Shudder at very low speed during sharp turning

d@mn - most likely 'torque bind' . From mis-matched tires if you're lucky, if not - center diff.

Some folks have found bad U joints on the drive shaft.

Carl

Usually it's air pressure in the tires.

d@mn - most likely 'torque bind' . From mis-matched tires if you're lucky, if not - center diff.

Some folks have found bad U joints on the drive shaft.

Carl

I'll assume you have done the obvious; check tires for wear/proper inflation, check for visible damage (torn boots of whatever) on front axles.

When was the last time you changed the fluid in the transmission? I ask because we experienced a similar issue in my wife's '02 Forester.

After replacing both front axles without eliminating the torque bind, I determined that it was being generated in the 5spd transmission, specifically the "viscous coupling/center differential".

I was told various stories about repairing this, and finally ended up replacing the transmission with a low miles junkyard box. At the time this appeared to be the quickest and easiest approach, and did cure the torque bind issue.

Subsequently, I disassembled the rear case of the original transmission. It was kind of a b____ getting the cases to separate, but otherwise fairly easy, and could undoubtedly have been accomplished with the tranny in the car. Getting the center differential assembly out was likewise easy (it sorta fell out into my hands), and there didn't appear to be any special shimming or alignment involved in putting it back together.

The "viscous coupling" part of the center differential was severely gummed up, and couldn't be turned by hand. I tossed the entire thing into my solvent tank for a couple days before taking it apart as far as possible, cleaning, re-assembling, lubricating, and re-installing it into the transmission.

Just out of curiosity, I swapped this transmission into my '99 Forry (I needed to service the clutch anyway), where it appears to be working just fine. Haven't put but about 1000 miles on it yet, tho, so time will tell.

In any event, because of where the center diff lives (at the back of the transmission in it's own chamber), it doesn't appear to get much fluid circulation. This suggests to me that frequent fluid changes in the transmission are probably indicated, and may well prevent the viscous coupling from becoming gummed up.

If torque bind is starting to become evident, however, flushing the tranny with light weight motor oil, or even Stoddard solvent (kerosene) just might clean things up for you. Worth a try in any event, as a new center differential assembly (you can't get just the viscous coupling part) will set you back $550, while a new tranny is $3500. I _only_ spent $500 on the junkyard transmission, but if I ever have to do it again, I will try a flush as detailed below, followed by replacing the center diff if the flush doesn't help. Live and learn.

My plan to flush the tranny would look like this:

Drain the existing fluid and re-fill with a light weight motor oil. (10W30, or maybe some of the "Marvel Mystery Oil" stuff)(or Stoddard solvent) Drive the car around a bit to circulate the oil. including some tight "parking lot" maneuvers to work the viscous coupling. If things appear to be improving, drain and repeat as desired. Finally drain and refill with proper gear lube. If you use solvent, a final flush with motor oil or gear lube is probably advisable to be sure you get most of the solvent out of the transmission.

If you try this, do post a follow-up to let us know if it helped at all.

ByeBye! S. Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101

I believe the center diff viscous coupling is sealed from the transmission fluid, so changing the trans fluid will not have any effect on manual-transmission torque bind.

Cleaning out the gummy silicone fluid will leave you with AWD as long as no wheels slip, a wheel starts to slip and the center diff will send all the power to the slipping wheel.

Still better than just front-wheel-drive, but not as good as a 50/50 front/rear torque split when a wheel slips.

Dave

I did recently change the tires on this thing, about a month back, but they are all brand new and exactly the same model. I'll see if there is a tire pressure difference somewhere.

Yousuf Khan

Can you feel the shudder in the steering wheel? If so, then you may be suffering from a problem that was inherent in Legacies and OBs of that era. I had it in my 2000 Legacy Brighton wagon. The power steering lines were too small in diameter, so at low speed there was not enough pressure in the system and it shuddered. This was especially true turning left.

For this problem Subaru sells an upgrade kit with larger diameter lines, although they do not guarentee that it would fix the probelm completely. I had the kit installed 5 or 6 years ago and the problem pretty much went away. Only happens now in extreme cold when pressure is low.

Gook luck.

Yes, I can feel it in the steering wheel. It's very slight, it's not like as if the wheel shakes visibly, just something I can feel through the hands.

Interesting, I'll probably look into this if the tire pressures don't fix it.

Yousuf Khan

I have checked the tire wear situation, but since these tires are so brand new (a month or two), not a lot of wear patterns are visible yet.

I haven't noticed anything wrong with the boots while the tires were turned to one side or the other. But I haven't checked from under since I don't have a car lift.

