Sounds like tire noise / air bubbles in axle oil

[01SubForest]

Thought we had some tire noise, a growl in the rear that gets louder with speed.

 

Had the tires check per the AWD system incases it was a wear issue putting the front and rear ratio out of whack. [i assume the front tires spin a bit faster]

 

Well the tires checked out, even swapped and rotated them all around and the noise stayed in the rear. Could be typical tire noise far as I know. Tires place didn't seem worried.

 

Did check the rear axle fluid on my own just to be safe, and it was a bit over full and the odd parts was it was just plum full of air bubbles. Like a frothy mix. Now this was not what you see when water get in oil, I know what that looks like. It was completely full of air bubbles, though very clean looking.

 

 

I wonder if I should just change it, doesn't hold a whole bunch but just regular 80/90???

 

Also wonder about does it need a POSI additive that have anti foaming agents in it???

[Fairtax4me]

Cavitation is pretty normal in the differential. Nothing to worry about as long as the fluid looks clean. Has it ever been changed though? The rear diff is under practically no load at all during normal driving so the fluid doesn't get hot and deteriorate. But if it's been in there for 100k miles, it should be changed just because it's old.

 

Growling with speed sounds like a wheel bearing.

 

Is this on an 01 Forester?

[nipper]

Bubbles are because it is overfilled, change the fluid and fill it to the proper level.

 

Foresters do have weak rear wheel bearings.

[idosubaru]

i would concentrate on the wheel bearings for now. have someone ride in the rear and try to diagnose if it sounds like it's from one side or the other. betting you find it's wheel bearing related. typical early forester issue.

[01SubForest]

http://www.ultimatesubaru.org/forum/showpost.php?p=979762&postcount=12

 

http://www.ultimatesubaru.org/forum/showpost.php?p=979943&postcount=16

[johnceggleston]

http://www.ultimatesubaru.org/forum/showpost.php?p=979762&postcount=12

 

http://www.ultimatesubaru.org/forum/showpost.php?p=979943&postcount=16

 

 

in the future i think you will get the same help if you just start one thread about your problem. those of us who are here every day are not going to pay more attention to the member with the most threads open. on the contrary, we might pay less attention. no offense intended, we're here to help.

 

now, if the noise didn't change when you put the fuse in, then it is probably not related to the drive train being powered. it could still be the rear diff, but the odds are low. it could be a wheel bearing and those odds are high, very very high compared to the diff.

 

if you have a mechanic's stethoscope use it to listen to each knuckle as you spin it with the wheel off the ground. if you do not have one, i got one for under 5$ at harbor freight, put your hand on the spring and spin the wheel. you may ''feel'' the noise with your hand.

 

i don't think you can over fill the rear diff, at least not through the fill plug. once it is full it will start to run out. so i would not worry about that being over filled or air bubbles in the oil.

 

check the bearings in the rear. if the left was done start on the right.

Edited December 18, 2010 by johnceggleston