First, I've had all the tires balanced to get rid of the obvious and first possibility.

But the vibration still persists, in fact, it's probably gotten worse over the last couple of months. The car sat for about two years without running before I got it.

It seems like the vibration starts around 25mph and is at its worst between 40-50mph. And it is noticably worse when throttle is applied as opposed to coasting.
Most of the vibration at first seemed to be coming from the right rear, but now it's pretty much throughout the vehicle.

At first I was thinking rear wheel bearings, but now I'm not so sure. Since it increases under load is the driveshaft most likely the culprit? I'd like some help with the diagnosis so I can decide which parts to start replacing first!

Oh, and if it is the driveshaft, where's the best place to get a replacement (since 83 U joints aren't replaceable).

 

It sounds to me like a U joint. I had one go out on my car, and it would vibrate very similar to the way youre describing. As the U Joint got worse, the speeds at which the vibration was worse or better changed too, it was kinda weird. Anyway, check with MazdaTrix for a new driveline, I suggest if you buy a new one to just buy their aftermarket one with the replaceable U Joints. Its cheaper than the Mazda driveline anyway . If you dont have the dough to go new, hit upthe local junk yards. I just did that today with my Dad for his -SE.

~T.J.

 

ya, most likely a u-joint, also on another minor note, btw what model u have? lsd might be goin out too (like mine )

Snake Eyes<l><l>

 

It's an 83 GSL.