMAGING THE UNIT INTERNALLY, WHICH COULD RESULT IN A COMPLETE LOSS OF STEERING.

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
7
Hydraguide™Steering
SYSTEM OPERATION
This literature with the illustrations shown covers the basic design of the HGA unit. Variations may be engineered
to suit special requirements.
The description of the operation of the HGA unit and the illustrations explain the functioning of the system for the
utilization of the hydraulic power generated by the engine-driven pump for power steering. Emergency manual
operation is also described.
Satisfactory performance of this system requires a well engineered installation designed for the particular
type of vehicle and the type and kind of service for which it will be used. Parker Engineering advice and
assistance is available and we welcome requests.
Information on the required engine-driven pump capacity and the power cylinder size and connecting lines are
provided through engineering contacts. A balanced cylinder design is preferred.
Figure HGA-1
DESIGN & FUNCTION
The HGA unit consists of a fluid control valve section and a fluid metering section which are hydraulically and
mechanically inter-connected.

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
8
Hydraguide™Steering
CONTROLVALVE
The control valve section contains a mechanically
actuated linear spool which is torsion bar centered.
The function of the control valve section is to direct fluid
to and from the metering section, and the cylinder, and
to regulate the pressure supplied to the cylinder. The
valve is provided with unique pressure chambers which
insure effective circuit isolation.
METERING SECTION
The metering section consists of a commutator and bi-
directional gerotor element, which contains an orbiting
rotor and a fixed stator. The commutator rotates at orbit
speed with the rotor and channels the fluid to and from
the rotor set and the valve section.
The rotor incorporates unique sealing vanes which are
spring and hydraulically forced into sealing contact
between the rotor and stator to reduce leakage across
the metering section.
The function of the metering section is to meter the oil to
the power cylinder, maintaining the relationship between
the hand wheel and the steered wheels. An additional
function of the metering section is to act as a manually
operated pump providing manual steering in the event of
an inoperative engine-driven pump.
Figure HGA-2
ROTOR OPERATION IN THE ROTOR SET (See Fig. HGA-3)
Each lobe of the rotor has a diametrically opposite lobe, therefore, when one lobe is in a cavity its opposite lobe is
at the crest of the stator’s convex form opposite the cavity. As the rotor is rotated, each lobe in sequence is
moved out of its cavity to the crest of the stator’s convex form and this forces each opposite lobe, in sequence,
into a cavity. Due to the interaction between the rotor and the stator, there are 42 fluid discharging actions in one
revolution of the rotor. When the rotor is moving, fluid is always flowing out of three of the cavities while fluid is
flowing into three other cavities, and one of the cavities is inactive as it changes from one of discharging fluid to
one of admitting fluid. The commutator rotates with the rotor and channels the fluid to and from the valve section,
and to and from the rotor set.
Figure HGA-3

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
9
Hydraguide™Steering
POWER STEERING OPERATION
When the spool is in center or neutral position, the
hydraulic oil from the engine-driven pump circulates
through the valve section, directly back to the reservoir
with sufficient pressure only to overcome friction of
valve channels and lines. There is no circulation of
engine-driven pump oil to or from the cylinder. Note
the center diagram showing neutral position (See
diagram on inside front cover) on which no directional
arrows appear in the metering channels. The oil
pressure at the two cylinder ports is equal and pro-
duces ineffective forces in the cylinder.
In order to accomplish a power steering maneuver, the
operator must rotate the steering wheel in the direc-
tion of the steering maneuver. The initial rotation of the
steering wheel rotates the input shaft which tends to
rotate the drive link and rotor set through the torsion
bar centering spring. Rotation of the rotor set and
spool which are coupled by the drive link, is resisted
by the cylinder pressure required to overcome the
steering forces. As the input shaft is rotated relative to
the spool, the centering spring is torsionally deflected.
Axial shift of the spool is induced by the ball which is
captive in the spool and engaged in the helical groove
provided in the input shaft.
When the spool is axially displaced within the body,
fluid channels are selected connecting the engine-
driven pump to the intake side of the rotor set via the
WARNING: ALL STEERING MECHANISMS ARE LIFE AND LIMB ITEMS. AS SUCH, IT IS IMPERATIVE
THAT THE INSTRUCTIONS IN THIS BOOKLETARE FOLLOWED TO THE LETTER. FAILURE TO OB-
SERVETHE PROCEDURES SET OUT IN THIS PAMPHLET MAY RESULT IN LOSS OF STEERING.
commutator. The exhaust side of the rotor set is
connected, through the commutator, to one side of the
cylinder while the other side of the cylinder is con-
nected to the reservoir. (See Figures HGA-1 and 2).
Further axial displacement of the spool results in
increased system pressure to provide the level of
pressure required. A portion or all of the hydraulic fluid
at the required pressure from the engine-driven pump,
depending upon the speed of steering, is directed to
the cylinder via the metering section, using cylinder
movement to accomplish the steering maneuver.
MANUAL STEERING OPERATION
In the absence of system pressure, the driver's
manual effort displaces the spool axially. When the
spool is displaced within the body, fluid channels are
selected connecting the rotor set, which is now acting
as a pump, via the commutator to one side of the
cylinder. The return flow from the other side of the
cylinder is channeled through a recirculation valve so
that the oil will flow to the intake side of the rotor set
via the commutator instead of back to the reservoir.
(See. Figure HGA-5) The recirculation valve is a ball
check valve in a channel connecting the return flow
chamber to the engine-driven pump pressure inlet
chamber. The recirculation valve is closed during
power operation.

