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Yes it can happen with an LSD. Essentially the center diff is a LSD. It happens when the viscous coupling gets over heated (on a manual tranny). The VC is a set of altenating discs

 

 

FRFRFRFRFR

 

F- front

R- rear

 

The plates have holes in them. When they spin at differnt speeds, the silicon fluid heats up, and mechanically hooks up the plates. When everything equilizes the liquid cools.

Now if this condition lasts for too long (and in a manual it doesnt take long), the fluid cooks and becomes a glue.

Front and rear axles spin at different speeds ( no road is complete straight). They need to have a diff in the center to alow this (manuals only we are talking about). When this ability is lost, you get torque bind.

 

It is usually caused (on a manual) by mismatched tires, driving on a falt, or an underinflated tire.

 

Hope that helped.

 

You can also search Viscous coupling and spend days reading.

 

 

nipper

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Thanks nipper...more qs.

1. What is the net effect of removing the rear halfshaft?

2. I realize long highway runs have the worst effect on the VC...the fluid gets constantly sheared...but its shot anyway...so do you think driving around town where you make lots of turns and get the hop is worse for the rest of the drivetrain (i'm guessing the center diff gets abused, rear too?) than just long shots on the highway?

3. How do i remove the rear halfshaft...do you think a shop would be willing to do it?

4. would this be related to that big thread about converting to 2wd..I cant seem to find it now but it was a raging debate as to weather it was possible...do you remember?

5. Oh and ive asked this b4 but never got a response...are the vc's interchangable...could i get one off a different model year at a yard...theoretically they should last forever...but mine's shot so that might not be a good idea...what if i had access to a known good one on a junker?

 

Thanks

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5- i think they are, just some have differnt calibrations then others. i am sure somone else will jump in on this.

4- i dont remember

3- it just unbolts between the carrier bearing and rear diff.

2- You can harm your rear diff, and the car will refuse to go where you point it on the slightest slick surface when it gets that bad. Its just dangerous. Also you will damage the tires, etc etc. You may also find it impossible to turn the steering wheel any great degree.

1- You get fwd.

 

nipper

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2. Are you serious? The other day i was on a freeway ramp and it had rained but i hit the apex and it started to oversteer like i was on ice. I was like wtf? I was able to correct it like you would if you were sliding in snow or ice so it did go where i pointed it but do you think this is related?

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2. Are you serious? The other day i was on a freeway ramp and it had rained but i hit the apex and it started to oversteer like i was on ice. I was like wtf? I was able to correct it like you would if you were sliding in snow or ice so it did go where i pointed it but do you think this is related?

 

hell yes ... its dangerous.

There is a tree out there with your name on it. Lets hope you never find it.

 

Please be careful.

 

nipper

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so thats a hell yes for that slide being related? musta been cause i couldnt explain it. freaked me out. so does this mean the whole drivetrain is toast? So if i drop the half shaft am i safe®? How long can i drive it like that?...LOL till it snows...been in awd so long i wouldnt know what to do. So sheet now you got me scared nipper. AARRRRGGGGG why me (this is just one tiny thing wrong in my life right now) maybe meeting said tree wouldnt be so bad. jk...sorta. thanks nipper...Oh do you think a shop would drop the shaft for me or would they say nononono too dangerous. Or can i do it myself...CHEAP tools and no lift?

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WHat? where did you get that from this thread?

 

I figured the VC thing would overheat wich is the cause of the torque bind. Driving 700 miles @ 80-90 mph for 7 hours straight wouldn't overheat the VC?

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I figured the VC thing would overheat wich is the cause of the torque bind. Driving 700 miles @ 80-90 mph for 7 hours straight wouldn't overheat the VC?

 

No, you are going in a straight line so the front and rear should be turning the same speed. If all the tires are not the same and/or the pressures are way off then it could cause a problem.

 

Normally the VC doesn't react until there is around a 100rpm difference between the front and the rear, at which point it provides about 28 lb-ft of resistance. What the curve looks like or where it goes from there I can't tell you, but it normally cannot transfer all of the engine's power and I would not rely on it to do so, even if it is "binding" and the car moves without a prop shaft. Nearly all 5-speeds have the same coupling, and Subaru makes a couple that are stronger for rally use.

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Without a rear drive shaft you are relying on the viscous coupling to make the car move. If it were not for the VC, the center diff would be open and you would just spin the rear output and not go anywhere. So all that is sending power to the front are small plates that may or may not stay stuck together and were not intended to transfer 100% of the car's power.

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I guess for 745 cad i could just buy a new vc. Anyway I just read thru the whole danger of driving w/o rear driveshaft thread...appears no consensus was ever reached. Did soa ever get back to you nipper? Turns out the guy who started the thread is also in SLC so im gonna try and touch base with him and see how its working. I agree jamal but im not planing on driving cross country like this...just tryung to buy time to get the money to fix it...If i get stranded 5 miles from home i really dont care...the vc is fried already so whats the harm if i experiement? Also Jamal can I pull a vc from a junkyard and try it? Will any 5mt awd suby work? Lots of junked subys here. Thanks for your input...your knowledge is appreciated.

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93 Forester 5 sp. Had a similar problem and found a big parking lot and did 15-20 figure 8's in reverse and this seeemed to have cleared up the problem, it hasn't returned..at least not yet..that was over a year ago.. apparently going in reverse forces the fluid back through those holes nipper was talking about and cleans them up. worth a try..

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Here's a somewhat crazy idea: remove your rear driveshaft and weld up your center diff. Of course, you'll need a new center diff along with the VC when you want to go back to AWD. If the VC can be opened, maybe you can weld that solid (remove the rear driveshaft, of course).

 

People weld up rear diffs for off-road applications, then disconnect one of the rear axle joints to drive on the road (3WD?). There are threads about it in the Off Road forum. This is the same idea applied to the center diff.

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