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Silver: 2009 Subaru Outback Limited Edition, 2.5 Liter EJ25, Automatic. Gem: 2002 Subaru Outback LL Bean Edition, 3.0 liter EZ30D, Automatic
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Discussion Starter · #1 ·
Hello all. I apologize if this has been brought up before, but I have been searching for information on this subject and not finding anything specifically like this.

For awhile now my car has been having some intermittent clunking/ grinding sound coming from the rear tires area that comes on really only when I'm accelerating slowly up the mountain by my house. It can get to be pretty loud, like a knocking, but then fades away, usually as I pick up more speed. Driving up the mountain in heavy traffic with many stops and slow acceleration seems to trigger it more, but then sometimes this symptom doesn't come on at all. It also can come on when driving on the highway at higher speeds, but usually when going up a large hill or accelerating, and then it goes away after a bit. It did it softly one time in the driveway and I thought it was the exhaust vibrating and nothing more, but today it got weirder.

Today I had to take a fairly long ride with my husband and it started doing this a lot. It began when we went through a small town with an intersection where we had to slow down, but not stop. As we proceeded on the road, which was uphill, the rear knocking became really loud. At one point I applied the brakes and the knocking knocked loudly and I could feel it thump back through the brake pedal. My husband was freaking out thinking we were going to lose our brakes, but after that moment the brakes seemed to work normally for the rest of the trip, though I could feel/ hear some grinding still in the rear.

I'm thinking it could be a sticking brake caliper, but could they make the knocking sound? What else could cause these symptoms. Any advice appreciated. Thank you!
 

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could be something like a brake dust sheild making contact with a moving part when the suspension articulates,...and just needs to be bent by hand away. (this would sound like someone banging on a soup can with a drum stick).

could be something weak in the suspension or bushings etc.

could be something worse,...like if you insert the FWD fuse and it stops. (leaving you with a front wheel drive car for the time, but no noise / no problem).
 

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Discussion Starter · #3 ·
could be something like a brake dust sheild making contact with a moving part when the suspension articulates,...and just needs to be bent by hand away. (this would sound like someone banging on a soup can with a drum stick).
The sound is something like a rock tumbler. It actually sounds a lot like the grinding the transmission would do on an old Toyota Corolla wagon I had years ago, but in a completely different place. This comes from the rear and sounds like it has to do with the axles, tires turning, and motion back there. It's not so much metallic sounding but the sound when I applied the brake today was more like a rhythmic banging. I recently had my differential gear lube changed along with my transmission fluid and everything there seemed normal to those who worked on it, according to them. This rear end sound thing has not been improved by it.


could be something weak in the suspension or bushings etc.
It is possible. I've been having a lot of squeaks in the rear. I'm waiting for some rubber restorative to arrive to treat what I can get to.


could be something worse,...like if you insert the FWD fuse and it stops. (leaving you with a front wheel drive car for the time, but no noise / no problem).
Do you mean if I take the FWD fuse out and drive it with it out? I could try that.
 

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Do you mean if I take the FWD fuse out and drive it with it out? I could try that.
in this year on you particular car, it is put it in. (older ones like before 2000, it was pull it).

this is out of a 2003 book, yours don't have sport shift or VDC/ VTD.

 
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Discussion Starter · #5 ·
Thank you very much! I just found the same page in my manual (under temporary spare tire) and it says the same.
Do you know what size fuse these cars take for that? I don't think I have any spares laying around.

I still wonder if the brake calipers could be causing all of this. It does seem like something is sticking or hitting.
 

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Thank you very much! I just found the same page in my manual (under temporary spare tire) and it says the same.
Do you know what size fuse these cars take for that? I don't think I have any spares laying around.

I still wonder if the brake calipers could be causing all of this. It does seem like something is sticking or hitting.
its possible, but I would think the calipers would make noise regardless of the angle of the car. (the tell on that, more noise when hitting the brake and some sticking when letting off).

however, other possibilities are stronger:

the dust shield flexes a bit when the suspension articulates, (had on banging on my own wagon a while back).

