Option code for LSD in a 915?

Oh Haha · 10-11-2006, 05:43 PM

Anyone know the option code for LSD. I believe my SC came with it but I suspect it needs replacement or adjustment. I have no experience with this type of setup. I'll be pulling the trans to look into the 5th gear issue discussed earlier this week. While I am in there I would like to check the LSD out.
Thanks,

john walker's workshop · 10-11-2006, 06:10 PM

all i know is there is a 12 stamped among the numbers on the rib under the diff if it has posi from the factory.

Goth · 10-11-2006, 06:17 PM

The option code on my 84 Carerra w/LSD is "220". I think the code should be the same for your SC. BTW; it also has the "12" stamped on the bottom of the trans case as mentioned above.

Hope this helps

MattAlpha · MattAlpha's Garage

Goth,
Do you happen to have a picture of this "12" where it is stamped on the transmission. I'm pretty sure that I'm not one of the lucky ones, but I'd like to make sure. My car has surprised me in the past. I do not fell like placing it on jack stands just to try the rotation test.
Thank you,
Matt

Wil Ferch · 10-12-2006, 05:38 AM

On the bottom raised surface....looking up...placed between transmission type number and serial number you should be able to see "12"....

915 limited slip???

- Wil

Bill Verburg · Bill Verburg's Garage

Hayden posted these a while ago
No lsd

w/ lsd

MattAlpha · MattAlpha's Garage

Very nice, thanks guys!

Grady Clay · 10-12-2006, 10:31 AM

OK guys,

What is the difference between M220 and M221 (BA p. 256)?
M220 – “Locking differential”
M221 – “Porsche-locking differential”
(There is the same distention in the Kindel list.)

I have seen LSD transmissions with an “11” in place of the “12”. What is this?

Best,
Grady

Bill Verburg · Bill Verburg's Garage

the first character is the type - G is a Getrag

the next 4 are the version -G5001 is an early Getrag 5 spd g50/01

1 as the next digit means open diff, 2 is M220 option lsd G50012 is a 40% lsd diff.

the next digit is the year

the last 5 digits are the serial #

can't find any info about M221 except it's in there starting w/ the '87 Getrags

Oh Haha · 10-12-2006, 03:39 PM

Mine is stamped:
915/62 731 4913 No "12".

Stupid question: If I don't have LSD, why would have I been able to leave two strips of rubber between first and second? Before flaming me for speed shifting, this was before I blew out 2nd doing this. I don;t drive like this anymore.

Bill Verburg · Bill Verburg's Garage

sometimes you just get lucky

Oh Haha · 10-12-2006, 05:37 PM

But I'm married.

Oh, c'mon, you were thinking it.

Thanks for the info, Bill. One less thing I have to worry about inside the tranny.

jazzbass · 10-12-2006, 08:56 PM

You might have gotten lucky and had a PO put in an LSD with a prior rebuild. Here's a simple test that will tell you for sure what you have, regardless of option codes or transmission stampings:

Jack the rear of the car up so both wheels are off the ground. Ebrake off, car in neutral. With your hand, spin one of the rear wheels. If the other wheel spins the same direction, you have an LSD. If they spin opposite directions, you have an open dif.

With any luck, maybe you'll find something from GT in there.

MotoSook · 10-14-2006, 11:44 AM

I've got a 915 with the stamp: 915/62 AT 731 3506

The output flanges spin in opposite direction. I'm assuming it's sans LSD, but does the 731 mean the 7:31 R&P? And what does the "AT" mean? I've never seen the "AT."

Bill Verburg · Bill Verburg's Garage

there were 2 systems used thru '81 and '82 up

for yours this is the trans id
731 3506
7- type
3- version
1-model year 1981
3506- serial #

if there was a lsd it would rear 915/61 12 731 3506

I have no idea what AT means

MotoSook · 10-14-2006, 12:21 PM

Thanks, Bill. Another trusted source has never seen the AT either.

Wil Ferch · 10-14-2006, 06:38 PM

Maybe you left two black stripes because you were pointed straight ahead ??

...might be a different story trying to put power down in a high-g, tight radius turn....

- Wil

jazzbass · 10-15-2006, 08:47 AM

Quote:

Originally posted by Wil Ferch
Maybe you left two black stripes because you were pointed straight ahead ??

...might be a different story trying to put power down in a high-g, tight radius turn....

Yep, that would be my guess. With an open dif, the power wants to take the path of least resistance. With the car level, pretty much equal weight on the rear tires and the same tires on each side, it's not impossible to spin both wheels at the same time. Both tires present the same load to the diferential, so they should, in theory, spin at just about the same time.

Now, if there is an imbalance, then one wheel will spin while the other doesn't. Like, one tire loaded in a turn and the other unloaded. Or one tire stuck in the mud and the other on the ground, a la My Cousin Vinnie.

MotoSook · 10-15-2006, 09:03 AM

I'm having a hard time believing that an open diff. will allow both tires to lay down rubber at the same time. Even on a perfectly level surface there will be an imbalance in the torque and grip at each wheel. When that imbalance occurs (likely at the initial application of power), the power will be tranfer to the slipping wheel (or wheel with less traction) and stay there.

Wil Ferch · 10-15-2006, 09:14 AM

I can't believe all the responses, with all this going round-n-round.....

....just jack the rear up and hand spin one of the tires...see what happens on the other side. If it spins in an opposite direction...there's no LSD or the clutch pack has worn even if it WAS delivered as LSD. If it spins in the same direction, you have LSD and a functional one at that.....

- Wil