2003 Legacy Outback vibration between 32 and 40MPH

[biggman100]

I have an '03 Outback wagon that all of a sudden developed a vibration, that seems like its from the rear, between 32 and 40MPH. Some background on this car. I bought it about a year ago with bad head gaskets, and then, while test driving it (i punched out the thermostat and drove it for about a week to see what else might be wrong with it), it blew the timing belt. I fixed all that, including new valves, gaskets, seals, timing belt, water pump, and then, after about 5300 miles, the bottom end started knocking, so, i went and got a used engine for it, installed that (in between the first and second engine though, the car sat roughly 4 months), and, all of a sudden the vibration started. It was never there before when i was driving it before the first engine completely went, and also wasnt there for the first 500 miles after i put this engine in, but, in the last 400 miles, it has slowly gotten worse. I have checked the rear diff, brakes, rear axles, rear driveshaft (the best i could anyway), tires (while checking all that, i found a broken rear sway bar link, but i doubt that is the cause), and everything else i could think of, and so far, dont see anything it could possibly be. I was thinking of putting the FWD fuse in to see if maybe its transmission related (the TC did slide out a small bit when i pulled the engine, but it went right back in), and, it was a quart low on transmission fluid, but only for maybe a day ( ever since i put the engine in, i have been very diligent about checking things), so, any idea on what i should possibly focus on that might be the cause?

[el_freddo]

Checked the rear wheel bearings? Ensure the handbrake is released to check for any unwanted bearing play with the wheel in their air.

If the handbrake is on this will hold the hub in tight and you won’t be physically strong enough to wiggle the wheel enough to overcome the hold of the handbrake. 

Cheers 

Bennie

[forester2002s]

Sounds to me like the rear drive-shaft, even though you've said that you have checked it.

They are difficult to check by hand, but can you get a crowbar on it  to see if it's loose?

[lmdew]

Does it change if you apply the brakes lightly?

Rotors could have rusted up a bit while sitting.

[biggman100]

Actually, it doesn't change whether accelerating, braking, or just driving steady, but, it has now also started doing it between 50 and 60 as well. I haven't been able to do much with it though, because it's currently around 7 degrees F out, and I don't have a garage anymore. It is starting to seem like it's the right rear that is doing it though.

[Numbchux]

Could be a few things. Usually a driveshaft or sticking caliper will be effected by throttle/brake use, but not always. If putting the FWD fuse in makes it go away, it's likely driveshaft or rear axle related. If it's a sticking caliper, spending some time at speed and then gently stopping will leave one brake VERY Hot (like, just hold your hand in front of the wheel, you'll feel it. Don't touch the rotor!)

Inspect all suspension bushings. Control arms, ball joints, tie rods and ends, steering rack bushings, etc. A combination of a slightly out of balance tire and a couple of old bushings, for example, can turn into a pretty good wobble.

[biggman100]

2 hours ago, Numbchux said:

Could be a few things. Usually a driveshaft or sticking caliper will be effected by throttle/brake use, but not always. If putting the FWD fuse in makes it go away, it's likely driveshaft or rear axle related. If it's a sticking caliper, spending some time at speed and then gently stopping will leave one brake VERY Hot (like, just hold your hand in front of the wheel, you'll feel it. Don't touch the rotor!)

Inspect all suspension bushings. Control arms, ball joints, tie rods and ends, steering rack bushings, etc. A combination of a slightly out of balance tire and a couple of old bushings, for example, can turn into a pretty good wobble.

I don't think it's brakes, because they are all new, and I made absolutely sure none of the pins, or any of the calipers were sticking. I typically drive between 80 and 140 miles a day, so I always make sure brakes are good. I'm starting to think it is either one of the rear cv axles, wheel bearing, or possibly the driveshaft. One thing I haven't tried though is to put the FWD fuse on, so, I will try that Wednesday when I drive it again. Ever since I bought this car, I have been over the suspension multiple times, because of my ultimate plan for it (my plan is to add a 3 inch lift and bigger wheels and tires for playing off road a bit), and, other than a broken rear left sway bar link, I haven't found any other issues there.