This is a huge job that no professional would attempt without a hoist. GM front-wheel-drive cars' drive trains are serviced by lowering the engine and transmission on the cross member. In many respects that makes the job much easier than on most other car brands, but there is one really major thing you must watch out for. Before the four cross member bolts are removed, they must be marked in some way, like spray paint, so it can be reinstalled in exactly the same orientation. Chrysler uses special bolts that are larger in diameter right under their heads to center the cross member. Ford usually welds their cross members in place. All three methods are fine, but it is only on GMs that the cross member can be inadvertently shifted to one side a little. That will result in "camber", one of the three basic alignment angles being unequal. An alignment technician can correct camber, but "steering axis inclination", (SAI), will also be unequal on both sides. That CAN be corrected on the alignment rack, but we rarely look at that unless we know we need to.
There is no spec given for SAI. A typical value might be 28 degrees. That is actually the angle, compared to true vertical, of the strut, as viewed from in front of the car. Shifting the cross member to one side will lower SAI on one side and raise it on the other side. Generally we want to see no more than 0.2 degrees difference side-to-side. When it gets over that, you will have the most miserable car to drive you can imagine. "Predictability" will be gone. At every tiny bump in the road, the car will dart in a different direction, and you'll never know which way it's going to go. Adjusting camber does not correct or change SAI. Correcting SAI will bring camber back to where it was. Camber has the biggest effect on tire wear and is the only one that is responsible for preventing a front-wheel-drive car from pulling to one side when you let go of the steering wheel.
To address your question, if you think replacing the transmission is something you want to tackle, start by getting a copy of the manufacturer's service manual and read through the many pages of instructions with line drawings. They will list any special tools required, and torque specs. I'm not sure how I would approach this with the car on the ground, but for sure, don't go near it until it is supported solidly on jack stands. Remember the center of gravity will shift when the cross member is unbolted.
A better alternative is to look for a nearby community college with an Automotive program. They will only take in cars that need what fits with what they're currently studying, so they wont work on your car in "Brakes" class, for example, and it could take a few weeks to get the car back, but if they feel it's a valid learning experience for a couple of the students, they will charge a lot less than any shop would. You would need to provide the transmission, and you'll be responsible for any problems with it. Those are responsibilities a shop takes on when they do the job.
You can also look for a "pick-your-own-parts" salvage yard. "Pull-A-Part" is a chain of very clean and well-organized yards I like to visit. The cars are already well-supported a few feet off the ground, but you have to figure out how to slowly lower the cross member with the engine and transmission on it. If you can do that, it is a dandy place to experiment and see if you want to try it on your car. You can do an internet search of the cities they're in and their current inventory. There are a lot of similar yards popping up all over the country.
Saturday, June 18th, 2016 AT 9:37 PM