Hydro-Gear RT-310 Installation and operating manual

RT-310™
Service and Repair Manual
BLN-0078
February 2023

RT-310TM i
TABLE OF CONTENTS
SECTION PAGE
Tear down and reassembly.....................10-12
How to Use This Manual...................10
General Instructions..........................10
Tools..................................................11
Torques...............................................11
Removal............................................12
RT-310TM Tear Down and Assembly........13-25
Fan and Pulley Assembly..................13
Control Arm Assembly.......................14
Side Housing.....................................15
Motor Shaft........................................16
Motor Block Assembly and Thrust
Bearing..............................................17
Center Section..................................18
Pump Block.......................................19
Swash Plate and Thrust
Bearing..............................................20
Input Shaft.........................................21
Bypass Assembly..............................22
Assembly After Complete Tear
Down................................................23
RT-310TM Exploded View...................24
RT-310TM Parts List.............................25
Glossary of Terms......................................26
SECTION PAGE
Foreword.......................................................1
Description and Operation........................2-5
Introduction.........................................2
General Description ...........................2
External Features RT-310TM...................4
Technical Specifi cations......................5
Product Identifi cation...........................5
Safety.............................................................6
Personal Safety...................................6
Tool Safety...........................................6
Work Area Safety.................................6
Servicing Safety...................................6
Troubleshooting...........................................7
Service and Maintenance..........................8-9
External Maintenance.........................8
Service and Maintenance
Procedures..........................................8
Fluids...................................................8
Fluid Volume and Level.......................8
Purging Procedures............................9

RT-310TM 1
Headquartered in Sullivan, Illinois,
Hydro-Gear® is a world leader in the design,
manufacture, and service of quality hydrostatic
transaxles for the lawn and garden industry.
The mission of our company is to be recog-
nized by our customers and the industry as a
world-class supplier and the quality leader in
everything we do.
This Service and Repair Manual is designed
to provide information useful in servicing and
troubleshooting the Hydro-Gear® RT-310TM right
angle hydrostatic transmission.
Also included is a glossary of terms that are
frequently used throughout the industry and in
Hydro-Gear service publications. Understand-
ing terminology is very important!
It is necessary, and a good shop practice, that
your service area be equipped with the proper
tools and the mechanics be supplied the latest
information available. All repair procedures
illustrated in this guide are suggested, but pre-
ferred methods of repair.
Internal repair procedures require that the RT-
310TM right angle hydrostatic transmission be
removed from the vehicle.
This is not a certifi cation, test or study guide
for a certifi cation test. If a technician is inter-
ested in certifi cation, they should contact an
agent representing the EETC (Equipment and
Engine Training Council) at [phone] or
their Hydro-Gear® Central Service Distributor.
Many distributors will be hosting certifi cation
testing. These study guides will cover most of
the products and manufacturers in our industry.
For more information about Hydro-Gear® or our
products, please contact your Central Service
Distributor, or call our Customer Service Depart-
ment at [phone].
FOREWORD

2 RT-310TM
This transmission uses a variable displace-
ment pump with a maximum displacement
of 3cc per revolution, and motor with a fi xed
displacement of 10cc per revolution. The vari-
able displacement pump features a trunnion
mounted swashplate with a direct-proportional
displacement control. Reversing the direction
of the swashplate reverses the fl ow of oil from
the pump and thus reverses the direction of the
motor output rotation. The pump and motor are
of the axial piston design and utilize spherical
nosed pistons which are held against a thrust
race by internal compression springs.
The check valves in the center section are used
to control the makeup fl ow of the fl uid to the low
pressure side of the loop.
A hydraulic bypass is provided to allow the ve-
hicle to be moved without starting the engine.
The bypass lifts the check valves off their seat
allowing oil to freely fl ow. This permits moving
the vehicle for a short distance at a maximum
of 2 m.p.h. (3.2 Km/h) .
INTRODUCTION
The purpose of this manual is to provide infor-
mation useful in servicing the Hydro-Gear® RT-
310TM right angle hydrostatic transmission. This
manual includes general descriptions, hydraulic
schematics, technical specifi cations, servicing
and troubleshooting procedures.
The transmission normally will not require ser-
vicing during the life of the vehicle in which it
is installed. Should other servicing be required,
the exterior of the transmission will need to
be thoroughly cleaned before beginning most
procedures. Do not wash the transmission
while it is hot. It is best to not allow direct
spray from a pressure washer to clean the
transmission.
GENERAL DESCRIPTION
The RT-310TM is a self contained unit designed
for the transfer and control of power. It provides
an infi nitely variable speed range between zero
and maximum in both forward and reverse
modes of operation.
DESCRIPTION AND OPERATION

