It takes from two days to five days to rebuild and install a transmission, and it all depends on the parts that need to be replaced. If the mechanic needs to take out the engine to reach the hard parts and replace them, you'll likely be looking at five days or even more.u003cbru003eIf the problem can be solved by just changing the filters, bands, and bushings, you might be able to drive your car again with the rebuilt transmission in two or three days.