Or is most of the issue going to be a function of choosing an MTL that fits the proper viscosity? I know some transmissions are going to feel more notchy with one lube over another, which to me says the fluid isn't allowing the brass synchro's to grab the gears cone, by which is going to cause gearmesh wear on the synchros & engagement teeth.
I don't think it is a matter of fluid being squeezed out as I stated in a previous post.
Sometimes you have to experiment with MTL fluids + , -5 cSt from the specified oil to find a smooth shift.
Quote:
...A modern gearbox is of the constant mesh type, in which all gears are always in mesh. The exception is the reverse idler gear which will be explained later. This constant mesh and the cut of the gears insure a rather quiet transmission. In any one gear, only one of these meshed pairs of gears is locked to the shaft on which it is mounted. The others are being allowed to rotate freely; thus greatly reducing the skill required to shift gears. Most modern cars are fitted with a synchronized gear box, although it is entirely possible to construct a constant mesh gearbox without synchromesh, as found in motorcycles for example.
Shifter Assembly: The gears resting on the top shaft, the input shaft, are locked onto that shaft and rotate at the same rpm as the engine. The bottom output shaft has synchronizers “splined” to this shaft, so they can move around as the gear ratio is changed. The gears on the output (bottom) shaft are allowed to rotate freely on the output shaft or on small roller or “needle” bearings, depending on the horsepower transmitted and the design. The output shaft will rotate at various rpms depending on gear selection. In first gear, for example, you want low output shaft rpm and high torque.
The shifter moves the associated linkage which connects to the shifter forks. The linkages position the shifter forks, and effectively “programs” the shifter forks in order to select the required gear ratio. I.E., for each shift lever position, the shifter forks are moved around to drive the splined synchronizers on the output shaft. The shifter forks have a bore so they can slide on the guide rods. There is a specified clearance between the shifter forks’ bore and the shifter fork guide rods. Lubricant effects: Too high a viscosity lubricant and the shifting will be hard and sluggish. More force will be required to go from one gear to another. Too thin an oil and the forks will wear, the clearances will increase, and the shifting will become sloppy and uncertain. The correct mix of base oil viscosities is needed here to insure good cold weather and hot weather shifting. Synthetics excel here because of their high viscosity index.
Synchronizer: The locking mechanism for any individual gear consists of a collar on the shaft which is able to slide sideways so that teeth or “dogs” on its inner surface bridge two circular rings with teeth on their outer circumference; one attached to the gear, one to the shaft. (One collar typically serves for two gears; sliding in one direction selects one transmission speed, in the other direction selects the other) In our illustration from above, the bottom or output shaft has splines that mate with the synchronizer “collar.” The synchronizer collar moves transversely on the splines, positioned by the shifter fork. When the rings are bridged by the collar, that particular gear is rotationally locked to the shaft and determines the output speed of the transmission. In a synchromesh gearbox, to correctly match the speed of the gear to that of the shaft as the gear is engaged, the collar initially applies a force to a cone-shaped brass clutch which is attached to the gear, which brings the speeds to match prior to the collar locking into place. The collar is prevented from bridging the locking rings when the speeds are mismatched by synchro rings also called blocker rings. Notice, before locking and speed synchronization, a lot of shearing takes place at the interfaces and for the reasons given above. Most synchronizer materials are of brass, but newer synchronizers can be made of strengthened graphite composites. Lubricant effects: A special Friction Modifier (FM) additive is incorporated into the base oil to allow just the right amount of friction before engagement. I.E., the FM gives rise to a specific coefficient of friction (COF) to allow engagement without “crunching.” Automatic Transmission Fluids (ATF) DO NOT have these specialized FM’s. Note, the specialized FM used in manual transmissions is NOT the same FM used in Limited Slip Differentials, nor is it the same FM used in Automatic Transmissions, nor is it the same FM used in engine oils. It is important to understand that there are different FM chemistries for different automotive applications!
http://auto.howstuffworks.com/transmission4.htm
