Rear Differential Failing?

Hi Gang,

 

I've got a 2000 Legacy GT Wagon 5 speed Manual Trans with 120,000 miles on it.

 

While making tight turns at any speed (it's particularly noticeable in parking lots) it sounds/feels like the right rear wheel is hopping or binding.

 

This problem only occurs after the car has warmed up thoroughly...usually after about 20 minutes of driving. When the car is cold, there is no problem whatsoever.

 

It occurs whether I'm turning the car right or left, but it does always seem to be the right rear wheel that's hopping/binding.

 

The Legacy GT model has a limited slip rear differential and it's a viscous LSD. Is that right? Nothing in my owners manual or my Haynes manual said anything about LSD specific oil. Am I right in understanding that the actual rear Viscous LSD is sealed and the oil changing maintenance DOES NOT require LSD oil?

 

I changed the oil in my rear diff about 2 days ago...but it has not appeared to make any difference in the problem. I put in 0.7 quarts of Valvoline 80W-90 Synthetic LSD gear oil, but it sounds like I didn't even need to use LSD oil...is this correct?

 

So is this really a failing rear limited slip differential?

I haven't found a single case online of someone else with the same problem.

I would think the rear diff would last for the life of the car?

 

Could I be completely wrong with the diagnosis?

If this was a wheel bearing, wouldn't the symptom be different?

Could this be something else?

 

Any thoughts?

 

Thanks in advance.

 

-Joey

Also check wheel bearing, brake caliper and center differential.

 

Begin with the brake caliper and wheel bearing since it's easiest. And I suspect these parts first since it's a problem located to one side.

Well, I checked the wheel bearings and they're great.

There's no play at all with either rear wheel.

 

I checked the brake calipers and they appear to be perfect as well.

No excessive play.

Both rear rotors appear to be thinner than spec, but I didn't have time to put a micrometer on them, but I definitely do not think they're warped since while rotating the wheels there was no dragging.

 

What can I check with the center differential? Should I just look for signs of leaking?

 

One thing I did find curious though...

When I rotated one of the wheels, the opposite side wheel rotated in the opposite direction! I thought that wasn't supposed to happen with a Limited Slip Differential?

I thought that was what an open differential should do or does my Subaru do this because it's a Viscous LSD and not a clutch type LSD or something else.

 

Also, there are no signs of leaking around the rear diff.

 

The CV joint boots look good...no signs of cracking or anything like that.

 

Any other thoughts?

 

Has anyone heard of a Subaru Viscous LSD failing at 120,000 miles?

If you worry about the differential - do an oil change and check the old oil for metal shavings. You may need to use a magnet.

Yes, I did change the oil in the LSD a few days ago.

 

Yes, there were very tiny bits of metal in the oil.

I've never changed the oil in a diff before so I have no idea if this is normal.

BTW, the oil in the diff was change about 16 months ago by my local mechanic.

 

Any other thoughts?

 

Is my only option to replace the viscous LSD?

 

Thanks in advance,

 

Joey

If the particles are big enough that you can feel them with your fingers you have a problem. If not then it's tricky, but you may still have a problem.

 

Just hope that your local mechanic didn't mess up and poured the wrong oil into the diff.

 

In this case the safest way is to take down the diff and have it checked. One alternative can be to get an used diff and replace the current, but check that you get the right ratio first.

Well, those particles in the diff oil were very small. I doubt I could feel them.

 

Yes, my original thought was that the mechanic that changed the oil over a year ago may have put the wrong oil in the LSD, but now I'm wondering if it even makes a difference. If the diff is a viscous LSD type, then isn't the limited slip part of the diff actually a sealed, non-serviceable part? So that as long as the weight of the oil was proper, I don't think it would make a difference if it was LSD oil or not.

 

Also, if this is a viscous LSD and it's failing, then wouldn't it act like an open differential after it's failed???

As this one heats up it actually causes binding, which seems to be the opposite of what you would expect to happen.

 

Any thoughts?

 

I'm pretty much thinking I'm going to buy a used LSD and replace this one, but I just want to make sure I'm understanding this problem and not about the throw money away.

 

Thanks in advance,

 

Joey

the noise is most likely a bad CV joint, not the diff. you sure its in the rear? sometimes things sound like they are coming from a different place than they actually are

First - if you are going to buy a new differential it's CRITICAL that it has exactly the same ratio as the old or you will crash your center diff.

 

As for LSD fails - there are several ways a failure can occur. It may be a bearing in the diff that's failing and not the LSD pack itself, and a failed LSD pack can either be completely open or it can experience binding issues. And depending on the construction the LSD behavior may vary. There are three different constructions when it comes to LSD:s on Subies.