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation Hydraulic Pump/Motor Division Greeneville, Tennessee
10
Exploded View
26. Ball
27. “O”Ring
28. Plug
29. Spacer
30. Drive Link
31. Rotor Set
31 a. Stator
31 b. Rotor
31 c. Spring
31 d. Vane
32. Manifold
33. Commutator Ring
34. Commutator
35. Seal Retainer
36. Seal
37. Washer
38. End Cover
39. Special Bolt
1. Nut
2. Dirt & Water Seal
3. Retaining Ring
4. Backup Washer
5. Seal
6. Screw
7. Upper Cover
8. Seal
9. Shim
10. Retaining Ring
11. Thrust Washer
12. Thrust Bearing
13. Thrust Washer
14. Spring Washer
15. Spacer
16. Input Shaft
17. Needle Roller
18. Drive Ring
19. Spacer
20. Torsion Bar
21. Needle Roller
22. Spool
23. Ball
24. Spring
25. Housing Assembly
25 a. Plug
25 b. “O”Ring
25 c. Ball
(*Items 2, 4, 5 included in HG500007 Kit)
(**Items sold in matched sets only)
FigureHGA-6
Vanes are specified on “HGA”units
with rotor widths smaller than 1.00.
* * *

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation Hydraulic Pump/Motor Division Greeneville, Tennessee
11
Service Parts List
USE WITH HGA SERVICE MANUAL EXPLODED VIEW
1 2, 4, & 5 3 6 7 8 9 10 11
Wheel Seal Snap Screw Upper Seal Shim Snap Thrust
Nut Kit* Ring (4 ea.) Cover Kit Ring Washer
026045 HG500007 401233 021434 (Fine) HGA016005X1 032840X1 033157X2 401367 400100
12 13 14 15 16A 16C 16B 16D 17 18 23
Thrust Thrust Spring Spacer Pinhole Wheel Mount Full Bolt Straight Needle Drive Ball
Bearing Washer Bearing Washer Shaft Shaft Groove Spline Roller Ring 5/16”dia.
063979 400075 401366 477277 089181 089180 089193 089178 040114 HGA013003 400013
24 25-A&B 25C & 26 27 & 28 29 32 33 & 34 37 38
Spring Plug & Ball Plug Spacer Manifold Commutator Washer End Cover
“O”Ring 1/4 dia. Assy. Assy.
401412 036147A1 G453570 415395A2 477235 HGA015001 HGA014000A1 028395 402803A1
22 & 25 Housing & spool are non-serviceable due to select fit. If either needs to be replaced the housing assembly must be replaced.

