I have a 2005 Subaru Outback, 3.0 H6, LL Bean, 5 speed auto. 150,000 miles. No engine codes.
I bought it took two years privately. I didn’t notice during the test drive, but it has a shake/shudder at 18-20mph and at 55-60mph. Only at those speeds and only during acceleration. During light acceleration it isn’t noticeable, but hard acceleration particularly on a hill at 55-60 the car can shake quite violently. Probably 50% of the time the 18-20mph shudder doesn’t occur. It feels like the whole of the front of the car is shaking from side to side.
It doesn’t matter what gear it’s in - auto/auto sport/manual 1st, 2nd, 3rd, 4th, or 5th. So it’s not engine rpm related. I’ve had the transmission fluid flushed. I’ve had two sets of tires. I’ve had the prop shaft replaced. It still does it, and it hasn’t got better or worse. It happens both during straight line and turns.
The engine runs smooth and the gear shifts are crisp and smooth.
Our local dealer doesn’t know what it is (they suggested prop shaft) and our highly recommended local transmission shop doesn’t know what it is. All CV joints have been checked.
I think the big clue here is that it is very vehicle speed dependent; 18-20 and 55-60mph.
Could it be something to do with the transfer clutches? Does this transmission have an electronic control computer that needs an update? (This is a first year model). Is there vehicle speed sensor used by the transmission that could be bad but that wouldn’t trigger an engine code? Unfortunately I can’t disable the rear wheel drive like on the 4 speed transmissions, there is no fuse to do that.
Any ideas would be really helpful. Thanks.