I just bought a '98 Forester which has a vibration when under load. Mechanic said I have frozen u joints and the prop shaft has to be replaced ($1100) because they are non-serviceable. I really hate being told what can't be done and I'm a cheap-skate, so I did a little searching and came up with http://rockforddriveline.com/replacem.htm. These guys have a whole line of u joints for "non-serviceable" drive shafts. I ordered three u joints for $110 and will replace them and test drive it. If I don't update this topic, it means all went well. Otherwise I will warn of the pitfalls. I would love to hear if anyone else has attempted this and what their success was.

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I tried with a cheaper set of joints. The install went smooth, but there wasn't an good way to keep the new joint properly centered in the shaft. The inner circlips didn't touch the yoke when the bearing caps were pressed all the way against the joint.

As a result the shaft was out of balance, I got it in balance by lightly tapping each cap with a punch to slide the joint a little one way or the other to center it. It took a long time, and lots of test driving to make sure it was right. After it was done I had to re-stake the yokes. It only lasted a few weeks and started vibrating again. To have it professionally balanced and have the joint welded in the proper place would have been about $125 per joint.

An all new drive shaft can be bought for about $425.

They don't fail very often so used is a great option.

 

Rockford and others make replacement ujoints.  A driveline shop or machine shop can install them, call around and see if you can find a place to do it for a reasonable price.