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Can I run a heavier weight oil in my CLSD?


Zmanco

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I have a Powerbrute CLSD in a 4.11 R180 with 75w90 Royal Purple synthetic gear oil and when it's warm it chatters around just about any street corner-type turn. Also, in 1st and second, and sometimes even in third, I can feel the direction of the car in a turn affected when I let up on the throttle as the clutches disengage. Usually it's no big deal, but sometimes it's pretty significant and it even makes a clunk loud enough to hear. My guess is that the CLSD is locking up more aggressively than I need.

 

Can I switch to a heavier oil? My thinking is that it would effectively give a lower breakaway torque when the diff is warm. In particular, what about using a 75w140? Normally I'd just run a trial with it, but I don't want to take a chance at damaging my ring and pinion gears with too thick of an oil.

 

Thoughts?

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Eliminating the chattering is one issue, but I'd also prefer it to not grip as hard when hot - in other words, allow more slip. The lockup isn't an issue when cold or even warm, only when hot. Could I try a thicker oil such as 75w140 without damaging the gears?

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Don't change the oil weight. Add LSD additive. You should be able to find it at any auto parts store. Chrysler, GM, Ford, it's all the same stuff. Just keep adding tubes or bottles until the chattering stops.

 

Hi Jon,

 

I appreciate your reply. I'm having chattering issues with my newly installed KAAZ. I used one tube of CRC fluid to my 80-90W Valvoline GL-5 gear oil.

 

I was considering adding more, but the CRC instructions say to not add more than one tube, but the "knockety-knock" is pretty annoying.

 

I'll add another 1/2 => 1 tube, give it a whirl and report back.

 

Thanks! -hughdogz :icon14:

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On the PowerBrute and the Nissan Motorsports CLSDs the only way to change lockup percent is to change the clutch/driven disc ratio. Its also helpful to get the driven discs REM treated. In the 350Z world the Nismo 1.5 Way CLSD is notorious for chatter. A number of folks have adjusted it from 100% lock to 80% by swapping out discs and REM treating.

 

Alternatively do what Jon suggests regarding friction modifier.

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I had some chattering when I first installed my 87 clutch type LS diff and used the friction additive to regular fluid. I changed to the Redline 75w-90 fluid with the friction modifier in it already. Chattering went away.

Just make sure you don't get the 75w-90NS as it does not have the modifier in it like regular fluid.

 

Aaron

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The worst one I've experienced is the Chrysler Powr-Lok, the ramps are very aggressive and they have severe chatter. I've had them take up to 3 tubes of additive to stop. That's always what we recommended to get them to stop when I worked at Randy's Ring and Pinion, and I never had a customer say that their diff had trouble from running more additive. I think the Ford stuff is the "densest" as a bottle of it is only 4 oz, so if you really have to add a lot that might be the least amount of actual oil displaced by the additive.

 

John makes a good point, if you want less lockup, you can change the clutch stack. The clutches work basically the same way a multiple clutch works in a car or a motorcycle. You have the disks and the plates. If you stack them up plate-disk-plate-disk-plate-disk then you'll get the most grip out of it. You could alternatively do plate-plate-disk-disk-plate-disk and get basically 2/3 as much grip or plate-plate-plate-disk-disk-disk and get 1/3. It's a bit of a PITA to pull it all apart to adjust it, but it can be done. I don't really get how they measure the 100% vs 80% thing, but in terms of stacking the clutches differently that's how you do it. This thread shows the stack in detail:

http://forums.hybridz.org/showthread.php?t=117818

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Thanks for the extra inputs guys. It may be that the right solution is to pull it out and change the clutch stack, but before I do that I'm thinking that a thicker oil might be enough. The only time it's an issue from a handling point of view is when the diff is hot. If it's cold or even just warm (driven easily on a 75 degree day), the amount of lockup feels fine. It's when it's a hot day (85+) and it's been driven hard (high speed running or lots of city driving with lots of turns) that it's troublesome with the agressiveness of the lockup. My thinking is that that 75w90 oil is thinning out and not providing as much lubrication between the clutch plates.

 

No one has said that running a heavier weight is going to cause damage to the ring and pinion so I'm thinking I'll try switching to some 75w140. It's a lot less work than messing with the clutch stack and might calm the lockup enough when hot.

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...

 

I'll add another 1/2 => 1 tube, give it a whirl and report back.

 

...

 

I added 2.5 => 3 tubes (4 oz each) and the knocking is more bearable now. I've noticed that once the oil warms up, it gets much less noisy around slow, sharp turns. This is really strange since this is opposite to what Zmanco is experiencing...

 

If it is still a problem, I'll go with some Redline CLSD oil like aarang mentioned.

 

Thanks guys, -Hugh

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Update: I decided to try switching to 75w140 Mobil 1 and added a tube of LSD additive as well. I had a track day this weekend and even in the paddock just after a session the diff remained smooth without any clunking even when making sharp turns to park. When I had the 75w90 + LSD additive it would get noisy and clunk when the diff was hot.

 

But before I declare "victory" I'll have to wait until next summer: the temps last Saturday stayed in the 70s vs. the 90s in the middle of the summer.

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