Let’s talk about transmission, baby. Not only is it a great Joy Division song, but it’s one of the most important components of a great restomod experience. If you’re upgrading your engine, you’ll need to have a transmission capable of handling the newfound power. Transmission can itself lead to increased power too, through the magic of gear ratios. In this article, we’ll go through the process of picking a new transmission and the upgrade itself, and will cover gear ratios in our next technical article.

When it comes to picking a new transmission, it can seem a little baffling. If you’re new to the technical side of cars, you’ll likely find it one of the densest and most confusing areas. Luckily, the first choice is fairly simple. Which type of gearbox do you want? There’s a few different types, but these are the four you’re most likely to encounter:

1. Manual: what it says on the tin. Driving stick may not be as common in the US as in Europe or Asia, but if you want the highest speeds and smoothest operation possible, you’ll need one of these. Simply put, if you’re driving a muscle car, you’ll probably want one of these. They also provide you with an extra level of relationship between car and operator, which cannot be underestimated.
2. Automatic: the old American faithful. Autos are the easiest way to drive, and not only that, they’re far from the sluggish setups they used to be. They still may not be as quick as a manual, but they’re good enough for everyday use, and are particularly useful in cruisers. Particularly good is the CVT, or Continuously Variable Transmission, that tends to provide a better ride quality than the older planetary autos.
3. Semi-automatics: you could write a whole article on semi-automatics, but they’re an excellent compromise. Set up with either flappy-paddles or a traditional shifter, they allow the driver to override the automatic transmission whenever they feel like it.

When you know what kind of transmission you want, you’ll need to acquire one. There’s a few avenues you can go down for this, all depending on what it is you’re looking for. If you want the ultimate in speed, many performance companies offer custom transmissions, you can source a classic example from a scrapyard or online (usually necessitating refurbishment), or you can order a modern transmission direct from a manufacturer. Your choice will ultimately depend on your budget. Unfortunately for our wallets, restomodding is not a cheap hobby, and a custom transmission can easily set you back over $2000. You’ll also need to make sure the transmission will fit the car, and purchase any additional parts you may need, such as a torque converter. These almost always come with pre-built transmissions, but if you’re getting a second-hand one, you could need to buy one separately.

Having found your perfect transmission, it’s time to fit it. This is no easy task, and not one to be attempted as your first foray into tinkering. That being said, once you know what you’re doing, you’ll be fine. Before we begin, something to bear in mind. If you’re upgrading an auto transmission, you’ll probably have to deal with a transmission cooler. These small heat exchangers keep transmission fluid cool, and when fitting your new transmission, should be cleaned thoroughly before being attached to the new one. Otherwise, debris and detritus from the old transmission can get in the new one, causing it to seize up. Manufacturers are keenly aware of this, and if they discover you didn’t clean the cooler before fitting your new setup, they won’t pay out. Cleaning one is easy, you just need to buy a cooler flush, which blast cleans the old cooler.

To install a new transmission, first, disconnect the positive battery cable, jack up your vehicle and secure it with jack stands. On vehicles with automatic transmissions, you’ll need to drain the transmission oil pan. This is located underneath your transmission. Many pans have plugs which you can remove to drain the oil, while some require the removal of bolts.

On a manual transmission, to drain the fluid, look for a recessed bolt on the base of the transmission, which will be the drain bolt. Loosen said bolt, and catch the fluid.

For the sake of brevity, from this point forward, we will assume you are installing a manual transmission, or a new automatic transmission with a converter already included.

Next up, you’ll need to disconnect a variety of components from the transmission. Remove the speedometer cable, cabling, vacuum lines, driveshaft, shift lever, and starter. There may be other components you’ll need to remove too, depending on the make and model of your transmission. Label the cables and other components that you’ll be reattaching later to avoid confusion.

Next up, get your transmission housing supported with a transmission jack. Remove the bolts holding the transmission to the engine and the crossmember. Disconnect the back drive rod from the bell crank, disconnect the clutch, and carefully remove the shift control assembly from your vehicle. Then remove the bolts holding the transmission to the bell housing and remove that too. If necessary, you can also remove the bell housing fairly easily at this point.

In theory, the hardest part is now done. You’ve done everything once, now things just need to be reversed. Lift the new transmission into the car and attach the main shaft.  Refit the back drive rod, clutch, shift lever, engine-to-transmission bolts, and cross member. Next up is the fun part, hope you labelled everything correctly! Reattach the driveshaft, wires, cabling, vacuum tubes, speedometer, etc.

All that’s left to do now is fill your new transmission with the correct fluid, according to its manufacturer, and give it the once over. Sit back, relax, and enjoy your smoother ride!