limited slip or torque biasing differential for a 968

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limited slip or torque biasing differential for a 968

Postby lrayner on Sat Sep 19, 2015 7:16 am

I am revisting a question I posted a few years back forum/viewtopic.php?f=3&t=2411 when considering this question for my 944 spec build. I ended up with a factory limited slip that time and have been very happy with it. The guy at Guard Transmission tells me that the factory set up is a true limited slip with a 40/40 set up, that is, it will go to 40% lockup on both acceleration and braking. The 924S is now sold :cry:

Any thoughts on what to go with for my 968, which will be driven on the street plus AX and maybe an occasional track day? Other than adjustable Koni's it is currently all stock, no MO30.

Leigh Rayner
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Re: limited slip or torque biasing differential for a 968

Postby Dan Chambers on Wed Nov 04, 2015 4:29 pm

A few years back (uhmmm ... quite a few) I put a Guards Transmission Torque-Biasing diff in my 944. These units work GREAT on acceleration, especially at AX's with tight apexes and off-camber layouts. They also do not have clutches that wear out. I got great performance out of my T-B diff.

There were two down-sides as I saw them: The Torsen or Torque-Biasing diff's are "open" when you brake. If you like to trail-brake or brake into corners, there's no assistance from the diff ... it's like you don't have anything back there. She's wide open. The other down-side: with all those gears whirring around, the T-B diff's generate a lot of heat. Not a big issue on the street or at AX's, but at the track, the transaxle gets HOT! My trans lube had to be changed after each TT event because of the heat stress on the gearbox.

Limited slip diff's aid you in both acceleration, and braking ... making late brake and trail-braking a real art-form to grasp. It's nice to know that when you need it, the late-braking/trail-braking aid just might hold you to your spot when you're trying to eek out that last milli-second or you're off-line due to some knuckle-head who dove the apex under you just as you were about to turn in. You can vary the amount of slip with a clutch-built limited slip diff (40%-60%, etc.), and most of the Porsche Tech's in town can work on those diff's with little worry and much expertise. The down side: all clutches wear out, and eventually you have to get into the limited-slip diff's for servicing. T-B diff's don't have this issue.

I pulled the trigger on one of the more stout Limited-slip diff's when I upgraded to the 3.6L engine and have been very happy with it since its inception into the Black Pearl: O.S. Giken. A little more $$ initially, but a good unit with reliable performance and durability in my experience. Great for trail-braking, and holds the torque on acceleration out of the corners.

Hope that helps.
Dan Chambers
"It's just a "well prepared" street car ... or a very, very well-mannered track car." :burnout:
1983 SC #91 3.6L, "Black Pearl" Livery
1987 944 (gone but not forgotten)
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