Merlo DBM 2000–3500 EV Rexroth Hydrostatic Transmission Service Manual [PDF] ENG

This PDF service manual provides detailed technical information for diagnosing and servicing the Rexroth hydrostatic transmission circuit used in selected Merlo DBM concrete mixers.

It is intended for qualified mechanics, service workshops and experienced technicians who understand mechanical, hydraulic and electrical systems. The manual covers workshop procedures that are not normally included in the standard operation and maintenance handbook.

The document combines hydraulic schematics, component layouts, pressure specifications and step-by-step testing instructions. It helps technicians identify the correct test points, understand oil flow through the system and determine whether faults originate in the pump, hydrostatic motor, valves, filters, speed-selection system or braking circuits.

The manual includes

• Complete Rexroth hydrostatic transmission circuit diagrams;
• Systems with fixed-displacement and variable-displacement hydrostatic motors;
• Identification of pumps, motors, valves, filters, actuators and pressure connections;
• Hydrostatic pump specifications and connection-point descriptions;
• Main, pilot and charge-pressure testing procedures;
• Standard pressure values at different engine speeds;
• Regulating-valve inspection and adjustment;
• Pressure-relief and pressure-cutting valve operation;
• Forward and reverse solenoid testing;
• Fixed and variable hydrostatic motor information;
• Variable motor displacement adjustment;
• Filter and thermocontact assemblies;
• Hydrostatic drive troubleshooting;
• Speed-selection and differential-lock circuits;
• Parking-brake and servo/brake circuits;
• Troubleshooting flowcharts for the drive and braking systems;
• Hydrostatic oil specifications;
• Required pressure gauges and diagnostic equipment;
• Metric tightening-torque tables;
• Information about thread-locking compounds, sealants and assembly lubricants.

Hydrostatic transmission circuits

The manual contains diagrams for both:

• Fixed-displacement hydrostatic motor systems;
• Variable-displacement hydrostatic motor systems.

The diagrams identify the hydrostatic oil tank, variable-delivery pump, heat exchanger, hydrostatic motor, cartridge filter, thermocontact, speed-selection actuators, control valves, parking-brake valve and brake caliper.

Hydrostatic pump testing and adjustment

A dedicated section covers the hydrostatic pump, part number 033112, including:

• Main ports and pressure-test connections;
• Mechanical and hydraulic zero settings;
• Pilot-pressure connections;
• Charge-pump circuit;
• Pressure-relief valves;
• Pressure-cutting valve;
• Forward and reverse control solenoids.

The manual explains where to connect pressure gauges and provides expected main, charge and pilot-pressure values at 900, 1600 and 2550 rpm. Test conditions and forward/reverse measurement points are also specified.

Valves and electrical controls

The service manual explains the operation and maintenance of:

• DA regulating valve;
• Va and Vb pilot-operated pressure-relief valves;
• Vs charge-pump pressure-relief valve;
• Vt pressure-cutting valve;
• Ea and Eb forward/reverse solenoids.

The forward and reverse solenoids can be tested using a 12 V DC supply, while the regulating and pressure valves include cleaning, inspection and adjustment instructions.

Hydrostatic motor settings

The variable hydrostatic motor section explains the main ports, pilot connections, drain connections and displacement-adjustment screws.

It also provides procedures for checking:

• Motor displacement-change pressure;
• Minimum and maximum motor displacement;
• Hydrostatic motor operating pressure;
• Propshaft rotational speed;
• Correct adjustment for naturally aspirated and turbocharged engines.

Speed selection and differential lock

The manual includes hydraulic information for the gearbox speed-selection and optional differential-lock systems. It identifies the speed-selection actuators, control valve, gearbox and oil supply from the hydrostatic pump.

Parking brake and servo/brake system

The final section covers:

• Parking-brake hydraulic circuit;
• Servo/brake circuit;
• Parking-brake control valve;
• Pressure switch;
• Parking-brake caliper;
• Brake-system oil supply;
• Troubleshooting procedures.

The troubleshooting flowcharts help identify problems such as a parking-brake warning light remaining on, insufficient charge pressure, a defective pressure switch or internal servo/brake leakage.

Oil and diagnostic equipment information

The manual specifies ESSO HVI 46, ISO viscosity grade 46 and DIN HLP 46 classification for the hydrostatic system. It also lists the recommended diagnostic equipment, including 600-bar and 40-bar pressure gauges, an rpm counter, thermometer and electrical tester.

Product information

Manufacturer: Merlo
Applicable models: DBM 2000 XS, DBM 2000 EV, DBM 2500 EV and DBM 3500 EV
System covered: Rexroth hydrostatic transmission
Document type: Workshop Service Manual
Manual reference: DBM-IDRO.01
Application: From SAV 741511 onwards
Language: English
Format: Digital PDF file
Number of pages: 39 pages

Important information before purchase

Please check your machine model, SAV number and hydrostatic system manufacturer before purchasing.

This is a specialised hydrostatic transmission service manual. It mainly covers the Rexroth hydrostatic drive, pressure testing, speed-selection system, differential lock and brake-related hydraulic circuits. It is not an operator’s handbook, spare parts catalogue or complete workshop manual for every machine system.

The procedures are intended for qualified technicians with suitable hydraulic pressure-testing equipment and appropriate workshop knowledge.