Clutch Pack Diff Fluid Info
 

With the following novel, I wanted to share another bit of info that I just gained. This is info that was out there, but obscured by all the internet noise and plenty of misinformation.

Different fluids make a HUGE difference in clutch pack LSD's. A couple years ago I purchased a Cusco Type-RS 1.5 way diff to replace my broken torsen in my 10AE. I installed the diff with the default clutch arrangement, filled it with M1 75w90, and set about breaking it in (I pre-lubed the plates when I assembled it). Immediately I realized that I had forgotten to add friction modifier it would bang skip and drag the inside tire, a real pain to drive. Pulled it back into the garage and added a tube of friction modifier. It got rid of the banging, but it was still far too grabby without much progressive action, It was locked or it wasn't. I thought maybe it would take a while for the additive to do its magic, but there was no improvement after a week. I pulled it all out again and restacked the clutches to the lowest setting in the Cusco instructions which was 60%. Refilled it with the same fluid and LSD juice, but the results were similar. It was definitely not as bad, but I still had to be agressive with some wheelspin to turn uphill into my driveway. I'm sure the neighbors were amused.

I went online to find somebody who had seen this before and got three suggestions in addition to lots of people that swore fluid didn't matter, it was a mechanical issue. The suggestions were to try dino oil, experiment with oil weights, and add more friction modifier. I dumped the M1 75w90 and put in Castrol HYPOY-C 85w140 with one tube of additive. Same result, shit. Drained a little out, and added a 2nd tube of additive, better, but still dragged tires and lacked smoothness. Next I went back to M1 75w90 with 2 tubes of additive, this was even worse than the Castrol. SHIT! Here I am with this $$$ diff, and all it's good for is causing understeer, followed by driving the car sideways, and making it trailer-hitch around slow corners.

AGAIN I started googling and ran across a Toyota truck forum where they were having diff issues after changing the fluids. They were also having problems with M1! One guy said it was so bad that he had trouble getting the truck to turn when he was pulling a trailer. It would just bind up until it didn't want to move anymore, letting off the throttle would then make the driveline unload with a BANG! He changed it out with Valvoline dino 75w90 and a bottle of additive and the problem disappeared. I thought I had eliminated the brand issue when I tried the Castrol, but it was worth a try. I ran out and bought a quart of Valvoline 'LSD Formula', and another tube of additive. Some had warned that too much additive could cause wear, but I don't see how that's possible unless you thinned the oil too much. Makes it more slippery right?

Anyway, dumped it all in and the difference is night and day, it works GREAT! You can still hear it scuff a tire under moderate power in a tight turn, and turning uphill into my driveway still makes it drag a little, but it's far more progressive and smooth with no grabbiness. Next time I change the fluid I'll leave out the extra additive and see if the Valvoline works by itself.

I broke my Kaaz 1.5 way diff in with some cheap ass dino oil, flushed it out and used the Kaaz 80W90 oil and it's been fine for over 2 years now. I do change the oil about every year though. It was chattery in low speed tight turns, but that went away in a couple of weeks. Smooth engagement and progressive lockup under power ever since.

If you drive it much, I'd change it more often than once a year. Clutch packs seem to be hard on oil, especially tight diffs, and they are a bitch to R&R. I've always heard you should change the fluid ever other oil change. It's easy and cheap too.

Oh, and the trick to making it easy is to take one of the plastic plugs out of the bottom of the trunk, run a tube from the trunk, over the muffler, and into the diff.

The Valvoline 75w-90 is exactly what I used no more than three weeks ago when installing an RX-7 clutch type limited slip in my car.

I didn't use any friction modifier at all and no problems thus far. Smooth as butter in the turns, no chirping or dragging of the tires and the clutches seem to be locking up just fine. Launches straight as an arrow.

Kaaz set to max locking with Kaaz oil and the thing is a peach. Just a little tire noise when making u turns.

That is awesome. I'm annoyed I didn't think of that!

What kind of diff is the RX7 one? I assume it's a cam type? 2-way?

I can't figure out why the hell I'd want to get all the plates working in this Cusco. The 60% stacking is as low as they recommend going. Set that way it is still a touch on the tight side for autocross unless I start lifting a rear wheel again. And for that it's just about right, or rather, it WAS. Guess I'll find out.

All I know is that my inside wheel doesn't ever spin when I put the power on. Sure the car straightens out a bit, but a little bit more power and that's no longer a problem. Maybe on an autox course you don't get that much time in a corner...?

I like the car to dance a bit under power. With the torsen I could choose to steer with the front or the rear, but the clutch pack ties the throttle to the steering wheel. I have to slide the ass end of the car in places that I could lay down power nice and clean before. The torsen was of course usless when you unweight the inside wheel, I think that's how I mangled the worm gears. On the flipside, when I do get it a little too sideways, the recovery is a LOT easier with the clutch pack. The torsen would just flip me the bird and let me spin.

clutch diffs are amazing.

My OSG isnt the same as your describing. sounds like you have the preload tuned really tight and its not the plates meshing that you are feeling.
you can run 80% plate faces with a light preload spring and it should fix your problem.

That's interesting, I didn't realize there were preload options. I'm using the springs that came with it and never saw any alternative options. With the back end up in the air, gearbox in neutral, and one wheel set down gently on a block of wood, it takes maybe 10 or 15lbs (maybe a little more, but it can be done when holding the wheel like a steering wheel at arms length) of force on the outside of the wheel in the air to get it to rotate independently, that seems like a reasonable amount of preload doesn't it? If I hit the clutch before I round a turn there is no binding or scraping at all. In a long sweeper you can feel it wanting to straighten out as you apply power, and turn in more as you back off. It appears to be working OK, I'd just like different angle options for the ramps.

i know there are 2 different spring settings in the OSG one for initial hookup and one for full lockup properties.

I assumed similar with other types.

what you are saying to me sounds like your initial spring is setup a tad aggressive.

here is an article i found a while back about tuning your differential.


If you are into doing work to test different setups like i am, this is what you need to do.


http://www.motoiq.com/MagazineArticl...ferential.aspx

try this... there is 4 pages.

"Finally the OS Giken Super Lock diff has a unique feature. In the pressure ring there are negative springs, that push the half’s of the pressure ring together, counteracting the wedging action of the cross shaft cams. These springs control the slope of the lock up curve or how quickly and smoothly the diff responds to the torque wedging of the cross shaft cams."

That explains why I never heard of those before. Kazz, Cusco, and OEM only have preload springs.

"Here are the cone springs used by OS Giken for adjusting the initial preload on the clutches. OS has three optional spring rates. Most other reputable brands of LSD have different weights of cone springs that you can use for tuning as well"


This is what i was reffering to in regards to your differential. its how much preload there is on the clutch plates themselfs. the "cone spring" is essentially a shim.
http://photos.motoiq.com/photos/585296905_2AocT-M.jpg

My preload springs are a set of 6 or so coil springs that sit in holes around the circumference of the pressure rings. They have no influence on the lockup besides providing a preload and taking up the slack. No tuning options besides more or less preload. Operation is all about the ramps.

It's the clutch type that was available in the 86-88 NA RX-7, if I'm not mistaken. I don't know much more than that. I've never opened it up.

It's the one mentioned in the Miata Turbo FAQ Wiki.

I almost used one, it was actually installed in my diff, but the guy I bought it from said it would 'bolt right up'. He (and I) didn't realize I'd need new stubs and axles. I returned it to him and got the Cusco. I never looked at it very hard either.