Limited Slip Diff Experience?

[Flightrisk]

I am considering fitting an LSD as part of a wider overhaul/upgrade of my C4 993's suspension and running gear and wondering if anyone out there has done the same? What did you fit and what has your experience been? Ultimately was it worthwhile?

Your thoughts and pointers would be much appreciated.

 

[matthewb]

I may be wrong but I have always been under the impression that 993 C4/C4S's came with LSD as standard.

M

 

[jboult]

I had a Porsche OE slippy diff fitted when I was having the gearbox/suspension work done recently. My old diff had pretty much imploded when the gearbox failed and the incremental cost for an LSD at that point was negligible compared to everything else I was spending. My indy had also recommended I consider putting one in anyway, even before that, as he'd been subject(ed) to a few test drives with me over the years.

The following is all in my humble opinion: caveat emptor and all that.

In everyday driving I wouldn't say you'd notice any difference, unless you're testing the laws of physics regularly or sticking one wheel on the wet stuff. My C2 stuck to the road pretty well as it was, although I did regularly complain about having to wait what felt like an age to plant the pedal when cornering (certainly compared to the 944). Now I feel like I can get the power down earlier and harder - definitely more confidently on both road and track. I'm perfectly prepared to admit this could be purely psychological! Is it really useful in the course of a working week for a daily driver, though? (NOTE: that's the question my wife keeps asking. She doesn't like the answer, apparently).

All in all I'm probably neutral on it. If you're regularly driving aggressively and beyond the traction limit of the car under power (normally understeer for us 993ers), or on track and looking to shave a little time, then it's an easy decision. Other than that it's probably just a more complicated and expensive piece of kit that you won't need. I like having it, but I wouldn't rush out to upgrade a car this way again unless it needed a new diff anyway.

My best performance upgrades have been driver training, above anything else. From your list of cars (especially the 968), I suspect you might do a certain amount of high speed/track stuff, so this might be preaching to the converted. However, if you haven't done that then give it a go - you might be surprised at how good the standard car is!

Cheers/John

p.s. Reading this back through I'm not sure it helps you!

 

[majorporsche]

From my experience racing my 993 RSR, which wont equate to a 993C4 but here's my experience. The LSD is noticable in three ways to me racing, traction off the line, if I get the back end out even a small bit the LSD will control the slide, ie it wont keep sliding unless I provoke it and the LSD will help pull the tail back in. Finally under breaking the LSD makes the car more stable. If using it on the road remember it will clunk and groan, it will make the car understeer a bit more ( easily counteracted on track ) and the plates/clutches on the LSD wear out and need replacing. I got my LSD from Colin at 9M and am very happy with it. It wont be cheap . I was going to say drive a 993C4 with one fitted but this might not answer your question as if it's an original day one fitment it will have worn out if not replaced.

http://www.ninemeister.com/default.aspx

 

[colt]

As you already have a lsd installed (std on all c4 models) a rebuild would be quite cheap and possible without removing the gearbox. You could also have it set up tighter than originally to make it more effective on track if required, Ive done this on a few Porsche in the past.
christian......................

 

[Flightrisk]

Thanks for all the replies, I am erring toward a fast road/occasional track day set up so think an LSD along with the 4wd are an 'insurance policy' against my over enthusiasm. I was originally told it was a 993 option and did not find it in the handbook codes so assumed it was not there.

After 120K I think its safe to say the original has had its day so a rebuild would be required, who is capable of doing that, an OPC only? My alternative option is to go for aftermarket replacement and narrowed it down to Carbonetic, Wavetrac or KAAZ as most likely candidates.

 

[colt]

No need to go genuine opc, they may never had had one apart! A decent porsche indie or a gearbox specialsit could overhaul the diff itself and taking out the unit from the gearbox is around three hours in and out. Repair set available from porsche, but better to go to guard trans in america for some uprated longer lasting parts with track days in mind.
Christian...................

 

[jboult]

As per the previous response, you should find plenty of people able to do the job. My Porsche indy definitely does it.

One caution about some after market units - they can be a little noisy, particularly the race derived units, depending on what you get. This may not worry you, but if the car spends most of its life on the road then it could become intrusive.

