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2000 Forester that shakes at higher speeds

My 2000 Forester recently started shaking while driving at highway speeds or while under engine load (hills, accelerating, etc). My first thought was that it was a problem with the alignment so I took it to my local tire shop. The car has 164K on it and has been without a Subaru specific mechanic since my last guy got fired a year ago, though I am trying to get an appointment with the only other Subaru mechanic in the area, outside of the dealership.

The tire shop found an issue with cupped tires (naturally they’d want to sell me tires) and told me that my passenger side rear CV joint was bad and they’d have to replace the axle. Since this sounded credible for the symptoms it was showing and they found me an axle for under $100, I told them to go ahead and replace it.

When I got it back the first time, I didn’t see any great improvement in the shaking. I also noticed that they’d forgotten to put the bolt back into the bottom of my shock absorber. o_O When I brought it back to them, they fixed the missing bolt and agreed to keep it for a week to trouble shoot where else the shaking might be coming from. In the process, they replaced spark plugs and wires (which it probably needed anyway) and did an oil change, but the shaking is still there after all their tinkering. They suggested the problem may be in the timing and that I should have that checked out.

I don’t think they’re right about that. The vibration feels (to me) even more like a CV joint problem now than it did before. It shakes more violently and at slower speeds the longer it runs so by the time I get to work (40+ miles) it’s almost constant. It stops shaking when you pop it into nuetral and let it coast suggesting it’s not timing or alignment - and making me think even more that it’s something to do with the drive train.

I can’t even call for an appointment with a Subaru specific mechanic until next Wednesday, but I still have some questions. Should I take it back to the tire place and have them check if the axle they installed was bad or just wait to see what the Subaru folks tell me? Do if you think it’s safe for me to drive it until I can get it into the other shop?

Thanks in advance for your help.

Ariel

No vibration when coasting in neutral might get some good ideas cooking. Have you been careful about running 4 matching tires (matched for brand, size, and tread depth) over the life of the car?

A bad CV joint is possible - when you take the load off then it is not stressed and no vibration. You have several CV joints; basically every wheel has CV joints. Other issues could be transfer case, and differential wear that is now leading to the vibration under load. A bad drive shaft would continue to vibrate with our without load.

Your current shop is clueless, so you need to go elsewhere. A good test run should tell a good mechanic some useful info. Have them run in gear and in neutral as you have to see the difference. If the vibration is more in your hands, look at the front wheels. If you feel the vibration in the seat of your pants then look to the back wheels as more likely the problem.

Any significant curb strikes, or pothole hits? This could be a tire with tread separation and/or interior cords coming apart. Vibrations can take time to sort out since there are multiple causes.

Thanks for the prompt reply! LOL! Thanks for confirming my suspicions about the tire shop. I can’t call myself an expert but I really didn’t think much of their suggestion, especially after I saw they left a bolt out of my shock absorber!

Yes, all four tires are matched - same brand and model and the two in front were bought together (a week ago) and the two behind were bought together the last time I got tires. No significant strikes or potholes though the tire shop should have been (I hope!) able to spot tire issues.

It really does feel like CV joints, though I’m no expert, and it’s more of a ‘rear’ feeling than something I’m feeling through the wheel. Would I be able to isolate the rear differential by taking out the AWD fuse and forcing it to go FWD? Or would that have no effect?

Ariel

Taking that fuse out will disable the rear so it will run on FWD. It will eliminate the rear when active as being a problem but will not necessarily eliminate the rear half shafts as a problem.
Worth a try, I think.

That rear axle they got…was it like the one in the attached link? “Used, inspected for splits, cracks, and tears”? “Just like you’d exepct when you buy a New or Rebuilt one”?

http://www.a1partsdepot.com/2000-SUBARU-LEGACY-Axle-Shaft-Passenger-Side-P65074.aspx?bing

Um, I mean no disrespect, but I was so stunned by the price that I looked for an axle in the $100 range. You got a used…and NOT rebuilt…axle.

be sure to point this out when you see your new Subie mechanic.

Oh, and I should point out that everything in the drivetrain and all of the rolling stock can be checked on a lift except for the struts…and even that point is debatable. I don;t think you need to resort to disabling the AWD. Inner CV joints, outer CV joints, bearings, pinion play, even the wear patterns on the differential ring gears. It can all be checked.

Good catch, MB.
No point putting a used half shaft in for any price. You can get a nice rebuilt one for that price after you return the core.

Perhaps that is why the prices were so varied? The tire shop was calling around while I sat there and his prices for the part ranged from $100 to $200 - and he wasn’t sure why the discrepancy. That would definitely explain it. From your explanation, I am sure it was used, though I didn’t get a chance to see it before it was put in.

I did swap it to FWD and while there was a little improvement, you can still tell there’s something not right. I still won’t be able to even call for an appointment with the Subaru mechanic until next week - will it make things worse if I drive it in the meantime?