6mt suspected differential problems

Good morning. I'm having trouble troubleshooting an ongoing problem with our 2012 Legacy 2.5i 6mt.

We have what seems to be a relatively common set of symptoms: pronounced thumping (that can be felt and heard) when turning, but only after the car has been driven for a few miles to warm it up. No sounds when driving straight at any speed. The sound is equally loud when turning in either direction. It is more severe on tighter turns, less so on wide turns. No sound during the first drive of the day, or anytime the car has not been driven in several hours.

Mechanic thought CV joints. Had them replaced. No improvement. We live overseas and there are no Subaru dealerships or Subaru specific mechanics that we can look to for a second opinion. We took it back to the mechanic (who has been very reliable diagnosing issues with others cars for us) and he was stumped after putting it on the lift and checking everything he could think of.

After doing some research online, it seemed that a failed viscous coupling matches our symptoms and is a common problem in Subaru's. However, after contacting some parts suppliers it appears that there are not readily available viscous couplings for 6mt. Even speaking with some part departments at Subaru dealers in the states didn't really clear things up for me. I've gone over some mechanical diagrams and I'm still stumped.

If anyone has experience or knowledge that can point me in the right direction I'd really appreciate it. I do most of the basic maintenance and repairs on our cars myself - but this is outside my comfort zone. What I'm hoping to do is go back to the mechanic and give him some guidance that might help him confirm the issue and come up with a list of everything I'll need to order for the repair.

Thanks!

Drive at low speed and take some turns, a locked viscous coupler will feel like the tire are jumping or skipping. Another analogy is the driveline will feel like it binding.

Do your Legacy's tire depth match front and rear? This is usually how the AWD is damaged in a Subaru (or any AWD vehicle).

Yeah make sure all four tires match in size, model and wear. Once that’s sorted I would try changing trans fluid.

Here is some center diff info on the old five speed trans, not sure any of the repair info applies to our 6MT:

https://www.subaruforester.org/threads/center-diffs-and-how-to-replace-them.46979/

Sounds exactly like my center diff when it went bad. The fluid inside the diff has overheated and broken down. That’s why it gets funky after the fluid is warm, it’s too thin/ broken down at that point.

Anyone who calls themselves a mechanic shouldn’t have any issues with it as it’s a pretty straight forward job.

Remove driveshaft

Remove transfer case cover

Pull out some washers

Pull center diff

Replace in opposite order.

You should be able to find the part around $400.

https://www.subarupartwholesale.com/p/Subaru__Legacy/CENTER-DIFFERENTIAL-ASSEMBLY/49248166/38913AA230.html?partner=googlebase_adwords&kwd=&origin=pla&partnerDevice=m&userLocation=9018948&gclid=Cj0KCQiAm4TyBRDgARIsAOU75spnnDPbWHpli1rvmmeh65m1I9h42BiLLfuWl3xBZOUykGLFptk-5qQaAtT2EALw_wcB

Good luck!

dgoodhue - That is pretty much exactly what it feels like

dgoodhue and NVAKeith - The tires are identical and evenly worn. I've always replaced them as a set of four. Tires here generally have to be replaced due to screws, nails, and other things damaging them long before the tread is worn.

NVAKeith - Unfortunately, based on the people I've spoken with, the 6mt is a completely different animal from the more straight forward 5mt.

stewdogg - Thank you for the info and the link. I'll probably make one more stop to discuss with the mechanic and then order the part.

 

NVAKeith - Unfortunately, based on the people I've spoken with, the 6mt is a completely different animal from the more straight forward 5mt.

How much work is it for the 6mt, is it definitely a full transmission removal? It looks like I might have this repair in my near future.