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation Hydraulic Pump/Motor Division Greeneville, Tennessee
12
Service Parts List
STANDARD PARTS THAT CHANGE WITH DISPLACEMENT
31C/D 31 Length of 35 Length of 36 Length of 39 20 & 21 30 19
Series Vane Kit Rotor Set Rotor Seal Seal Rubber Rubber 5/16-24 Thread Torsion Bar** Drive Link Spacer
Set Retainer Retainer Boot Seal Boot Seal Bolts (7 ea.)
Before Date After Date
Code195-94 Code195-94
HGA 08 506607 HGA087010 .501 099070 1.522 032626 1.648 021269 021428 BASE-A10506 HGA013008 4772480184
HGA 10 506606 HGA107010 .626 099071 1.647 032618 1.786 021280 021356 BASE-A10525 HGA013008 4772480196
HGA 12 506611 HGA127007 .751 099072 1.772 032619 1.923 021283 021311 BASE-A10538 HGA013008 4772480209
HGA 14 506610 HGA147005 .876 099073 1.897 032627 2.066 021290 021306 BASE-A10550 HGA013008 4772480221
HGA 16 506609 HGA167005 1.001 099074 2.022 032628 2.203 021292 021382 BASE-A10562 HGA013008 4772480234
HGA 20 ——— HGA207005 1.252 099075 2.272 032620 2.511 021294 021357 BASE-A10525 HGA013005 4772480196
HGA 24 ——— HGA247005 1.502 099076 2.522 032629 2.753 021295 021444 BASE-A10550 HGA013005 4772480221
HGA 28 ——— HGA287005 1.752 099077 2.772 032621 3.026 021296 021358 BASE-A10538 HGA013006 4772480209
HGA 32 ——— HGA327004 2.002 099095 3.022 032759 3.313 021349 021435 BASE-A10562 HGA013006 4772480234
*Use part number 020206 on assemblies manufactured prior to date code 195-94
**Torsion bars are unit specific. To select the correct replacement, measure the diameter of the center section of the bar and the length between holes, then select
the correct base number from the following chart:
Base Number Bar Center Diameter - in. Length Between Holes - in.
401360 0.147 5.00 - 5.62
401363 0.160 6.00 - 6.50
401368 0.160 5.00 - 5.62
401413 0.154 5.00 - 5.62
401432 0.147 6.00 - 6.50
401435 0.139 5.00 - 5.62
401627 0.139 6.00

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
13
Service Procedure
WARNING: SINCE SOLVENTS ARE FLAMMABLE, BE EXTREMELY CAREFULWHEN USINGTHEM.
EVENA SMALL EXPLOSION OR FIRE COULD CAUSE DEATH OR INJURY.
WARNING: EYE PROTECTION SHOULD BE WORN.
WARNING: OSHAMAXIMUMAIR PRESSURE REQUIREMENTS SHOULD BE COMPLIED WITH TO
PREVENT INJURY.
CLEAN WORK CONDITIONS
It is a must that the system be kept free of dirt or
foreign matter in the oil circuit. Cleanliness in servicing
this power steering system is absolutely necessary.
If it is necessary to disassemble any of the units, make
sure that a clean work bench or table is used. (A piece
of clean wrapping paper makes an excellent dispos-
able top).
Outside dirt should be cleaned off before disconnect-
ing lines and port holes should be plugged immedi-
ately after disconnecting lines.
Finish cleaning off outside dirt before placing on work
bench.
When disassembled, parts should be cleaned only in
clear-clean petroleum base solvent and blown dry with
clean, dry air. Other solvents may cause deterioration
of rubber seals. Avoid wiping parts with cloth and
never steam clean hydraulic steering assemblies.
SERVICE PROCEDURE
For service information on the steering pump (engine-
driven) and power cylinder, see information provided
by the manufacturer of these units.
For servicing the HGA unit and the system, see
instructions in the following sections.
Servicing of HGA Unit Page14
Filling and Air Bleeding the System
WhenDrained ofOil Page24
HydraulicFluid Page24

