rear diff, axles or what?

[dean]

Any advice on what could be wrong with my 96 Legacy Brighton based on the
following description?

When I go in reverse and turn sharply, for example to parallel park, I can
hear a shudder and the car behaves as if it had hexagonal wheels: it jerks
and hesitates to roll. I can't really tell if the noise is coming from the
front or the back. Driving in the city and on highway I did not notice
anything weird with the drivetrain (doesn't pull to one side and it makes no
noise when turning in the streets). To get more details on the problem, I
did the following test.

1. if I go forward (on an empty parking lot) and turn the wheels all the way
to one side I can make 3 or 4 full circles without any problems but after
that, the car starts exhibiting the above mentioned jerking and shudder
similar to what one experiences when a front axle is gone bad on a FWD car.

2 if I do the same, but going in reverse, I can also make a few rounds with
no noise or problems but after the 5th turn the shudder and noise increase
to the point that one can barely drive the car. It rolls very rough, it
produces an awful sound (as if something is being ground down), brutal. It
even stalled on me once as if I had a parking brake on. After doing several
circles and upon hearing and feeling this problem I stopped the car and got
out (wheels fully turned), only to see that the car jerks forward (slightly)
about every second. I could hear something turning and hitting in the same
rhythm as the car was jerking. As soon as I straightened the wheels and
drove straight, the noise and roughness was gone.

Could this be a worn/bad axle and how would one figure out what side and if
it is front or back?

Could it be the differential? Front or back? How to tell/test?

Anything else that could produce the above mentioned symptoms?

Please help with your advice before I turn to the dealer for
inspection/repair.


(My Legacy is AWD, 2.2l, 173k km, manual(clutch near the end of its life),
front right axle replaced more than 50k km ago, front diff/trans oil changed
10k km ago, rear diff not checked recently)

 

[Florian Feuser /FFF/]

<snip>
1. if I go forward (on an empty parking lot) and turn the wheels all
the way to one side I can make 3 or 4 full circles without any
problems but after that, the car starts exhibiting the above mentioned
jerking and shudder similar to what one experiences when a front axle
is gone bad on a FWD car.
<snip>

I had the same problem with a 95 Legacy L at just over 150k miles.

It was the center differential which is AFAIK not a separately
replaceable/rebuildable part from your manual tranmission. I replaced
the entire assembly with a used one from the junkyard - parts and labour
just under $1000 US.

What happened is that the viscous coupling - a clutch pack of several
disks embedded in silicone - has burnt out either by reaching its
'natural' end of life or by some sort of asymmetry in your car's drive
train.

E.g. This usually happens when people run on their doughnut-size spare
for too long and too fast.

florian /FFF/

 

[Sparky Polastri]

Something to check before replacing transmission....

Newer subies do that if there is not proper tire inflation. Even 4 pounds
lower on one side will make that happen. Check your air first. Something
about the limited slip stuff having "give" for turning that gets over worked
if the tires have different radius.

 

[Florian Feuser /FFF/]

Something to check before replacing transmission....

Newer subies do that if there is not proper tire inflation. Even 4
pounds lower on one side will make that happen. Check your air first.
Something about the limited slip stuff having "give" for turning that
gets over worked if the tires have different radius.

Good point - I may have been wrong to assume that the OP made sure to
have equal pressure in all tires. Another thing to consider is uneven
wear - this could give away any existing asymmetry in the drive train.

My 95 Legacy tires were shot when I bought the car; the car was crabbing
sideways and fishtailing pitifully. The tires may even have caused or
accelerated the failure of the clutch pack.

In any case, if the problem really only occurs after doing a few donuts
at max steering angle, it may be futile to worry about it. After all,
the center differential is SUPPOSED to bind under certain conditions
when "slippage" [read: different RPMs at the wheels] occurs.

In my experience, the car would bind after any prolonged drive,
especially in turns after a stretch of highway driving.

good luck

florian /FFF/

 

[dean]

Thanks for your input...

I always make sure the tires are inflated to spec and I often check the
amount of thread left on them. This is in part due to several posts I read
on this subject back when I bought the car. I never used the small spare
tire (it still looks very new) nor let anyone tow my car with only two
wheels jacked up. The car does not have a hitch so it never towed a trailer.
I do not do any offroading.

That said, then it could as well be the center LSD(limited slip diff). All
in all, I am a bit surprised that a center differential would burn at 170k
km. It is possible that the first occurrence of the problem happened to me
almost a year ago. After a 4 hour hwy drive I was pulling into a U shaped
driveway when it happened: binding and grinding was horrible. After the car
cooled down and for the remainder of the trip, this had not repeated and
therefore I kind of forgot about it thinking it might be due to the CV
joint. But when you said the same thing happened to you after a long drive I
remembered that incident. Since that trip, my wife drove it mostly to work
and back (20 km commute) so there was not really a chance to experience it
again.

Anyway, I did call Subaru and got a quote on the replacement of LSD that is
definitely making me think about the other option suggested in some posts on
this subject - just continue driving it. If the LSD fails (presumably the
silicone liquid inside lost its viscosity), can I then ignore the problem
and drive the car with a bad LSD? If it is bad, is it in "open" or in
"locked" mode? If "open", will it behave as a FWD such that rear wheels
don't get any power from the transmission and do the front wheels 100% of
the power in that case? If "locked, is it still AWD?

too many questions, I know...

thanks for your advice, I will continue investigating on NG and USMB...

regards
Dean

Something to check before replacing transmission....

Newer subies do that if there is not proper tire inflation. Even 4
pounds lower on one side will make that happen. Check your air first.
Something about the limited slip stuff having "give" for turning that
gets over worked if the tires have different radius.

Good point - I may have been wrong to assume that the OP made sure to
have equal pressure in all tires. Another thing to consider is uneven
wear - this could give away any existing asymmetry in the drive train.

My 95 Legacy tires were shot when I bought the car; the car was crabbing
sideways and fishtailing pitifully. The tires may even have caused or
accelerated the failure of the clutch pack.

In any case, if the problem really only occurs after doing a few donuts
at max steering angle, it may be futile to worry about it. After all,
the center differential is SUPPOSED to bind under certain conditions
when "slippage" [read: different RPMs at the wheels] occurs.

In my experience, the car would bind after any prolonged drive,
especially in turns after a stretch of highway driving.

good luck

florian /FFF/