Clutch or Torsen LSD front diff info needed .

discopotato03 · Post by **discopotato03** » Thu Mar 27, 2008 10:46 pm

Hi all , I've been wondering for a while how I'm going to get around the front traction issues with an open front diff center and the open center L AWD gearbox . The obvious prob is that this system would feed all the power out any spinning wheel and its not a practical thing to lock the center diff on hard surfaces .
The rear of an RX Turbo is not an issue because its rear R160 diff has a clutch plate type LSD center .

My suspension mentor reckons with a front LSD the center open diff shouldn't get the opportunity to waste all the power because neither end diffs will allow major wheel spin .

He spoke at length about the pros and cons of Viscous Torson and Plate diffs and really the Viscous comes out a pretty poor 3rd . From my research the transmission engineers (performance minded ones ) agree that the Viscous is a cheap option rather than a sophisticated one .

Clutch plate LSD's are probably the most tunable of the three because the spider ramp angles can be varied and the static plate pre load set to whatever you want .

The Torson type is a really interesting design because it has many positive abilities that no other purely mechanical system has . You could say its proactive rather than reactive because of the way it senses load variations .
Being a combination of worm and spur gears means that it virtually instantaneously senses the load difference created by one wheel losing traction and the worm and spur gears on the side that has grip won't allow those on the unloaded side to spin out of control .

Anyway long story short I need either a clutch or Torson LSD to get all the grunt to the ground .

More cost , cheers A .

Wilbur · Post by **Wilbur** » Fri Mar 28, 2008 9:22 am

I might have missed it, but was there a question in there ?

brumbyrunner · Post by **brumbyrunner** » Fri Mar 28, 2008 10:10 am

You're fourth option is a Suretrac.

discopotato03 · Post by **discopotato03** » Fri Mar 28, 2008 1:53 pm

If you mean the AP Suretrack gadget thats a bastard of a device , most people think they are very harsh . I imagine it would feel like a tame detroit locker with syncro hubs instead of dog clutches !

There are a few variations on the Gleason developed Torsen LSD , T1/T2/T3 .
The T1 is the cross axis worm and spur gear type , T2 the purely Helical type and T3 the small diameter type generally found in AWD center diffs .
The general wave seems to be to flick those Suretrack things in favor of just about anything for front diffs .

Yes there is a question in here , has anyone used a front LSD (not inc Viscous or Suretrack) and what did you think of it ?

Cheers A .

PeeJay · Post by **PeeJay** » Fri Mar 28, 2008 4:58 pm

When I was was playing with the low range on my box there was a torsen diff on ebay for $1000, I nearly got it but couldn't think of any way to justify the expense.

Now that I've changed from the L AWD box to a Forester one with the VLSD center it's amazing how much better the car handles. I only have open centers front and rear, but the difference is amazing, I almost don't get understeer any more.

Gannon · Post by **Gannon** » Sat Mar 29, 2008 8:03 am

I think you will be very interested in this Front diff interchangeability: The true answer

Basically,.. the front diff in all subaru 5 speed transmissions is interchangable, from the 5sp in the 86 L-Series right through to the 2004 WRX STI

Which means you can use any Front LSD designed for any 5sp Subaru transmission
Clutch.
Helical.
SureTrac.
VLSD.
Open.
*insert all other brand names here*

Very interesting read

vincentvega · Post by **vincentvega** » Sat Mar 29, 2008 8:18 am

discopotato03 wrote: Anyway long story short I need either a clutch or Torson LSD to get all the grunt to the ground .
More cost , cheers A .

what sort of power are you talking about? You are only running an EA82T arent you? Sounds to me like you are wasting your time spending big money on a front LSD that will make your car a bitch to drive on road

discopotato03 · Post by **discopotato03** » Sat Mar 29, 2008 7:25 pm

Vincentvega getting an EA82T powered RX to spin the inside front wheel is no effort - my tired bog stock 86 274K old one does this now if provoked .
Admittedly my RX has a fair bit more roll stiffness than a std soft mushy RX so its cornering geometry change is less and it works its tyres a bit harder .

The point is if you can do it with front wheel drive the situation won't be any better with and open center diff AWD - open centre power dividers ALWAYS sent the power out to the path of least resistance and that in this case is any wheel with low/no traction .

What I want to run is some form of front LSD that will limit this and not be a hassle when driven sedately . Plenty of performance AWD cars have them so its just a case of finding out which one has the best characteristics - that probably means a one way clutch type with low static pre load or one of the lower torque bias ratio Torson centers .

Cheers A .