Could be, but then that raises the another question?

If there is no problem with the freely turning "off the ground wheel test" then is there a problem with an "off the ground wheel test" where it doesn't turn easily?

 

Hello,
The answer regarding the wheel test being a fallacy is that it's a bit tricky to explain and I'll try to give you a bit more detail. As I tried to explain in that long technical post on page 2, when the car is on the road you very quickly and easily overcome the pre-load on the differential. This is what I am talking about when I say that it's acting like an open differential. The preload on the differential doesn't put enough load on it to make it lock up. There's just not enough force there.

The reason that the wheel test is useful as a basis for determining the condition of the LSD is that it gives you a rough idea of how much friction the discs are still generating. It's something that you can measure over time and see that the differential is wearing. But when you do this test the differential isn't truly locked. The ramps are still pressed inward, instead outward into their locking position. It's really just an empirical gauge of where the diff sits relative to it's new condition.

It's kind of like running on a dyno. A dyno is a very useful tool but it's all relative. For it to be useful as a tuning tool you first need to run a baseline. Then you can modify your car and see changes over time and how much power they give you. Porsche has published what the LSD should show at rest when it's new. When it starts to drop substantially then you know that it's not going to lock up the way it's supposed to in the field. Does that make more sense?

Also, look at this new OS Giken differential for example. They are claiming it's a zero pre-load LSD so the wheel test shouldn't work on that differential. Not having tested one I cannot tell you if this is the case or not. But the point is that it's not a universal test that you can use in all situations.

Someone asked about gear oil. I know Paul Guard really like the LE stuff. I personally try to stay out of the oil "wars". Both engine and gear oil gets debated on the internet more than almost anything else when it comes to car guys. For every oil you can find people who love it and people who hate it. I personally tell people to use what the factory told you to use. Mobil and Shell have both been OEM for Porsche in recent years and are both good products. For synchronized gearboxes I am not a big fan of Redline. I think it's too slick, and see it causing issues for some people. For a dogbox or sequential gearbox it's a great lubricant, but I don't put it in my own cars. In my personal cars using modern Borg-Warner synchros I use Mobil.

 

2 questions.

1)How safe is the wood blocks so the car doesn't slide around on them when letting it down, you have them glued together or anything?

2)When are you ready to get rid of the PCCB brakes? I have a nice new rebuilt set of 8 piston/4 piston Brembo 15"/14" floating rotor setup I'll trade when your ready, lol.

 

lol

How is your piggy bank coming along? Time for a GT3 yet?

 

Simple answer. When the torque on both wheels are the same such as in every day driving on a flat ground, LSD work like a open diff. LSD will do it's job when the other wheel slip such as during a hard and fast turn on track or off road where one of the wheel come off the ground. The "one wheel off the ground" test I demonstrated basically show you that if the torque on the wheel are NOT the same (all the torque is on the other wheel contacting the ground) then the force of the engine will transfer to the wheel with least resistance which will be the one off the ground. All cars came with open diff in the 1930's that is why many get stuck in a mud hole and can not climb out if one wheel is off the ground

Here is simple tutorial on how LSD work:

http://auto.howstuffworks.com/differential.htm

and a nice LSD tutorial video from the 1930's LOL

http://www.youtube.com/watch?v=K4JhruinbWc

Awesome. Looks like the weather is going to hold up. Look for me since there maybe couple F430 and GT3

You lost me at hello You might want to address this question with Matt at GT gear

Oh man, the wood block method is not for everyone. I had to go to blue collar technical college for an advance degree to learn how to use it to raise a car ... not to mention yearly continue education lol

Best not to use wood block but rather use a proper jack stand if you never done it.

I already got some steel rotors. Thanks for the offer

 

killer thread mike. thanks for taking the time doing the writeup.

 

You are back! how was the fatherland? Did you get to drive on the burger ring or just the autobahn? I bet you don't miss the "hot wine" lol

Glad you like the write up. Let me know if you decide to take on the project. Infinion this weekend?

 

unfortunately, track schedule changed and was closed both fri/sat. the only 2 days i was free to roam! went there friday irregardless. place was disserted. there's some development going on. looks like they are making it a big resort for car nuts and track junkies.

the autobahn wasn't that much fun with lots of road construction paired with a very slow car (Merc A-klasse). i did got it up to 178... kmh.

i don't think i can sneak out this sat from family. they missed me.

