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Center diff questions


Hi all-

I just bought a good clean VR-4 as my main street car. My line of work means it's bad politics to drive a non-Mitsu, and I've always wanted one anyway. Got lucky with a good one from a trusted source. Very stock except rear LSD already done.

I see lots of posts here about the rear diff conversion, but nothing about the center diff. From a handling and balance perspective I can tell you that the center diff has a very big effect, and I'm sure that the works rally VR-4s all had mechanical clutch limited slips.

Ralliart sells an Evo3 center mechanical(clutch) LSD but no longer lists anything for the VR-4. My question is this: what have people done about the center diff/coupler in their cars? Viscous units overheat and have non-pregressive lockup...on the other hand they don't wear until overheated or two-wheel towed (during which they fail permanently) or make noise.
 

THEKID

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May 18, 2008
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bergen county nj
here ya go quaife front and canter lsd available link
 


RRE are cool, ok. But Quaifes are TorSen gear diffs, unpredictable in racing use (lift a wheel, and they don't limit slip at all). I want mechanical clutch-plate 1.5 or 2-way limited slip. That's what Ralliart has always used.

I've driven an early GpB Quattro with Torsens and it's a handful. Excellent for a street car - little wear, no noise, torque-biasing, but relies on resistance from the low-torque wheel.

So, clutch LSDs? Answer me this and I can go a certain distance on my own: what are the differences in the transfer case between gvr-4, Eclipse, and Evo 1-3?

A
 

Lonewolf64

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May 17, 2006
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I know I have seen Kaaz LSD units for our cars and they are clutch type and still provide limited slip effect even when wheels are in the air.

I just found Kaaz for sale from Shep's site. click
 

GVR-4

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Apr 22, 2002
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Asheville, NC USA
You may know this, but the center diff is in the tranny. The transfer case doesn't contain a dif.
 

H05TYL

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Quoting musketeerracing:

From a handling and balance perspective I can tell you that the center diff has a very big effect, and I'm sure that the works rally VR-4s all had mechanical clutch limited slips.




Nope, works vr4's first had locked centre diffs, and later had viscous ones.

A atb (like the Quaife one) would be the best option.

Until I can afford the Quaife atb i'll stick with the factory viscous in one of my cars, and the locked centre in the other.
 

OK, we're getting warmer, but...

Shep doesn't actually list a Kaaz center diff for our application. And the Kaaz USA page doesn't seem to have one either (let me know if I'm on the wrong page): click

I do see that Shep lists a viscous delete collar, which is interesting to us because...

...I think you'll need that also if you're going to upgrade the diff. If the VR-4 is laid out like all the Evos I've built, then the spider gear open differential is in the gearbox, as GVR-4 says, but the viscous coupling unit - the thing that controls the slip - is actually in the transfer case. If you just put a clutch limited slip in the gearbox where the current open diff is, you'll end up with two limited slip systems fighting each other - the clutches (or quaife) in the gearbox, and the viscous couple downstream toward the rear. That would make for some weird dynamics.

Ralliart does list an Evo III clutch-plate center diff. Anyone know if that would fit in, as GVR-4 says, the gearbox?

Oh - and that's interesting about the works rally cars. I'll have to drag out some of my old books on that, maybe I can find out more. It is possible to rebuild viscous couplers with higher locking torque, but it doesn't make them any better in terms of lockup progression.
 
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kartorium

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Dialcaliper or someone was mentioning a ralliart viscous unit with high rating. Most likely that would be a good option for you. There are also ATS, cusco and kaaz units available, however I'm not sure if Kaaz actually has a center, just front and rear I think.
 

toybreaker

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Apr 30, 2006
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Quoting musketeeracing:
I think you'll need that also if you're going to upgrade the diff. If the VR-4 is laid out like all the Evos I've built, then the spider gear open differential is in the gearbox, as GVR-4 says, but the viscous coupling unit - the thing that controls the slip - is actually in the transfer case. If you just put a clutch limited slip in the gearbox where the current open diff is, you'll end up with two limited slip systems fighting each other - the clutches (or quaife) in the gearbox, and the viscous couple downstream toward the rear. That would make for some weird dynamics.



The viscous coupler is in the transmission in the vr4's
 

H05TYL

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km255 vr4 boxes and w5m33 vr4 and evo 1, 2, and 3 boxes are all laid out the same, and the viscous coupling is in the end of the gearbox (right next to 5th gear).
The transfer case is only a right angle drive - nothing else.

Evo4+ is different.
 

jepherz

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I don't see why the same clutch packs wouldn't work in vr4s as they do in any of the early evos since we have the same transmissions. One thing I could see being an issue is the outter gear on the center diff. If you look at jack's transmissions site, they show a few different types of center diffs. He mentions that "center diff A will not work in transmission B" and vice versa. Also, I think if you're running one of these clutch pack center diffs, although I've never seen one in person, I'm guessing they don't have the two output shafts that insert into the stock viscous coupler. As you are saying, that would make the lockup methods redundant.
 


Well, that IS useful info. Thanks guys.

Who is this "jack's transmission site"?

Just been driving the VR4 today. It's awesome! I love the twin trip meters, the different trims on the blower flaps (more feet, or more face), and a dozen other things. Also this car is completely clean, original, and absolutely everything works. Even the leather is good. Very happy.

Long throw on the shifter though!

1915/2000
 

Struc

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Nov 24, 2008
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Oconomowoc, WI
Quote:
Long throw on the shifter though!



