Doesn't the LSD make it so both wheels spin at the same speed, with the same amount of power?

For Example: Even If one side loses traction, the other side would not receive more power; would it?

 

There are a few different types of LSD designs.

The type typical in our transmissions is a clutch type. This variety comes in varying levels of % lock-up and methods of providing the lock-up. I don't recall the factory setting (something like 40% or 60%) but the motor sport variety are around 80%. This means that if one tire has zero traction, the other is receiving the advertised lock-up percent. ie the traction wheel is receiving 80% power. Over time the clutch packs wear down and the LSD's ability to LS is diminished.

The 968 uses a torsen LSD, which is a gear type, torque biasing design. These redirect power from the slipping wheel to the one that has traction.

In order to have the same power always applied to both wheels, at the same speed, would require a spool. This is actually not a differential, because it does no allow a differential in wheel speeds. It's basically an axle coupling sleeve with a flange to bolt the ring gear.

When it comes to which is more probable to damage a CV, I would say the LSD variety. Here's why; the LSD will allow a higher potential of acceleration on a surface with varying traction and therefore have the potential to load one CV with more force when the other begins to slip. With an open diff', you would not be able to accelerate as quickly on the same surface and therefore not be able to transfer the same amount of weight to the rear tires.

Does this mean I think LSD's lead to broken CV joints? No. I think driving style, part wear and lack of maintenance play a much bigger role than the differential ever could.

I suppose I should add that my view on the LSD having the ability to break a CV over an open diff', comes from off roading. Typically when I see an axle failure (that's not from "driving" like an idiot) is when a vehicle using a locker (100% lock) or a spool, is climbing a very steep grade (front end almost off the ground due to weight transfer to rear). This puts almost all of the propulsion duty and weight of the vehicle on the rear axles. Lets say they're both sharing 50% of the load, when one tire goes from nice clean and grippy rock, to rock covered in sand. Its ability to propel the vehicle will drop to nearly 0, leaving one axle with the duty of handling 100% of the propulsion load. If the axle isn't strong enough it will twist and snap. The same scenario with an open differential would not break an axle, since the tire that losses traction will just spin and you and your 4X4 will go backwards down the hill, until traction is regained.

 

One of my left cv's failed after a panic stop. Locked up the brakes on the highway and drove off with the characteristic 'thump-thump-thump'. So brakes / braking habits might be a factor in cv life.

 

In my 1988 951 (with LSD) I have launched pretty hard at the drag strip with 225s and 245's and I never really had a big issue with wheel spin and I have never broke a CV. In my 1986 951 2.8L (Open I believe) I took it to the drag strip fitted with 255s. I did have issues spinning the tires and I did have a odd result...

 

Don't the late offset 951s have larger CV joints than the early offset ones?

 

They went to a lower Spline Ct. (25) than the previous 951 (33) but the bolt PCD remained the same. The jury is out weather or not they actually beefed the cages. I think they did it to get a stronger axle shaft or CV off the shelf from a BMW. If someone has an old one laying around, mic the ball dia. and outer cage width. If the ***** are 17.5mm (type 4) then they are the same as the prev. 951, if 20mm then Porsche got smart and went back to a Type 2 CV which is stronger than a Type 4. I've been running the Type 2's for 1000's of miles and complete clutch drops and haven't busted one yet. The Axles are solid 4340 Chromoly and thru-hardened which twist torsionally under sudden heavy load. Besides the poly trans mount I designed which saved the CV's , I believe that's why I never busted the NA tranny and I abused that poor thing....

This pic shows the beefier cages/larger ***** on the Type 2 CV's.....

 

Thanks for all the input and discussion. Just curious about this idea; So i figured i would exercise the minds of you RennListers...

That's why we're here right?

HA ha.

^ Those CVs look awesome... I want them!

 

the cause of CV death is the POS trans mount on the late cars. if you have some time to spare i would highly suggest finding a way to adapt the early mount to your car. the mounts will bolt onto your late trans (unless you have the turbo cooler, then you need to make a plate, i can show you how), you just need to get the mounts in the car.

 

The key is to keep the trans from moving under torque or cornering and not transmit gear noise/vibrations.... Even the 4 corner rubber mounted version allows too much movement for my taste, so I fixed that too....

 

Actually LSD would put more load in to the CV joints due to cross loading. With an open diff if a wheel graps traction quickly it will be moved through the diff. With an LSD there is better chance it will tend to lock up the drive line sligthly. Realisticly however heat is the biggest factor. Heat from the exhaust cooking the grease at the CV joint. This happens mostly on the driver side inboard joint.

 

sort of.. The Lock up percentage in the LSD is probably not enough to help much. Remember limited slip is just that. Limited slip. It is not a 100% locked diff.

 

Nice looking pieces. Don't appear dissimilar to the ones LR offer. Of course there is the question that beefing these up only transmit the load further along the line...to more expensive and time consuming fixes?