I have all kinds of issues with the rear end on my 1988 Volvo 245 and i don't think its the universal joint alone. Some times the drive shaft will bind and shudder. It does not happen in reverse. Along with that i have a constant wheering sound that changes if i take my foot off the gas. Its still there but not the same, lets say a different tone.

What i have done it checked the oil in the rear and its full and clean. Im losing hope here. If the rear is shot how much could it cost to fix it?

Have you gotten under the car and checked the driveshaft from tailshaft to rear-axle flange for looseness?

Then look & feel for sticking calipers.
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240s: 2 drivers and some parts cars

You say you don't think it's a U-joint alone...

Why?

Have you checked them? Specifically the rear-most one? It might feel tight, and still be bad/binding.

That's sure where I'd start.
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-Matt I ♥ my ♂

Binding and Whirring changes when you get off the gas.
I would first look to see if the Pinion Nut is tight.

With the Pinion nut lose: When driving forward and the cut of the Ring and Pinion, the pressure is inward. So the pinion is trying to get sucked in toward the Differential Ring Gear. That would cause whirring and an occasional bind.

Going backwards; the movement wants to push the pinion outward so you don't have the Pinion and Ring grindinging each other. The pinion is just pushed out to it's 'normal' position.

It's best to drop the rear of the driveshaft off the Rear flange to test this BUT You can grab the driveshaft all the way back by the rear axle and push it in toward the axle and then pull it toward the front of the car and see if there is back and forth movement on that rear flange. Chock the tires and take it out of gear to test this.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/

Are you certain it's the rear end? Unless run bone dry, those units are robust and tend to last forever with normal power.

In addition to a failing carrier bearing, you may also have a worn transmission tailshaft bearing, which can exhibit similar behavior.

Have you notice trans fluid under the car?

It could be your center bearing is going. Spray some wd-40 and sees is it makes a difference. It also possible that your pinion bearing in its death throws. If its about ready to go as you described, you will be able to detect some play in it. Just give it a good shake at the rear u-joint.

I solved this problem by changing my rear tires. My car rearend use to whine at between 35 - 60 mph, and it sounded like bearing.

I was using Goodyear tires. I am now running Yokohamas, and sound is gone.