Martin S.

it may cost you. About 15 hours of labor at $100 an hour, + the cost of the LSD. The Guard is about $2,200, + $1,500 in labor, $4,000 by the time you pay tax on the LSD, etc. Santa, where are you when I need you????

delanobe

Is this LSD option so expensive? A few weeks ago I found out (by accident) that I had this option (M220?) but I never really knew where it was good for?
So, what's the use of it?

Regards

graham_mitchell

It reduces rear wheelspin/improves traction.

Terry Adams

There were 2 factory options.
224 Automatic Brake Differential Traction System $963
P08 Torque Limited Slip with ABD $1253 (Which I ordered)

Like Litronics ($1536), not very expensive when ordered with the car.

You only have to experience a near slide exiting a turn on a damp road, and see the light come on, to know you invested wisely.

As mine is probably by now worn out, I will consider the Guard unit if/when it is time for other work "while we are in there". As a "safety measure", not a mod, you understand.

Martin S.

How Stuff Works
basically there are two (2) types of limited slips, the Clutch Type which is what Porsche sells and the Torsen (Torque Sensing Differential) below. This information came from the "How Stuff Works" web site. Before launching to to the details, know that the Guard clutch pack LSD and the Porsche Motor Sports LSD are very popular items with racer types. The Guard appears to be extremely well made and I have been told is nearly indestructable. The Porsche Motorsports Clutch Type (You don't have this...you have the garden variety of Porsche LSD that is not all that rugged. I burnt my clutches up in two (2) weekend at the track ) as I was saying, the Porsche Motorsports LSD is also very popular...and it may be less expensive than the Guard. But with the dollar against the Euro, who knows these days. The real heavy duty racer types I have spoken to seem to prefer the GUARD...Alex Job Racing and others swear by the Guard. When the gods are good to me with some extra cash, and ONLY AS A SAFETY MEASURE , I plan on getting the Guard.

Clutch-Type Limited SlipThe clutch-type LSD is probably the most common version of the limited slip differential. This type of LSD has all of the same components as an open differential, but it adds a spring pack and a set of clutches. Some of these have a cone clutch that is just like the synchronizers in a manual transmission.

The spring pack pushes the side gears against the clutches, which are attached to the cage. Both side gears spin with the cage when both wheels are moving at the same speed, and the clutches aren't really needed -- the only time the clutches step in is when something happens to make one wheel spin faster than the other, as in a turn. The clutches fight this behavior, wanting both wheels to go the same speed. If one wheel wants to spin faster than the other, it must first overpower the clutch. The stiffness of the springs combined with the friction of the clutch determine how much torque it takes to overpower it.

Getting back to the situation in which one drive wheel is on the ice and the other one has good traction: With this limited slip differential, even though the wheel on the ice is not able to transmit much torque to the ground, the other wheel will still get the torque it needs to move. The torque supplied to the wheel not on the ice is equal to the amount of torque it takes to overpower the clutches. The result is that you can move forward, although still not with the full power of your car.

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.

Conclusion...LSDs are really helpful for track work...they are a definite advantage, especially on short tracks. They have been noted by some to induce understeer...simply dial it out with your adjustable sway bars. Oh, you don't have adjustable sway bars, well that is another long story. Too long for this thread!

Mark in Baltimore

LSD also helps with braking stability.

delanobe

So wich one is option code M220 (ABD)?

Tia

seege

Martin, 15 hours is alot of labor and I assume that this quote is to remove the transaxle from the car in the process.It may be worth your while to find someone who will make the change with the drivetrain in place. It seems that I've seen a thread here with someone(ViperBob maybe?) saying it can be done much faster.I'm not advocating using the cheapest possible mechanic just the most efficient. I hope Santa is good to you.

TrackJunke

This is what my option code says,
• 220: Locking Differential 40%
• 224: Automatic Limited Slip Differential
Does this mean I have an LSD? If so, how much should I expect to pay to replace the worn out clutches?

kary993

I do no thave access to the PET right now but the locking percentages are in the PET. They are different for 2 wheel .vs. 4 wheel drive cars. I want to recall it was 25/40 and 15/25 for 2wd and 4wd respectively. Something like that anyway.

Martin S.

Replace worn out clutches? Well there is a test to see if the LSD is still working. They disconnect on e of the drive shafts and put a torque wrench on the axle stub. There should be (I believe) 35 ft lbs of resistence (As I recall...I don't have shop manuals). If you fail that test...you can opt to have the LSD removed and repacked with new clutches. Heavy duty clutches are available, or so I was told at ANDIAL when I had my 993 G 50 LSD rebuilt a few years back...they were about $800 a set as I recall...but once again, it is "as I recall".

Some folks such as Steve Weiner at Rennsport in Portland, OR suggest that the stock LSD is not rugged enough for the track...just replace the factory unit with the GUARD unit.

Now as to the calculations behind the 15 hours, you can put a clutch and flywheel in a 993 2 wheel drive car without removing the transmission; I have seen it done. However, my source for the 15 hours for the LSD installation comes from a Factory trained Porsche mechanic with impecable credentials. He also has years of experience at one of the premier Porsche shops in SoCal. I have known this chap for five (5) years and have found him to be a very diligent technician. He tells me he is unable to install a LSD without removing the transmission from the car. Others may claim that they can...that is fine by me. I choose to belive this guy.

If you think 15 hours is bad, another shop told me 20 hours to extract the present LSD and install a Guard LSD. It all comes down to, whom do you trust?

And by the way, what will I do if I ever get a real job and will not be able to post on Rennlist every day, more or less. Gee I hope my boss is not reading this!

Alan C.

Martin,

Do you mean without removing the engine? I have done that.

Also if anyone wants a factory LSD I have one in the garage. Send me a PM with an offer.

kary993

Who doesn't have one in there garage that tracks their car I have one also if anyone is interested.

Martin S.

Send us both an offer, although I am a long ways away from pulling my factory LSD. Alsn has one ready to go!

DamonsCarrera

Another data point, my mechanic charged me $900 to remove and replace the gearbox, changing the LSD a few years ago

-Damon
'94 325i
'95 993