 

mikymu, I really think this thread is very informative and we all thank you for the time you have taken and your desire to help us all improve our cars, you are really great, said that, I am still confused, I understand that an open differential will let both wheels turn independently that way the car will not have any problems at tight turns, the downside is the slipping effect that results when one wheel/tire loses traction and all of the torque is lost since it cannot be transferred to the gripping tire, LSD will limit the percentage of slip and will transfer torque to the gripping tire, I think we all get the principle, my confusion is how much speed, torque or acceleration difference will be necessary in order to consider the off the ground test valid, since a LSD will allow a difference of speed between wheels. I've been tracking my car '08 GT3 for a year now (18-20 track days more or less), I cannot say that my car is having real issues related to the differential, even though my car often wiggles a bit under heavy braking (or maybe I'm just too much of a rookie to really tell?), Is there any other way to determinate a faulty LSD?,
regards,

 

You bet Gus

I don't pretend to be the expert but I like to share what I learn by talking with Matt at GT gear and also real life experience. Back to your question. My OEM LSD came with a super low pre-load of 9.6 lb/ft. At the time of rebuild it only has 2 lb/ft left as demonstrate by Matt. All I can base on the condition of my LSD before Matt test it on the bench is the static state "wheel off the ground test" as I have demonstrated and clearly contrasted with my E46 M3. I don't know how to demonstrate functionality of our LSD when considering speed, torque and acceleration.

The static state "wheel off the ground test" may not be exact science but it give you a very good idea of what your LSD is doing or not doing. I was told our OEM LSD is dead after 1 track event and I think your LSD is most likely long gone Tail wiggle is one of the sign of a bad LSD.

Jack up your GT3 and do the simple test. Let me know what your LSD is doing

 

"""Also, look at this new OS Giken differential for example. They are claiming it's a zero pre-load LSD so the wheel test shouldn't work on that differential. Not having tested one I cannot tell you if this is the case or not. But the point is that it's not a universal test that you can use in all situations."""

Matt,

The wheel load test does work on the OSgiken. Some day I am going to have to put a torque wrench on mine and see how much it is.

Peter

 

From another forum: "Fortunately the Porsche Field Technical manager was scheduled to be there that morning, so I stuck around to talk to the guy. His response was that the 2010 model LSD only works under load, so you can't just throw it up on the hoist, spin one wheel and watch the other turn as you could in the past."
Perhaps this is why the OPs discs showes so little wear?

 

fantastic thread, thanks

 

There's a couple things that don't jibe with that theory. First off, if it was a zero pre-load diff in Mike's car, why did his have a Nm test rating scribing into the case. Furthermore, we've been seeing discs come out with similar wear well back into the 996 GT3's. That sort of wear (or lack thereof) is typical of pretty much every GT2 or GT3 LSD we've had apart in recent years.

The biggest thing is that even if it was a zero pre-load LSD, it would show wear. That's really the issue here. While you can (and we do) tune an LSD using the preload and various thicknesses of belliville washers, it's not what makes the differential lock. What makes the differential lock is the friction discs biting onto the plain plates. It's conceptually identical to your clutch biting onto your flywheel. Even after 50 miles there will be swirl marks on the flywheel from the clutch disc spinning against it. These differentials are coming apart without those signs of wear, after guys like Mike have been to the track and hammered on them. There should be some sort of wear we can see!!!

I don't have the camera with me today, but I'll snap a shot of the plates that came out of a 996 GT3 LSD that I did yesterday. The customer didn't want them back, so I still have them here. This car had 25K mi on it and you'll see that the tooling marks from when the plain plate was cut to thickness and made flat are still there. Then I'll post a picture of some takeout factory ZF plain plates from a 930 LSD. You'll see it's night and day. My opinion is that it has nothing to with preload or no preload. It has to do with friction and there's just not enough of it there, even when the ramps do their job and push apart and try to lock up the LSD.

 

Hello Peter,

I would be interested in any additional information you can provide. The infomercials I am seeing on the other forums don't really enlighten me into how this patented system works and does what it does. I'm always interested in expanding my knowledge base and if you can give us some more details on the functionality of the Giken, I for one would be interested. It might be more appropriate to start a new thread and not sidetrack Mike's here, but if you posted some technical data on that diff. I would want to read it and further educate myself.