If you haven’t already removed or installed a transmission, there’s only one thing you need to know: it sucks. They’re big, dirty, and heavy, and they require a certain amount of precision to install. Here’s how to make the job slightly less painful.
DISCLAIMER: Don’t hurt yourself. If you hurt yourself, blame yourself.
The job of installing a transmission is daunting because they are awkwardly placed in the center of the underside of your car (we’ll get to FWD complications later). It’s also really heavy and it needs to be lifted up, then pushed forward to mate with the engine. Generally, the transmission needs to be aligned perfectly with the crankshaft in the engine to slip together. This is all very difficult when you’re on your back, lifting a 150 lb chunk of greasy metal a few feet into the air, with almost no room on the sides.
Professional shops generally have two things that you don’t: a lift and a transmission jack. A lift allows the installer to raise the car in the air, so that the mechanic doesn’t have to lay on the floor, in a puddle of transmission fluid. A transmission jack is a special jack for— wait for it— transmissions. It is specially adjustable to articulate the transmission into whatever yoga pose is required to get it to mate with the engine, all without the need for the mechanic to deadlift the weight of a college freshman. Another bonus of transmission jacks is that they let you lift an automatic transmission without damaging the pan on the underside.
Of course, you don’t have one of these. Nor do you have a lift. What do you have? You have a floorjack and an engine hoist. If you don’t have an engine hoist (or engine crane. Whatever.), you can rent one relatively cheaply. Generally, the cost to rent one for a weekend isn’t much less than the cost to buy, especially used. You can probably find both an engine hoist and a floor jack for less than $300, with a little Craigslist-Fu. You’ll also need a cheap ratchet strap.
So, armed with your tools, get the car on jack stands and move the hoist over the rear of the engine. Route the ratchet strap around the front of the transmission and up to the hoist arm. Support the rear of the transmission with your floor jack. You can now lift the transmission from both ends carefully and without the risk of a hernia.
There you go. You can lift your transmission carefully into place without fear of it crushing you.
Of course, you’re going to have to modify your method for a FWD transmission, as well as for however your car is set up. For what it’s worth, manual transmissions are usually lighter. In my case, I now have a perfectly functional, leak-free commuter car that won’t be a pain to drive in daily traffic.