I am currently in the auto business and I have been since the age 18. I think you will find that the most effective way to gain business besides Word Of Mouth, is to market directly to your clientel. In my experience the type of people that are going to need
someone like you to fix their car, are mid to lower income people who are driving and rely on their older vehicles which often need repair. Not those who drive newer cars and have a warranty....Right ? So try to determine the best way to get those types of people to "see your Ads." Try publications that the average Joe will always see...
Like your local pennysaver, or clipper magazine, you know, the free newspaper that gets delivered to everyones home. It
will be a minimal expense for you to put a small business card size ad in there, and that paper gets sent to everyone. And for those of you who think no-one reads it, you are probably one of the folks driving a newer car under warranty.
Also, try an A-Frame, a small fold up sign in front of your store, but remember it has to have something on it that will make people STOP! Something Like "FREE INSPECTIONS TODAY !" and then just upsell your people to a brake job or tranny flush to cover the cost of the sticker.
These are just some ideas, the bottom line is, MARKET YOURSELF TO THE PEOPLE WHO WILL MOST LIKELY BE HANDING YOU MONEY....after all, we are in this to make a buck right ?
GOOD LUCK, HOPE THIS HELPED