Limited Slip Differential
 

Hello,

are the 911 LSD compatibles with 914 gearboxes? In other words, can I mount a 911 LSD in my 2.0 side shift 914?

Thanks!

Yes

Your welcome

901 to 901
915 to 915

I never heard of anyone mixing them.

The 914 is a 901 trans

If you have a 901 transmission there are three possible ways to add one: first is a factory unit which are guarded by their owners like the gold in Ft Knox, second is a Quaife unit and last is the GT or Guard unit. They all work on different principles, require $$$$$ to install and setup and will most surely change the way the car handles and drives.

Not that simple. This should help:
http://i205.photobucket.com/albums/b...1DiffTypes.jpg

The mag case 911 gearboxes (which includes the 1969 type 901s) use the same differential as the 914. The very early 915 gearboxes also use that same differential.

If one were to acquire a factory ZF LSD for the 911/914 be sure to get the proper LSD stub axles flanges to go with it. The length is greater and the open diff flanges will be too short. Our LSD or TBD does not require LSD flanges. You can use the stock open differential flanges with our units.

Kind Regards,

Matt Monson
Guard Transmission LLC

Never heard of the different output flange length. Any numbers on the difference in measurements?

The length to the step on a standard open diff flange is 56mm. The length to the step on the LSD version is 61mm.

Thanks for sharing your expertise, Matt.

Matt is right. And you need to make sure you keep your own ring gear with the replacement LSD. There are some difference ring/pinion ratio's out there as well. The mid 80's 915 I just had apart had the magnetic speedo parts in it and it did look a bit different from the 1973 unit I have.

Considering that the earlier 915s used 7:31 ring and pinion, while the later ones used 8:31, that's not a surprise. :)

--DD

Part Number
 

I know we discused how rare these outdrives are, but do you have a part number for them? Just to see if they might still be available from PORSCHE.

Thanks.

I have a 915 ZF limited slip mounted in my 901 trans in my 914-6. (The 901 ZF limited slips are very to find) It also requires the 915 CVs to be used and adjusted for length to be able to be locked (snapring) onto the 914-6 half shafts. It makes the whole differntial section slightly off-center, but there is enough lateral slop in the CVs to not make this a problem. 30 races later no problems.

Boy, you got that right, found a guy with 2 NOS in the box factory LSD, 1st he seemed like he would let one go (wanted one for my factory "Six" after being hinted a price, I offered, but no, then I even pulled out a few of my RSR bits, still no, then was hinted another price, said OK, but again no:(

904 lsd
 

I have a 904 limited slip in a 901 gearbox. I am thinking of selling the diff and replace it with a Quaife. I need to find out if the Quaife acts like a real LSD in that it works in deceleration as well as acceleration. If not I will have to use a Guard Transmission LSD in my 914 race car.
914racer

Matt and mike...Tony at Stuggart Specialist here in KY had some pictures of the two types of flanges side by side...I think they were here on pelican...or he may still have them...

Quaife is most known for torque-biasing differentials (TBDs), aka Torsen differentials. These use worm gearing to bias torque to the wheel that is turning faster as long as the slower turning wheel (the inside wheel) does not loose traction completely. The traction on the inside wheel is effectively multiplied by the worm gearing into a torque bias towards the outside wheel. If traction gets too low then the inside wheel spins and all the benefits are lost. It works on acceleration and I don't see why it should not work on deceleration but people say they do not. It may be that the torque bias is not a stabilizing one and so it does work, but not in the manner desired.

An "LSD" is usually referring to a plate clutch type limited slip differential which simply tries to maintain equal wheel speeds across the axle using static friction and preload and then kinetic friction when things start slipping. This works the same on power and off power. It is a stabilizing (understeering) influence in both regimes.

Some differentials for Formula SAE combine both the torque biasing and clutch plate types into one unit.

Some race cars use a spool, just a straight piece of metal making sure that both wheels spin the same speed (except for torsional windup). This introduces a lot of understeer unless you make the rear end very stiff like a kart, in which case if you are cornering at high g and unload the inside wheel, while still driving the outside wheel, you get a torque vectoring effect, helping to turn the car.