Help with a driveline diagnosis

[libertyordeath]

Hi All

 

Recently joined to start a thread but have been reading legacygt for a while.

 

I have an recent issue that has come up on my 2012 BR Liberty (wagon, CVT, 2.5, 199k kms (123k miles) over Christmas. My nearest 'subaru whisperer' is over an hour away and it's our only car for the minute, so attempting to solve the issue myself until I cannot, and have to drag it way across town.

 

Issue started with a vibration when accelerating reasonably hard, in straight line, from a standing start. Vibration seems to go away at higher speeds (say 60kmh / 40mph and above) and there is no effect to fuel economy. Vibration seemed to come from a number of places, but seemed central to car, no knocks just a 'throbbing' under reasonable acceleration load. Also seems to go away after a while, ie worse when the car is cold?

 

Parts replaced so far:

 

1. Initially, I suspected front LH wheel bearing (has happened before and was replaced). Replaced front LH wheel bearing again after 12months of the 2nd one.

 

2. Replaced rear LH wheel bearing (wife hit a curb and popped 2 tyres a few years ago, thought perhaps the rear had gone like the front did as above, just a little later)

 

3. At this point, over the New Year break, I took it to a local mechanic who drove it and immediately said the rear diff had gone. Couldn't fix it for 3 weeks, I was on break so just did it myself. So rear diff has been replaced.

 

4. Still no better, I swapped the rear engine mount (that hangs onto the back of the centre diff) rubber as the original one looked compressed and whilst not broken I thought it might have softened and allowed more vibration. Still no good.

 

5. Finally, have swapped out the centre drive shaft with a good condition used one, the original one definitely was stiffer and clicked so felt this was a good change.

 

Whilst a little better, THE VIBRATION REMAINS!

 

My thoughts move now to rear CVs (the vibration seems to come from the centre/rear but so hard to tell....) - they look fine, and had no play when I swapped the diff so didnt give them a second thought. They don't click, and I have read they rarely break?

 

ANY THOUGHTS WOULD BE GREATLY APPRECIATED......

[Scubaboo]

I've not had that problem yet so unfortunately I cant give you much from experience.

 

However from what you mentioned, you have replaced 2 tires.

 

Were the new and old tires' tread thickness within Subaru's allowable tolerance?

 

Subaru has some of the smallest allowable tread difference of all the awd manufacturers.

 

I assume the tires replaced were front and back of one side of the car? If so it may have affected your center diff?

[libertyordeath]

Mmm good sleuthing there Scubaboo. Thanks for your thoughts.

 

Yes have replaced tyres when popped, decided to put the worn right side on the back and two new ones on the front. Tread depth quite varied between front and back. Exactly the same tyre type when replacing.

To add some additional info, I have been 'reasonably' caring for a slow leak on the rear right for a good while now, topping it up but occasionally it probably is lower than it should be. Perhaps this has loaded up the centre diff?

[Infosecdad]

You need the same tread depth on all four tyres or the diff may start binding as the wheels will be turning at different speeds. Subaru says within 2/32 if I remember correctly. The question now is whether the damage to the diff is permanent or not. I would get four tyres of the same brand/type and tread depth and see how it feels.

[Scubaboo]

Tread difference front to back would be putting stress on the center diff. Allowable difference is only 2/32 or 3/32 front to rear IIRC.

 

I had to replace 4 tires that were not even half worn because I had run 1 rear tire low on air enough to damage the sidewall. I bought a new rear pair at first but my fronts were worn enough to be just past tolerance so I ended up getting new fronts as well.

 

But do check the easy stuff first. Lots of stuff like worn drivetrain mounts and prop shaft bearings can cause shaking too.

[libertyordeath]

Thanks for the thoughts guys, I am going to stop madly swapping drivetrain parts and throw some new rubber on and see if that does anything.

 

I will report back.

[Scubaboo]

Hope that fixes it for you.

 

You will need to get tires in spec in addition to any other repair anyway so thats a good a first step as any.

[FLlegacy]

I would also have the wheels checked out, I would assume any competent tire shop would do this but just want to say it out loud so it doesn't get missed. Curbing wheels can cause them to bend/warp.

[silverton]

4. Still no better, I swapped the rear engine mount (that hangs onto the back of the centre diff) rubber as the original one looked compressed and whilst not broken I thought it might have softened and allowed more vibration. Still no good.

 

I'm assuming you mean the pitch stop, the one that bolts to the firewall and the top of the bellhousing on the transmission? If so, now inspect the transmission crossmember mount, you may find it's torn.

[pinesol]

I'm assuming you mean the pitch stop, the one that bolts to the firewall and the top of the bellhousing on the transmission? If so, now inspect the transmission crossmember mount, you may find it's torn.

 

There is no pitch stop on these cars.

[Scubaboo]

It doesnt have a pitch stop in the rear in the traditional sense, but I believe the front mount by the radiator serves the same purpose.

 

It was probably moved there to be closer to the front subframe cradle the motor is now mounted to for this platform.

