Car (and steering wheel) shake/vibration at highway speeds
My 2001 Vulcan is shaking at highway speeds. The steering wheel is shaking back and forth (left to right/right to left) at above 40mph, but especially at 60+mph. The vibration comes and goes - it's not constant, though is noticeably worse when it's hot out (I'm in San Antonio now, so that means on the afternoon drive home). The thing is, it's not constant, as I said. It's bad for a few seconds, then goes away, then comes back, then goes away, then comes back, and so on.
I just replaced my front tires. They were badly worn (especially on the inside portion of the tire). They had a lot of miles (more then they should have), so this is not unexpected. Before I replaced the tires this afternoon, it was noticeable at most speeds most of the time. Confusing, I know. Imagine how I feel. On the old tires it seemed like something was just out of round. Like the car was going up slightly, and then down slightly, rhythmically at parking lot speeds. This is not the case now. But the vibration/shimmy/wobble/whatever you wanna call it remains.
Originally I thought it was a lost weight on the right tire. It looked like one had come off at some point, but I couldn't be too sure, because I never really paid attention. I did have my car in recently to my trusty family mechanic (to chase down a wonderful electrical problem that was frying my coil packs rather quickly). He said "you REALLY need new tires" and that he noticed my car shakes at highway speeds, which he attributed to my old tires.
Like I said, I just replaced the front ones (the back right is next, but the back left is maybe at half tread and is going to have to wait until I'm out of school and actually have, you know, money). The tires were balanced, but I couldn't really tell on what type of machine. And I'll admit I'm not 100% confident they did the best job at it.
The strange thing is, it seems like the wobble/shake/vibration moved from one side of the car (the LEFT) to the other (the RIGHT). The same rims remain on the same sides of the car that they have since I've owned it (they did each tire separately due to a miscommunication - my spanish and their english wasn't on the same level, apparently, lol). Before the new tires, the car pulled slightly to the right. Now it pulls slightly to the left.
Now I'm curious what it could be. Should I get them rebalanced? Could it be the transmission/axle? I will say that it appears to be slightly more noticeable when the car is decelerating or coasting, and goes away a tiny bit under load, but this isn't always the case. It's one of those things that it seems like, but it's not always repeatable.
I know very little about suspensions, but I'm a quick learner, and lucky enough that I have the tools and the ingenuity to figure out how to fix/replace most anything on a car when I need to. Just need some help to point myself in the right direction so I can do down the list of things to check (and how to check them).
I will add this. The car is not making any sounds that I do not know where they're coming from. The P/S whines when turning when the levels get a little low (it's a new p/s so either there's a leak I need to track down, or I need to flush it properly this time), and the engine whines under load, but it's not a new whine (i.e. it's been doing that for years). I've tried turning the wheel as far right and left as it would go and accelerating and it didn't hop or grind or click. The rotors are new, but probably a little warped due to the fact that they're cheap and have been on a wobbling/shaking/vibrating front end for a few months (they're under warranty so in the next month or so I'm going to take them in and have them replaced switched out under warranty). Also, this weekend, if I have time, I'm going to move the front tires to the rear and see if that has any effect.
Any and all advice would be greatly appreciated!