RT-310TM 3
Figure 1, Hydraulic Schematic
EXPANSION
TAN
K
SYSTEM CHECK
VALVES MOTOR
OUTPUT
SHAFT
PUMP INPUT
SHAFT
BYPASS
PUMP MOTOR

4 RT-310TM
EXTERNAL FEATURES RT-310TM
Figure 2, External Features
Motor Shaft
Control Arm
Motor Shaft
Bypass Arm
Case Drain / Fill Port
Input Shaft
Expansion Plate

RT-310TM 5
TECHNICAL SPECIFICATIONS
TECHNICAL SPECIFICATIONS
Overall Transmission Reduction 3:4:1
Input Speeds
Maximum Hi-Idle (No Load).....................rpm 3000
Output Torque
Continuous.......................................lb-ft[Nm]
Intermittent.......................................lb-ft[Nm]
5.8 [7.8]
10.0 [13.6]
Pump Displacement.................in3/rev [cc/rev] .18 [3.0]
Motor Displacement.................in3/rev [cc/rev] .62 [10.2]
Output Shaft Diameter.......................in [mm] .625 [15.8]
Output Shaft End Type Keyed
Weight of Unit............................................lb [kg] 9 [4]
Figure 3, Product Label
1610-1001
2 275 X1 4761
2D Q Code
Year Built
Date (Julian - Day of Year) Type of Product and Build Information
Serial Number (unique for that model - for that day
BOM Model Number
PRODUCT IDENTIFICATION
The model and confi guration of the RT-310TM can be determined from the label found on the
transaxle.

6 RT-310TM
SAFETY
This symbol points out important safety
instructions which, if not followed, could endan-
ger the personal safety and/or property of your-
self and others. Read and follow all instructions
in this manual before attempting maintenance
on your hydraulic motor. When you see this
symbol - HEED ITS WARNING.
WARNING
POTENTIAL FOR SERIOUS INJURY
Inattention to proper safety, operation, or
maintenance procedures could result in
personal injury, or damage to the equip-
ment. Before servicing or repairing the
hydraulic motor, fully read and under-
stand the safety precautions described
in this section.
PERSONAL SAFETY
Certain safety precautions must be observed
while servicing or repairing the hydraulic motor.
This section addresses some of these precau-
tions but must not be considered an all-inclusive
source on safety information. This section is
to be used in conjunction with all other safety
material which may apply, such as:
1. Other manuals pertaining to this machine.
2. Local and shop safety rules and codes.
3. Governmental safety laws and regula-
tions.
Be sure that you know and understand the
equipment and the hazards associated with it.
Do not place speed above safety.
Notify your supervisor whenever you feel there
is any hazard involving the equipment or the
performance of your job.
Never allow untrained or unauthorized person-
nel to service or repair the equipment.
Wear appropriate clothing. Loose or hanging
clothing or jewelry can be hazardous. Use the
appropriate safety equipment, such as eye
and hearing protection, and safety-toe and
slip-proof shoes.
Never use compressed air to clean debris from
yourself or your clothing.
TOOL SAFETY
Use the proper tools and equipment for the
task.
Inspect each tool before use and replace any
tool that may be damaged or defective.
WORK AREA SAFETY
Keep the work area neat and orderly. Be sure
it is well lit, that extra tools are put away, trash
and refuse are in the proper containers, and dirt
or debris have been removed from the working
areas of the machine.
The fl oor should be clean and dry, and all ex-
tension cords or similar trip hazards should be
removed.
SERVICING SAFETY
Certain procedures may require the vehicle to be
disabled in order to prevent possible injury to the
servicing technician and/or bystanders.
The loss of hydrostatic drive line power may result
in the loss of hydrostatic braking capability.
Some cleaning solvents are fl ammable. Use only
approved cleaning materials: Do not use explo-
sive or fl ammable liquids to clean the equipment.
To avoid possible fi re, do not use cleaning sol-
vents in an area where a source of ignition may
be present.
“Discard used cleaning material in the ap-
propriate containers according to local, state,
and federal regulations.”

