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Mercedes Coupes/Sedans/Wagons 1974-1984 Repair Guide




See Figure 1

Click image to see an enlarged view

Fig. Fig. 1: Cross-sectional view of the Garret TA0301 turbocharger operation

There is no particular maintenance associated with the turbocharger. It should also be noted that a turbocharger cannot be installed on an engine that was not meant for one, without incurring serious engine damage.

The exhaust gas turbocharger is a Garret Model TA 0301. It uses the aerodynamic energy of the exhaust gases to drive a centrifugal compressor which in turn delivers high pressure air to the cylinders of the diesel engine. The turbine wheel and the compressor wheel are mounted on a common shaft. The turbocharger is mounted between the exhaust manifold and the exhaust pipe. For lubrication and cooling, the turbocharger is connected directly to the engine lubrication system.

A boost pressure control valve (wastegate valve) is attached to the turbine housing to insure that a certain boost pressure is not exceeded. Should the boost pressure control valve malfunction, an engine overload protection system will prevent a failure of the engine.

OPERATION Turbocharger

The exhaust gases of the engine are routed via the exhaust manifold directly into the turbine housing and to the turbine wheel. The velocity of the exhaust gases causes the turbine wheel to turn. This turns the compressor wheel which is directly connected to the turbine wheel via the shaft. The turbocharger can obtain a maximum of approximately 100,000 rpm; the fresh air drawn in by the compressor wheel is compressed and delivered to the pistons of the engine.

At idle speed, the engine operates as a naturally aspirated engine. With increasing load and engine rpm, (increasing velocity of the exhaust gases), the turbine wheel accelerates and boost pressure is produced by the compressor wheel. The boost pressure is routed via the intake manifold to the individual cylinders.

The exhaust gases produced by the combustion are routed into the turbine housing and from there into the exhaust pipe.

Boost Pressure Control Valve

In order not to exceed the designed boost pressure, a boost pressure control valve is installed on the turbine housing. The boost pressure is picked up at the compressor housing and connected to the boost pressure control valve via a connecting hose. If the maximum permissible boost pressure is obtained, the boost pressure control valve starts to open the bypass canal for the exhaust gas around the turbine wheel. A part of the exhaust gas flows now directly into the exhaust pipe. This keeps the boost pressure constant and prevents it from increasing beyond its designed limits.


  1. Remove the air filter.
  3. Disconnect the electrical cable from the temperature switch.
  5. Loosen the lower hose clamp on the air duct that connects the air filter with the compressor housing.
  7. Remove the vacuum line and crankcase breather pipe.
  9. Remove the air filter and air intake duct.
  11. Disconnect the oil line at the turbocharger.
  13. Remove the air filter mounting bracket.
  15. Disconnect the turbocharger at the exhaust flange.
  17. Disconnect and remove the pipe bracket on the automatic transmission.
  19. Push the exhaust pipe rearward.
  21. Remove the mounting bracket at the intermediate flange.
  23. Unbolt and remove the turbocharger.
  25. Remove the intermediate flange and oil return line at the turbocharger.

To install:
  1. Installation is the reverse of removal. Before installing the turbocharger, install the oil return line and intermediate flange. Install the flange gasket between the turbocharger and exhaust manifold with the reinforcing bead toward the exhaust manifold.

Use only heatproof nuts and bolts and fill a new turbocharger with 1 /4 pint of engine oil through the engine oil supply bore before operating.