John

 

[colt]

Just a note, if you change any of the basic components of the final drive then you would need to check the depth of mesh ,preload and backlash of the crown-wheel and pinion, This does not apply if you rebuild your original lsd changing only internal parts, as the relationship to the drive pinion will not change. To check and set up these things requires a complete transmission strip and therefore will be very expensive. The vast majority of indies and dealers would not have the required special tools to check this or somebody with the skills to operate them efficiently. A lot of garages just go about changing pinion bearings and diff bearings along with diff housings (which in non lsd form can wear out there internal gears) and just hope the new parts are not to far away from the size of the old ones, many times they will be lucky and get away with just putting them in. Unless it's an absolute mile out and very loose or tight ,you won't know about the incorrect setup until thousands of miles later when your ring and pinion are worn out and howling like a vauxhall Ha van ,that or your bearings will be under too much preload and will overheat and wear out far quicker than they should. but that is not the same as checking the values with the proper tools (old vw items i think) and some engineer's blue on the driving faces of the ring gear and pinion. Its an old fashioned thing to do these days and many mechanics would have never seen it done properly by an old boy! only read about it in the manual! If your going to put different parts into your gearbox (new or used) including any of the following then some or all of these values should be checked (each ring and pinion has its own quietest running point and also backlash value, they are engraved on the actual items themselves and are factory matched in production by running on a special machine to determine the best running pairs of components and there quietest running spot.)
depth of mesh is the distance of the pinion from the center of the ring gear teeth and only requires checking if you renew either the ring and pinion themselves or pinion bearings or the transmission case. the diff bearing preload and backlash require checking if you change the diff unit itself(but not its internal components), either or both of the diff siderace bearings or again the casings and of course the ring and pinion. the less parts you change the less likely the values will alter ,but anythings possible in component manufacturing tolerances!
Make sure if these critical values require checking that your garage have the tools before you give them the job.
Many people assume that the gears are matched together in production,this applies to the actual gears sets themselves and the ring and pinion, but in reality the items are all made separate and then a few "boffins" spend all day running gears together and rings and pinions and they pair items which meet or exceed there noise and lash limits. At this point they become pairs of gears and get engraved with matching numbers and set aside for use in the transmission assembly line. It's is in theory possible that you could replace only one part of a gear set or pinion(as long as the remaining item was not worn out)( a complete no no according to all manufacturers) and by luck arrive at a set which also meet noise and lash limits but of course you would have to rely on old fashioned ears and eyes and not the multi million pound machines gear manufacturers employ. Thinking about it i expect Porsche don't actually make and match the gears ,it's probably done by a third party supplier as gear manufacturer is not a simple industry.



Christian.........................

 

[szklarek]

I have a 993 C4 - as a matter of interest how does one know if the LSD is 'shot'. Also with the C4 how many LSD's are there - one at the rear for sure but is there also one on the front axle?

Regards
Anton

 

[colt]

All models of 993 with lsd are only on the rear wheels, viscous clutch for centre diff with no lock up function (unlike 964 c4 which had plate type centre diff with hydraulic lock up function and continuously variable torque split) no lsd in front axle, you would not like the torque steer forces it would create if you did!!
Regarding how to tell if its worn, I have seen no factory info to determine how to asses it, lots of people are saying at blah blah mileage it must be shot, and many people are also saying if the rear is jacked up and both rear wheels don't turn in the same direction of rotation when one is spun by hand (lsd transfers torque to other wheel and hence it goes the same way) ,trouble is these lsd have an active lock up action caused by a movable friction cup (one each side) and so will exhibit little or no lock up without a load on it,them being set up with little preload which would make it operate all the time load or not . Ill see what i can find out.
Christian..................

 

[szklarek]

Thanks Christian. I see your point about torque steer if I had a front lsd!

Anton

 

[Mark Elder]

ORIGINAL: szklarek

I have a 993 C4 - as a matter of interest how does one know if the LSD is 'shot'. ...

Likewise - any insights into symptoms of an expired LSD would be interesting. I was completely unaware (but it's obviously now I think about it) that it would wear relatively quickly.