LSD differential

[mhurwitz]

I was always told that my 71E had the limited slip diff option……but I saw it with my own eyes yesterday. My mechanic is in the process of rebuilding my trans right now and pointed it out.
How rare is this option?
Is it desirable, or one of those options that you can take it or leave it?
I’ve owned it since 1979…..so as far as drivability, it’s the only thing I know.
As always, I really value the opinion of the people on this forum.
It never ceases to amaze me how knowledgeable some of you are.
Thanks,
Mark

[icarp]

The more HP you have the more you notice it is there . It is your friend .
The smoother you drive the less you notice the effect , or sometimes you want to induce a response
and the LSD will help you do that . Get abrupt with your driving and you will have a handfull .
I love them ! The 911 is already good at putting the power to the rear wheels , the LSD improves
the rear power distribution .
Keep It !
Ian

[Matt Monson]

I hope he bench tested it to see if it’s still in spec. Now would be the time to rebuild it, and update the obsolete wave washers if they are still inside.

[kevingross]

I would say the LSD is desirable from the perspective that not all transmissions came with them, the factory ones are scarce nowadays, and if you are an autocrosser or track person, they make a big difference. The four-clutch versions are particularly hard to find. Street-only, though, you probably will never notice the difference the LSD makes.

Agree with Matt about rebuilding and replacing the wavy plates with the newer components.

[Bill Verburg]

Originally Posted by kevingross

I would say the LSD is desirable from the perspective that not all transmissions came with them, the factory ones are scarce nowadays, and if you are an autocrosser or track person, they make a big difference. The four-clutch versions are particularly hard to find. Street-only, though, you probably will never notice the difference the LSD makes.

Agree with Matt about rebuilding and replacing the wavy plates with the newer components.

The only 901, 911, or 915 trans w/ 2 disks were the '85 & 86 915/72, /73

all previous versions of the ZF lsd came w/ 4 friction disks per side, std config was 2 inner the 2 outer for a nominal 40% dif , optional was alternating outer then inner for a nominal 80% dif. Actual lockup was set by the preload

generally lsd are considered a plus for any performance application, though they can have some annoying side affects and can be down right dangerous on fully slicked surfaces

[stownsen914]

Pretty sure that particular LSD (assuming it's factory original) is relatively rare

[manbridge 74]

Originally Posted by Matt Monson

I hope he bench tested it to see if it’s still in spec. Now would be the time to rebuild it, and update the obsolete wave washers if they are still inside.

Who sells the up rated parts anymore?

I’ve rebuilt two recently and did not see much wear. I read the heat generated was high in these if under severe duty. I don’t think the hole size in the case allowed effective cooling…

[Matt Monson]

Originally Posted by manbridge 74

Who sells the up rated parts anymore?

I’ve rebuilt two recently and did not see much wear. I read the heat generated was high in these if under severe duty. I don’t think the hole size in the case allowed effective cooling…

I’m only talking about the design change from wave washers to Belleville washers. You just replace it with the later parts from a 915 or 944.

While I no longer offer clutches and plates for these, my washers also fit and can be used.

[manbridge 74]

👍🏿

[mhurwitz]

Originally Posted by Matt Monson

I’m only talking about the design change from wave washers to Belleville washers. You just replace it with the later parts from a 915 or 944.

While I no longer offer clutches and plates for these, my washers also fit and can be used.

I will surely talk to my mechanic re this….thanks

[Bill Verburg]

Originally Posted by manbridge 74

Who sells the up rated parts anymore?

I’ve rebuilt two recently and did not see much wear. I read the heat generated was high in these if under severe duty. I don’t think the hole size in the case allowed effective cooling…

heat in track use was an issue, which is why all the factory track cars have trans coolers

for street use not so much

here's a pic of a '70s 915 RSR ti lsd showing the smallish holes in the case, these limited the flow of of fluid through the unit




and an SC 4 plate small hole iron unit



per factory documentation for '85 they opened up the holes for better fluid flow but at the same time lost 1/2 the friction disks




I was surprised when I rebuilt my '84 915/67, 4 plates per side and large holes, this is undocumented in the factory literature


any how
a comp of the various 911 lsds

[gled49]

I always replace the early wavy pressure plates with the Belleville pressure plates as Matte says. I also replace the inner friction plates with updated ones. Both the Belleville and the friction plates carry 928 part numbers.

[gled49]

The radial groves in the inner lamina keep the plates from sticking and reduce noise. The pressure plates and the inner lamina are all 2.0mm. The pressure adjustments are done with the outer lamina that come in 1.9-2.0-2.1mm thickness and carry 917 part numbers. Beware of parts with 951 numbers that were part of a multiple supersession that was costly and not necessary.

