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#48473 - 17/04/02 10:49 AM LSD friction modifier makes the LSD LESS EFFECTIVE!
OffroadX Offline
Member

Registered: 17/08/00
Posts: 13692
Loc: Baltimore, MD
Looking at RedLine's site about to buy some of their LSD friction modifier in the hopes of making my LSD actually WORK worth a damn and noticed they have 75W90 and 75W90-NS oils. The regular 75W90 already has the LSD friction modifiers, the NS doesn't. The NS type says "recommended for manual transmissions and non-limited-slip transaxles that recommend 90 WT oils. Can be used in racing limited-slip units to increase lockup and reduce wheel spin" which I take to read that the friction modifiers actually make the LSD less effective.
Indeed, I just got off the phone with a tech at RedLine. Told him I was running Mobil 1 (which includes the modifier) w/ my LSD and I wasn't satisfied with the performance of the LSD and I was about to buy some of Redline's LSD friction modifier additive thinking it would make the LSD operate better until I read what they said about their NS-type oil.
He agreed and said I was going in the wrong direction. Adding the modifier only makes things more slippery and the clutches would be less likely to grab and kick the LSD into action. His advice was to go with an additive-free oil like their NS-type and add just enough of the additive to get rid of any chatter in turns.

Well, back to the old drawing board!
Brent
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#48474 - 17/04/02 07:05 PM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
Toy4x4Guy Offline
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Registered: 07/04/02
Posts: 248
Loc: TN
I'm suprised people are having problems with their LSDs. On my 2002 it seems to work pretty well. Granted, I don't do rock crawling or anything so I've never had one tire in the air. When I first bought my Xterra I took it to a gravel lot and stomped the gas a couple times and each time I left TWO markes about 6 feet long indicating both tires were getting power. Also, ever now and then when I get on it in a curve I get a little feel of both tires kicking in.
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-Toy4x4Guy

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#48475 - 18/04/02 05:57 AM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
Cygnus-X1 Offline
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Registered: 15/02/01
Posts: 1976
Loc: Alexandria, Virginia
I don't think any amount of friction modifier or gear oil is going to do squat to the LSD. Not enough to notice anyway. It is designed so that the a wheel has really gotta slip before it will engage. There is no magic additive that will make it work any different. That's just how it works. I can feel it kick in on wet boat ramps, and on steep inclines in the rain if I really mash the accelerator for a second or two. Under normal driving conditions I can't feel it...probably because it is not designed to work with just minor slippage. There is no additive that will all of a sudden change that fact or make the factory LSD feel like a locker or something.

FWIW, the X's LSD works exactly like every other LSD equipped 4x4 truck I have ever owned. I think it works just fine for it's intended purpose (but I agree that it's not all that great). You'd have to get a whole different LSD unit if you really expect to feel an improvement.

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#48476 - 18/04/02 08:32 AM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
OffroadX Offline
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Registered: 17/08/00
Posts: 13692
Loc: Baltimore, MD
I hope to prove you wrong soon...

Brent
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#48477 - 18/04/02 11:23 AM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
pinoy Offline
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Registered: 27/08/01
Posts: 481
Loc: TinleyPark, IL.
I'm wondering if that holds ture with conventional oils also? I've put the modifier in just so it doesn't chatter. Haven't tested it off road yet but haven't had any problems with it so far on the road. I take it the modifier is only needed for the chatter and nothing else?

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#48478 - 19/04/02 07:02 AM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
OffroadX Offline
Member

Registered: 17/08/00
Posts: 13692
Loc: Baltimore, MD
Yup, just enough to eliminate any chatter, be it synthetic or dino oil. Most of the oils on the market have the additive already in at about 5% anyway. So far of the ones on the shelf at 5 different parts stores yesterday, I only found 1 brand of 80W90 (Coastal) that was not LSD-compatible (said for top-off only), though there was some Castrol at one store that said nothing at all about LSD compatibility. I could get some of RedLine's NS-type, but I don't feel like waiting or coughing the $ just yet.

