brandon

Wondering if someone could educate me on the difference between the Locking Differential and the Automatic LSD. Curious EXACTLY how each works (if there is a previous thread on this or even a website with a good discussion on differential basics, that would be great). Secondly, what does each really mean in terms of performance?
Thanks & Merry Christmas

E. J. - 993 Alumni

According to the expert Steve, a locking diff is the same as LSD. Here is a cut and paste from a former discussion. You can also click on the search button above (below the post a reply button on the top right) and serach for ABD and LSD - you will get lots of good info.

"LSD is a mechanical differential. No electronic control at all. Gohere to see how a differential works - our kind is the clutch type limited Slip. This site (how stuff works) is a fantastic resource. I can lose myself here for hours and learn somthing useful on the internet to boot. Has whole automotive section with motors and gearboxes etc...
E. J."

Good luck,

E. J.

brandon

E.J., thanks for the pointer to the "How Stuff Works" site - I had completely forgotten about it. Although I'm smarter now on the types of differentials out there, I'm even more confused as to what type of power transfer system my car has.
The option code I have is M220.

On Robin's site M220 is shown as Locking Diff (40%), which makes me suspect that it's a Torsen type mechanical LSD. His site lists M224 as Automatic LSD.
The 993 FAQ page shows 220 as Locking Diff (40%), 224 as ABD, and MP08 as Active LSD.
My Porsche 911 Red Book shows 224 and MP08 (ABD and Active LSD), but no mention of 220.
Soooo...
I'm wondering if my car (or all stock 993s?) has perhaps the torsen type of LSD and that the MP08 option is an improved (clutch)version of LSD. I'm also wondering what kind of performance difference (under turning acceleration perhaps) is there between/amongst the differential types?
Still a bit confused (normal state for me, but still hopeful)

E. J. - 993 Alumni

For what its worth, my car has 220 and 224 - LSD and ABD as I understand it. You could not get one without the other. I have always assumed 220 to be the 40% locking limited slip type. Beyond that, I only know that with the car jacked up, I turn one wheel and the other turns too. Means it's still working.

E. J.

JonSeigel

FWIW, my '93 C2 has 220, but not 224. Therefore, either (1) you don't necessarily have both 220 (LSD) and 224 (ABD) or (2) 220 necessarily means you also have 224 in 993s, but not 964s.

BTW, does anyone know what option 231 is? I haven't been able to get the answer anywhere.
Thanks,

E. J. - 993 Alumni

964s did not have ABD therefore no 224.

E. J.

brandon

Hmmm. I should have mentioned mine does not have the 224 code (but the ABD dash light shows up w/ battery power on).
I vaguely remember a thread from a while back that said that both wheels turning when jacked up didn't necessarily mean LSD (can't remember the specifics tho').
E.J., I think you and I might have whatever the stock differential is for this car and that the MP08 code is perhaps the upgraded LSD.
Anyone else out there have the MP08 code, 220, 224 & know for sure what they have?

993Widebody

From everything I read, and this topic comes up a lot.

1) 993s do not have any type of standard Limited Slip, it was only available as an option.

2) If your 993 has limited slip M220, then it has ABD M224(Active brake differential?)

3) Limited slip is a means to divert power to one wheel when the other is slipping.

4) ABD recognizes that a rear wheel is slipping and under 40 mph will apply brakes to regain control of the wheel that is slipping.

5) I'm not sure, but I think the MP08 option is simply Porsches option code for grouping M220 and M224 together since the car is only available with both options, not one or the other.

6) The cheap way to tell if you have limited slip and it is working is to jack up the rear wheels with the car in neutral, disengage the emergency brake - turn one rear wheel forward and the other wheel should rotate in the opposite direction.

Hope this helps and please correct me if I got anything wrong.

brandon

Rob, thanks for another data point in my quest for "the truth" There seems to be a bit of conflicting info here - I CAREFULLY checked the codes on my options sticker under the hood and it only has 220 but not 224.
I also did a little more reading on the Rennsport site about differentials and it talks about several types, but doesn't get specific about which cars have what.
I'll take as many data points as folks out there have on this and try to figure it out - what car do you have & what options listed (seems 220, 224, and MP08 are the ones in question).

brandon

Rob...my apologies - and apologies to others if I've caused confusion (or worse). I said I carefully checked the codes under the hood (just didn't write them down as carefully) - I do have the 224 code. I'm guessing by E.J.'s previous post that I do have both a LSD and ABD. I was told (by the dealer) that I didn't have it, so I was spring loaded to believe it.
Sorry

Snoops

Soory to be niave. But where do I locate what type od LSD I have? Where to I find the code 220.

Thanks

993tt

Actually, the wheels should turn the same way if you have a limited slip. If you have just a normal differential then they should turn in opposite direction.

brandon

I haven't gone so far as to jack up my car yet (need to remove the engine tray at some point anyway). When I do I'll check the relative rotation of the rear wheels. Until then, though...

Does anyone out there NOT have 220 or MP08 as an option?

DE experiences from those without?

I've searched the previous threads & there is wide variance of opinion on the benefit, durability, and operation of LSD.

My only experience thus far with traction limits on this car has been autocross - certainly didn't notice slipping of the primary drive wheel unless I intentionally induced it by overpowering the car to tail slide it around a hairpin. Haven't driven it yet in a wet environment where I can afford to get the tail loose SAFELY & explore differential traction.

Thanks to all for your responses.

E. J. - 993 Alumni

Hey Flash,

I have 100k on my car and I track it at least once a month. The factory LSD still works - if you were behind me coming out of the oak tree corner at VIR you would know it.

If you are really worried about it for the track, then pay the $1500 one time fee and upgrade or add the guard or GT LSD.

E. J.

brandon

Not worried. I've got the same option codes you do. VIR - well, I won't be moving to VA until summer of '03 - but I'll keep the challenge in mind

Until then I'll keep up the mantra...heel, toe...slow in, fast out...

Thanks -