That was done earlier this year. The front diff and transmission are the same unit, so they both get changed at the same time. I think the rear diff was also done at the same time.

That's a possibility, that's why I asked in here.

It is my understanding that the "viscous coupling" part of central diff is a sealed unit, and its fluid is never replaceable. Only the outer gearing of the central diff gets lubed by transmission oil in the normal way.

Yousuf Khan

Lightning McQueen: "What are you talking about?" Mater: "I dunno."

I was gonna say "The center differential lives in the same fluid as the gear train . . ." But when I thought about it, there was an O-ring . . . So I looked back thru some fotos I took after I disassembled the center diff/viscous coupling.

Darn it, Dave, that VC was a sealed unit. Wonder why I didn't notice that; sometimes I'm kinda slow :-P

Anyway, 'taint no mo; it's been reworked with good ol' 90WT in place of the silicone. What's the saying? "A little knowledge is a dangerous tool."

Wonder if I should put the original transmission back in now, or wait 'til it fails on the snowiest day of the season? Sigh.

Er, um, Yousuf, a.a.s gang, please ignore the part about flushing the transmission; as Dave suggests, it won't do a bit of good.

If anyone's curious what the internals of one of these things looks like, email me directly and I'll send along a couple of fotos.

ByeBye! S. Steve Jernigan KG0MB Laboratory Manager Microelectronics Research University of Colorado (719) 262-3101

It wont fail, you just have slightly less-good AWD.

Now too bad we didn't know just what the fluid was, you could just clean 'em and refill 'em.

Dave

Dave

Just an update, after I checked the tire pressures, I did notice that one of the tires (the left front) was about 3 psi higher than the other three, so I've adjusted that one down to the same level as the others. So far, it seems to be shuddering a bit less. Not totally stopped shuddering, just not as much as before. Maybe it takes a bit of time to settle down.

It's interesting, in the past I've had air leak problems on my tires where after a couple of months, some of the tires may have lost more pressure than the difference I've seen here, but it never resulted in a shudder until now.

Yousuf Khan

My 2003 OBS 5sp center diff went around 150,000kms. Same symptoms: parking maneuvers caused a shudder - almost a clunking that goes with the speed of travel. It happens in neutral, so it's not gear related. And it happened only once the car was warmed up. That's what tipped me off. A 10 minute drive down the highway was enough to warm things up, and then I couldn't park without the shudder.

The dealer scared me into doing it right away by telling me that the expensive transmission could eventually get damaged by leaving the diff alone. $1600 or something like that.

All is well now, 50k kms later.

I've read 'rumors' that making figure *s/tight maneuvers IN REVERSE can alleviate some center diff symptoms.

I've never tried it and it seems weird.

I think I've seen pics/article on-line where some Aussies are disassembling the center diffs and replacing the fluid to make them engage more quickly for some kinda off-road use. So, maybe it IS possible to rebuild one?

good luck (don't forget to check the U joint on the driveshaft)

I've read 'rumors' that making figure 8s/tight maneuvers IN REVERSE can alleviate some center diff symptoms.

I've never tried it and it seems weird.

I think I've seen pics/article on-line where some Aussies are disassembling the center diffs and replacing the fluid to make them engage more quickly for some kinda off-road use. So, maybe it IS possible to rebuild one?

good luck (don't forget to check the U joint on the driveshaft)

Ouch! So far, it doesn't happen in neutral yet. And it's unrelated to how warm the transmission is: it'll happen warm or cold. So I'm hoping that this means that mine is not as serious as what happened to you.

I'm still investigating the tire inflation pressures to see if they make it go away. I've never had to worry about the tire inflation tolerances this much before. Usually I could keep the tires within 2 psi of each other.

Yousuf Khan

Yeah, that does sound weird. Can't see why that should work, but I'll keep it in mind.

Well, I'll play with the tire pressures some more. Maybe these tires are just more sensitive to tire inflation than any of my previous set?

Yousuf Khan

"S" on this thread said he took his apart and drained the fluid (which leaves you with slightly less good AWD), so if you had the fluid to put in (a bucket of it so you could re-assemble the viscous-clutch unit submerged) you'd be able to rebuild your own.

Dave

One thing I learned while dealing with the torque bind due to tire pressure is that the "stick" gauges absolutly suck balls.

Get a "dial and needle" type for a few bucks more. (Which should still be under 20). Then use a sample of five or six tests to get a read>> My 2003 OBS 5sp center diff went around 150,000kms. Same symptoms:

I got a dial'n'needle, but I also got a digital unit, which reads out in increments of 0.5 psi.

Yousuf Khan