RT-310TM 7
TROUBLESHOOTING
In many cases, problems with a hydraulic sys-
tems are not related to a defective hydraulic
unit, but are caused by slipping drive belts,
partially engaged bypass valves, and loose or
damaged control linkages. Be sure to perform
all operational checks and adjustments outlined
in Service and Maintenance, before assuming
the hydraulic system is malfunctioning. The
table below provides a troubleshooting check-
list to help determine the cause of operational
problems.
WARNING
Do not attempt any servicing or ad-
justments with the engine running.
Use extreme caution while inspecting
the drive belt assembly and all vehicle
linkage!
Follow all safety procedures outlined in
the vehicle owner’s manual.
TROUBLESHOOTING CHECKLIST
Possible Cause Corrective Action
Unit Operates In One Direction Only
Control linkage bent or out of adjustment Repair or replace linkage on vehicle pump assembly
Drive belt slipping or pulley damaged Repair or replace belt/pulley on vehicle pump assembly
Vehicle Does Not Drive/Track Straight
Vehicle tires improperly infl ated Refer to vehicle manufacturer suggested tire pressure
Control linkage bent or out of adjustment Repair or replace linkage on vehicle pump assembly
Drive belt slipping or pulley damaged Repair or replace belt/pulley on vehicle pump assembly
Brake Partially Engaged Disengage Brake, Replace damaged brake components
Unit Is Noisy
Oil level low or contaminated oil Fill to proper level or change oil
Excessive loading Reduce vehicle loading
Loose parts Repair or replace loose parts
Air trapped in hydraulic system Purge hydraulic system
Brake Partially Engaged Disengage Brake, Replace damaged brake components
Unit Has No/Low Power
Engine speed low Adjust to correct setting
Control linkage bent or out of adjustment Repair or replace linkage on vehicle pump assembly
Drive belt slipping or pulley damaged Repair or replace belt/pulley on vehicle pump assembly
Oil level low or contaminated oil Fill reservoir to proper level or change oil
Excessive loading Reduce vehicle loading
Air trapped in hydraulic system Purge hydraulic system
Brake Partially Engaged Disengage Brake, Replace damaged brake components
Unit Is Operating Hot
Debris buildup around transaxle Clean off debris
Oil level low or contaminated oil Fill to proper level or change oil
Excessive loading Reduce vehicle loading
Air trapped in hydraulic system Purge hydraulic system
Brake Partially Engaged Disengage Brake, Replace broken, missing or frozen return spring
Transaxle Leaks Oil
Damaged seals, housing, or gaskets Replace damaged components
Air trapped in hydraulic system Purge hydraulic system