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
14
Service Procedure
SEAL REPLACEMENT INSTRUCTIONS
For numerous installation you may want to purchase the J26910 tool kit available from KENT MOORE TOOL
DIVISION, 29784 Little Mack, Roseville, Michigan 48066 - Phone [phone].
Caution: Follow the instructions and do not disassemble the Hydraguide unit upper cover (7) to replace the shaft
seal (5).
1. Remove the steering wheel nut (1), steering wheel
and steering wheel column, if applicable. Refer to
page 18 for instructions on removal of steering
wheel column.
2. Remove the dirt seal (2) over the end of the
Hydraguide unit upper cover, if applicable. Discard
this part.
3. Remove the retaining ring (3), do not discard, this
part must be reinstalled during assembly procedure.
4. Remove the seal package parts (4) (5) from the
Hydraguide unit by one of the following methods:
a) If the Hydraguide unit has not been removed
from the vehicle, rotate the Hydraguide unit
input shaft either clockwise or counter clockwise
to pressurize the system and force the seal
package out. Discard these parts.
b) If the Hydraguide unit has been removed from
the vehicle plug three of the four ports in the
Hydraguide unit and pressurize the other port
with air pressure to force the seal package out.
Discard these parts.
5. Note: Clean the Hydraguide unit input shaft (16)
and upper cover (7) seal bore to remove particles
of dirt, felt, lint, etc. with a clean, lint-free rag.
Caution: excessive particles of felt or lint can cause
the new seal package to leak.
6. Cover the end of the Hydraguide unit input shaft
with cellophane tape to protect the new seal (5)
when it is assembled over the sharp edges of the
input shaft.
7. Lubricate the new seal using hydraulic oil and
install the new seal (5) with lip side first, onto the
Hydraguide unit input shaft.
8. Remove the cellophane tape from the Hydraguide
unit input shaft.
9. Assemble the new washer (4), with small end first,
onto the Hydraguide unit input shaft and push the
new washer and the new seal (5), previously
installed, down into the Hydraguide unit upper
cover. (A short piece of metal tubing 15/16 mini-
mum I.D. x 1-3/16 maximum O.D. or a 7/8 deep
well socket may be used to push these parts into
place.)
10.Assemble the previously used retaining ring (3)
onto the Hydraguide unit input shaft and down into
the Hydraguide unit upper cover groove. Be sure
the rounded edge of the retaining ring (3) is faced
inward.
11.Assemble the new seal (2) onto the Hydraguide
unit input shaft and down into the Hydraguide unit
upper cover (7) counter bore.
12.Assemble the steering column, if applicable.
13.Assemble the steering wheel and wheel nut,
torque the wheel nut to 35 ft. lbs.
SERVICING OF HGA UNIT
Refer to exploded view, Figure HGA-6 for parts identification.
The spool (22) and the housing (25), the commutator (34), and commutator ring (33), as well as the rotor (31B)
and the stator (31A) are not separately replaceable because they are selectively fitted at the factory. If the spool
or housing need replacement, the complete housing assembly must be replaced. If the commutator or the
commutator ring need replacement, both must be replaced as a matched set. If the rotor or stator need replace-
ment, the complete rotor set (31) must be replaced. The pin in the end cover is not separately replaceable. If the
pin or end cover need replacement, the end cover and pin assembly (38) must be replaced.

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
15
DisassemblyProcedure
Plug the four port holes and clean the exterior of the
unit thoroughly. Then remove the plugs.
1. To prevent possible distortion or damage to unit if
placed directly in vise, the following procedure
should be used. Insert “o”ring tube fitting, with
tube nut or fitting cap attached, into one of the four
threaded ports in the housing. Clamp the fitting in
a vise in a manner which will locate the seven end
cover bolts in an upright position. (See Figure
HGA-7).
2. Unscrew the seven special bolts (39) from the end
cover (38). Note: Special care should be used in
the following steps to insure protection of the
ground and lapped faces of the components.
Avoid scratching or nicking of finished sur-
faces.
3. Remove end cover (38) by bumping it sideways
with a soft hammer to loosen it from the rotor seal
(36) and seal retainer (35), and lift from unit.
Caution: The washer (37) and commutator (34)
may adhere to the end cover, and may be
removed with the end cover. Do not attempt to
remove pin because pin is press fit in the plate
and is non-serviceable. (See Figure HGA-8).
4. Remove the rotor seal (36) and seal retainer (35)
by bumping the can sideways with a soft hammer
to loosen it from the housing and lift off the rotor
seal and seal retainer. Discard the rotor seal.
5. If the wear washer (37) and commutator (34) were
not removed with the end cover (38), remove these
parts from the HGA unit.
6. Remove the commutator ring (33) from the mani-
fold (32), by a sliding and lifting motion. Care
should be used in the handling of this fragile
component.
7. Remove the manifold (32) from the rotor set (31)
by sliding and lifting motion.
8. Remove the rotor set (31), spacer (29) and drive
link (30) as an assembly by grasping the spacer
and removing the assembly with a sliding and
lifting motion. (See Figure HGA-9).
9. Separate drive link (30) by sliding the rotor set (31)
on the spacer (29), allowing the drive link teeth to
clear the spacer hole. Remove drive link and
separate rotor set from spacer. Use extreme
caution to keep vanes (31D) and springs (31C)
from falling out. When handling the rotor set,
pressure should be applied to the rotor (31B)
by gripping the rotor set between the fingers
and urging the rotor into contact with the
stator (31A). (See Figure HGA-10)
Carefully protect against damage to side faces.
Note: The rotor (31B) and the stator (31A) must be
kept in a matched set.
Figure HGA-7
Figure HGA-8
Figure HGA-9

