LSD choice for 31-spline 8.8" Cobra diff

[Dan Baldwin]

Long time no post!  Z is gone, but I need a new LSD for the current ride: ~530hp LS2 FD RX-7

 

The T2R that was been in it is worn out  Apparently it's not unheard of.

 

Looking at options for a new limited slip carrier, got it down to:

Eaton Posi (clutch-type)

Yukon Duragrip (supposedly an Eaton posi clone for less $$$)

Eaton Detroit TrueTrac (helical gear type similar to T2).

 

Definitely like the rebuildability aspect of the clutch-type units after a helical wore out on me.  But apparently these clutch types don't employ ramps like the old R200 clutch LSDs which increase clamping with applied torque.

However, Eaton literature implies that it *does*:  "When torque input increases the clamping load on the clutch packs increases."

 

I guess that the clutches do see a smidge more clamping due to the force from the pinion gears trying to push the side gears apart, but it couldnt' amount to anything like as much with the Salisbury/Nismo ramp style.

 

Anyway, need something that will give good torque bias ratio and still be very streetable, while able to tolerate hard track usage on Hoosiers, and occasional drag strip or Texas Mile runs.

 

I think I'd be OK with any of the three options listed above, but looking to tap into the vast knowledge reserves of HybridZ before deciding.

[JMortensen]

The Eatons are not very torque sensitive. There is a bit of misalignment of the spider gears that very slightly changes it under load, but for the most part it's the springs that load the posi. I used to work for Randy's (who makes Yukon). Their stuff is pretty much a direct copy of the Eaton. It's durable, but because it isn't torque sensing you might have to load it up tight enough to avoid wheelspin that it acts like a spool. They do sell different clutch packs and springs so that you can adjust it. I sold a lot of them and never had a single issue. If you find some old timers they might remember the problems that Eaton had in the 60s with the 12 bolts, but that's ancient history, they're pretty bulletproof now.

 

The Truetrac is like a Torsen but cheaper and less aggressive. I think the difference is 5:1 TBR vs 2.5:1 or thereabouts. There is another option if you have some money to spend called a Wavetrac. I don't have any experience selling them so I never got any feedback on them, but the theory is that it works like a helical and then there is a camming action on top of that that makes it lock up tighter. I am pretty sure they make it for the 8.8, in fact I think that was the first application they made IIRC.

http://www.wavetrac.net/

[Dan Baldwin]

Thnks, Jon!

Doh...  Really want to avoid ridiculous preload.  LOVED the clutch R200 in the Z.  No probs holding 250hp on Hoosiers, picking up the inside front exiting corners, with next to no breakaway torque (bought with ~23 lb-ft, 18 lb-ft last time I'd checked it).

 

Supposedly the TrueTrac is between T2 and T2R in terms of torque bias.  Seeing a range of 2.5-3.5 for it.  Good enough, maybe?

 

Is the Yukon a direct enough copy of the Eaton Posi to also have at least a smidge of additional lockup under load?

 

Still on the fence...

 

What about Auburn cone-type?

Edited April 11, 2013 by Dan Baldwin

[JMortensen]

Yeah, the Yukon is functionally the same as the Eaton.

 

Most of the Mustang guys do the T2R from what I have read.

 

Auburn is like the Yukon/Eaton but uses cones instead of clutches. The steel cone is forced into a slightly smaller cone machined into the housing creating friction. They have a regular and a PRO series, the PRO has more lockup and chatters. When they wear out you're buying another one.

 

I'd rate them Wavetrac, then the T2R, then the T2 or Truetrac, then the Eaton or Yukon, then the Auburn Gear.

[Dan Baldwin]

Perusing the 'stang forums, found multi SoloII champion who has used the T2R in the past, but then they started failing on him.  Now he's apparently back to clutch-type (Auburn or Eaton).

 

Wavetrac doesn't make sense to me.  Seems like a mild locker/torsen combination.  For there to be any differential action, the 4x convex/concave interacting faces have to be worked apart, presumably against a spring preload.  But after 1/8 of a turn, the convex feature is being indexed against the next concave feature, with the preload *adding* to slip.

Seems like it would act like T2/TrueTrac with a 4x/rev anti-slip/pro-slip action superimposed.

Anyway, at $1200 it's not a contender...

 

Starting to lean towards the TrueTrac.  Unfortunately they insist on non-synth gear oil, and I'm not adding a cooler.

Really hate the idea of a ton of breakaway/preload on a clutch-type though.

 

Hell, I might just run the "standard" Ford Racing TractionLok as used on the factory '03/'04 SVTCobras for less preload (presumably) and remove the rear bar if required for rear thrust grip.

 

Yeah, the Yukon is functionally the same as the Eaton.

 

Most of the Mustang guys do the T2R from what I have read.

 

Auburn is like the Yukon/Eaton but uses cones instead of clutches. The steel cone is forced into a slightly smaller cone machined into the housing creating friction. They have a regular and a PRO series, the PRO has more lockup and chatters. When they wear out you're buying another one.

 

I'd rate them Wavetrac, then the T2R, then the T2 or Truetrac, then the Eaton or Yukon, then the Auburn Gear.

Edited April 11, 2013 by Dan Baldwin

[SUNNY Z]

I just installed a brand new trac loc in my 8.8 IRS. Can't beat the price. $219 to my door from buyfordracing.com .

 

I'll be able to tell you more on this in a month when i've gotten some track time