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'04 Subaru Outback vibrates at 25-30mph during acceleration

This has been happening for the past 6 months or so. I recently had new ball joints, 4 wheel alignment, and 4 wheel balance. Even with this I’m noticing a very slight high frequency vibration at highway speeds. I noticed on one of the front wheels that a weight fell off, so this might explain the high speed vibration.

However - When I’m starting at 0mph, and accelerate to say 50mph for example, the car vibrates rather substantially as the speedometer moves from around 25mph to just past 30mph. After those speeds it goes away.

I’ve also noticed that it tends to be worse if I’m going up hill, which, according to the laws of physics, would tell me that going uphill would put more pressure on the front end, given it’s heavier with the engine there. If I’m going downhill it vibrates much less.

When I drive I tend to not accelerate quickly, meaning, I don’t ‘punch’ it, and accelerate gradually instead. If I’m driving on a level, well-paved road, and accelerate quicker than regular, the vibration seems to not be as heavy.

Can anyone recommend fixes and any other tests for this? Struts, control arm, steering knuckle, drive shaft ?

Thanks for reading


To see if the wheels have anything to do with the trouble I suggest you swap the front and rear wheels to see if that changes things at all. A simple thing to try and possibly at no expense if you do it yourself.

This is something I was wondering. Before I had the ball joints and tire alignment, I had been driving on these tires, so I was wondering if that threw off the wear on them - also before I did the alignment and ball joints, I did have the front and back tires swapped. Also the front tires are a couple months older(or younger) than the back.

Vibration only under power many times points to an inner CV joint failing.

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I was reading symptoms of worn out CV joints, of which vibrations were one of them. How can I test to see if the CV joints need replacement? Visual? Moving the CV axle? I’m not a mechanic, so pardon the question - but the inner and outer CV joints are parts of the axle, meaning I would need to replace the entire axle instead of the individual CV joint? Since I bought the car used and am not sure of the wear on both sides, whatever I replace on one side, I would replace on the other so I know the condition of each and they’re balanced.


Front wheels up on ramps, rear wheels chocked, emergency brake on, transmission in neutral. Check for sloppiness at all CV joints and fore-aft drive shaft universal joints. Repeat with rear wheels on the ramps.

Going up hill transfers weight from the front wheels to the rear wheels. So that puts more pressure on the rear, not the front. What physics text do you use?

I would think the angle of the road would put more pressure against the heavier section of the vehicle, and vice versa. Maybe it transfers to the rear of the vehicle at an extreme angle like 70 degrees. Imagine that road?

Mr. Photog016, your thinking is wrong .

A faulty locking-type torque converter (if automatic) can cause a similar symptom.

Does it say anything that the car vibrates more while going uphill versus downhill?

A friend who is a part-time mechanic will be looking at the CV axles soon, and I’ll also mention the torque converter.


The main problem was with the wheels(tires) as Cougar mentioned.

I bought the car used and the front and rear tires were at a much different state of wear - so now I’m at a cycle of replacing 2 tires at a time - Next time I’ll replace all four.
The front tires are a few months old while the rear(previous front) are nearly a year and nearly bald after many miles.

I swapped the newer front tires to the rear, had new tires put on the front, 4 tire balance, and now the vibration issue has mostly been alleviated. There is still very slight high frequency vibration at highway speeds and I’m wondering if the slight difference in tire wear is causing that. Of course the roads here in Rhode Island aren’t exactly pristine condition either!

Anyway, I’ll still have a friend check the state of the CV axles and other components of the suspension system.

Thank you all for the help, ideas, and time with this.


This will start an argument but I suggest you do an internet search as to why it is recommended to put two only new tires on the rear no matter if front or rear wheel drive.

Edit: When I wrote this I focused on the two new tires and slept through the part about being an all wheel drive vehicle. Get two more tires now.

Good for you OP for getting that stubborn vibration vamoosed!

On all-wheel drive cars it is very important that all 4 tires are the same, for wear and tread. When there is a mismatch it can damage the drive system over time. If you damage the drive system the price for 4 new tires will seem cheap compared to the repair cost of the drive system. Having matching tires may also clear up the rest of the vibration you are feeling.