Cub Cadet BDU-10-21 User Manual
BDU-10/21
Hydrostatic Transmissions
Service and Repair Manual
BLN-50327
January 2009
BDU-10/21
Table of Contents
Table of Contents
Description Page
Introduction ......................................................................................................3
General Description.......................................................................................3-5
Fluids...............................................................................................................6
Safety Precautions ...........................................................................................6
Maintenance....................................................................................................6
Troubleshooting Diagram.................................................................................. 7
Troubleshooting Chart....................................................................................... 8
Minor Repairs ............................................................................................. 9-14
General Information......................................................................................9
Shaft Seals............................................................................................. 9-10
Charge Check V alves.............................................................................10-11
Bypass Valves ............................................................................................11
Easy Ride V alves ........................................................................................11
Charge Pumps ..................................................................................... 12-14
Major Repairs ........................................................................................... 14-21
General Information.................................................................................... 14
Disassembly Procedures....................................................................... 15-17
Reconditioning & Replacement of Components ............................................ 17
Assembly Procedures ........................................................................... 17-21
BDU-10S Parts Drawing & Parts List........................................................... 22-23
BDU-10L Parts Drawing & Parts List. .......................................................... 24-25
BDU-21L Parts Drawing & Parts List. .......................................................... 26-27
Page 2
BDU-10/21
Introduction/General Description
Introduction
BDU-10/21
The purpose of this manual is to provide information useful
in servicing the BDU Hydrostatic Transmission product
line. This manual includes unit and component description, troubleshooting, maintenance, and repair procedures.
A transmission normally will not require servicing, other
than the vehicle manufacturer’s recommended fluid and
filter changes during the life of the vehicle in which it is
installed. Should other servicing be required, the unit must
be removed from its installed location and thoroughly
cleaned before beginning most procedures.
General Description
The BDU Hydrostatic Transmission is designed for the
transfer and control of power. It provides an infinitely
variable speed range between zero and maximum in both
forward and reverse modes of operation. The BDU transmission can be mounted to a variety of transaxles including
most HYDRO-GEAR models.
The BDU transmission is a “U” style transmission with a
variable displacement pump and a fixed displacement
motor. The variable displacement pump features a cradle
swashplate with a direct-proportional displacement control. Reversing the direction of tilt of the swashplate
reverses the flow of oil from the pump and thus reverses the
direction of the motor output rotation. The fixed displacement motor uses a fixed swashplate. 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 fluid supply for the BDU-10L/21L transmission is
contained in an external reservoir and passes through an
external filter prior to entering the transmission and feeding
the fixed displacement gerotor charge pump. Excess fluid
in the charge circuit is discharged over the charge relief
valve back to the charge pump inlet. Constant flow across
a small fixed orifice connecting the charge circuit to the
transmission housing supplements the cooling flow.
BDU-10L Transmission
The BDU-10S transmission has a self-contained fluid
supply and an integral filter. The fluid is forced through the
filter by positive “head” on the fluid in the housing/reservoir
with an assist by the negative pressure created in the pump
pistons as they operate.
BDU-10/21
Charge check valves in the center section are used to
control the makeup flow of fluid to the low pressure side of
the loop.
A spool type bypass valve is utilized in the transmission to
permit moving the vehicle for short distances at low speeds
(2mph) (3.2 km/hr) without starting the engine.
Page 3
BDU-10/21
The BDU-21L transmission offers an optional Implement
(auxiliary) pump. The auxiliary circuit provides a rated flow
of 1.5 gpm (5.67 l/min) and 500 PSI (34.5 bar) operating
pressure at a 3200 RPM pump speed.
Fluid from the charge pump flows first to the implement
control valve, then to the charge relief valve and charge
check valves in the center section. This requires an “open
center” type control valve to allow fluid flow to return to the
transmission. A check valve is included to allow oil to be
drawn into the charge circuit should flow returning from the
implement circuit be insufficient to charge the closed loop.
A relief valve must be included in addition to the implement
control valve.
The BDU-21L offers an Easy Ride Valve option. The Easy
Ride Valve acts like a high pressure spike suppressor in
the system loop. The valve opens under high acceleration
loads. The result is a dampening of the aggressiveness,
without affecting the overall efficiency of the transmission.
General Description
BDU-21L Transmission with Easy Ride Valve
Option
BDU-10S Hydrostatic Flow Illustration
BDU-10/21Page 4
General Description
BDU-10/21
BDU-10L/21L Hydrostatic Flow Illustration
BDU-21L/A Hydrostatic Flow Illustration
BDU-10/21
Page 5
BDU-10/21
Maintenance
Fluids
The fluids used in HYDRO-GEAR products have been
carefully selected, and only equivalent, or better products
should be substituted.
Typically, an engine oil with a minimum rating of 9.0 cSt
(55 SUS) at 230°F (110°C) and an API classification of SJ/
CD is recommended. A 20W-50 engine oil has been
selected for use by the factory and is recommended for
normal operating temperatures. For colder climate operation (see chart), a change to a 10w-40 engine oil may be
necessary. Another alternative that will provide excellent
all climate performance and extended time between oil
changes is a 15W-50 synthetic engine oil.
SAE VISCOCITY GRADES
20W-50
10W-40
15W-50 Synthetic
-35
o -5o
AMBIENT AIR TEMPERATURE oF
15o 60
o
100
o
Maintenance
Check the transmission cooling fan for broken or distorted
blades, and check to see that the fan is securely fastened.
