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Summary of Contents for Danfoss LDU21C
- Page 1 Service Manual LDU21C Closed Circuit Axial Piston Transmission www.danfoss.com...
- Page 2 Service Manual LDU21C Closed Circuit Axial Piston Transmission Revision history Table of revisions Date Changed April 2025 Updated schematic 0102 May 2020 First edition 0101 © Danfoss | April 2025 AX342138485422en-000102...
- Page 3 Service Manual LDU21C Closed Circuit Axial Piston Transmission Contents Introduction Overview......................................5 Warranty......................................5 General Instructions..................................5 Remove the unit..................................5 Keep it clean....................................5 Lubricate moving parts................................5 Replace all O-rings and gaskets............................. 5 Secure the unit..................................... 5 Safety Precautions....................................6 Unintended machine movement............................6 Flammable cleaning solvents..............................
- Page 4 Service Manual LDU21C Closed Circuit Axial Piston Transmission Contents Required Tools and Standard Procedures Required Tools....................................22 Standard Procedures..................................22 Charge Check/HPRV Adjustments............................22 Checking for proper charge check/HPRV operation....................22 Minor Repair Shaft Seals......................................23 Removal......................................23 Inspection....................................23 Assembly......................................23 Charge Check/HPRV..................................24 Removal......................................24 Inspection....................................24...
- Page 5 LDU21C Closed Circuit Axial Piston Transmission Introduction Overview This manual includes information on the installation, maintenance, and minor repair of LDU21C pump. It includes a description of the unit and its individual components, troubleshooting information, and minor repair procedures. Performing minor repairs may require removal from the vehicle/machine. Thoroughly clean the unit before beginning maintenance or repair activities.
- Page 6 Service Manual LDU21C Closed Circuit Axial Piston Transmission Introduction Safety Precautions Always consider safety precautions before beginning a service procedure. Protect yourself and others from injury. Take the following general precautions whenever servicing a hydraulic system. Unintended machine movement Warning Unintended movement of the machine or mechanism may cause injury to the technician or bystanders.
- Page 7 Service Manual LDU21C Closed Circuit Axial Piston Transmission Introduction Symbols Used in Danfoss Literature WARNING may result in injury CAUTION may result in damage to product or property Non-reusable part, use a new part External hex head Internal hex head...
- Page 8 General Description Basic Design LDU21C is a kind of U-style HST hardware, including a closed circuit variable displacement piston pump with DDC (Direct displacement control) and a fixed motor. LDU21C is specially designed with optimized performance, size, and cost, in order to fulfill the demand of the mobile applications marketplace. This document provides the detailed specifications and features for LDU21C.
- Page 9 Service Manual LDU21C Closed Circuit Axial Piston Transmission General Description Schematic Diagram Customer should provide external charge circuit. P400548 *L1, L2, L3 and L4 are (Case) Drain ports. *E1 and E2 are Charge Inlet ports. © Danfoss | April 2025...
- Page 10 Check/High pressure relief valve with orifice As an option, LDU21C offers Check / HPRV with an orifice produce a larger neutral deadband. In some applications, it is desirable to use Check / HPRV with an orifice to expand null dead band, which would help provide a larger margin of safety for vehicle movement in neutral and provide easier adjustment of the vehicle linkage for machine neutral.
- Page 11 Control lever movement changes the speed and rotating direction of the motor by increasing or decreasing the swashplate angle. The swashplate control arm can be located on ether left or right hand side of the LDU21C. Control Handle Requirements Maximum allowable control arm torque is 35 N•m [309.8 lbf•in].
- Page 12 Service Manual LDU21C Closed Circuit Axial Piston Transmission Operation Left hand side viewing from input shaft (when pump located upside) Input shaft Output shaft P400611 Right hand side viewing from input shaft (when pump located upside) Input shaft Output shaft...
- Page 13 LDU21C Closed Circuit Axial Piston Transmission Operating Parameters Overview This section defines the operating parameters and limitations for LDU21C with regard to input speeds and pressures. For actual parameters, refer to Operating Parameters in the Technical Specifications section. Input Speed Minimum speed is the lowest input speed recommended during engine idle condition.
