jaeger86

I had a small transmission leak in my 1986 Carrera and took it into my local Porsche repair shop to fix. On picking up the car he remarked that I had LSD and although owning the car 21 years I had no idea. I was wondering what the difference is between LSD and non LSD and how you can tell which one is in your car. Is having LSD a big deal if not tracking the car? Thanks, Curt

wildcat077

Curt,

When the rear of your car is on stands , if you spin one wheel , the other one will turn in the same direction !
The transmission code is stamped on the top of the gearbox but it's really difficult to see when it's on the car ...
I don't have LSD on my 89 911 but my 944 race car does, i drove one race weekend with a borrowed non LSD gearbox and didn't see much of a difference, although i'm
guessing with high horsepower cars it must make a big difference.

Cheers
Phil

theiceman

Phill my 915 has it on the bottom of the gear box and is easy to see,
if you see a 12 in there you know it has limited slip.

When coming into a round about and slowing down into that roundabout in the wet you might notice the limited slip as you turn in.

What i have always wondered is am i supposed to be adding some type of modifier to my swepco gear oil if I am running LSD ?

i can never seem to get a straight answer and what i should be using if any.

wildcat077

Clive my 911 is a G50 but the 944 has a LSD gearbox , i use Mobil Delvac 75w90 synthetic in both cars.
I buy a 20Liter pail and it lasts me a couple years , last i remember i paid around $200.00 dollars, never had an issue yet !

You know how oil debates can get ... lol

Cheers
Phil

theiceman

funny thing is both my 944 and 911 have LSD. not sure it has ever activated though lol..

Bill Verburg

Unfortunately the lsd in your 915 was a 2 year only version of the previous nominally 40% ZF used since day 1. RoW got 915/73 and US got 915/72 for both '85 & 86 w/ this lsd

The differences from the older ZF and the '85-86 version are,
case on the last version has 4 large openings around the core where the friction occurs, This is good because it allows for better circulation of fluid for cooling the core
while still nominally a 40% the # of friction disks was reduced by 50% from 4 per side to 2 per side, for performance use this is bad as it similarly reduced the possible torque split, As a result these are what are known as 'snow ' lsd rather than a performance lsd. Another side effect of this mod is that their action is way less intrusive to the driver. The older 40% weren't particularly intrusive either but did make their presence know in tighter turns and of course in track use. The actual amount of intrusiveness is determined by the preload which is set during assembly and the condition of the drive/driven disks

The older ones could also be modified to a so called 80% by changing the order of the disks, stock they had 2 outer friction disks then 2 inner friction disks, just change that to outer inner outer inner and voilà an 80% lsd.

The /72 & /73 did receive several other worthwhile mod such as
improved main bearing assembly, still not as good as the old Mg case steel girdle but better than the other Al case models
much improved geometry on the double lock bands on the 1 & 2 syncros, lesser but still positive improvements on the all the other locking bands in the syncros

best fluid for all 915s w/ or w./o lsd is Swepco 201, the only time to use a friction modifier is to reduce the action of the lsd

here is the boss on the bottom of the trans which IDs it as a 915/73 w/ lsd

theiceman

Thanks Bill good info.

jaeger86

Very informative thanks very much. Curt

jaeger86

I wanted to add that while the mechanic was replacing the trans seal and gasket for the leak I had him replace the shift coupler bushing accessed through the tunnel. What a difference the new bushing makes as the 915 feels like new with the slop removed. Curt