[Graham]

<img src="/forum/images/smilies/968/dry.gif" class="smilie" alt="" />



I know about the wheel lifting issue



but they are maintanance free are they not?



Graham

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[flash]

what wheel lifting issue?



i've not heard of any issues with the unit

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[tsj9197]

I added a torsen to my car to autocross, and I love it.

no maintenance cause it's all gears, no clutch plates to wear out like on most LSDs



yeah, what is this wheel lifting issue? i don't have that.

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[rustech]

I think he's refering to the tight radius turns at slow speeds that drags one of the tires a bit. I recall reading something about it in the past. The clutch type is more forgiving.



My AWD expedition does it at slow turning speeds also.

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[KensCab]

The "torsen" that is being refered to, I believe, is a Gleason Torsen. This is a gear locking differential similar to a Detroit Locker. Upon "sensing" slippage the gears will "lock-up" both wheels. The "limited slips" have plates, some what similar to clutch discs, that compress into each other upon sensing a slippage. These "plates" do loose their effectiveness over time just as a clutch disc would. This is kind of a simplistic way to describe the differences, I hope it helps.



The Limited Slip is the most "forgiving", or least noticed, a torsen unit can lock-up and with both wheels spinning in unison, same revolutions, around a corner will create some noise, a locker will "unload" sometimes with quite an alarming racket, and at first you will wonder if you should stop and look if something broke and fell out but you can get use to it. Short wheel base vehicle compound the effect. Like a locking diff's in a Jeep or early Bronco. I have a "Gleason Torsen" in the front and a Detroit Locker in the rear of my early Bronco for 4-wheeling, great off-road, but can be a pain in the ass on the street!

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[Jim Child]

I do fine with the Torsen unit on my race car. I haven't had any maintenance issues with it.

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[GREYGHOST]

There is a Issue with the torsen unit in our cars, if you run a serious autocross

setup i.e good shocks and R-compound tire, with little or no fuel in the tank.

the right rear tire will lift of the ground in a hard slow right hand corner, taken

in first or second gear. the left front is fully compressed on the bump stop and

the right rear is fully extended that lifts the wheel and tire. at this point there is no

resistance for the torsen to work with, so it becomes a open diff at this point. <img src="/forum/images/smilies/968/sad.gif" class="smilie" alt="" />



the cure is as bad as the disease. what we have found is that you have to run a

full tank of fuel to get away from the lift. that 17 gallons more than I would normally run. I usually start a event with the fuel light on, If the course has a slow hard right turn I will go fill it up, if not then no worries run it empty.



this problem is on both suspension setups the base and the m030 with stock bars.

right know I working thought the problem working with the rear alignment and

ride height adjustments. looking to add a heavy front bar.



thanks Rob

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[flash]

interesting - i have yet to experience this problem (or even hear of it) - i do have the GT unit though - come to think of it, i haven't heard of anybody hitting the bumps stops much either - are you sure your front suspension is ok? sounds soggy

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[Graham]

Thats the problem explained.



Thanks RCS 968.



Any Torque sensing unit including the Quaife ATB will work like that I have been told.



Is the GT a clutch type?



Graham

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[flash]

no - it's also torque sensing, though a different set of ratios - that bumps stop thing has me bugged - that just sounds like a real problem - you should not be hitting those - if you are, then you need more damping, either by spring or strut

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[Jim Child]

[quote name='RCS968' date='Mar 20 2005, 02:49 PM']There is a Issue with the torsen unit in our cars, if you run a serious autocross

setup i.e good shocks and R-compound tire, with little or no fuel in the tank.

the right rear tire will lift of the ground in a hard slow right hand corner, taken

in first or second gear.  the left front is fully compressed on the bump stop and

the right rear is fully extended that lifts the wheel and tire. at this point there is no

resistance for the torsen to work with, so it becomes a open diff at this point. <img src="/forum/images/smilies/968/sad.gif" class="smilie" alt="" />[/quote]



Do the rules allow you to run stiffer springs and double adjustable shocks? If so you would be able to dial this behavior out. I've never encountered this problem on the track. However, on a race track you don't find 1st gear corners, and the 2nd gear corners you find are probably a lot faster than what you're describing.

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[GREYGHOST]

[quote name='flash' date='Mar 20 2005, 12:44 PM']no - it's also torque sensing, though a different set of ratios - that bumps stop thing has me bugged - that just sounds like a real problem - you should not be hitting those - if you are, then you need more damping, either by spring or strut

[right][post="2103"]<{POST_SNAPBACK}>[/post][/right][/quote]



In the SCCA Solo2 program you have to run the spring delivered on the car from the factory, the shocks are free and yes I have some special Double adjustables by Koni, they are valved extremely stiff to the point that if I adjust the compression of the shock up the front will pogo over the bumps. Rebound is so stiff that on a course it will jack the car down on the stops that increase the spring

rate. this is one of the ways that Solo2 competition stock catagory cars have to combat soft factory spring.



the front Koni Strut that I use started life as a 944 turbo cup series shock, for the

series run in Germany. Much Stiffer than any M030 or Koni Yellow sports.



just for grins we run a g-cube which measures the G's that we are able to pull and

peak. the high peak that I have seen on a concrete course is 1.28 of lat accel. with a constant of 1.19 in a sweeper. as in my signature you will notice that the inside tires have a little daylight under them. at the this event I was pulling 1.18 though this corner.



