how do you tell if front rotors are bad. we just had ours replaced and I kept the old ones to inspect. They have some nicks in them I need to look at what the thickness should be. Goodyear graham tire told us they needed replaced.
Usually this is determined by measuring the thickness against the manufacturer’s recommended minimum limit. A brake shop might replace the rotors even if they meet the minimum, if it is close. Better to be safe than sorry with brakes. Or the shop may have determined the discs were glazed, and given the thickness, couldn’t be safely resurfaced.
If you have an automatic xmission, it wouldn’t be that surprising for a 2004 to need new rotors. Less likely with a manual. But it depends on driving habits and the type of driving, city vs urban.
You seem to have a certain amount of distrust of this shop. Yes? If so, maybe ask some friends, coworkers, etc for recommendations for a neighborhood independent mechanic. Someone who specializes in Chevy’s. They can do brakes and bearings just as well as a tire shop, and a good one might make you feel more comfortable with them doing the work.
Most chain auto parts stores will have a rotor micrometer and spec book to determine if there is sufficient thickness to machine them for reuse. I like to allow for .030" from minimum before machining to allow for that much material removal. If you have pitting (which is what I think you are referring to when you say there are nicks in them), the rotor thickness is a moot point unless you are okay with doing the whole job again in a few months. Pitting will continue to get worse and will eventually cause pulsation and very rapid pad wear.
Simple answer, if you press on the brakes and you feel a pulsing your rotors are probably bad. Rotors these days are very fragile and improper torque is a common reason for failure.