question about torque biasing diff

I am undecided between the Guard TBD and their more traditional LSD. I have owned several cars with plate or clutch type LSD differentials, so I understand how they work. With the TBD, I realize if a drive wheel is lifted, all torque is lost to that wheel, same as an open diff. But, if the inside rear begins to spin, remaining in contact with the road surface, I assume torque is distributed to both drive wheels. Is that correct? Otherwise, I don't see its value.

That is correct. However, the torque to the non-slipping wheel will be limited to about 5 times the minimal torque being absorbed by the slipping wheel.

Do A Google Search on 'Torsen Differential' to Understand the Operation of the ATB (Automatic Torque Biassing) Differential. Automatic Torque Biassing - (in a Nutshell) - Transfers Drive proportionately to the wheels in proportion to their grip - Assuring Drive at all times..... So In Your Example - "if the inside rear begins to spin, remaining in contact with the road surface" Power will be transferred to the Outside Wheel Proportionately until Everything Becomes Equal. If You Use the Fitted 'Open' Differential - Loose Grip/Traction on one Wheel = Loose Grip/Traction on Both Wheels...................... Look Up 'Torsen ( TOR que SEN sing) Differential'

If i understand correctly we're talking about one drive wheel in the air and the other spinning? Either way I think you're in a heap of trouble!

No, the assumption is, the inside drive wheel is beginning spin, and the outside is in firm contact and not spinning. I realize if one drive wheel is in the air with TBD, you have nothing.

I have been considering same decision. My driving is mostly street and a few DEs per year. I lean toward the TBD for street because no wheel hop on slower corners. But I understand that TBD on track is a problem with wheel lifting as you mentioned and also with alligator humps on corners of many high-speed tracks. I also lean toward LSD for track because of braking lock-up, allowing later braking. Guardtransmission.com also has a "which one should I choose" page. Go to guard main site, click Products at top, Click on Cayman at left, then click on "Which diff type should I choose" (in red). I would have posted a link but there is not a distinct link as far as I can tell. Can anyone comment on street-ability of LSD?

Thanks for that Gator, almost makes that I don't need to say anything, maybe the one thing you didn't take into account is Price........:hilarious:

This issue is confusing to me because when you ask Guard about which differential is best, they say for any track use the LSD and only use the TBD for autocross. I'd like to see a point - counterpoint between Motordrive and Guard on the subject. This is copied from Guard's web site. The most typical installation choices for our differentials are as follows: (a) Street / autocross – Torque-biasing suitable for most applications, especially autocross. 40/25 (or 40%) LSD for mid-performance street cars. (b) Street / track – 40/25 LSD for light tack use, with stock suspension. 60/40 LSD if car has stiffer suspension and/or power upgrades. (c) Track only – 50/80 LSD Limited-Slip differentials provide lock-up on both acceleration and deceleration. The amount of lock-up on accel and decel can be adjusted by selection of the internal plate sequence and/or ramp selection. Lock-up on deceleration allows late braking and aggressive entry into high speed turns, reasons why all professional Porsche roadracing teams utilize LSDs, rather than TBDs. Torque-Biasing differentials provide lock-up on acceleration only. The amount of lock-up increases as the amount of torque increases. On deceleration, lock-up is negligible, making the TBD ideal for the slower-speed turns of Autocross. (in the same slow speed turn, an 80% LSD would very likely cause unwanted understeer.) A Torque-Biasing differential performs like an open diff whenever one of the drive wheels approaches lifting off the ground. Lock-up and traction are lost until both drive wheels are again planted firmly on the pavement. Distinct limitations exist when a TBD is incorrectly used in a rear-engined for high speed track race car. A great deal of confusion is caused by “optimistic” sales information distributed by companies that only offer Torque-Biasing Differentials, or when a TBD is described by a vendor as a “Limited-Slip Differential”. As Guard offers both differential types, we try to present as much information as possible, so that an informed choice can be made based on suspension set-up and intended use of the vehicle. Too often, we have seen the full potential of a car severely limited by use of the incorrect differential type, or by a low quality Chinese “knock-off LSD” that fails to provide long-term performance. Thank you for your interest --- ¬ Paul Guard

You know, I was thinking about putting that in there, but I though if I did it would sound less neutral. Yes, an LSD costs about twice as much as a TBD, and then there is the added cost of removal/rebuild/installation to consider. So a TBD is a much more affordable solution, both initially and long term.

