Basics To Basic

The art of shifting gears is being lost. Every year more and more drivers are opting to have their gears shifted for them rather than doing it themselves. In fact you can probably count the number of new 4x4 models available with manual transmission on two hands. That's a sad state of affairs.

Maybe the problem is that drivers just don't understand how a manual transmission works. Maybe they just haven't looked inside one to know what's going on under that stick with the numbers and the "R" on the top. It's time for a look inside these strong reliable units that allow you to creep along, slam gears, or pick and choose exactly what you want from your transmission.

We recently took a freshly refurbished NV-4500 five-speed manual transmission from National Drivetrain to our local transmission shop, Transaction, and tore it apart just to see what's inside. National Drivetrain sell parts for axles, transfer cases, and transmissions as well as complete new and rebuilt units ready for installation, and National will deliver straight to your door. Transaction has been building transmissions in its Sun Valley, California, shop for ages and can remove and service your current box or help you upgrade to something stronger.

A manual transmission has four attributes visible on the exterior: (A) the input shaft that splines into your clutch and takes rotational power from your engine; (B) the output shaft that splines into your transfer case and delivers rotational power rearward; (C) the shift tower (top plate) that houses the shift rails; and (D) the case. The case is where all the gears are carried. Some transmissions, such as this NV-4500, also have a tailhousing for additional gear space.

The bottom of the shift tower shows the shift rails and forks. The stick of the transmission enters the top and has a pivot point. As you move the stick from side to side it connects to different shift rails. As you move the stick forward and backward the selected shift rail slides back and forth. The shift rails have shift forks attached that drop down into the transmission and engage the different gears 

Inside the top of the transmission are many gears that ride on bearings on the mainshaft. When you are in Neutral, none of the gears are engaged to the main shaft, but gears are spinning on the main shaft from the corresponding gear on the countershaft. This is known as a constant mesh transmission.

Below the mainshaft are the countershaft and the reverse idler gear. The countershaft has the smaller of the gears for each gear engaged. For example, if the First gear ratio is 5.61:1 then the input shaft will turn 5.61 times for every rotation of the mainshaft when in First gear.