8 RT-310TM
SAE 0W-40 has been approved for the RT-
310TM for all season applications where opera-
tion needs to occur in both winter and summer
seasons. SAE 20W50 has been approved for
non-winter applications where operation does
not occur in ambient temperatures below 40°
F. Biodegradable oils are not approved for
this unit as they degrade too quickly when in
service.
“All fl uids should be handled and disposed
of according to local, state, and federal
regulations.”
FLUID VOLUME AND LEVEL
The RT-310TM is factory fi lled with 540 ml (18.26
fl uid ounces).
When fi lling the unit with oil make sure the
RT-310TM is level with the bypass in the open
or neutral position. Fill the unit at the fi ll port
(fi ll port should be facing up). Once the unit is
completely full of oil wait one minute for the oil
to settle add more if necessary.
After adding oil to RT-310TM the always follow
the purging procedure located on page 9.
Note: “Any and all Hydro-Gear components
removed and replaced during service are
recyclable.”
SERVICE AND MAINTENANCE
NOTE: Any servicing dealer attempting
a warranty repair must have prior ap-
proval before conducting maintenance
of a Hydro-Gear® product unless the
servicing dealer is a current Authorized
Hydro-Gear Service Center.
EXTERNAL MAINTENANCE
Regular external maintenance of the RT-310TM
should include the following:
1. Check the vehicle operator’s manual for
the recommended load ratings. Insure
that the current application does not
exceed load rating.
2. Inspect the vehicle drive belt, idler pulley(s),
and idler spring(s). Insure that no belt slip-
page can occur. Slippage can cause low
input speed to the transmission.
3. Inspect the vehicle control linkage to the
directional control arm on the transmission.
Also insure that the control arm is securely
fastened to the trunnion arm of the transmis-
sion.
4. Inspect the bypass mechanism on the trans-
mission and the vehicle linkage to insure
that both actuate and release fully.
SERVICE AND MAINTENANCE
PROCEDURES
Some of the service procedures presented on
the following pages can be performed while the
transmission is mounted on the vehicle. Any
repair procedures as mentioned in the repair
section of this manual must be performed after
the unit has been removed from the vehicle.
The unit should be thoroughly cleaned before
any service procedures are performed.
FLUIDS
The fl uids used in Hydro-Gear® products have
been carefully selected, and only equivalent, or
better products should be substituted.

RT-310TM 9
SERVICE AND MAINTENANCE
PURGING PROCEDURES
Due to the eff ects air has on effi ciency in hy-
drostatic drive applications, it is critical that it is
purged from the system.
These purge procedures should be imple-
mented any time a hydrostatic system has
been opened to facilitate maintenance or any
additional oil has been added to the system.
Air creates ineffi ciency because its compres-
sion and expansion rate is higher than that of
the oil approved for use in hydrostatic drive
systems.
The resulting symptoms in hydrostatic systems
may be:
1. Noisy operation.
2. Lack of power or drive after short term op-
eration.
3. High operation temperature and excessive
expansion of oil.
Before starting, make sure the transmission is
at the proper oil level.
The following procedures should be performed
with the vehicle drive wheels off the ground,
then repeated under normal operating condi-
tions.
1. With the bypass valve open and the engine
running, slowly move the directional control
in both forward and reverse directions (5 or
6 times), as air is purged from the unit, the
oil level will drop.
2. With the bypass valve closed and the engine
running, slowly move the directional control
in both forward and reverse directions (5 to
6 times). Check the oil level, and add oil as
required after stopping the engine.
3. It may be necessary to repeat Steps 1 and
2 until all the air is completely purged from
the system. When the transmission moves
forward and reverse at normal speed purg-
ing is complete.

