1979/03/07 Caterpillar

Engine Mounted Exhaust Brake Systems Can Be Used To Extend Service Brake Life


3406 Truck Engines

Exhaust brake systems have been approved for use on Caterpillar 3406 Truck Engines. Either the "Jake Brake" Model C346, made by the Jacobs Manufacturing Company, or the exhaust restriction type, like the Williams Brake, can be used. None of these brake systems are sold or installed by Caterpillar, but are available from the manufacturers. Formerly, exhaust brake systems were not approved for use on any Caterpillar engines.

The Model C346 Jake Brake has all the parts needed for installation on current 3406 Engines. It operates on the exhaust valves to use engine compression as a brake. The unit is activated by a control switch. Other switches are connected to the accelerator and the clutch pedal to permit operation only when the accelerator is released and the clutch is engaged. The Jake Brake can be adapted to all 3406 Truck Engines, but on earlier engines new fuel injection lines must be installed inside the valve cover as follows:

For 3406 Engines before 92U20453 equipped with direct injection fuel system, turbocharger and aftercooler (DITA), install six new 9N5319 Fuel Injection Line Assemblies.

For all other 3406 Engines before 92U17820, install six new 7N8371 Fuel Injection Line Assemblies.

NOTE: Engines in some trucks have the turbocharger mounted in a low position. These engines will need a new turbocharger outlet pipe, which is not yet available. Information about this pipe will be published as soon as possible.

Exhaust restriction type brakes (like the Williams Brake) use a valve in the exhaust line between the turbocharger and muffler to increase exhaust back pressure. The back pressure causes brake action in the engine. The exhaust line valve is operated from the vehicle air system by a solenoid valve and a control switch. A switch on the fuel system permits operation only when the accelerator is released.

During installation and operation of the Williams Brake, or any other brake of the exhaust restriction type, some precautions must be taken to prevent engine damage.

1. Back pressure in the exhaust manifold must be limited to a maximum of 35 psi (240 kPa) by an orifice in the exhaust line valve, and the size of the orifice must not be variable. For a Williams Brake, the correct orifice is a .875" (22.23 mm) diameter hole. This orifice will give the correct back pressure, and permit a braking effect at the flywheel of approximately 180 HP (134.2 kW) at 2100 rpm.


A back pressure of more than 35 psi (240 kPa) can cause valve float, and high cost engine damage is possible.

2. The maximum permissible engine rpm during brake applications is 2400 rpm.
3. The maximum added weight hung from the turbocharger must not be more than 25 lbs (11 kg).

Exhaust brake systems make use of the engine for vehicle braking action. When correctly installed and carefully used, these systems can extend the service brake life and permit easier, safer operation.

Caterpillar Information System:

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