The Eaton CL450 is our “soft fourth” transmission, with the 28 percent step from fourth to fifth. The soft fourth allows the use of a two speed axle without the confusing swap shift in fourth and fifth speeds. The CL457 is the conventional short fourth 5-speed, for those that still prefer it. And the CL450 is a straight 5-speed with an 8 to 1 low and reverse ratio a real benefit when a steep grade must be negotiated.
Nomenclature-CL Stands for Clark. 1st number stands for nominal torque capacity (nom. 400/lb./ft.). 2nd number is number of forward speeds. 3rd number denotes specific gear set. Constant mesh in all gears, including low and reverse, is a CL450 feature as is helical gearing throughout, including low and reverse.
The Clark split-pin synchronizer is used in 2nd, 3rd 4th and 5th gears. Greater bearing capacity in the CL450 is achieved by the use of numerous needle roller bearings, and tapered roller bearings at main support locations. Shift forks have replaceable bronze inserts. The shift pattern is of the standard progression type with all shifts having the same throw at the lever.
THE CLARK SYNCHRONIZER AND HOW IT WORKS FOR YOU
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.