10 RT-310TM
TEAR DOWN AND REASSEMBLY
HOW TO USE THIS MANUAL
Each subassembly illustrated in this manual is
illustrated with an exploded view showing the
parts involved. The item reference numbers
in each illustration are for assembly instruc-
tions only. See page 25 for part names and
descriptions. A complete exploded view and
item list of the transmission is provided at the
end of the repair section.
GENERAL INSTRUCTIONS
Cleanliness is a primary means of assuring
satisfactory life on repaired units. Thoroughly
clean all exposed surfaces prior to any type
of maintenance. Cleaning of all parts by us-
ing a solvent wash and air drying is usually
adequate. As with any precision equipment,
all parts must be kept free of foreign material
and chemicals.
Protect all exposed sealing surfaces and open
cavities from damage and foreign material. The
external surfaces should be cleaned before
beginning any repairs. It is best to not allow
direct spray from a pressure washer to clean
the transmission.
Upon removal, it is recommended that all seals,
O-rings, and gaskets be replaced. During
installation lightly lubricate all seals, O-rings
and gaskets with a clean petroleum jelly prior
to assembly. Also protect the inner diameter of
seals during installation by covering the shaft
with a cellophane or plastic wrap material. Be
sure all remnants of this covering are removed
after servicing.
Parts requiring replacement must be replaced
from the appropriate kits identifi ed in the Items
Listing, found at the end of this manual. Use
only original Hydro-Gear replacement parts
found at www.hydro-gear.com or at your Hydro-
Gear Central Service Distributor.

RT-310TM 11
TOOLS
TORQUES
REQUIRED TOOLS
Miscellaneous Sockets
Three Jaw Puller 3/8” Deep
Flat Blade Screw Driver (2) 1/2” Deep
Torque Wrench 1/4” Allen
Air Impact Wrench T-25 Torx Head
Rubber or Neoprene Mallet T-20 Torx Head
Breaker Bar
Needle Nose Pliers
Large External Snap Ring Pliers
Small Internal Snap Ring Pliers
REQUIRED TORQUE VALUES
Item Description Torque Operation
67 Bolt 1/4-20 135-185 in-lbs (15.25-20.9 Nm) Fan/Pully
34 Screw, hex washer 1/4-20 105-155 in-lbs (11.86-17.51 Nm) Control Arm
7 Plug 110-150 in-lbs (12.42-19.94 Nm) Case Drain
56 Screw, M4 X 16 12-20 in-lbs (1.36-2.25 Nm) Bypass arm
23 Screw, HFHCS 5/16-18 230-290 in-lbs (25.98-32.76 Nm) Center Section Bolts
21 Check plug 320-400 in-lbs (31.64-45.19 Nm) Check Plug in Center Section
22 Check plug 320-400 in-lbs (31.64-45.19 Nm) Check Plug in Center Section
6 Bolt, self tapping 10-32 25-50 in-lbs (2.82-5.64 Nm) Expansion Plate
5 Screw, hex fl ange 1/4-20 85-115 in-lbs (9.60-12.99 Nm) Housing Screw

12 RT-310TM
REMOVAL
NOTE: It is necessary to remove the RT-310TM
from the vehicle before performing the
repair procedures presented in this
section.
Beforestartinganydisassembly,make
certain that your work area is neat and
clean. Clean the external parts of the
RT-310TM.
The following procedures are pre-
sented in the order recommended for
a complete tear down of the RT-310TM.
Do not disassemble the unit any farther than
necessary to accomplish the required repairs.
Reassembly is accomplished by performing
the “Assembly” portions of the procedures. If
the unit has been completely disassembled, a
summary of the assembly procedures, in the
order in which they should occur, is given on
page 23.
Figure 4, RT-310TM

RT-310TM 13
FAN AND PULLEY ASSEMBLY
Refer to Figure 5
1. Remove the bolt (67).
2. Remove the washer (66).
3. Remove the pulley and fan (65 & 64).
4. Remove the pulley hub (62). A hub puller
will be required for removal.
5. Remove the seal (61).
Inspection
1. Check all components for excessive wear
or damage. Replace if necessary.
Assembly
1. Reassemble all parts in the reverse order
of disassembly.
2. The seal (61) will need to be replaced with a
new seal from the seal kit.
3. When tightening the bolt (67), refer to the
table on page 11 for the required torque
values.
4. The pulley hub (62) will need to be replaced
if it is removed from the input shaft.
Figure 5, Fan & Pulley Assembly

