Hi! here’s to hoping someone has some advice for me…
I have only had my Forester since November, and it’s my first time with an AWD vehicle. I’ve noticed recently that when I accelerate, I can feel a shaking. Slow speeds it’s more of a minor easy rocking/wobbling/side-to-side shaking sensation, which immediately abates if I take my foot off the gas. When I have to push her harder, say, getting up to speed on the on-ramp for the interstate, it’s a much more pronounced shaking and vibration, and it is worrisome. again, as soon as I let it coast, it’s smooth. Press the gas, immediate vibration.
So. I called a mechanic, and he says it sounds like a broken axle. I take it in, and it’s NOT a broken axle, but he says I need a new wheel bearing on the left rear, AND that the right rear wheel is more oval or egg shaped rather than round, so that it needed to be replaced, and that may be causing the shaking. So, I call the tire place he suggested, they don’t carry my make tire, and recommend yet another place, so I take it there, and THEY tell me that the right rear tire/wheel is absolutely fine, but it’s my motor mounts that are bad. They also confirmed the wheel bearing on the back left, and quoted me $700 to fix the mounts and bearing.
My problem is that the first guy I took it to is supposed to be a local Subaru specialist, and came highly recommended (I’m new to the area). When he tells me one thing another place (a Big-O tire store) flatly denies is the case, whom do I trust?
Also, could the bad wheel bearing be causing everything, since that IS the one thing they both named as a needed repair? and how much should I expect to pay for that?
Sorry for the length! and thanks sooo much for any feedback.
Does the engine idle near glass smooth or is there any roughness? Just wondering if this could be an engine performance problem, which could be caused by any one of a number of things. Fuel flow due to a clogged filter, weak pump, etc. could cause this.
A worn front halfshaft (which can exist with no noise problems) or loose suspension component (most likely being a tie rod) could cause this type of vibration problem.
You should be aware that when it comes to tires on an AWD you should not mix and match them. At some point it may be best to install a full set.
Speaking as a long time Subaru tech I would be skeptical of the motor mount diagnosis. A mount can fail on anything at any time but motor mounts have never been an issue with Subarus; ever. As much as I try to jog my memory I can only remember replacing mounts on a Subaru one time and even that was due to extenuating circumstances not related to a quality issue.
Hope some of that helps.
As far as I can tell, it idles fairly smoothly. A little low (around 500rpm) when it’s warmed up, but smooth.
I have thought of the fuel filter, and since I’ve had the car have not had it looked at specifically, so that will be a priority (though I did have a mechanic just give her a once-over before I drove her across the country, and he said everything looked good).
The halfshaft… is that the same as an axle? and I’d have thought the Subaru mechanic I took it to a few days ago–who told me it wasn’t an axle-- would have looked at the suspension as well; But, I plan to call him tomorrow to let him know the other shop claimed it wasn’t the wheel, so I’ll ask him if he checked the other stuff.
I have been told that I should not replace just one new tire. So thank you for that confirmation!
So, I suppose first step is fix the wheel bearing? and see if that alleviates anything? What should I expect to pay for a wheel bearing job? One guy told me “around $400”. I looked it up on automd.com, and that site estimated $181.
I feel helpless. I am trying to educate myself, but when each person I go to tells me something different, I get the feeling they all just want a piece of the action, at my cost.
Next question: is there any chance it could have anything to do with the auto transmission? I have noticed (and I may just be being paranoid) that it seems to “surge” a little each time I feel it change gears. I mean, it changes, and doesn’t have any problem switching from park to reverse to drive or whatever, but it just feels slightly touchy.
sidenote: I just moved to the Colorado mountains after having grown up in the southeast, where we have a few hills, but no Rockies. Plus, I am experiencing AWD for the first time and honestly just don’t know what to expect. But when I go up these mountains on the interstate, it feels so weak and slows waaay down, and then it’ll kick into a lower gear and rev up to 4000rpm and sounds so loud! And there are other Subies that look just like mine racing around me… is that normal? Or do I just suck as a driver and not know how to handle it out here?
Again, so sorry for being long-winded, thanks for bearing with me!! Kudos to all of you who spare a bit of your day to help out those in need 
Cheers!
Don’t apologize for being long winded. At least you’re providing info about the problem, which is seldom the case on this board.
Yes, the halfshaft is same as the axle shaft. The problem with diagnosing those is that it’s commonly assumed, even by mechanics, that a shaft must be loose and click or even knock to be bad and that is not always the case. Sometimes they’re perfectly quiet, tight as can be, and yet they’re still bad due to odd wear patterns on the ball races.
One thing I would strongly suggest you do since you mention it’s an automatic transmission is check the final drive oil level. This is NOT the same as the automatic transmission fluid.
A binding ring gear due to low or no oil can cause a vibration or surge and eventually a catastrophic transmission failure. This is not a rare phenomenom on Subarus and is usually due to one of 2 things. Either an internal seal leak where the gear oil is lost into the ATF or the most common cause; someone draining the final drive by mistake while changing the engine oil. This should not happen with a bit of common sense but unfortunately it has happened many times.
The slightly rough idle could be minor or it could be major. If the car were mine the first thing I would do is connect a vacuum gauge to the intake manifold and see if there’s anything going on there that could point to a major problem such as low compression due to a tight cylinder head valve, etc.
A vacuum test is very simple to do and only takes a few minutes. The difficult part sometimes is finding a mechanic who will use this cheap and invaluable tool.
There is no set figure for a vacuum reading; it varies by altitude, barometric pressure, etc. but generally a rock steady 17" to 21" is what is looked for.
The wheel bearing could also be behind this problem and it’s difficult to say about the repair costs as it can vary so much by locale, where the parts are procured, etc. Four hundred sounds high for my neck of the woods but could be fair in San Francisco.
Main thing now though is check the final drive oil now! There should be a dipstick on the passenger side of the transmission. Down low and maybe hard to see but give that an inspection before risking a loud bang and destroyed transmission.
Hope some of that helps and always feel free to post here for advice. There are a lot of people willing to help although granted, it can be difficult at times to figure out a car problem over the net.