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Bad VLSD?


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6 replies to this topic

#1 wtdash

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Posted 31 January 2008 - 08:07 PM

The snow is getting deep here in N. Idaho....and the berms of plowed snow are getting tall.

So I parked my '90 Wagon w/its '91 auto and rear 3.9 VLSD into the side of one, and 'stuck' it there.....

(BTW, I have the 4WD Diff Lock Mod installed and it was in use.)

....I wanted to see if 3 wheels were spinning. But I only had one @ the front and one in the rear. :confused:

I'm confused because I expected to see both rears turning.

The back end kicks out if I punch it in slippery conditions....isn't that a 'sign' of an LSD? And I don't recall that happening on my other Legacy AWDs???

Even had a little excitement on snow/ice covered Snoqualmie Pass when it downshifted to 2nd to pass a few cars and the rear end went sideways @ 40. :burnout: My passenger wasn't quite so enthused, though.

I got the VLSD used w/unknown mileage. Do they wear out? And if so, are they serviceable? If I jack up the rear end and both wheels spin in the same direction a valid test for a VLSD?

It does have the 'sticker' labeling it as a 3.9 VLSD, too.

Thanks as always!

#2 WoodsWagon

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Posted 31 January 2008 - 09:04 PM

They lock tighter the hotter they get, so getting agressive with the wheel spin might have helped a bit. But by then you have patches of ice under your wheels.

Clutch pack LSD's are better for stuck situations. The viscous ones are better at dynamic situations.

#3 Manarius

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Posted 31 January 2008 - 09:49 PM

VLSD's do wear out eventually. If yours has a lot of miles, I bet it's worn out.

#4 nipper

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Posted 31 January 2008 - 09:57 PM

Viscous couplings take a little while to get going, and they dont spin. They just transmit as much force as is required, unless your really really stuck.

The nice old LSDS with clutches worked oposit the VC. The mechanical LSD was always transmitting power to both wheels, untill the clutches were overrun by the mass of the car with differnt speed of the wheels.

The VC is free wheeling untill there is slip. The slip is required to heat up the fluid to get the VC to engage. If its really cold outside, its possible to take longer for the coupling to heat up then it would normally if the car has been parked.

nipper

#5 Suzam

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Posted 31 January 2008 - 10:18 PM

+1 on nipper's reply.

I can get the VLSD rear in our MY01 to clunk hard while going 15 mph and spinning the wheels with WOT in the snow. The rear will spin then a HARD engagement. Scared the heck outta me until I figured out that was going on.

VLSD isn't the same as the old posi unit or limited-slip diffs.

Give it more juice and it should get you going.

#6 rayfordmachen

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Posted 01 February 2008 - 12:08 AM

Hmmmm, wtdash's post now has me wondering about my 93 Impreza AWD. On snow covered logging roads the Impreza just doesn't compare to my old 87 GL wagon that had pushbutton part time 4WD. I'm not so sure it's worn out as suggested for wtdash or just isn't fair to compare the two different types. But, wtdash, you say it doesn't seem to be the same as your other AWD Subaru? Interested in what you decide - worn out or just the characteristics of VLSD. This Impreza can keep me going and get me out of jams in the snow but I'm going back to the part time 4WD models. They really work better for me on snow covered backroads which is what I like most.

Nipper,
When you say "nice old LSDS with clutches" is that referring to the part time 4WD with pushbutton like my old 87 GL Wagon? I'm reading everything I can find on comparing the various 4WD systems and differentials and still not understanding it all.

The nice old LSDS with clutches worked oposit the VC. The mechanical LSD was always transmitting power to both wheels, untill the clutches were overrun by the mass of the car with differnt speed of the wheels.
nipper



#7 nipper

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Posted 01 February 2008 - 12:20 AM

Nipper,
When you say "nice old LSDS with clutches" is that referring to the part time 4WD with pushbutton like my old 87 GL Wagon? I'm reading everything I can find on comparing the various 4WD systems and differentials and still not understanding it all.


noooooooooooo

Limited slip differntails had either cone clutches or clutch packs in them.

On AWD
http://www.autozine....ction_4wd_2.htm

On Limited Slip Differentials

http://auto.howstuff...ifferential.htm
http://www.houseofth...fferentials.htm




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