Anything to quiet a noisy Subaru front differential?

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4
Location
Staten Island, NY
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'05 Legacy 4EAT automatic with 114k miles. Car is new to me as of earlier this year and I noticed a slight whistle/howling noise from the front diff while cruising at 60mph. Goes away if I decelerate or accelerate. Only makes the noise in that "sweet spot" of maintaining constant speed on flat ground. Sometimes it's louder or quieter and I have yet to determine if temperature has anything to do with it. Fluid seemed to be in good, clean shape with nothing of concern on the magnetic drain plug. Just the usual black/gray sludge you'd usually find on any diff with some miles on it. Ring and pinion also look good verified with a borescope stuck down the dipstick hole and drain plug. No weird wear pattern or chipped teeth. Everything visually looks perfect. I'm guessing the pinion bearing is the problem here. Not a particularly easy thing to replace on these and I'm guessing I've got some time on it. It hasn't really worsened in the 3000 miles I've put on the car. I just want to quiet it down a bit. I refilled with a conventional 75w-90 but I'm wondering if there's something I can add that will help. I know bandaids are just bandaids. I'll get around to fixing it one day but that may not be for another year or two. The noise is a bit annoying on extended drives.
 
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6,667
Location
California
Subarus(and Audi quattro) are sensitive to tire differences - the quickest way to kill a Subaru is mismatched tires. All four tires should be the same brand/model/size and be within a 5-10% difference across the set for treadwear. Check to see if all the tires are the same brand/model and then work up to wheel bearings. The diffs/transfer unit in a non-turbo Forester/Impreza and Outback/Legacy isn't anything special - the front and rear diffs are standard open units and the center diff is a viscous unit.
 
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14,874
Location
NE,Ohio
Originally Posted by nthach
All four tires should be the same brand/model/size and be within a 5-10% difference across the set for treadwear. Check to see if all the tires are the same brand/model and then work up to wheel bearings. Tthe front and rear diffs are standard open units and the center diff is a viscous unit.
3/32 is the published spec for treadwear differences. Also your info is incorrect.. the center diff being a viscous unit is only true on some manual transmissions. automatics used a MPT clutch mostly.
 
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731
Location
North of you Idaho
Originally Posted by Rand
Originally Posted by nthach
All four tires should be the same brand/model/size and be within a 5-10% difference across the set for treadwear. Check to see if all the tires are the same brand/model and then work up to wheel bearings. Tthe front and rear diffs are standard open units and the center diff is a viscous unit.
3/32 is the published spec for treadwear differences. Also your info is incorrect.. the center diff being a viscous unit is only true on some manual transmissions. automatics used a MPT clutch mostly.
I believe the newer 3.6R's use a viscous unit, and they are fairly common now that they put the motor in two of their more popular vehicles. The viscous unit may have gone bye bye with the change to CVT! As for the tire spec, the data I have is roll out, but my tires are probably bigger than most. My data is for 255/55/18, 0.125 side to side is max acceptable difference total diameter, on the same axle, same brand tires all four corners. Front to rear 0.250 max, Larger diameter need to go in the front! "Subaru Tribeca" Also, does mention measuring tread depth but is vague and says straight up 1/8 inch under wear in any tread depth from the other tires is out of spec. 3/32's Put them in front if a pair match. I measure my tires closely every winter when I put my snows on, and its time to do that this week I believe!
 
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2,456
Location
NJ
If you've ruled out a bad wheel bearing, and a difference in tire diameter, I'd try some Amsoil Severe Gear 75W-110 or 75W-140.
 
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