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
16
DisassemblyProcedure
10.Reverse the HGA unit in the vise to place the input
shaft (16) in a vertical position. Using a center
punch, mark the upper cover flange (7) in relation
to a similar mark placed on the port face of the
housing (25) to facilitate reassembly. (See figure
HGA-11).
11.Remove the four special cap screws (6) by using a
5/16-12 point socket.
12.Grasp the input shaft (16) and with a smooth
upward motion, remove the input shaft (16), upper
cover (7) and spool (22) assembly from the
housing (25). Note: Avoid applying side forces
to the spool which would cause binding of the
closely fitted assembly. Never use excessive
force to remove the spool from the housing.
13.Remove and discard seal (8).
14.Remove the upper cover (7) with shaft seal pack-
age (Items 2 thru 5) intact. Remove spacer item
(15).
15.Remove shims (9) from either upper cover (7)
cavity or from face of thrust washer (11). Count
and record the number of shims to aid in reassem-
bly of unit.
Figure HGA-10
16.Remove seal (2), retaining ring (3), using proper
snap ring pliers. Discard seal (2). Remove and
discard backup washer (4). Remove and discard
seal (5).
17.Remove the retaining ring (10), thrust washer (11),
thrust bearing (12), thrust washer (13) and spring
washer (14) from input shaft (16). Note: Retaining
ring is twisted design. Do not straighten ring.
18. Remove the needle roller (17) by using a pin
punch of .125-inch max. diameter for a minimum of
.625 length. The input shaft (16) should be placed
on a block of wood (to avoid shaft damage) and
the needle roller (21) removed by impact, using
light hammer blows. (See Figure HGA-12).
19.Remove the torsion bar (20) and spacer (19) by
inverting the spool assembly and allowing the
parts to fall free. Do not remove needle roller (21)
from torsion bar. (See Figure HGA-13).
Figure HGA-12
Figure HGA-13
Figure HGA-11
MARKS

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
17
DisassemblyProcedure
20.Remove the drive ring (18) by placing the end of
the spool (22) on a table surface. Rotate the input
shaft (16) to extremes of travel until the drive ring
falls free. (See Figure HGA-14).
Figure HGA-14
21. With the spool assembly in the same position as
the step above, rotate the input shaft (16) in a
clockwise direction until the actuator ball (23)
disengages from the helical groove in the input
shaft. Lift out input shaft. Caution: The actuator
ball may fall free and care should be used to
not lose it.
22.Do not remove the ball retainer spring (24)
unless replacement is required. If necessary to
remove this spring, discard the retainer (24) if
moved.
A screwdriver may be used to assist in the prying
of the spring over the shoulder of the spool (22).
Care must be used to avoid scratching or nicking
of the spool outside diameter and control edges.
(The following procedure is optional).
23.Return to the housing (25) which is mounted in the
vise. Remove the plug and roll pin assembly (28).
A steel ball is captivated by the plug and roll pin
assembly. Care must be used to avoid the loss of
the ball. Remove ball by shaking after housing is
removed from the vise. Discard “O”ring (27).
This completes the disassembly of the HGA unit.