I wish that we could run a stiffer spring in stock but we can't <img src="/forum/images/smilies/968/sad.gif" class="smilie" alt="" /> we have to work with what we have been allowed in the rules.



I have been running National Scca Solo2 event for the past 17 years. In my past last three trips to Nationals I have not finished any lower that 3rd. i.e this was in my

friends Boxster S. The 968 was retired in 2000 because of a class issue, know that it has been cleared up, it is one of the favorites along with these others Rx-8, 350Z

and older e36 m3, and mr2 turbos. fun class good competition.



thanks Rob

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[Graham]

Thanks guys,



I think the wheel lifting thing shouldn't be a problem so the Torsen should be ok.



Reliability is the main thing



Graham

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[bob blackwell]

No reliability issues with my factory Torque Sensing (Torsen) differential. the only maintenance I have done is to replace the fluid with SWEPCO. The car currently has 105, 257 miles on it. Good luck, Bob Blackwell.

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[flash]

something sounds abnormal somewhere - i think i would do 2 things on the car with the bump stop issue - first, measure your springs to see that they are making full rate - they may have gone soft - second, if they check out ok, get a bigger bar up front for sure, though that is likely going to introduce understeer issues - i did some full power full turn plows prior to installing my suspension mods, just to see what happens, and though it was very soft by my standards, i was nowhere near the bump stops - something doesn't sound right

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[rustech]

I would get some aftermarket 250s and paint them black to look stock! <img src="/forum/images/smilies/968/unsure.gif" class="smilie" alt="" /> <img src="/forum/images/smilies/968/tongue.gif" class="smilie" alt="" />

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[Graham]

Found this on how stuff works



The Torsen differential* is a purely mechanical device; it has no electronics, clutches or viscous fluids.



The Torsen (from Torque Sensing) works as an open differential when the amount of torque going to each wheel is equal. As soon as one wheel starts to lose traction, the difference in torque causes the gears in the Torsen differential to bind together. The design of the gears in the differential determines the torque bias ratio. For instance, if a particular Torsen differential is designed with a 5:1 bias ratio, it is capable of applying up to five times more torque to the wheel that has good traction.



These devices are often used in high-performance all-wheel-drive vehicles. Like the viscous coupling, they are often used to transfer power between the front and rear wheels. In this application, the Torsen is superior to the viscous coupling because it transfers torque to the stable wheels before the actual slipping occurs.



However, if one set of wheels loses traction completely, the Torsen differential will be unable to supply any torque to the other set of wheels. The bias ratio determines how much torque can be transferred, and five times zero is zero.



*TORSEN is a registered trademark of Zexel Torsen, Inc.



Hummer!

The HMMVV, or Hummer, uses Torsen® differentials on the front and rear axles. The owner's manual for the Hummer proposes a novel solution to the problem of one wheel coming off the ground: Apply the brakes. By applying the brakes, torque is applied to the wheel that is in the air, and then five times that torque can go to the wheel with good traction.



I thought this illustrated the problem in a novel way



Graham

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[flash]

i get that the diff stops sending to the one wheel, bummer, but that's the nature of the low ratio the stock diff is set at - that doesn't result in much lift though, nor does it result in bump stop issues - it sounds like you have a problem somewhere in your suspension that is resulting in contact with the bump stops



i would seriously measure the springs and torsion bars for rate, and also test both sway bars - if any of those has gone soggy, and it does happen, then you could easily have this problem - shocks have nothing to do with it when it somes to resistance to load, so while they may seem "stiff" they still do nothing in providing resistance to cornering load, especially in slow corners

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[Greimann]

they are valved extremely stiff to the point that if I adjust the compression of the shock up the front will pogo over the bumps. Rebound is so stiff that on a course it will jack the car down on the stops

This why he is on the bump stops. That and a 1.18 corner G-load! <img src="/forum/images/smilies/968/ohmy.gif" class="smilie" alt="" />

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[kamran haghbin]

what bobby is saying is more correct, the wheel lifting hs in the car not the diff. if the diff is ever in question, take a look at the audi RS6 in scca racing. the audi quattro system in the RS6 is the exact same system in all audi quattro models using 3 torsen differentials. and when a company can be that succesful in racing it is only to that one advantage (excludint FSI technology in LeMans) it is to that system.

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