S-Chassis.com - Visualize your manual trans

Saw a couple questions that lead me to beleieve some do not have any visual idea whats going on in thier manual trans's. Curious if I can describe the some of the workings of a typical five speed in text, here goes:

The manual transmission has 3 rotating members that are in constant mesh.

The one connected to the engine is the input shaft.
The one connected to the drive-shaft is the output shaft.
The one that connects the input shaft to the output shaft is the countershaft.

If you turn a gear in mesh with another gear, you will see that the drive and driven gear turn in opposite directions. If you add an additional gear in mesh with the second gear, the first and third turn in the same direction. This is the basic idea behind the counter shaft.

Wen you move your stick in the cockpit your turning a linkage which consists of a rod with a 90 degree tab at the end, not that unlike an old skeleton key. As you move the shifter left and right, the tab rotates counter clockwise and clockwise about 5-10 degrees. When you press the shifter forward and backward, it moves the tab in and out.

In a five speed, there are 6 gears. 1 2 3 4 5 R. All the gears are paired up next to each other. 1 with 2, 3 with 4, and 5 with R. As such, 3 gear selectors are required to shift between 6 gears.

Each pair of gears has its own gear selector. A selector is a metal collar with longitudinal splines on the inside and one lateral grove on the outside. The grove on the outside is connected to a fork, shaped like a big "C" which is connected at a 90 degree angle to a rod. At the end of this rod is a small tab shaped like a small "U".

Your shifter rod, with its tab, sits in the channel created by the 3 gear selector rod's "U" shaped end-tabs. As you rotate the shifter knob left and right, your tab turns a few degrees clock or counter clock aligning with a different gear selector. When aligned, pressing forward or back pulls or pushes on the gear selector.

The gear selector sits on a hub which is splined to the input shaft. When the engine is running, it is turning the input shaft (unless the clutch is engaged). Since the input shaft is splined to the hub, the hub turns as well. Since the gear selector is in mesh with the hub it also turns.

The drive gears free-wheel on the input shaft, however they are in mesh with the counter shaft. In order to transfer power from the input shaft to the counter shaft, a gear must be locked by a selector with the hub. When you push the selector into first gear, for example, the gear selector begins to slide off the hub, across the synchro, and into the first gear.

The gear selector stops about 1/3rd the way across the first gear. The gear selector is still partiall resting in mesh with the hub it was on before it was moved. In this way the gear selector collar is locking the hub(which is splined to the input shaft) to the first gear(which is in mesh with the counter shaft).

The counter shaft has a gear at the end, which is in mesh with the output shaft at all times.

And so, power flows from the engine into the flywheel, through the friction disc, which is splined to the input shaft, into the first/second gear selector hub, which is in mesh with the first/second gear selector, which is in mesh with the first drive gear, which is in mesh with the first counter gear, which is on the same shaft as the fourth gear counter, which is in mesh with the output shaft.

Common problems translated:

Wont go into X gear:

Either the teeth on the synchro, which would ordinarily allow the selector to slide over it to ease mesh with the drive gear, are damaged....or

The X,Y gear selector rod is bent or mishapen.

Pops out of X gear:

As I explain above, the gear selector has longitudinal splines, but it als has 3-4 splines which are not part of the billet. They are seperate little peices held in place by the hub, are slightly different shaped then the other splines, and are spring loaded. When the selector passes over the syhcnro and the drive gear, these little tabs are allowed to pop out a little bit which basically locks the selector in place. When those springs break, missing, worn, or the tab itself gets worn or damaged, theres nothing to hold the selector in place, and torque will kick it back out of mesh.

Also cause by bent forks, when the rod is mishapen by user force, and pops back out after tension is relieved from the user.

JMB