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I have a 2001 Subaru Forester L with auto trans. I started hearing a really loud clunking noise (as the wheels turn) as I was driving near my house. I immediately took it back to my garage. The noise is very brutal, as in something is ready to break and break badly. The motor and everything jerks pretty bad with the noise while the wheels are rotating.

First inspection, it had a really bad busted inner CV joint on the passenger side front, which I noticed had lots of play. Replaced with a
new axle, but the problem is still there, no change at all. It really sounds like the noise is coming from inside the transmission, like the
front differential is ready to go??? It only makes the noise when running in gear while driving or with all wheels lifted off the ground.
It doesn't seem to make the noise / jerk when turning the wheels by hand. I took a rather large video (over 150MB) so I'll provide a link to the video below, any help would greatly be appreciated.

 

https://sendvid.com/om7qyxz4

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That is a horrible sound. I cringed hearing it...

Definitely sounds drive train related. Check the front diff fluid, the trans fluid, inspect all axles to make sure they're not broken. Check drive shaft for play (though it does sound like it's coming from the trans/front diff) always good to start with the basics. 

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Can't see the video right now. But description reminds me of when the bearings failed on the pinion shaft on one of my ea82 cars. When engine braking, the slop would allow the pinion to screw forwars.and hit the differential carrier. Bad noise and felt in the car, 1 or 2 per wheel revolution. When under load or acceleration, the pinion would screw back, away frim the differential carrier, and everything seemed normal. Got it home by feathering the gas pedal so it could never engine brake. On the way, the seals failed, and the atf when into the diff. The transmission just started to slip due to low fluid as I pulled it into the garage.

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Can't see the video right now. But description reminds me of when the bearings failed on the pinion shaft on one of my ea82 cars. When engine braking, the slop would allow the pinion to screw forwars.and hit the differential carrier. Bad noise and felt in the car, 1 or 2 per wheel revolution. When under load or acceleration, the pinion would screw back, away frim the differential carrier, and everything seemed normal. Got it home by feathering the gas pedal so it could never engine brake. On the way, the seals failed, and the atf when into the diff. The transmission just started to slip due to low fluid as I pulled it into the garage.

 

Without watching the video, I'm not sure if you'll get a full understanding of just how bad a sound this is... I've looked up every video I can find on cars with a bad axle, drive shaft, differential noises, etc. and all fail in comparison to this. I don't know how to explain it, other than say a cv axle broke in half and one half was still in the trans turning while driving knocking against the body... clunk, clunk (very loud) with each rotation.

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That is a horrible sound. I cringed hearing it...

Definitely sounds drive train related. Check the front diff fluid, the trans fluid, inspect all axles to make sure they're not broken. Check drive shaft for play (though it does sound like it's coming from the trans/front diff) always good to start with the basics. 

 

Yes, it's BAD! I checked all cv axles first, that's why I ended up replacing the front pass one. All others seemed to be fine, no excessive play, ripped boots, etc. I checked the drive shaft for play and it seemed to be ok from what I know. Trans fluid is at the right level, but I haven't drained it, the diff fluid or anything like that yet.

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I'm trying to go into as much detail as possible in explaining the noise and the tests that I've done. Sitting in my garage with all wheels on ground as you would drive it, idling or being revved in Park, no noise at all. Put car in any forward gear or reverse, go to move even a foot and clunk, clunk as it moves. Same as with the car on jackstands and all wheels off the ground. If you put it in gear and wheels start spinning, clunk clunk. That's how it's being tested in the video, on jackstands.

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Does it make the noise when you're powerbrake it? Like... Drive gear with foot on break and rev the rpms a little? Or ONLY when the wheels are turning. Also try reverse to see if a different angle load changes it.

Edited by golucky66

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Does it make the noise when you're powerbrake it? Like... Drive gear with foot on break and rev the rpms a little? Or ONLY when the wheels are turning. Also try reverse to see if a different angle load changes it.

 

It makes the exact same noise in any forward gear or reverse. When you apply the brakes to slow it down, the noise gets louder and more harsh as it slows down until the wheels stop moving. I haven't tried to power brake it.

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I can try to power brake it, but since the wheels aren't going to move I doubt it will do it. From all test I've done, it only does it when the wheels spin.

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Then it's probably in the front diff unfortunately, if it goes away when the wheels aren't turning. As some other posters said above.

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Noise gets worse when you brake?

It's not the brakes themselves, is it? Something loose? Flapping around?

Just a long shot...

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Noise gets worse when you brake?

It's not the brakes themselves, is it? Something loose? Flapping around?

Just a long shot...

 

Yeah, the problem is definitely not in the brakes, axles or even the driveshaft.I've finally ruled that stuff out by this point. I've got my $ set on buying a new (used) trans because it's definitely internal. I'm going to drain the front diff in the next few days and prepare for the carnage...

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Sounds like either the Ring gear is missing a tooth, or the spider pin has fallen out and is hitting the case in one spot as it goes around. Rev the hell out of it and it'll eventually puke chunks out the bottom of the diff case!

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