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Identifying LSD!!!

 
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TJC  



Joined: 04 Apr 2010
Posts: 809
Location: Central-ish Arizona, USA

PostPosted: Tue Mar 16, 2021 4:07 am    Post subject: Identifying LSD!!! Reply with quote

Hello Group, I'd like to mine the collective for some definitive information as there are many here who are much brighter than I am on all things 931.

Regarding LSD in our vehicles, are there any ways to identify, by stamping on the case for instance, whether a Porsche snailshell or Audi transaxle was equipped with LSD from the factory? I am of course familiar with the old "put it in gear spin the input shaft, (trans out of the car of course), and see if both stub axles move in the same direction, or the spin a tire method, however it dawned on me that those methods may not be absolute, especially if the vehicle/transaxle has been out of use for 30 odd years or so. It could be possible that a LSD may not "lock up" as there may not be sufficient "friction" to do so...maybe...just a thought!

In any event, before I tear into taking a side cover off for a proper inspection, I just thought that perhaps someone here could shed some light on the subject if they know of any "marks". Unfortunately I do not have access at this time to see what option codes were on the vehicles I'm dealing with, so any assistance would be greatly appreciated.

And just one more thing if I may. I believe I read somewhere here in the past that 1980 and earlier USA Turbos that were equipped with the optional sport suspension option, M471 I think off the top of my head, which included the 5 stud hubs, etc. also included a LSD snailshell trans. Any validity to this?

Thanks in advance and stay healthy!
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Rasta Monsta  



Joined: 12 Jul 2006
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Location: PacNW

PostPosted: Tue Mar 16, 2021 4:32 am    Post subject: Reply with quote

IMO, your frail human appendages are not strong enough to break the clutch pack free even if the LSD is completely shot.

In other words, if are are unable to counterrotate the rear tires by hand (gearbox in neutral), you likely have an LSD.

Are we talking about the 80 Getrag unit, or the later Audi one?

Also, per PET, M471 is "sport suspension" only. LSD has a separate option code.
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Carrera RSR  



Joined: 08 Jan 2010
Posts: 2194
Location: Somerset, UK

PostPosted: Tue Mar 16, 2021 6:07 am    Post subject: Reply with quote

Snailshell will have a /12 after the usual serial number if it has a factory installed plate LSD.

Forget the input shaft. Spinning one output shaft should see the other spin in the same direction if either plate or ATB LSD. If they rotate in opposite directions its an open diff.
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TJC  



Joined: 04 Apr 2010
Posts: 809
Location: Central-ish Arizona, USA

PostPosted: Tue Mar 16, 2021 9:54 am    Post subject: Reply with quote

Thanks Guys.
The first trans in question is the '81 Audi unit that is already out of the car and currently up for sale. I did not think that it had LSD as the usual "test" indicated that it didn't. However when cleaning it up a bit I found another number stamped into the case just under the shift linkage where it enters the transaxle. That number is 53 and I thought perhaps Porsche used that to ID whether it had LSD or not, like the /12 on the earlier units. I do remember that little tidbit from earlier discussions regarding LSD.
The reason I referenced the M471 option is that I seem to remember Dan mentioning something about the strong possibility of an '80 having LSD if it had the sport suspension as well. My '80 doesn't seem to have it, but to be honest, that car has pretty much been sitting since I found it.
Thanks again!
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'95 BMW 318i/5 ..."Pearl"
'80 Porsche 924 Turbo..."Pogo"
'81 Porsche 924 Turbo...Parting!
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"

Still on the Prowl!

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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Tue Mar 16, 2021 2:49 pm    Post subject: Reply with quote

Found more info on some nerd site:

http://924board.org/viewtopic.php?t=22829
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TJC  



Joined: 04 Apr 2010
Posts: 809
Location: Central-ish Arizona, USA

PostPosted: Wed Mar 17, 2021 1:09 am    Post subject: Reply with quote

Rasta Monsta wrote:
Found more info on some nerd site:

http://924board.org/viewtopic.php?t=22829


Thanks for that Rasta...it be bookmarked now!!!

On another note, did you get my last PM re: the front "bulkhead" hood latch support panel that you're looking for and did you score your seat floor pan piece? I'm most likely going to start my chop-chop next month after I get the shop addition more complete if no one wants the entire shell.
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'80 Porsche 924 Turbo..."Pogo"
'81 Porsche 924 Turbo...Parting!
'87 Porsche 944 NA... "Liebchen"
'02 Porsche Boxster..."Sunbeam"

Still on the Prowl!

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MikeDanger  



Joined: 21 Nov 2002
Posts: 636
Location: Denver

PostPosted: Sat Mar 20, 2021 11:58 am    Post subject: Reply with quote

Rasta Monsta wrote:
IMO, your frail human appendages are not strong enough to break the clutch pack free even if the LSD is completely shot.

In other words, if are are unable to counterrotate the rear tires by hand (gearbox in neutral), you likely have an LSD.

Are we talking about the 80 Getrag unit, or the later Audi one?

Also, per PET, M471 is "sport suspension" only. LSD has a separate option code.


hate to tell you, but youre wrong about that. I almost bought a car with factory LSD (had the original invoice) and when I spun one wheel, the other didn't spin.
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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Sat Mar 20, 2021 2:24 pm    Post subject: Reply with quote

Over the past 40 years, is there any chance the transaxle was changed?
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Fasteddie313  



Joined: 29 Sep 2013
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PostPosted: Sat Mar 20, 2021 9:23 pm    Post subject: Reply with quote

Could have been a viscous lsd instead of a plate/clutch type lsd.. (Subaru)
I think they work more like a torque converter than a clutch..

My G31 LSD takes over 90 ft/lbs to get it to slip..
Maybe I could
Budge it just an inch or so by hand, but nowhere near able to just counter rotate the rears by hand..
Even a very worn one I would expect to put up quite some resistance..

On the other hand a viscous type is pretty easy to turn slowly, but the faster you turn it the more difficult it becomes..
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anthonimartini  



Joined: 17 Feb 2020
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PostPosted: Sun Mar 21, 2021 5:39 am    Post subject: Reply with quote

oddly enough the 931 i tore apart had a factory optioned limited slip with standard 4 lug brakes. seems odd to me that someone would opt for the lsd over the huge brake upgrade. either way im happy i ended up with it as 944 brake donors are cheap and plentiful and the the g31 lsd is absolutely unobtanium.
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