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
18
Inspection and Replacement
Visually inspect all parts and replace those parts
which are not in good condition. The following finished
surfaces should be inspected for abnormal wear,
scoring or damage.
1. Housing (25) bore and ends.
2. Valve spool (22) outside diameter. Some burnish-
ing due to use may be observed.
3. Valve spool (22) control edges.
4. Valve spool (22) splines.
5. Input shaft (16) seal area. Check for rust, pitting
and excessive wear. Light circumferential polishing
due to seal contact may be observed.
6. Input shaft (16) helical groove. Note the contact
pattern created by the actuator ball (23). Surface
should be free from pits chipping or surface break
down.
7. Thrust bearing (12) and thrust washers (11) and
(13). Inspect for pitting of rolls and faces of thrust
washers.
8. Drive link (30) pin slot. Width of slot must not
exceed .001 inch difference at any point in its
length.
9. Drive link (30) teeth.
10.Torsion bar and needle roller assembly (20).
Difference in diameter of needle roller (21) should
not exceed .001.
The following parts may show a polish pattern due to
the rotor action and the circular motion of the commu-
tator. The sides of these components are ground and
lapped and should be free from nicks, burrs and
scoring.
1. Spacer (29).
2. Manifold (32).
3. Rotor (31).
4. Commutator (34) and Commutator Ring (33).
Note: Thickness difference between commuta-
tor and commutator ring (33) shall not exceed
.002 inch.
5. End cover and pin assembly (38).
Note: The rotor set (31) requires special attention
in handling to avoid nicks and scratching. It is
recommended that the rotor (31B), stator (31A),
vanes (31D) and springs (31C) be checked in the
assembled condition. To inspect the rotor set,
place the assembly face down on the lapped face
of the end cover (38) and check for freedom of
rotor rotation within the stator. The action of the
spring loaded vanes may be observed during
rotation. The vanes should move freely in their
slots, without bind, due to the forces of the
springs. (See Figure HGA-15).
Using a feeler gage, check the rotor (31B) to the stator
(31A) clearance as shown in figure HGA-16. If there is
more than a .007 inch clearance, the rotor set (31)
must be replaced. Note: This applies to rotor sets
with and without vanes.
Carefully lift the rotor set assembly (31) from the end
cover (38) and measure the thickness of the rotor
(31B) and stator (31A). Thickness difference between
the rotor and stator shall not exceed .003 inch.
The internal splines in the rotor should not allow
abnormal wear or damage.
Figure HGA-15
Figure HGA-16

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
19
AssemblyProcedure
IMPORTANT; Before starting assembly, clean all
parts with clean petroleum base solvent and air
dry. Do not wipe dry with rags. Be sure all dried
paint chips have been removed from edges of
lapped surfaces. Unless otherwise indicated, DO
NOT oil parts before assembly.
1. Insert ball (26) into its cavity in the housing.
2. Install new “o”ring (27) on plug and roll-pin assem-
bly (28) and install in the housing (25) to 10-14 ft.
lbs. torque.
3. Reclamp housing (25) in the vise as shown in
Figure HGA-11.
4. Assemble thrust washer (13), thrust bearing (12),
thrust washer (11) and retaining ring (10) on input
shaft (16).
5. If the retaining spring (24) has been removed, install
a new retaining spring. The spring must fit tightly.
6. Insert actuator ball (23) into ball seat located
inside spool (22).
7. Assemble wave spring washer (14) over thrust
washer (13) and thrust bearing (12). Insert the
input shaft (16) into the spool, engaging the helix
and ball with a counter-clockwise motion. This
operation is best done while holding the spool in a
horizontal position.
8. Using the mid-section of the torsion bar (20) as a
gage, insert the gage between the spool end and
the thrust washer (13). (See Figure HGA-17). This
will position the spool in the necessary radial
relationship with the input shaft spline teeth for
assembly of drive ring (18).
9. Place the input shaft (16) and spool (22) assembly
in a vertical position, with the shaft end on the
table surface.
NOTE: Rotate the input shaft (16) out of the
valve spool (22) until input shaft will no longer
rotate. There will be a gap of approximately
.350 between end of valve spool (22) and thrust
washer (13) if the drive ring (18) is assembled
properly.
10.Insert the drive ring (18) into the spool (22) end by
visually aligning an internal space on the drive ring
with a tooth on the input shaft (16) split, and allow
the drive ring to drop to the limit of its travel. If the
drive ring does not engage the input shaft spline, a
slight rotation of the input shaft will allow the drive
ring to become fully engaged. Remove torsion bar
(20) gage. (See Figure HGA-18).
CAUTION: The HGA will not function properly if
the correct relationship of spool, drive ring and
input shaft is not achieved.
11.Install spacer (19) over torsion bar and pin
assembly (20) and insert the assembly into the
spool (22) end.
12.Align the cross-hole in the torsion bar (20) with the
cross-hole in the input shaft (16) and insert a .120
diameter pin punch to maintain alignment.
13.Insert the needle roller (17) into cross-hole in input
shaft (16); and while retracting the pin punch,
engage the pin in the torsion bar (20) cross-hole.
14.Initiate press of needle roller (17) into torsion bar
(20) with a few light impacts. Press needle roller
flush with outside diameter of input shaft (16) using
a 1/2”drive socket of 11/16 size for supporting the
input shaft. (See Figure HGA-19). With a few light
impacts on a .120 diameter pin punch, drive
needle roller (17) approximately 1/32 below the
input shaft (16) O.D. (See Figure HGA-12).
Figure HGA-17
Figure HGA-18