______

plenty of bushings etc. and things get worn, might be easy to see on a lift, if things like that are not fixed what you get is tire wear or something else breaking.
___

and the AWD system sends more power to the rear when going up hill.

____

I would have hoped in the period that the dealer had your car they would have inspected it, looking for obvious issues, and or were listening actively for them during test drives.
 

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Discussion Starter · #7 ·
its possible, but I would think the calipers would make noise regardless of the angle of the car. (the tell on that, more noise when hitting the brake and some sticking when letting off).
It definitely did that today. It was the first time I felt it in the brakes and had the noise happen while braking. It usually does it on an incline when I've braked or slowed down and am moving forward again.

and the AWD system sends more power to the rear when going up hill.
Yes, this definitely seems to happen when the power is in the rear.

I want to try driving it in 2 wheel drive like you said, and see if I can still hear it. Is it okay to keep it like that for a few days? Does using the 4wd override cause any other wear and tear? The manual only talks about using it very short term.


I would have hoped in the period that the dealer had your car they would have inspected it, looking for obvious issues, and or were listening actively for them during test drives.
Right! RIIGHT!! You would think! I mean, I'm rather disgusted that a lower radiator hose wore out just WEEKS after the engine work. I mean, couldn't they say, hey your radiator hose looks bad, mind if we change it? I certainly would have gone for that and gladly paid what little extra it cost. They brag about their "all points inspection with every service" but I never got that. Seen other customers getting the little check sheet but I guess that's only for the new cars. I even had them rotate the tires so they should have been able to see the brakes or might notice an axle with too much play in it, but nope, not a word was said about anything. Anyway, excuse my rant.

I will try to figure out what I can about this. Thank you for your help.
 

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Yes, this definitely seems to happen when the power is in the rear.

I want to try driving it in 2 wheel drive like you said, and see if I can still here it. Is it okay to keep it like that for a few days? Does using the 4wd override cause any other wear and tear? The manual only talks about using it very short term.


.

it saves no gas. I don't think it does any real harm over a few days, the fuse is there to stop torque bind from using the temp spare or a odd mismatched tire as a spare

,...and I am sure people looking for higher gas milage have tried it for a long long long long time, and may have done something wrong through sheer neglect of what are parts that are made to be connected and turn. although its just a heavy car that wants its AWD and shutting it off does not help that,...vs. part time AWD / 4wd vehicles,...(somewhere here there is discussion of people doing this,...I guess something positive out of a beater car on the road missing some of its parts)..

so what you get, a heavy front drive car., that may not drive or handle as well as it does with all 4 wheels getting power as you are use to.
 
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I would suspect the rear diff mounts. They tend to break and then the diff moves around when you accelerate. I would also inspect the trailing arm bushings.
 

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I would suspect the rear diff mounts. They tend to break and then the diff moves around when you accelerate. I would also inspect the trailing arm bushings.
Agreed.

As well as the drive shaft u-joints and carrier bushing.
 

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Drive shaft u-joints are a likely suspect. It will take about 1/2 hour on the lift to pull the shaft and test the u-joint bearings. They should feel smooth when rocked back and forth, not notchy or lumpy. If they are marginal, they will cause all kinds of intermittent problems that will have you worried about the transmission, rear differential and drive shafts.

Unfortunately sold as an assembly only. Aftermarket replacements are about $425 US.

This is apparently a common problem on many high mileage all-wheel drive vehicles, not just Subaru but Honda CRV, etc as well.
 

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U-joints make their noise at about 4x the cadence the wheel turns, so if you get more than one or 2 noises per wheel revolution they go higher up on the list.
 

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Discussion Starter · #13 ·
Hello everyone. Thank you so much for all of the responses.

I drove to work yesterday in the AWD and there was no incident except for a bit of the rumbling/creaking noise when I climbed the mountain and was accelerating at steep angles. I didn't deactivate the AWD yet. Got as far as finding the spare fuses in the lid of the fuse box but then I didn't know whether to use the 15 amp or the 30 amp fuse and the manual didn't specify. I've done a bit more reading up on it and the consensus is it doesn't matter. It looks like the 30 amp fuse should go in there, so maybe I'll use that one.