[Matt Monson]

Originally Posted by gled49

The radial groves in the inner lamina keep the plates from sticking and reduce noise. The pressure plates and the inner lamina are all 2.0mm. The pressure adjustments are done with the outer lamina that come in 1.9-2.0-2.1mm thickness and carry 917 part numbers. Beware of parts with 951 numbers that were part of a multiple supersession that was costly and not necessary.

Where are you sourcing the grooved plates?

[jjeffries]

My two cents: a very desirable option for the discriminating driver. Would like to have an LSD in my 82 SC.

John

[evan9eleven]

I love mine! I rebuilt it myself a few years back (the photo above from Bill V’s post with the whole diff spead out on the workbench is mine.) I rebuilt to 80% technically… but Matt explained to me that it isn’t really 80%. Maybe he can chime in on that. I rarely notice it being there except in low speed turning situations (like making a parking lot U-turn or something.)

More details on my thread here: https://forums.pelicanparts.com/porsche-911-technical-forum/975965-915-rebuild-itb-efi-project-here-we-go-8.html#post9901938

[Coastr]

I have one in my 83. Not sure it makes much difference in my driving but I like to hear it working and spin the wheels when it’s in the air, just to see them spin together.

They are pretty rare and generally you’d choose one with an LSD over one without, all other things equal. Yes they will whip the tail around in low traction.

[gled49]

Been using these parts for 30 yrs, discovered them after dealing with the 951 multiple suppression. This info has been in Porsche parts system for years.
Cup spring: 928 332 555 00
Inner disc 2.0: 928 332 551 00 (with radial groves)
Discs with external splines 1.9-2.0-2.1: 917 332 552 (10-11-12)
These parts fit in all multi plate diffs including coarse and fine spline.

[kevingross]

Originally Posted by gled49

Been using these parts for 30 yrs, discovered them after dealing with the 951 multiple suppression. This info has been in Porsche parts system for years.
Cup spring: 928 332 555 00
Inner disc 2.0: 928 332 551 00 (with radial groves)
Discs with external splines 1.9-2.0-2.1: 917 332 552 (10-11-12)
These parts fit in all multi plate diffs including coarse and fine spline.

One caution: I have serviced some later models' differentials that come to me with 2.5 mm cup springs 928.332.555.20 (Belleville washers) rather than the 2.0 mm version you list, 928.332.555.00. Rather than trying to remember which LSD gets which parts, my practice has been to measure what I find, check the Porsche parts diagrams to confirm. Sometimes you get LSDs that have been swapped in from who knows what original transmission. So measure the case and stack, check for reasonable break-away torque. And of course it doesn't help that there are errors in some of the WSM descriptions of how to measure BAT...

The 951 parts I think you were referring to were perhaps the 2.50 mm clutch discus used in the final version of the 944 series LSD, with correspondingly thinner pressure rings (ramps). Cheers,

[Matt Monson]

Originally Posted by gled49

Been using these parts for 30 yrs, discovered them after dealing with the 951 multiple suppression. This info has been in Porsche parts system for years.
Cup spring: 928 332 555 00
Inner disc 2.0: 928 332 551 00 (with radial groves)
Discs with external splines 1.9-2.0-2.1: 917 332 552 (10-11-12)
These parts fit in all multi plate diffs including coarse and fine spline.

Porsche Classic recently re-released some of these parts. They only released the 2.0 friction disc (still under the original 917 part number) and no longer make the 1.9 and 2.1mm ones. They look like the the ones pictured on the left in your shot.

I asked about where you are sourcing the ones on the right, because those are mine. Or I should say were mine. We stopped making that version about 15 years ago.




This is what we manufacture now. These are for the GKN factory LSDs. As I stated before we no longer service the ZF product line. These clutches are too aggressive for the steel used in the original discs with external splines. Our steel plates are heat treated. ZF ones are not. There were a couple instances of people installing our clutches with ZF plates. They cut like butter. Since we make parts for race cars, and Porsche Classic supports their own LSD now, we stepped away from the market. All it takes it one scathing thread on Rennlist about how Shop A "ruined" someone's freshly rebuilt gearbox using Guard's "inferior" parts for me to walk away.

There's also the age of the other parts. The housings in particular are wearing out in the cars where they are still being used in racing, especially spec 944. Nobody wants to pay the expense to magnflux the housing for cracks every year or two. I don't want to have my upgraded parts anywhere near a catastrophic failure of the LSD housing in a race car that goes into a wall. I carry a massive insurance policy, but don't ever want to have to use it because someone or heaven forbid someone's estate, is looking for a fall guy.

Regards,

Matt Monson
Guard Transmission LLC