14 RT-310TM
Figure 6, Control Arm Assembly
Refer to Figure 6
Disassembly
1. Remove all items previously discussed in
the recommended order.
2. Mark the orientation of the control arm (33)
before removal.
3. Remove the screw (34).
4. Remove the control arm (33).
5. Remove the seal (32).
NOTE: O-ring(31)islocated inside the control
arm (33)
Inspection
1. Inspect all parts for wear or damage. Re-
place as necessary.
Assembly
1. Reassemble all parts in the reverse order
of disassembly.
2. Install new seal (32) from seal kit.
3. When tightening the screw (34), refer to
the table on page 11 for the required torque
values.
CONTROL ARM ASSEMBLY

RT-310TM 15
SIDE HOUSING
Figure 7, Side Housing
Refer to Figure 7
Disassembly
1. Remove all items previously discussed in
the recommended order.
2. Remove the two screws on the expansion
plate (6) and the nine screws on the side
housing (5).
3. Remove the expansion plate (3).
4. Remove the bladder (4).
5. Remove the side housing (2) by gently pry-
ing the housings apart using a screw driver.
Inspection
1. Inspect the bladder for holes, tears or dam-
age. Replace if necessary.
Assembly
1. Reassemble all parts in the reverse order
of disassembly.
2. Apply a bead of sealant around the perim-
eter of the middle housing face.
NOTE: Remove all old sealant from the main
housing (1) and the side housing (2)
before applying new sealant.
3. Align the side housing (2) with the main
housing (1). Use care not to smear the seal-
ant bead.
4. Install the nine housing screws (5).
5. Install the bladder (4). Note the tab on the
bladder only allows for it to be installed in
one direction.
6. Upon reassembly, prior to oil fi ll, apply a
stripof Scotch® tape or similar to the holes
on the expansion plate. The tape is applied
to the outside and will be removed once as-
sembly is complete. Press the tape fi rmly to
achieve a good seal around the holes.
7. Install the expansion plate (3) and two screw
(6).
NOTE: When tightening the screws, refer to
the table on page 11 for the required
torque values.

16 RT-310TM
MOTOR SHAFT
Figure 8, Motor Shaft
Refer to Figure 8
Disassembly
1. Remove all items previously discussed in
the recommended order.
2. Remove the seal guard (49).
3. Remove the retaining ring (48).
4. Remove the seal (47) and washer (46).
5. Remove the motor shaft assembly (43).
Inspection
1. Inspect all items for wear and or damage.
Assembly
1. Reassemble all parts in the reverse order of
disassembly. The seal (47) will need to be
replaced with a new seal from the seal kit.

RT-310TM 17
MOTOR BLOCK ASSEMBLY AND THRUST BEARING
Figure 9, Motor Block and Thrust Bearing
Refer to Figure 9
Disassembly
1. Remove all items previously discussed in
the recommended order.
2. Remove the motor block assembly (24)
and thrust bearing (28). Slide a plastic putty
knife between thrust bearing and housing.
Compress the pistons to slide the block as-
sembly out.
Inspection
1. Check each piston for proper operation by
pressing the pistons in and releasing them
in the block bore. Disassemble the pump
cylinder block. Check for piston/block wear
in the cylinder bore. Inspect the pistons (27),
piston springs (25) and thrust washers (26)
for excessive wear or damage.
NOTE: Thrust washers (26) may be held in
place in the piston by residual oil.
Assembly
1. Reassemble the pistons, springs and wash-
ers into the cylinder block and set aside.
2. Reassemble the thrust bearing into the
housing (28).
3. Coat the pump running surface with clean
motor oil.
4. Using a plastic putty knife compress the pis-
tons of the motor block as it is reassembled.
NOTE: Care must be taken to prevent the
scaring or scratching of the center section
sealing face during this step.
5. Reassemble all parts in the reverse order
of disassembly.