[libertyordeath]

Thanks silverton, yes the transmission crossmember mount was replaced. (https://www.ebay.com.au/itm/164071243617)

 

This actually tightened up some of the vibration, which is leading me to think the issue is coming from either the centre diff, or the CVT.....

[libertyordeath]

I am not sure its wheel based, FLlegacy but thanks for offering help.

 

It only occurs under load, ie. when I back off at any speed it stops immediately. It also seems to go away at higher speeds and if I floor it over 70kmh say, there is no vibration.

[08SpecB_DE]

My money is on one or both of the front cv shafts. 9/10 times they fix the problem that you're experiencing.

[libertyordeath]

Thanks 08SpecB_DE - its a good hunch, but do you think there would be vibration transferred through the steering wheel?

 

I don't have any at all, which made me skip over front CVs as the issue.

[dgoodhue]

With different types of tread depth on the front and rear, you are killing the center differential. If it isn't your current problem, it will be a problem. Temporarily, you can put 1 of the new tire on the front and 1 of the new tires on the rear, this will take speed mismatch in the center diff. It will put the mismatch into the front and rear differentials. Open differentials will not get damaged from mismatched tires.

[08SpecB_DE]

Thanks 08SpecB_DE - its a good hunch, but do you think there would be vibration transferred through the steering wheel?

 

I don't have any at all, which made me skip over front CVs as the issue.

 

Nope, only in the seat/body. The vibration going away when you let off the gas is your indicator.

[Scubaboo]

Nope, only in the seat/body. The vibration going away when you let off the gas is your indicator.

 

How did you end up confirming it was axles in your case?

[08SpecB_DE]

How did you end up confirming it was axles in your case?

 

I've been wrenching for 16 years.

[libertyordeath]

For the sake of the argument, I am going to do the front CVs as well I think.

 

The weird part is, whilst being the most obvious failure point on high mileage Subarus, the vibrations make it so unlikely. Also the lack of noise (my old Brumby would TELL you when the CVs were cooked!) and no knocking on full steer just made me skip over them.... But it has to be the CVs.

 

Finally, the weirdest part is that the vibration goes away (fully, from a standing start) after a long drive (>80km) - just disappears until something cools down again I am guessing.

[Scubaboo]

I've been wrenching for 16 years.

 

I'm sure you have. I hope I didnt come across as challenging your idea. I am actually wondering what to watch out for and how to confirm axles, I am looking at another Subaru that has a bit of driveline shudder that looks pretty clean otherwise.

[creep_nu]

had a similar issue with my TL. everything else was solid but still getting a driveline vibration. took it to a shop to confirm my suspicions and it ended up being one of the CVs was gone...replaced both and she rode perfectly again.

[08SpecB_DE]

I'm sure you have. I hope I didnt come across as challenging your idea. I am actually wondering what to watch out for and how to confirm axles, I am looking at another Subaru that has a bit of driveline shudder that looks pretty clean otherwise.

 

Not at all and I apologize if I sounded standoffish. Cv replacement is the most common fix when pertaining to a complaint of vibration only on acceleration. I've had shafts pass the visual and physical (check for play) inspection, so they only get you so far. You need to get the car up in the air, safely. A lift is preferred but level ground and jack stands will suffice. Have someone sit in the car and get it up to 40 or 50mph. You should be able to see one axle wobble more so than the others. A shudder sounds more like a transmission, center diff, or rear diff issue but thats just where my mind goes.

 

Liberty: The problem going away sounds a little strange. Not sure if you mentioned that before, but if you did, I'm sorry I missed it. A sticking caliper may be the culprit. Make sure the pistons compress the same on both sides, the guide pins easily move in and out and that the pads are not stuck in the brackets.

[Scubaboo]

Not at all and I apologize if I sounded standoffish. Cv replacement is the most common fix when pertaining to a complaint of vibration only on acceleration. I've had shafts pass the visual and physical (check for play) inspection, so they only get you so far. You need to get the car up in the air, safely. A lift is preferred but level ground and jack stands will suffice. Have someone sit in the car and get it up to 40 or 50mph. You should be able to see one axle wobble more so than the others. A shudder sounds more like a transmission, center diff, or rear diff issue but thats just where my mind goes.

 

Liberty: The problem going away sounds a little strange. Not sure if you mentioned that before, but if you did, I'm sorry I missed it. A sticking caliper may be the culprit. Make sure the pistons compress the same on both sides, the guide pins easily move in and out and that the pads are not stuck in the brackets.

 

Thank you, that's very informative!

[DrD123]

Another potential cause for a vibration/binding sort of feeling that is worse when the car is cold could be the center differential, but that's usually apparent when turning... a worn cv joint could be it - haven't had that go on my car, but on our last van, the inner cv joints went on both axles (1 at a time...), but it would only vibrate on acceleration, not deceleration (granted - it's an fwd van) - the inner joints made no noise when they were dying, though. I wouldn't think a cv joint issue would go away when warm, but maybe lubrication is marginal for some reason, and as the grease warms up it smooths things out?