[Alx]

I recently bought a 2008 3.0 litre 5 speed auto, with a clunking noise coming from the front-end of the vehicle. I thought at the time that the noise was from the obviously toast CV joint (torn boot, grease everywhere). Having replaced the CV shaft, some of the noises went away, but the car still clunks when coasting down rough sealed roads. This has been annoying (and worrying) me.

So I put the car up on stands and after playing around with a few things I notice there is a lot of freeplay through the front diff. What I'm talking about is that I can rotate one wheel an inch and a half (along the circumference of the wheel) before the other one rotates in the opposite direction. And when the other wheel finally begins to rotate, there is a loud "clunk", coming from the diff.

So to cut a long story short, I have observed the movement causing the noise through the diff oil drain hole. Basically when I rotate a wheel (with the car on stands), what appears to be the innards of the differential within the alloy casting moves backward and forward at least 1/4 inch, causing the clunking noise. I have a video of it, but no idea how to post it. I can email it if anyone is interested. You will have to excuse the noises in the background (neighbor's leaf blower and me grunting as I lie under the car, move the wheel and try to hold the phone steady).

I guess the good news is that the diff oil is good, i.e. no metal chunks, burnt smell or anything that seemed out of place. The diff doesn't make any other noises like whining or grinding when I drive, so I am inclined to think that it is still mechanically OK - for now.

I am now resigned to the fact that this car needs more than I can provide and will have to go in to a transmission specialist. But can anyone provide any ideas on what the cause of this movement is? How much am I up for? I'd like to be forewarned before I turn up to my local transmission shop!

I have spent a lot of time googling this problem, and it doesn't seem very common.

 

[cardoc]

So now that you have changed the diff fluid, is the noise gone?

Post the vid on You Tube and then post the address to the vid here.

 

[Alx]

Thanks cardoc, and merry Christmas!

No, changing the oil did not help - I fear this problem is something that fresh oil won't solve! The mechanics of differentials and auto transmissions are a bit beyond my technical abilities, but it seems to me like something has come adrift (or loose) inside the casing.

I have uploaded clip to youtube here:

IMG 0489 - YouTube

 

[cardoc]

I don't see any "play" in the gear. That gear is where the output shaft of the transmission meets the drive gear for the diff assembly.

How much was the wheel turning between the clicks?

Are you having issue with turning? Any wheel hop/skipping?

I've attached a diagram of the diff so you can see what it is like inside.

You may want to go ahead and ask around about a good tranny shop in your area. Maybe post on Club Liberty Index Page for a reliable shop. The tranny has to come out to repair it.

 

[idosubaru]

I can rotate one wheel an inch and a half (along the circumference of the wheel) before the other one rotates in the opposite direction. And when the other wheel finally begins to rotate, there is a loud "clunk", coming from the diff.

That is actually completely normal. They all do that. You'll have to get some specific measurements to compare - like get someone else to do it or find another Subaru to do it too in order to see if yours does it more than normal.

Did you do it to the back wheels and see how quickly those pair up/engage? Rear diff is different than fronts but might ease your mind.

Having replaced the CV shaft,

Aftermarket CV axles are low percentage so if it was replaced with any aftermarket unit that was a mistake, it's very possible you have a bad axle.

Clunking - can you describe it more?

1. Is it definitively central or drivers/passengers side? (have someone stand outside the car on both sides while driving past, making the noise or hang your head out the window while driving).
2. happens at any speed?

I would check:

1. sway bar bushings - grab the bar, see if it slides/moves?
2. struts - these can be hard to check - but look for strut leakage, sounds while loading it statically if you can.
3. control arm bushings

If it is a front diff then I'd try to get a used transmission. They are usually widely interchangeable across many years though I'm not sure how it works with the 5speeds, newer CVT's, etc. But I'm not sure how it is downunder, in the US used transmissions are easily acquired and there's a national database of junkyards, searchable by distance and lowest price, craigslist, ebay, etc. Those same sources are also ways to track down what other years transmissions are compatible with yours.

 

[Alx]

Thanks cardoc - that is a good link that I will use.

I'd describe the noise as a metallic "clunk" rather than a click. The wheel is turning about 4cm or roughly 1 1/2 inches between clunks. I was just turning it back and forth by this amount (and no further) in the youtube clip.

I am not too sure exactly what I am looking at through the diff drain hole (having never seen an outback diff removed) - I think it is the ring gear, although it is hard for me to tell from the line drawings in the service manual. I think you might have posted the exploded drawing for the rear diff rather than the front diff. I can not find an exploded drawing in the service manual that clearly shows the relative positions of the front diff and the casing (for instance on pages 5AT4 to 13).

I have a suspicion that the carrier bearings are loose, although grossgary describes the noise/movement as normal in the comment below yours. I would be at a complete loss to explain how these could come loose though. It worries me that this amount of movement in the diff is not going to be healthy for the gear teeth in the diff or, for that matter, the rest of the driveline over the longer term. Particularly since I can hear a definite clunk when driving, and I am reasonably confident I have ruled out the other "usual suspects" in the suspension.

When I changed the diff oil there was a small amount of sludge on the magnet, and the oil was just a shade darker than honey colour. Nothing caught my attention as being unusual.

I don’t know a lot about the vehicle’s background. Given the amount of dust and mud I have cleaned, and the places I have found sticks and vegetation, I can assume that the car has been driven over rough dirt roads probably many weekends. The service history was not perfect either, so I knew that I was taking a risk when I bought it.

I’ve had a couple of wins though – changed 4 litres of the transmission fluid and the filter – it shifts much smoother now, and replacing the front CV shafts has eliminated a bunch of noises and made the steering much more positive. The posts on this site have been a valuable reference.

Grossgary, thanks for the tips. Yes, I have replaced the CV shafts (both now) with aftermarket ones, but not long enough ago for them to have failed. I will monitor them closely and if it turns out to have been a mistake I will buy OEMs. I replaced them separately, and on both occasions there was a marked improvement in the handling and noise. The one I just took out was a remanufactured shaft with nothing “obviously” wrong with it, but the steering now feels noticeably more positive and with less vibration.

I am fairly confident I have eliminated the potential sources of the noise you have listed. Struts are good, sway bar and control arm bushings are fine.

The noise is most noticeable when I am coasting (i.e. not using the accelerator) at low/moderate speeds (20-40mph), on a bit of a rough road. I can hear the noise through the floor pan from the front-center of the vehicle and it is definitely not normal road noise. I have a theory that it is being caused by the wheels travelling at slightly different speeds over the bumps and one side going a bit faster, then the other, with the noise being basically caused by what I can hear in the diff when I’ve got the car on stands (see previous post with link to youtube clip).

I haven’t tried your suggestion WRT the rear diff yet – I will take a look tomorrow and see if it has a similar amount of free play.

I take your point about used transmissions – these units should last quite a long time if serviced and treated well. Having said that, I would hope I wouldn’t be replacing this one at 65000 miles

 

[cardoc]

Have you had an alignment recently?

 

[Alx]

cardoc, yes have had an alignment done just after purchasing vehicle. Do you think it could be related?

I have just compared the free play movement through the rear diff as suggested by grossgary - it is less than half what I get through the front, and with no loud "clunk" once the diff engages either.

I will update this post with the findings once I take the car to a Subaru specialist early in the new year.