zechunique

My option code sticker lists 220 (Locking Differential) and 224 (Active Brake Differential). As I search on these, I get a large number of unrelated results, and I'd like to learn more about this specific option on my car. I understand that this is a good option to have on the track...

Can any of you touch on the following questions? (Yeah, I know - that's a question - sorry)

Where is this factory component?
What is the difference between the "locking" and the "active brake" attributes?
How does it work? (factory device specifically)
At 17 years old (and 50K miles), is it probably worn out at this point?
How can I check its condition?
Should I consider replace/repair for track purposes?

Thanks for any good leads...

Bill Verburg

LSD & ABD are both good things, for track use LSD is the more important player

w/o LSD/ABD a 993 has 3 channel brake hydraulics and ABS, only 1 p/v(#6) comes off the ABS pump(#3)


w/ LSD/ABD a 993 has 4 channel brake hydraulics and ABS, 2 p/v(#6) come off the ABS pump(#3)


ABD is a low speed mechanism to get power to the ground it's more useful at parking lot speeds and for icy, snowy conditions

factory 993LSD used in g20/21 is a nominal 25/65 asymmetrical unit that is prone to wear, if it has never been rebuilt it will certainly need it by now.

GT or a recommended GT shop can rebuild them to a much better spec than oe

Spidey 993

I had a 993TT that was converted to 2WD.

I took it in for a oil change, and the mechanic spins the rear wheels. If the other wheel spins in conjunction, your differential is working. If not, its an "open differential". That is a about as basic test to determine if your LSD is working or not.

Mine wasn't, the "clutch pack differential" was basically gone, so I went to Guards Transmission (GT) and they rebuilt my differential and had a mechanic put it back together. Matt (GTgears) is on the board here, and extremely helpful.

I was told these differentials may only last 30k miles or so, so its not uncommon to have them go out and needing serviced. You can always upgrade your diff to a higher quality, extra $$ if you plan on tracking your car.

Bill Verburg

probably but not necessarily, stock ones do wear out quickly

all it means is that the lSD is not working under that condition, if the diff was built w/ a light preload any wear will lower the preload causing less LSD action at light loads. These diffs rely on load to activate the ramps that clamp the drive/driven plates firmly together they are nominally 25% on acceleration and 65% on deceleration because of the ramp angles but that has only superficial bearing on what the actual breakaway torque will be.

here is a pic of the ramps, the round pinion is forced into the ramp area under load causing the LSD halfs to spread thereby increasing the clamping force

Stealth 993

A bunch of info is in the owners manual.
ABD only works to 40mph, & it makes it so the car goes straight when on slippery roads. It can also prevent you from doing spins, or donuts on purpose.

Mine only kicks in on snow when I punch it, or on a wet track after I spin out then try to spin the car around quickly to get me pointed in the right direction.

Spidey 993

I never knew what ABD was for, very interesting.

And, whatever Bill say's, rules. It was just my experience and not absolute by any means.

zechunique

Thanks a lot for the info!