Replace the fan if damaged.
Keep the transmission clean. Grass clippings and dirt will
influence the cooling efficiency of the fins on the transmission housings. Avoid high pressure fluid washes, compressed air is the preferred method of removing loose
debris. Avoid the immediate area of the lip seals or damage
may occur.
Check to make sure the bypass valve and linkage is
operational. The bypass valve should be fully released
before operating the vehicle. It should extend approximately 0.22" (5.588mm) from the hex nut.
Inspect the transmission for leaks at the lip seals, damage
to fittings, hoses, the filter, or to the housings. Check the
oil level and add oil as necessary to bring it up to the proper
level. Refer to vehicle owners manual.
Safety Precautions
Certain procedures may require the vehicle to be disabled
(wheels raised off the ground, engine disconnected, etc.)
in order to prevent possible injury to the technician and
bystanders.
Some cleaning solvents are flammable. To avoid possible
fire, do not use cleaning solvents in an area where a source
of ignition may be present.
The loss of hydrostatic driveline power may result in the
loss of hydrostatic braking capacity. Proper brake maintenance becomes very important should this condition
develop.
BDU-10L
BDU-21L/A
BDU-10/21Page 6
Troubleshooting Diagram
OPERATES IN ONE DIRECTION ONLY
OPERATING HOT/LOSING POWER
BDU-10/21
BDU-10/21
NOISY UNDER LOAD
Page 7
BDU-10/21
Troubleshooting Chart
WARNING!!!
THE VEHICLE SHOULD BE ON LEVEL GROUND AND
THE ENGINE DISABLED BEFORE PERFORMING ANY ADJUSTMENTS
SYMPTOM - OPERATES IN ONE DIRECTION ONLY
POSSIBLE CAUSE CORRECTIVE ACTION
-Inspect control linkage -Repair or replace
-Inspect drive belt & pulleys -Repair or replace
-Inspect check valves -Repair or replace
-Inspect easy ride valves -Repair or replace
SYMPTOM - NOISY
POSSIBLE CAUSE CORRECTIVE ACTION
-Check oil level & condition -Fill to proper level or change oil
-Check for excessive loading -Reduce vehicle loading
-Check brake setting -Adjust brake to proper setting
-Check for loose parts -Repair or replace loose parts
-Check bypass valve operation -Repair or replace valve or linkage
-Check inlet flow conditions -Repair or remove obstruction or leaks
-Inspect check valves -Repair or replace
-Inspect easy ride valves -Repair or replace
-Inspect auxillary circuit -Repair or replace
SYMPTOM - LOW POWER
POSSIBLE CAUSE CORRECTIVE ACTION
-Check engine RPM -Adjust to correct setting
-Check drive belt & pulleys -Repair or replace
-Check oil level & condition -Fill to proper level or change oil
-Check for excessive loading -Reduce vehicle loading
-Check brake setting -Adjust brake to proper setting
-Check for loose parts -Repair or replace loose parts
-Check bypass valve operation -Repair or replace valve or linkage
-Check inlet flow conditions -Repair or remove obstruction or leaks
-Check operating temperature -Repair or replace unit
-Inspect check valves -Repair or replace
-Inspect easy ride valves -Repair or replace
-Inspect auxillary circuit -Repair or replace
SYMPTOM - OPERATING HOT
POSSIBLE CAUSE CORRECTIVE ACTION
-Check bypass valve operation -Repair or replace
-Check for debris buildup -Clean off debris
-Check oil level & condition -Fill to proper level or change oil
-Check for excessive loading -Reduce vehicle loading
-Check brake setting -Adjust brake to proper setting
-Check cooling fan for damage -Repair or replace
-Inspect check valves -Repair or replace
-Inspect easy ride valves -Repair or replace
-Inspect auxillary circuit -Repair or replace
Page 8
BDU-10/21
Minor Repair
Minor Repair
BDU-10/21
General Information
Minor repairs may be performed, following the procedures
in this section, without voiding the unit warranty.
Cleanliness is a primary means of assuring satisfactory life
on either new or repaired units. Cleaning parts by using
solvent wash and air drying is usually adequate. As with
any precision equipment, all parts must be kept free of
foreign materials and chemicals.
Protect all exposed sealing surfaces and open cavities
from damage and foreign material. The outer surfaces must
be cleaned before beginning any repairs.
It is recommended that all O-rings and seals be replaced.
Lightly lubricate all O-rings and seals with a clean petroleum jelly prior to assembly.
Plug/Fitting Torques
If any plugs were removed during servicing, they should be
torqued as indicated in the accompanying table:
Shaft Seals
Lip type seals are used on the pump input shaft, pump
through shaft (not all models use the through shaft), motor
output shaft and displacement control shaft. These seals
can be replaced without major disassembly of the unit.
However, replacement of the seals generally requires
removal of the transmission from the machine.
To replace the pump input shaft seal, first remove the
retaining ring from the housing.
Carefully pull the seal out of the housing bore. A “hook” type
tool may be used to grasp the seal and pull it out, or a slide
hammer type puller may be used to remove the seal. Care
must be taken so as not to damage the housing bore, shaft
sealing surface, or bearing. Once removed, the seal is not
reusable.
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Lip Seal Removal
BDU-10/21
Page 9
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