DC640

I just changed the gear oil after 2 track days and some street driving (600 miles) after the initial Guard LSD install.

I noticed some slush the was drained out (looked like new metal friction residue from new plates).

Nevertheless, shifter feels super smooth and I think my new LSD internal is happy w new oil.

Matt = where do u recommend I buy the mobile dev gear oil? That is what u recommend right? I plan to change gear oil every 12 physical track days, engine Oil every 6 track days.

mark kibort

not really. street LSDs have very little friction. (20ftlbs sometimes)
they are very effective on the race track, in fact, the lighter winding of the LSD is actually a good thing in most cases. (too tight makes for a very loose car on 2nd gear turns).

its probably ok. for example. if you are going out of a driveway slowly and turning and you stop with one rear wheel lifting in the air due to the race cage making the chassis stiff, you wil probably get stuck! the LSD has very little grip. But, coming out of a 2nd gear turn, you will stilll leave two black marks!

use a gear oil with modifiers for use in LSD diffs. redline 75-90 NS (no slip) is one really good rear end oil.

GTgears

There's not a shakey head big enough...

The fastest 944 and 968 racecars in the country use our LSD set at 50/80 or 80/80 and a gear oil with NO friction modifiers.

And Redline NS does NOT have friction modifiers in it. The NS stands for No Slip. Their marketing is the exact opposite of everyone else. All of Redline's oils have modifiers in them except for the NS brand.
http://forums.pelicanparts.com/porsc...right-now.html
Bullet Point #4 "Contains extreme pressure additives like our 75W90 GL-5 oil, but lacks friction modifiers to balance slipperiness"
They go on to say that it helps with weak lock up LSDs and helps to create maximum lock up in racing (points 6 and 7)

Regards,

Matt

por944s2

The oils is changes at least annually and delvac has been used for he last few years. U assume he car needs to be in e air to do the break away test? Thank you all for the input.

mark kibort

Matt, shaking right back at cha! when i said friction modifyer, i was refering to its effect vs the normal brand. (whether something added or not was not the point). The NS brand version is for LSDs.

the LSD is probably pretty weak as most stock LSDs are. But, as i said , that can be a good thing for most new and seasoned racers.

just jack one side of the car up. put a torque wrench on a lug nut (not accurate, but you will get the idea) and see what force it takes to move the wheel, while the other one is still on the ground. you will be amazed about how low it is. the spec is somewhere in the 20ft-lb range. Not enough to get you out of a sand trap or one wheel on snow and the other on pavement, although its better than an open diff for sure.

the 928 LSD came in a few flavors, but the older versions were wound a little tighter than the newer versions up to the electronic variable versions. (i.e. '87) I think mine is about 25ft-lbs. when you have things going on that seem like your LSD is broke, it usually is a broken swaybar up front. (the car leans over so much , it lifts the rear inside wheel and it spins wildly in turns)

Matt Romanowski

Mark - You know you're arguing with the guy who built the LSD in question, right? I'm guessing Matt knows what he is talking about (most of us do).

mark kibort

I just noticed I offered the same advice that matt did. Im not arguing with him over semantics and friction or no friction modifiers. I was trying to help the OP'er figure out what he has. Its not uncommon for folks to think their LSD is bad, when it actually is fine. the test we both recommended is easy to do and doesnt require the car to be in the air. just lift a wheel and spin the raised wheel. a torque wrench on the lug works well too. should be about 15 to 20ft-lbs of torque. my guess, is that it will be ok.

Oddjob

You will not lose traction with one wheel in the air with a clutch type LSD. Theoretically can lose traction w/ a TBD when one wheel is off the ground (or loses all grip). Because of this, TBDs (unlike LSDs) can cause a car to have some odd behavior in very slippery conditions, like snow/ice.

The stack pre-load is not the how much the diff locks up under engine driven or wheel driven loading. There are reasons not to do it, but you can setup a diff with zero preload and have a very high locking rate under load.

mark kibort

You think I just started doing this stuff??????
yes, clutch types can make one wheel spin, almost like open diff when the wheel is off the ground. Not the ones with a higher percentage lockup
This is why you get wheel spin with a broken swaybar for example, and when it fixed, you don't get the wheel spin.

I'm very familiar with setting up race cars with the high % lock limited diff. Have seen many a car get too much lock up and have them be almost undriveable (but fun) by the insistent owner

Now, correct me if im wrong, but the 951s use a similar LSD to the 928 in their transaxles, right?

Oddjob

Is that a rhetorical question?....

FYI - a limited slip that doesn't limit slip is called an open diff.

No idea what 928s came with, but apparently they were 0/0. 944/951s used a ZF 40/40 diff from the factory.


Kidding aside, I have never used a very low locking rate LSD (although I dont consider the 944 40/40 very high locking), so maybe some of the factory 20/xx LSDs are capable of spinning wheels. But again, seems like that would be an indication of a failed/failing LSD unit. I don't see the point of setting one up that light.

GTgears

Your guess would be wrong. IIRC the factory ZF LSD (which is not what he has) Porsche tells you is worn out around 38ft/lbs. While my clutches are a bit more aggressive than Porsches and my belleville washers have more crown, and therefore more spring rate to them, I generally tell people they are getting pretty close to worn out around 35ft/lbs.

Some people do experiment with low or no preload set ups, even on my LSDs. However, I know for a fact that Precision did not do this. Like most of my customers, they give me some guidance on application and I build them an LSD based on the information provided. I built this LSD and have a record of EXACTLY how it left my facility.

por944s2,
You've answered every question I have asked correctly. This thread hsa pretty much suffered a Kibortian. Jack up just one wheel, do not put the car on a lift because you want the resistance of the other tire on the ground. Shoot me a PM with that number or post it here if you prefer. We'll go from there, but my gutt is that your LSD needs to be rebuilt.

As for the rest, I'm walking away. If I wanted to argue with a fool I would just go yell at my bathroom mirror for a while...

KaiB

Now THAT'S funny; God bless you Matt.

I was wondering how long it would take - now that Mark is back. I believe the answer is exactly 6 hours, 23 minutes.