Retarder complete

A complete retarder or intarder provides wear-free braking through the drivetrain and reduces the load on the service brakes during long descents and frequent braking. In most heavy-duty applications, it is a hydrodynamic auxiliary brake: a rotor moves fluid against a stator, and the resulting heat is dissipated through a heat exchanger. A retarder is a separate unit that can be mounted in the drivetrain, for example behind the gearbox. An intarder works on the same hydrodynamic principle but is integrated into the gearbox. On a ZF gearbox, the intarder may be located at the rear while still forming part of the gearbox. Depending on the type, a complete unit includes the housing, rotor, stator, controls and seals, among other components. Before replacement, check whether the heat exchanger and connections are included in the supplied configuration.

Retarders and intarders are found on MAN TGS and TGX vehicles with suitable ZF Ecosplit, AS-Tronic or TraXon configurations, and on Mercedes Actros and Arocs vehicles with a compatible transmission configuration. Coaches such as the MAN Lion’s Coach and Mercedes Tourismo may also have a retarder or intarder. The engine family, such as MAN D26 or Mercedes OM 471, does not determine the retarder or intarder on its own: the transmission code, year of manufacture, mounting flange, gear ratio, cooling circuit and electronic control are also decisive. Parts must therefore always be identified using the vehicle’s chassis number. A visual comparison or selection based solely on the model name is never sufficient.

Examples of intarders include ZF Intarder versions fitted to suitable ZF Ecosplit, AS-Tronic and TraXon transmissions in MAN trucks and buses. Examples of separate retarder units include Voith retarders fitted to suitable MAN and Mercedes buses. Certain Mercedes Actros and Arocs versions also have a secondary water retarder. An integrated retarder may also be fitted to buses with ZF EcoLife or ZF Ecomat gearboxes and to suitable Allison 3000 or 4000 transmissions. A secondary water retarder may also be found in compatible Mercedes PowerShift 3 configurations. Examples of relevant Mercedes PowerShift 3 gearboxes are the G 230-12 and G 281-12; whether a retarder is fitted depends on the version. The version fitted depends on the transmission and vehicle configuration.

In MAN trucks and buses, the ZF Intarder is a hydrodynamic auxiliary brake integrated into the gearbox. It is found with certain ZF manual and automated gearboxes, including AS-Tronic and TraXon versions. The ZF Retarder R3500 / R4100 is a hydrodynamic auxiliary brake fitted as a separate unit in the drivetrain. These types are specified for certain MAN TipMatic versions, among others. Some MAN buses use Voith DIWA transmissions with an integrated retarder; the exact version depends on the bus model and transmission.

Mercedes trucks and buses may have a hydrodynamic oil retarder that uses oil as its working fluid to slow the drivetrain. It is found in several generations of Mercedes trucks. The Aquatarder SWR is a Voith water retarder that uses engine coolant as the braking medium and was offered on certain Mercedes Antos and Arocs versions, among others. The VIAB Turbo Retarder Clutch combines a fluid coupling with a retarder and is used, among other applications, in heavy-duty Mercedes Arocs SLT tractor units for controlled starting, manoeuvring and braking.

Some Mercedes bus models and transmissions may have a hydrodynamic retarder. The Secondary Water Retarder (SWR) is also used: an integrated water retarder that uses coolant as the braking medium.

It is also important to distinguish between systems that use transmission oil and versions with a separate fluid circuit. The fluid specification, filling procedure, connection dimensions and pressure range must match the documentation for the transmission in question. A retarder or intarder that fits mechanically is not necessarily electrically or thermally compatible.

Typical symptoms include insufficient braking torque, delayed engagement, jerky control, fluid leaks or rising transmission or coolant temperatures during prolonged braking. Causes range from worn shaft seals and contaminated control passages to insufficient cooling capacity, a faulty control valve or internal damage to the rotor and stator. An EBS (Electronic Braking System) warning does not, on its own, prove a mechanical fault: the braking system may also disable the retarder or intarder as a precaution.

Start by reading the fault codes and live data, including the requested and actual retarder or intarder operation, fluid temperature and any pressure signals. Then check for leaks, fluid level and fluid quality under the specified measurement conditions. Measure system pressure with a suitable pressure gauge at the specified test point and compare the reading at each control setting with the manufacturer’s specification. Verify temperature readings with an external contact thermometer and check how the temperature changes between the heat exchanger inlet and outlet. Finally, inspect the connectors, wiring and coolant flow before removing the unit.

A targeted repair may be sufficient for an external leak or a faulty sensor. Replacing the complete retarder or intarder is advisable if there is internal breakage, severe overheating, damaged housing mounting surfaces or metal particles in the fluid circuit. After removal, check the mounting surfaces, seal seats and axial play against the transmission specifications; a new unit will not compensate for a damaged gearbox connection. Flush a contaminated circuit, remedy the cause of any cooling problems and use the specified fluid and seals. Complete the installation by checking for fault codes and carrying out a test drive under controlled load. If you are unsure which version is fitted, technical support can help match the retarder or intarder to the correct transmission configuration.