Bulletin 2751-001-M1/USA Service Manual
HGA Hydraguide™
Hydraulics
Parker Hannifin Corporation
Hydraulic Pump/Motor Division
Greeneville, Tennessee
20
AssemblyProcedure
15. Assemble spacer (15) over valve spool (22), against
spring washer (14). If so constructed, the inside lip end
of spacer must be toward the spring washer. Place
assembly, spool end first, into housing (25). Caution:
Avoid applying side forces to the spool which would
cause binding of the closely fitted assembly.
Note: If neither the input shaft (16) or upper cover (7)
are replaced, the original shims (9) may be reused.
However, if in the inspection of parts, damage is
found to the shims, discard these shims and replace
with new parts of equal thickness.
16a. Place shims on top of the thrust washer (11). Coat seal
(8) with clean grease and place in upper cover (7)
counterbore. Assemble upper cover onto input shaft (16)
and rotate to align punch marks previously made during
disassembly. Note: If a new upper cover is used no
angular orientation is required. However, it is
necessary to align the upper cover (7) and housing
(25). Replace with screws, finger tight, and then use a
pilot ring or a worm drive type hose clamp tightened
around the upper cover flange and the body pilot
diameter to achieve the required alignment. Now tighten
screws to 18-22 ft. lbs. torque. (See Figure HGA-20).
NOTE: If any of the input shaft (16), housing and
spool, torsion bar or upper cover (7) have been
replaced, the following procedure for checking and
shim adjustment must be used.
16b. Re-assemble as in “a”above using the required new
parts. After torquing the four screws (6) revolve unit in
vise so that the input shaft is pointing downward. In
order to determine that the unit is shimmed correctly,
the drive link (30) must be in its proper position. To do
this, grasp the input shaft (16), pull downward, and
prevent rotation. Engage drive link splines in spool (22)
and rotate to position spool essentially flush with end of
housing (25). Remove drive link and orient drive link
slot to engage torsion bar needle roller (21) and insert
drive link. Observe relationship of spool end to body.
The valve spool must protrude .020 ± .0025 from the
adjacent counterbore surface. If within spec. no
additional shimming required. If not within .0025, add or
remove shims (9) until this requirement is satisfied
repeating assembling steps as outlined in “a”above.
(See Figure HGA-21).
16c. The correct shimming must be checked on the vehicle
or on a suitable hydraulic test stand. The amount of
steering effort required to steer the vehicle when the
vehicle is at rest on dry pavement must be equal within
three inch pounds. For example: if twenty-one inch
pounds is required to steer to the right, not less than
eighteen or more than twenty-four inch pounds should
be required to steer to the left.
If a test stand is available to place a load between
cylinder ports in the same manner as on the vehicle, a
test stand should be used. Add shims to increase
steering efforts in a left turn, subtract shims to
increase steering effort in a right turn.
17. With the drive link (30) installed as described above,
assemble two assembly posts into the housing (25) as
shown in Figure HGA-22. These assembly posts can be
made by simply cutting the heads off of two bolts similar
to the special bolts (39).
Figure HGA-20
Figure HGA-19
Figure HGA-21