- Page 14 BC282717470618. Temperature Maintain fluid temperature within the limits shown in the Technical Specifications section of LDU21C Technical Information Manual BC282717470618. Minimum temperature relates to the physical properties of the component materials. Cold oil will not affect the durability of the pump components, however, it may affect the ability of the pump to provide flow and transmit power.
- Page 15 Service Manual LDU21C Closed Circuit Axial Piston Transmission Technical Specifications General Specifications Design U-style HST with variable displacement piston pump and fixed motor Direction of Rotation Clockwise Counterclockwise Recommended Installation Position Discretionary: The housing must be filled with hydraulic fluid...
- Page 16 Service Manual LDU21C Closed Circuit Axial Piston Transmission Technical Specifications Features Units LDU21C Cleanliness per ISO 4406 22/18/13 Efficiency (charge pressure filtration) β15-20=75(β10≥10) Filtration (recommended minimum) β-ratio Efficiency (suction and return line β15-20=75(β10≥10) filtration) Recommended inlet screen mesh size µm 100-125 ©...
- Page 17 Service Manual LDU21C Closed Circuit Axial Piston Transmission Fluid and Filter Maintenance Fluid and Filter Recommendations To ensure optimum life, perform regular maintenance of the fluid and filter. Contaminated fluid is the main cause of unit failure. Take care to maintain fluid cleanliness when servicing.
- Page 18 Service Manual LDU21C Closed Circuit Axial Piston Transmission Pressure Measurements Port Locations and Gauge Installation The following table and drawing show the port locations and gauge sizes needed. Port Information Port Identifier Port Size Wrench Size Pressure Obtained Gauge Size, bar [psi]...
- Page 19 LDU21C Closed Circuit Axial Piston Transmission Initial Startup Procedure Startup Procedure Always follow this procedure when starting up a new LDU21C installation or when the transmission has been removed. Warning This service procedure may require disabling a vehicle/machine (raising the wheels off the ground, or disconnecting the work function) to prevent injury to the technician and bystanders.
- Page 20 Service Manual LDU21C Closed Circuit Axial Piston Transmission Troubleshooting Overview This section provides general steps to follow if you observe undesirable system conditions. Follow the steps listed until you solve the problem. Some of the items are system specific. We reference the section in this manual of more information is available.
- Page 21 Service Manual LDU21C Closed Circuit Axial Piston Transmission Troubleshooting Item Description Action Shaft alignment Misaligned HST and prime mover shafts create noise. Align shafts. Charge check/HPRVs Unusual noise may indicate sticking valves. Possible Clean/replace valves and test the unit. contamination.
- Page 22 Service Manual LDU21C Closed Circuit Axial Piston Transmission Required Tools and Standard Procedures Required Tools The service procedures described in this manual can be performed using common mechanic's hand tools. Special tools, if required, are shown. When testing system pressure, calibrate pressure gauges frequently to ensure accuracy.
- Page 23 Service Manual LDU21C Closed Circuit Axial Piston Transmission Minor Repair Shaft Seals Removal 1. Using a snap ring pliers, remove retaining ring (F125). 2. Use a slide-hammer style puller to remove seal (F115, F210, H210). Be careful not to damage the shaft or seal bore when removing the seal.
- Page 24 Service Manual LDU21C Closed Circuit Axial Piston Transmission Minor Repair Charge Check/HPRV The high pressure relief and charge check valve assembly may be removed for cleaning and replacement of the O-rings. These valves are factory set and are not field adjustable. Refer to the transmission model code for the factory setting when ordering replacements.
- Page 25 Service Manual LDU21C Closed Circuit Axial Piston Transmission Torque Chart Plug Size and Torque Chart Item O-ring Plug Wrench Size Torque N•m [lbf•ft] MA1, MA2, MB1, MB2, 3/4-16 UNF 5/16 internal hex 39.2 [29] L1 ,L2, L4 Plugs (REVERSE SIDE)
- Page 26 Phone: +86 21 2080 6201 Danfoss can accept no responsibility for possible errors in catalogues, brochures and other printed material. Danfoss reserves the right to alter its products without notice. This also applies to products already on order provided that such alterations can be made without subsequent changes being necessary in specifications already agreed.
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