 

But you should check the differential - there should be a sticker on it that specifies if it is a LSD or not together with the ratio. But I'm not 100% sure since it varies by model and model year.

whitetiger,

Yeah, I thought of that as well...

Both CV joint boots are perfectly clean, no cracks or anything.

Plus, if it was a CV joint, wouldn't it bind whether the car was warmed up or not?

Also, the symptom is totally different than what I've experienced in the past with a worn out CV joint.

The symptom is definitely a severe binding where you can hear and feel the right rear wheel stopping, dragging, and hopping.....but again, it only does it once the car has been driven for 20 minutes or more.

 

At this point, I think I'm going to drop the LSD this weekend and take a look at it. I just wish I could find an exploded view diagram of the LSD so I could better understand what's going on in there.

 

Thanks for the help, guys.

Here you go: http://opposedforces.com/parts/legacy/us_b12/type_26/train/differential_individual/

 

But be very careful since the differential is one of the pieces in the car that is a high-precision item where you need to be very exact to get the pinion to match the crown gear. This is if you decide to disassemble the differential. But it's no problem to remove the rear lid and inspect it.

Thanks so much for the diagram...that really helps me to understand the diff.

 

So is it possible to replace just the VLSD component inside the differential or do you just have to replace the whole darn thing?

Are these things pretty expensive?

Am I better off scouring the junk yards for a whole rear LSD?

 

Also, is it possible that this whole problem could be a failing center differential?

(I would think if it was a failing center diff the problem wouldn't seem to be biased towards one side like mine).

 

Thanks again for all the help.

I need to save as much money as possible (ahhh the life of a photojournalist) and I also plan on keeping this car until at least 200,000 miles (hopefully).

 

Cheers,

 

Joey

the VLSD is not serviceable. you would need a new unit. the vlsd unit should not be strong enough to bind the axle. its a very small aux unit off to the side of the spider gears that cannot transfer enough TQ to cause binding IMO. if you put the car on jack stands, try spinning one back wheel while holding the other and see if you can the nose to happen. if ther is binding on the diff, it would be more likely that the spider gears are chewed up and not spinning freely.

The easiest and cheapest solution for a damaged diff is to get an used one from a junkyard.

 

Repairing or modifying an existing is expensive in parts and labor.

^thats what i did when i blew my diff up. destroyed the spider gears. found a used r160 with the 4.11 ratio only 36k miles on it for $150 on this forum no less.

I've been super busy with my schedule so I haven't jacked the car up to try the above mentioned test from whitetiger...

 

I can relay a symptom that I forgot to mention in my original post that may help shed light on this diff problem.

 

At any speed, in any gear, if I step hard on the accelerator and the engine is spinning above 3500 RPM, I get a high pitch whining noise coming from the rear of the car.

If I push in the clutch, and rev the engine the noise mostly disappears. There's a little, more faint, high-pitch whine, but I have to really rev the engine hard....up to 5000 RPM to hear it.

 

So I have no idea if that helps with the diagnosis.

At this point it seems pretty certain that it's the VLSD and I'm going to need to replace it ASAP.

If anyone has any good tips on finding one, I'm all ears.

Thanks in advance for any continued help.

 

-Joey

Alright, I finally got around to testing this rear diff.

First, I warmed the car up by driving around for 30 minutes.

I then jacked up the rear of the car.

If I spin one rear wheel, the Ghe other wheel spins in the opposite direction as expected.

Finally, I dropped one rear wheel so that it was firmly planted on the ground and the tried rotating the other still elevated rear wheel. With maximum effort I was able to turn the wheel slowly, but if was sort of jerky...it would rotate a little and then it would sort of jerk or pop forward a couple inches. The popping was also inconsistent as I was rotating the wheel...meaning there was no pattern to it.

 

Okay, so does this prove that the problem is definitely my rear LSD?

If I'm understanding everything right the this is it...I've got a bad rear limited slip differential.

 

Any thought on finding a replacement?

 

I'm going to start looking at junkyards here in the Maryland/Washington dc area.

I'm no expert, but I just replaced the rear diff in my 05 GT. I did a google search for the r160 rear end which the 05 GT has. I found one in FL $336 shipped, 40,000 miles on it.

 

I also posted a thread here about 4 junk yards that called me and had rear diffs.

 

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^yes, diff issues occur during movement regardless of what the engine/clutch is doing. but then again it could also be trans/center diff/drive shaft related too.

Well, I finally repaired my problem...

The problem ended up being the center differential and NOT the rear differential.

The Viscous Coupling failed.