Engines Engine Braking System, Optional Constant-Throttle Valves (MBE900 only) constant throttles are deactivated when the accelerator or clutch pedal is depressed. The ABS system, when active, also deactivates constant-throttle braking. Jacobs Engine Brake A Jacobs engine brake is a hydraulic-electric engine attachment that converts a diesel engine into an air compressor. This is done by changing engine exhaust valve operation. An engine brake is not a substitute for a service braking system, except in emergencies, be- cause it does not provide the precise control available from the service brakes.
To increase braking performance, the Mercedes-Benz MBE900 engine can be equipped with constant throttles in each combustion chamber. Small valves built into the cylinder head allow a small amount of compressed air to escape through the exhaust port during the combus- tion stroke. The constant-throttle valves are open during the entire time that the engine brake is activated. Al- though some braking ability is lost because the valves are constantly open, constant-throttle braking is quieter in operation than other types of engine brakes. The Jake Brake is controlled by a single, dash-mounted paddle switch with three positions: OFF, LO and HI.
Jacobs Engine Brake Operation When only the exhaust brake is installed, a two-position switch on the dash controls the engine braking system. The exhaust brake is only active when the engine speed is between 900 and 2,700 rpm. Depressing the accelerator or clutch pedal deactivates the exhaust brake. The ABS system, when active, also deactivates the exhaust brake. WARNING Don’t use the engine brake if road surfaces are slip- pery. Using the engine brake on wet, icy, or snow- covered roads could result in loss of vehicle con- trol, possibly causing personal injury and property damage.
When both the exhaust brake and the constant throttles are installed, a three-position switch on the dash con- trols the engine braking system. The exhaust brake can be used alone or together with constant-throttle valves for steep or long grades. Like the engine brake, the To engage the engine brake, the dash switch must be in the LO or HI position and both the clutch and throttle pedals must be fully released. To disengage the engine 4.27