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Currently viewing: 1935 Chevrolet Repair Manual » Transmissions » Synchro-Mesh


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Synchro Mesh Transmission (Master Model Passenger Cars and 1/2 Ton Trucks) Construction

The synchro-mesh transmission is designed and built to meet the needs of present day traffi.; conditions; and in operation permits even the inexperienced driver to shift gears smoothly and noiselessly.
The synchro-mesh transmission, used in Chevrolet passenger cars and % ton trucks, has all the necessary fundamentals for successful synchromesh operation which have been used by various divisions of General Motors during the past few years. This transmission is the finest type built today. Millions of Chevrolet cars driven for many millions of miles have this same type of transmission and the owners of these cars and trucks have experienced no mechanical trouble with them.
Fig. 106— Sliding Clutch Sleeve and Synchronizing Drum
Second speed and high speed gears are of the silent gear type. The second speed gear is a constant mesh gear and is mounted to the rear of the spline shaft, next to the rear bearing, to insure greater rigidity for this gear. Between this second speed gear and the main drive gear is a sliding clutch
When the sleeve is moved towards either second or high speed gear, by means of the gear shift lever, and before the clutch sleeve teeth can sleeve, which is splined on the inside and outside and fits over the spline shaft. This sleeve permits engagement into either second or high speed gears.
The sliding clutch sleeve has three lugs at each end with cams at the corners of each lug which engage with corresponding cams on the synchronizing drum. See Fig. 106. The synchronizing drum consists of a steel stamping loosely splined to the spline shaft by means of three legs which include the synchro-mesh servo cams. This stamping sup-ports a bronze internal cone which engages with a corresponding external cone integral with the gear to be engaged.engage, the cams on the lugs of the sliding sleeve come into contact with the servo-cams on the drum legs, causing the drum cone to be pressed against the gear cone. The frictional grip between these two surfaces then compels either the faster or slower turning gear to assume the same speed as the mating gear, and when this is accomplished the frictional pressure is released. The clutch teeth can then fully engage with each other without clash.
In order to insure the cams of the sleeve making contact with the servo-cams on the synchronizing drum, a barrier, which is called a synchronizing spring, is placed between the sliding clutch sleeve and the drum. As the sliding clutch sleeve is moved toward the gear to be engaged, it first meets the pressure of the synchronizing spring. This causes the synchronizing drum to be squared up and pressed against the external cone on the gear, and this initial pressure causes the drum to rotate sufficiently to bring the servo-cams into positive alignment. After the servo-cams have made con-tact the synchronizing spring pressure is released so as not to interfere with the proper action of the synchronizing drum.
Fig. 107— Operation of SynchroMesh Transmission —No. 1
The sequence of events during gear engagement may be briefly summed up as follows :
1. Clutch sleeve moves by means of gear shift lever taking up end clearance. Fig. 107.

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