10 things in your car you didn't know you could fix
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Changing Disc Brake Pads
Changing worn-out disc brake pads is a straightforward job. The best way to tell if they need replacing is a visual inspection. Some pads have a groove that serves as a wear indicator; if not, look through the caliper to see if the pad looks thin. Otherwise, some cars have a warning light to let you know if the pads are nearly worn down to the rivets, while others have brakes with a strip of metal that starts to squeal against the rotor when the pads are worn way down.
When it's time to change the pads, make sure you have jack stands, basic hand tools, and a C-clamp (to push the caliper piston into its cylinder) on hand. If badly worn pads have severely scored the rotor, this would also be the logical time to replace that; it slips off the hubs once the caliper and its bracket are removed.
Replacing the Alternator
In most cars, a warning light will tell you when the alternator is dying. If not, you'll know soon enough when your car stalls (from running off a depleted battery) or won't turn over when you try to start it. Novice mechanics can replace dead or dying alternators as long as the alternators are accessible from the top of the engine. (If they're down around the bottom of the block, they can be impossible to see and you have to work by feel to get them out and replace them; that takes experience.)
To do the job, you'll need wrenches, including a socket wrench. Some cars might also require a special tool to take the tension off the belt. And be sure to do things in the proper order. Unbolting the alternator before detensioning the belt could cause both of them to bind up so that you won't be able to budge either of them.