It seems mean to make her have to climb up the mountain with only 2wd, but I suppose it would offer diagnostic hints.

The plan now is I'm going to a friend's house later this week to examine the car. He has a pneumatic jack, tools and has been a mechanic/ truck driver for many decades. I'll be doing the work, but at least I'll have adult supervision. The plan is to jack up the tires, feel them for play. Take them off and check the brakes, axles, bearings, tie rods and whatever else I can see in there.

Checklist:
Brakes - Rotors, Calipers and pads
Axles and Tie rods
Wheel bearings
Boots and bushings
Rear Differential mounts
Universal and ball joints
Trailing arm bushings
Carrier arm and bushings
Drive shaft and U-joint

It will be good to get in there and have a look. Hopefully I can locate the problem and work out my own schedule of maintenance items. The AT-205 arrived and I got a spray bottle so I can hunt out salvageable rubber and hopefully rejuvenate it along the way (I know not to get any in the brakes).

Thanks again for everyone's help! I'll let you know the results of the examination and I'll try to get pictures if I find anything interesting.
 

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I don't think it would be cruel, ...it would just be like driving a front drive 3600 lb 200hp minivan up the same grade..

...I guess it would suck if it was muddy and you had no tread on the tires to bite.
 

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Discussion Starter · #15 ·
Hey all. Tonight I drove up the mountain in front wheel drive. I put the 30 amp fuse into the awd slot and the "FWD" light came on on the dash. I then proceeded to ascend the mountain, and sure enough, I still heard the sound in the rear. Turning off the AWD does not make the symptoms go away. So, there's that.

Other than the intermittent noise, the car drove very well even on the front wheels. She still keeps impressing me by being a very powerful car. I'm looking forward to getting a closer look at things underneath on Friday.
 

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Well the drive shaft is still turning due to the rear wheels spinning, just no power to it. Same goes for the rear differential.

So any concerns related to u-joints or bushings are still in play.
 

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Discussion Starter · #17 ·
Well the drive shaft is still turning due to the rear wheels spinning, just no power to it. Same goes for the rear differential.

So any concerns related to u-joints or bushings are still in play.
Yes, I'm not sure what (if anything) tonight's experiment rules out.
I will be inspecting the undercarriage on Friday and will report what I find. Thanks!
 

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Yes, I'm not sure what (if anything) tonight's experiment rules out.
I will be inspecting the undercarriage on Friday and will report what I find. Thanks!
Carrier Bushing I think can be ruled out. Clunking there would be load related.
 

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Discussion Starter · #19 ·
Okay, I am back from the underneath examination/ automotive tutoring session. There I was, wending my way through the car's underworld with an impact wrench. It was quite an experience.

The bearings seem to be good. There wasn't any "play" in anything. Tires were on quite firmly, no wiggles. When I took them off, I discovered I need brake pads, like NOW! Rear passenger side tire (where I perceived the strange brake behavior the other day on the road with my husband) the rotor's out ridge is broken off for a bit. I photographed it, below.

I examined bushings in the area. Some looked okay, some looked Eh, what I believe is called an inner, rear control arm bushing is pretty much obliterated. There are some shreds of rubber I can poke with my finger, but hardly anything that could be rightly called a bushing anymore. I sprayed the rubber bits all with a spritz of the AT205 in a spray bottle, but those inner control bushings, they need help, and I need to do something about that rust.

Mounts and carriers along the differential and drive shaft seemed to be snug and secure. I felt the drive shaft itself and it seems snugly in place. I think those control arm bushings could be responsible for a lot of squeaks, and maybe even the uphill creaks and clunks.
 

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Discussion Starter · #20 ·
Pictures didn't upload in last post. Here they are.

Also, why the star carved into my rear diff? Is that a Subaru thing?
 

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