Unless your credit status is absolutely A1 right now your going to struggle financing that sort of money, as bank just don't want to lend right now.
You should be allowed copies of the accounts. You need to have an accountant look at these and they can give realistic vaulation to the business (e.g. whether its worth the investment) and your likely returns on that money too.
Then you need a very good business plan as well. If you search them online using google you can find inspiration. I just did that, then fully researched everything and then wrote my own business plan that went down a storm. Don't just write crap though, as the bank will want you to explain many things in it, and if you don't understand what you've written you be looking silly. lol.
A good business plan, good accounts (which prove the business is solid and you can afford repayments of your loan), coupled with a bloody good credit rating should see you through.
Its by no means a guarantee though; and you'd be expected to have some experience in either management (to run the garage) or experience of the trade of the business to develop it further.
I'm sure there is a lot more to consider, but thats what comes to mind.
Good luck!