What a great thread. I was wondering about the differences myself. I'm going ATB, I do a lot of AutoX, and anything is better than the stock unit.

I'd like to comment on the Guard recommendation. TBD is their recommendation for Auto Cross. That makes sense because Auto Cross is more like street. There are tight turns where lock on acceleration is very beneficial, without giving you the under steer that would come with an aggressive LSD. LSD is their recommendation for track. Why? Well because here you have long fast straight that have you doing 100+ mph, so now you can benefit from the LSD during braking. Also, the turns aren't as tight, so a little added under steer is easier to deal with. Furthermore, TBDs have not been found to hold up well in higher horsepower applications. If a wheel does lift, the TBD will see severe stress and wear. When used in a high horsepower car on the track, that turn where the lift occurs comes over and over, lap after lap, beating the snot out of the TBD until it's toast. Though this is an important consideration, it is also important to realize that not a single ATB has failed in any Cayman since they've been introduced. They've been in cars for a long time now, most of them owned by track junkies who use them in this environment regularly. I think (not sure, Tess can confirm/deny) that the Quaife ATBs come with a lifetime warranty. No one has used it. I believe that the Cayman's mid engine layout (which keeps more weight on the rear wheels) and it's ABD (which doesn't allow the ATB to ever really see any prolonged wheel lift) are responsible for the high reliability that we've seen when the ATBs are used in Caymans. So, to me, the real difference is the stability under braking that an LSD provides. I've had my car get squirly during braking. I can appreicate that benefit. So the question for me is, is that benefit worth the added cost and maintenance of an LSD. I haven't actually found the answer to that question yet. I am on the fence and when the time comes for me to install a new differential, I'll have some serious thinking to do.

Quiafe do give a Lifetime warranty, but it excludes North America, something to do with the legal systems being incompatible. But I have said: if there is an issue then I will act as go between. But I can confirm so far no issues. What has come forward is on a Trackday last Friday I broke a right hand driveshaft (well not the shaft but the outer pot joint) so we will examine why at the end of this week. and I will post the reasons.

:hilarious: Sorry Guys, Yea the outer CV Joint.

Were you hearing clicking for some time before the failure? Or did it fail quickly without warning. My experience with CV joints has always resulted in loud clicking as a warning that they're going. My 944 Turbo used to eat them up (running extra boost). This is the first I've heard of one going on a Cayman. The usual cause of a CV joint failure is failure of the rubber CV joint boot, which allows the lithium grease to leak out and water to leak in. Once water gets in, the balls and journals rust and then they destroy themselves. A hung up parking brake can also cause problems, as it applies a lot of heat to the hub/joint. Something else to consider, are you running an aftermarket exhaust? If so, are the pipes close to the CV joint boot? (unlikely) I wonder what killed yours.

To be honest, previous to the Trackday......no issues. On the day, with the engine revving at 6500 + and a Peltor type helmet (with intercoms fitted) you hear F....... nothing.......so it could have been clicking but you wouldn't hear it. I didn't realise until and it retrospect that last five laps I did, I was chasing down a 933 RSR, went into a double apex corner called Druids and had to "Collect" the car (I just put it down to me going in "Too Hot") but it then happened on the next corner (Lodge) so I just did a cool down lap, came in and told the guys to put the road wheels back on. Now they should have spotted the CV grease on the rim, but didn't (they probably wanted to get home, as it was the end of day) It was only then on the drive out of the circuit that the clicking was obvious .......when I dipped the clutch, the clicking disappeared......so at first I thought Clutch. But when I stopped to have a look I noticed the CV grease......everywhere !!!!!