Eaton Clark 280V, 280VHD Transmission Service Manual

This manual has been prepared to provide the customer and the maintenance personnel with information and instructions on the maintenance and repair of the CLARK Transmission.

Eaton Clark 280V Transmission Service Manual
Extreme care has been exercised in the design, selection of materials and manufacturing of these units. The slight outlay in personal attention and cost required to provide regular and proper lubrication, inspection at stated intervals, and 
such adjustments as may be indicated will be reimbursed many times in low cost operation and trouble free service. In order to become familiar with the various parts of the transmission, its principle of operation, troubleshooting and adjustments, it is urged that the service person study the instructions in this manual carefully and use it as a reference when performing maintenance and repair operations.

Whenever repair or replacement of components parts is required, only Clark-approved parts as listed in the applicable parts manual should be used. Use of “will-fit” or non-approved parts may endanger proper operation and performance of the equipment. The Clark Equipment Company does not warrant repair or replacement parts, nor failures resulting from the use thereof, which are not supplied by or approved by the Clark Equipment Company.

Eaton Clark 280VHD Transmission Service Manual
The Clark split-pin synchronizer prevents the clashing of the gears and increase the speed of shifting. In a conventional transmission which does not have synchronizers the absence of gear clashing is dependent entirely on the skill of the truck driver. By double-clutching and split second timing of engine speeds with the gear shifting movement, a driver can synchronize the speeds of the engaging gears and thereby prevent the damage to gears by clashing when a fast shift. The splint-pin sychronzier performs the same function with or without the “double-clutching” operating even though the driver does not accurately time his gear shifting movements. It also mechanically prevents the driver from completing the shift to the point of gear engagement until the engaging gears have reached the same or synchronous speeds. This is known as the blocking action of the synchronizer and it is this action that makes the operation of shifting a transmission having synchronizers different from one which does not have synchronizers.

Upon shifting gears in these synchronized transmissions the first part of the gear shift lever movement brings the blockers into contact. The blockers momentarily prevent further movement of the shift lever and the pressure exerted by the driver to complete the movement, is transferred by the blockers to the synchronizer providing the force necessary to synchronize the gears being engaged. When the engaging gears have reached the same speed, the blockers automatically disengage, permitting the gear shift lever movement to be completed. Therefore, to properly shift a synchronized transmission a steady and continuous pressure must be applied by the driver to the shift lever until the shift is completed. Under normal conditions this action is instantaneous.

Sometimes difficulty is experienced in shifting a synchronizer when the vehicle is standing still. This is caused by the fact that the disengagement of the blockers requires relative rotation and with the vehicle at rest and with the engine clutch released, there may be at times, no relative rotation of the engaging gears. Under these conditions, the same continuous pressure should be applied to the shift lever and at the same time, the clutch should be engaged slightly. This will give sufficient rotation to unblock the synchronizer and allow the shift to be completed without difficulty.