924Board.org

[Sava]

I've been researching LSD trannys for my 1980 931, but I'm having some trouble figuring what I would switch out if I were to get a 951 or 944S2 tranny.

Could I simply bolt in a 951 tranny or would it require me to replace the torque tube?

And would the CV joints from my 931 still work with a 951 tranny?

This is the first car I've worked on(My dad recently bought it for me).

Sorry if these questions seem stupid, I'm working on learning this car inside and out.

-Nic
_________________
1980 931
First Real Car

[Paul]

Neither of those will bolt in, plus they have the wrong gear ratios.

Why do you want an LSD?
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Sava]

My dad and I are hoping to race our 931 later on in its life.So, he asked me to see if I could get a tranny with LSD instead of an open differential. From what I know, which is very little, there are advantages with LSD over the open.

Are there any options for the 1980 snailshell transmission?

Thanks for your patience

-Nic
_________________
1980 931
First Real Car

[Paul]

Nic a good 931 snailshell tranny is a rare find, finding a good one with a good LSD is super rare.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Sava]

Let the search begin, luckily I have quite a while before the car will meet the track. This will most likely be my holy grail of sorts.

Thanks for the help Paul

-Nic
_________________
1980 931
First Real Car

[ideola]

Recommended reading.

If I'm not mistaken, the snailshell LSD is identical to the 915 & 930 LSD of the same era. The PCA guy that fitted my 931 snailshell LSD said it appeared to be identical to the 915s he had worked on. In any event, finding an LSD for a snailshell is indeed a challenge, and then you have the messy 2nd gear syncrhos to worry about in the snailshell...

I'm fairly certain that all 931s came with the same size drive shaft, 25mm IIRC, whereas the NAs came with smaller drive shafts, so you would want an Audi unit out of a series II 81-82 931.

According to 924RACR, the 951 LSD is a direct fit for the Audi-based gearbox that came in the 81-82 931s, which might be your best option. However, the 944/951 gearboxes have a very tall 5th gear...according to bass gt, there is a whopping 50+ mph difference between 4th and 5th, which makes that gearbox undesirable for a track-based 931.

You could also consider a 968 6-speed , but they are spendy, and you'd definitely be in for some custom fabrication. This is the direction bass gt is going.

Depending on exactly what your needs are, you could also consider an Audi box with an aftermarket LSD from either Phantom Grip (simsport is running one...click here, or do a search using "phantom grip", all terms, and simsport as author) or Quaife, although the only guy I know of currently running a Quaife (bass gt) is moving in a different direction. Then there's the boys at Guard to consider.

As for the axle shafts, I believe that if you leave the suspension as is, the 924/931 axle shafts should work regardless of the gearbox. If you switch to the 944 alu trailing arms, you have to get the longer 944 axle shafts.
_________________
erstwhile owner of just about every 924 variant ever made

[ideola]

One more thing: you could also consider an Audi V8 torsen-based diff, although many folks here think that the torsen setup is less than ideal in a race car...

See here.
_________________
erstwhile owner of just about every 924 variant ever made

[Sava]

Thanks ideola, I've got a few options to persue. I might be able to pick up a snailshell LSD, if I recall I met a man who had two at his disposal. If that doesn't work out I will look into the audi torsen-based difference.

Can't wait to get this car running!
_________________
1980 931
First Real Car

[ideola]

If he has two at his disposal, please let me know. I'd be interested in the second unit.
_________________
erstwhile owner of just about every 924 variant ever made

[v8carreragts]

The snailshell uses the late 930 LSD. It is a different spline than the early unit.

I personally like the snailshell over the AUDI based boxes. It's stronger (IMO) and lighter and pute the weight further forward.

To swap to an AUDI based box you need to replace the torque tube. It's not difficult but can be time consuming because you need to drop the rear suspension. You will also need to cut the 2 extensions off of the rear torsion bar tube that the mounts for the snailshell attach.

If you use a 6 spd you need to use the 5 spd torque tube. The 6 spd torque tube is shorter because the 968 had a deeper bellhousing than the 944.

[Paul]

You also would need a new shfiter assembly (Everything including the shift lever to the trannsmission.)
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.