Noise from rear end of an H6

[TrekLawler]

Hello everyone,
I'm hoping I can tap into some Subaru experience here . I have a 2001 Outback L.L. Bean with 260,000 miles on it. The car is absolutely in excellent shape and I've taken very good care of it mechanically. However it has recently developed a very odd noise from the rear differential that has me baffled.
Sometimes when you put it into reverse (and only in reverse) it gives a very loud clunking noise, almost gives you the impression that a CV or u joint on the drive shaft has gone bad, but these have been replaced in the last month, so have been ruled out. At other times if it doesn't clunk when putting it into reverse it will give the clunk as you're backing up. I've pretty much isolated it to the rear differential however can't imagine anything that could go bad which would only cause this to happen when the car is put into reverse, but am open to ideas and suggestions. Any thoughts would be appreciated.

Thanks,

[1 Lucky Texan]

could you listen back there outside the car while someone else backs it up? See if the sound is at a wheel or more central.

could be something with a brake pad/caliper or the parking brake parts inside the rotor.

also, there are bushings at the differential mount that could be destroyed. control arm bushings too.

You said the ujoint was OK, there's also a carrier bearing. dunno if it could clunk though.

at that mileage - I suppose a rear CV joint could be bad.

[TrekLawler]

Thanks Lucky Texan,
Both half shafts have been replaced with new CV's so I'm hoping that isn't a problem . It's definately more central, I haven't been able to stand outside of it when someone else is in it however have hung out of the car in an open parking lot and can hear it, it sounds like metal on metal since it's a clanging noise (if that makes sense) almost like the front wheels were engaging and then as the car was rolling backwards the rear was unloaded and then caught up and the pinion gear hits the ring gear.
I thought about the brakes as well however the car freely rolls backwards when put into gear and the noise will not present itself until you give it some gas (if it doesn't clunk going into gear).

One thing I forgot to add is it doesn't do it all the time, sorry.

Thanks for the thoughts though, you've given me a couple of other items to look into with the bushings as I'll check them.

[CNY_Dave]

Was the driveshaft fully serviced or just one or two u-joints replaced? The rubber mount for the carrier bearing could be shot.

The rear trans mount might need new rubber bushings, ditto the rear diff.

[cardoc]

https://www.youtube.com/watch?v=PhiP...s&feature=plcp

And the fix for now so I don't have to remove the diff carrier was to remove the skid plate, clean the bushings with brake cleaner, inject 3M Window Weld into the gaps, let it set for the afternoon and over night. The following was the result. The body and suspension moves, not the diff.


https://www.youtube.com/watch?NR=1&v...ture=endscreen


Its funny every time I see it.



,

[TrekLawler]

Originally Posted by CNY_Dave

Was the driveshaft fully serviced or just one or two u-joints replaced? The rubber mount for the carrier bearing could be shot.

The rear trans mount might need new rubber bushings, ditto the rear diff.

Thanks Dave,
both U joints were replaced as one of them was pretty stiff and grinding a bit. The rubber mount on the carrier bearing was checked out and looked OK with very little movement. My first thought was it was a U joint as that is what it sounded like.

Thanks,

[TrekLawler]

Thanks Cardoc,
My son and I are going to go out this afternoon and check these out. When I removed the differential just about two weeks ago to replace the half shafts and CV joints the rear diff bushings looked very solid as they supported the diff when I removed the front mount.

But I've seen weirder things.

Thanks for the feedback.