Yeah, replaced the shifter on mine before I even got it running. Buy a 1G Eclipse shift arm and throw it on. It's a lot shorter than the GVR4 one.
 


Another good bit of advice, thanks!

Found Jack's site, but not the photos you're referring to. If someone could send me there I'd appreciate it.

Another technical question, then. If the coupler is in the gearbox, and if another thread that I read about with a center diff failure is correct in saying the rear wheels were laying patches, does the coupler couple the front to the rear, or the rear to the front? I know that sounds funny but the point is until the coupler tightens you'll get more drive to the upstream (mechanically closer to the gearset) end. In Evo4-9, the coupler works on the rear, so the car is essentially a FWD with a dragging axle until slippage. How does the GVR4 work?
 

H05TYL

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no, the centre diff behaves just like an open diff when there is no slippage, all four wheels are driven together, until one end is spinning faster than the other (loses traction) - then the output shafts turning at different speeds heat the fluid in the viscous unit (which is attached to both) and causes it to bind up, limiting the amount of slip - hence being a limited slip diff.


The principal is exactly the same as a rwd car with a viscous limited slip differential - it's not one wheel drive until traction is lost, and then 2wd.

All of the non-active (not electronic) centre diff equipped mitsi's behave in the same manner.

Possibly where the confusion comes from is in the case of a Skyline GTR which has no centre diff at all, but an electro hydraulically actuated wet multiplate clutch. In the Nissan the car is Rwd until traction is lost, at which point the computer activates a hydraulic ram, which engages the clutch pack transmitting drive to the front wheels also.
 

H05TYL

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No, the centre diff behaves just like an open diff when there is no wheelspin occuring, it drives all four wheels equally. When one pair of wheels starts turning faster than the other pair (front-rear) this causes the different speed of the output shafts from the centre diff (to both of which the viscous unit is attached) heats the fluid inside the viscous unit causing it to bind up and limit the amount of slippage.
Note that the lsd effect is initiated by difference in rotational speed , not torque.

Exactly the same principal as a viscous lsd in a rwd vehicle, it doesn't drive one wheel only until slippage occurs, and thereafter drive both.

All of the mitsubishi 4wds without active (electronic) centre differentials behave in this manner. (This is why the badge says, "Full time 4wd").

A possible source of the confusion is the Nissan Skyline GTR, which does not have a centre differential in the traditional sense. Instead it uses an electro hydraulically operated wet multi-plate clutch to engage drive to the front wheels. Under normal conditions the car is Rwd only, when the computer senses wheelspin it operates a hydraulic ram which engages the clutch plates. (This is located in the rear of the gearbox housing, to one side of the output shaft and is driven by chain).
 

Dialcaliper

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Even the Evos have "full time" 4WD (as does the AYC in the rear), since besides the electronic pack, they still have a separate open diff setup, just like we do with the viscous coupling. Also, the front diff on an evo is in the transfer case with the center diff - the transmission has a single output.

The The GT-R has an electronic clutchpack that is decoupled from the drivetrain during normal operation until slipping occurs. The Haldex setups found on most Volkswagens and some Audis are also set up like this, except in a FWD configuration. (The Bugatti Veyron also uses a RWD Haldex setup - just much beefier and fancier.)

Porsche uses a setup with only a viscous coupling that is always rotating slightly and transferring a small amount of torque to the front (~5%), and no center diff. When the rear wheels slip, the coupling can transfer a fixed amount of torque to the front wheels, based on the rear slippage, but it reacts faster than a typical VCU because it's geared to already be spinning slightly. (Changing the tire diameters will actually mess this up)

It wasn't me that mentioned the Ralliart Evo I-III VCU - it was one of the NZ or Aussie guys. Alex at DSG said it was in his catalog for ~$800. Paired with a Cusco Tarmac gear, it could make for a pretty sweet RWD biased setup.

Quoting H05TYL:
No, the centre diff behaves just like an open diff when there is no wheelspin occuring, it drives all four wheels equally. When one pair of wheels starts turning faster than the other pair (front-rear) this causes the different speed of the output shafts from the centre diff (to both of which the viscous unit is attached) heats the fluid inside the viscous unit causing it to bind up and limit the amount of slippage.
Note that the lsd effect is initiated by difference in rotational speed , not torque.

Exactly the same principal as a viscous lsd in a rwd vehicle, it doesn't drive one wheel only until slippage occurs, and thereafter drive both.

All of the mitsubishi 4wds without active (electronic) centre differentials behave in this manner. (This is why the badge says, "Full time 4wd").

A possible source of the confusion is the Nissan Skyline GTR, which does not have a centre differential in the traditional sense. Instead it uses an electro hydraulically operated wet multi-plate clutch to engage drive to the front wheels. Under normal conditions the car is Rwd only, when the computer senses wheelspin it operates a hydraulic ram which engages the clutch plates. (This is located in the rear of the gearbox housing, to one side of the output shaft and is driven by chain).

 

H05TYL

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Wgtn, NZ
I thought that would be the case with the "active centre diff" evo's, but I wasn't 100% sure. I've never taken one apart before. Early Evo's, vr4's and GTR's I have however had the pleasure of disassembling.

It's a good idea to differentiate between later Evo's (4+ which have the differentials in the transfercase) and the Evo 1-3's which have the same setup as (and which parts from are compatible with) vr4's.

The GTR (attessa) system is operated by hydraulics, which are controlled electronically.
 
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