The AUSubaru.com.au Forums

My 2007 Forester developed a vibration in the front end after 3500 km. Subaru have told me that the vibration is caused by the front drive shaft being out of balance - apparently this is a common problem.
To fix the problem, Subaru replaced the front right hand drive shaft with an STI drive shaft. Subaru have also told me that despite that fact that the STI drive shaft is lighter than the standard drive shaft, it is not necessary to replace the front left drive shaft with an STI drive shaft.

I am concerned that the imbalance between the standard drive shaft on the left front and the STI dirve shaft on the right front will lead to more problems. Can anyone offer any advice? Should I insist that Subaru replace the left front drive shaft with an STI drive shaft as well?

Nah it wont be an issue unless the other one is playing up you wont have to replace it

Balance is the key issue, weight shouldn't matter too much. So long as the shaft is in and balanced there's no reason to be worried.

Technically the momentum of a lighter shaft would be smaller than a heavier one, but at such a small diameter it probably wouldn't affect the torque transfer from the box to wheel. I wouldn't worry.

I would still insist on them replacing the other side too, just for good measure.
If they admit that it is a common problem then I wouldn't accept having a driveshaft in the car that they have indirectly indicated will probably fail!