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How To Quiet A Noisy Front Diff???


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7 replies to this topic

#1 pearlm30

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Posted 24 March 2008 - 07:17 AM

The 98 Forester I just picked up came with a very noisy front differential. Check the dip stick and it looked like ATF:eek: . Dont know how long the previous owner run the car like that. Maybe a new trany would be needed in the future?
Drain all the ATF out and refill with 75w 90 and its still very noisy.
Any suggestion to quiet it down? Thicker and heavier weight? Lucas additives?:confused:
Thanks

#2 john in KY

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Posted 24 March 2008 - 08:53 AM

It's been my experience that once the noise starts, the clock is ticking. Justs gets worse over time.

#3 porcupine73

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Posted 24 March 2008 - 11:03 AM

Hi. Does it have an auto trans? If so, it sounds like the shaft seal that separates the front diff gear oil from the auto trans fluid may be bad, allowing the fluids to mix. ATF isn't good for the front diff because it does not have enough extreme pressure EP additives for the hypoid style diff. Gear oil is bad for the auto trans because the sulfur and such EP additives can corrode parts in the auto trans.

#4 Gloyale

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Posted 24 March 2008 - 12:55 PM

Hi. Does it have an auto trans? If so, it sounds like the shaft seal that separates the front diff gear oil from the auto trans fluid may be bad, allowing the fluids to mix. ATF isn't good for the front diff because it does not have enough extreme pressure EP additives for the hypoid style diff. Gear oil is bad for the auto trans because the sulfur and such EP additives can corrode parts in the auto trans.


This doen't really happen often on the 4eat. More common on the old 3spd.

The 4eat, the pump is between the diff and trans ections. The pump would have to start leaking.

Pearl, are you sure you checked the correct dipstick, on the passenger side?


I was able to quite a noisy diff in my Legacy by adjusting the diff bearing retainers 3 notches(turned left side *in*, right side *out*) to place the ring gear a hair closer to the pinion(.015 mm, or .006in. Every notch = .05mm, or .002 in.)

In this case, because it was a manual, I could feel the backlash was to large just by going off and on the throttle. There was alot of jerking and bucking going on-off-on throttle. Adjustment eliminated the noise and helped the bucking immensly.

But on an automatic, it's harder to tell if the noise is from being too *loose* or too *tight* Either can make noise

Just remember, the ring gear is to the drivers side(left) of the pinion.

So if you need to tighten it, run the left holder in a notch or 2, and the right holder out the same amount.

Loosening would be the opposite, left out, right in. alway by the same amount.

Unless you have a really good grasp of this and a mental picture of the insides, I wouldn't try it.

#5 pearlm30

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Posted 24 March 2008 - 07:46 PM

Thanks for all the suggestions. I think the auto trany diff. fluid was drained and filled with ATF, who know how long its been running like that bu previous owner.
Do I have to take apart the trany to gain acess to ajust the diff.? If so, I dont think I have the ability to do it.
The whine noise is really loud and still looking for a way to quiet it down
Any other advice?
Thanks again

#6 grossgary

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Posted 31 March 2008 - 08:31 AM

yes the trans has to come out and apart and it's a rather technical and complicated job to do it right. there are some complicated adjustments that need to be made.

the simple solution would be to adjust the retainers, they are located on the outside of the transmission. doesn't require anything more than disconnecting the axles from the transmission, if you even have to do that. but knowing how to adjust them properly is the tricky part if it's even possible. going the wrong way or too much will ensure the end of your trans.

#7 Turbone

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Posted 31 March 2008 - 10:13 AM

Drain the front diff (not the tranny) and use this in it.
http://forums.nasioc...tty's" cocktail

It cant hurt and it could help for a while. But once the whine starts, its only a matter of time. I would start looking for another tranny now, that way you will be ready.

#8 uniberp

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Posted 31 March 2008 - 04:49 PM

Drain the front diff (not the tranny) and use this in it.
http://forums.nasioc...tty's" cocktail

It cant hurt and it could help for a while. But once the whine starts, its only a matter of time. I would start looking for another tranny now, that way you will be ready.


It probably is an outside chance, but make sure the tires all match in diameter. I usually see worn out tires on the front on used Subes in car lots, and I know it makes a big difference in how the drivetrain sounds.




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