Brent
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#48479 - 22/04/02 11:03 AM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
OffroadX Offline
Member

Registered: 17/08/00
Posts: 13692
Loc: Baltimore, MD
I put in the Coastal 80W90, which contains no LSD friction modifier additive. I didn't add any modifier of my own initially, and since I'm having no problem with the diff "chattering" I think I'll keep it that way.

Immediately after changing the oil, I did a couple of "tests" in my parking lot. I backed both rear tires against the 5" tall square-top curb and tried to ease up onto it. It's just enough to keep me from making it without any inertia. Just as the tires started to climb and the contact patch left the pavement, both rear tires started to spin and my rear end started inching to the left down the slight slope of the lot. Hmm, so far so good.
On Saturday I went to an industrial park and did the old "RTI" thing on a loading ramp in 2WD. As soon as one of the rear tires left the ground, it just spun and the other side really didn't push at all. Probably asking too much from that one.
Today in the rain I would break the tires loose when pulling away from intersections/lights and it felt like I was getting more traction than if one tire were spinning, always got a decent push.
Just got back from lunch and I went behind a vacant strip mall to the loading area and did a few peel-outs. I consistently laid down two marks on the gritty/sandy pavement. That's the best test yet.

Brent
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#48480 - 22/04/02 07:27 PM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
pinoy Offline
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Registered: 27/08/01
Posts: 481
Loc: TinleyPark, IL.
Thanks for sharing that info. Brent. Once again you've been extremly helpful.

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#48481 - 23/04/02 11:13 PM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
*paul Offline
Member

Registered: 16/08/00
Posts: 822
Loc: New Zealand
I was driving my 2WD out in the desert this weekend. One thing I noticed while blasting along deep sandy roads (trying to keep from getting stuck) is that the X would plough the front wheels straight ahead when I turned into a corner. Once I learnt to momentarily back-off the gas pedal the front wheels would immediately hook up again in the direction they were pointed.

Under these conditions the axle was locked up and therefore the vehicle resisted turning. Dropping the power momentarily relaxes the LSD clutches enough to allow sufficient diff action to initiate the turn.
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-Paul
2007 Nissan X-Trail
New Zealand (ex San Diego)

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#48482 - 24/04/02 01:17 AM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
Todrick Offline
Member

Registered: 08/08/00
Posts: 7759
Loc: Arizona
its not an LSD thing its a 2wd in sand thing

with out the front wheels pulling in the direction you turn, as they would on a 4x4, a 2wd's front wheels just plow ahead especially at speed...

basicly if you are in the desert in a 2wd and you turn the wheels and the truck doesnt turn... its not the LSD, its the fact that you are going too damn fast...

otherwise how do you explain all the 2wd trophy trucks with lockers that have no problem turning

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#48483 - 24/04/02 05:37 AM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
Cygnus-X1 Offline
Member

Registered: 15/02/01
Posts: 1976
Loc: Alexandria, Virginia
Quote:
Originally posted by OffroadX:
Just as the tires started to climb and the contact patch left the pavement, [b]both rear tires started to spin and my rear end started inching to the left down the slight slope of the lot. Hmm, so far so good.
[/b]
So it's working as it normally should then. Hasn't your LSD always worked this way? Mine has. Just curious. It sounds like whatever oil you had in there was the problem, not the LSD itself.

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#48484 - 24/04/02 12:27 PM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
*paul Offline
Member

Registered: 16/08/00
Posts: 822
Loc: New Zealand
If you actually know what's inside the clutch-pack style LSD and analyse it you will recognise right away that it is a kludge of a design. If one wheel has no traction the locking effect is limited to the preload on the clutch pack. Power is lost to the spinning wheel.

(the effect of LSD preload can be determined by measuring the torque required to turn one wheel when raised off the ground. It's very, very low in our case.)

With better traction, the locking effect is subsequently improved as the clutches are compressed further by the diff spider assembly trying to "expand" under torque.

As traction is gained (by the wheel with the least traction) the tendancy to lock and therefore turn the wheel with better traction is improved. With good traction (and applying lots of power) you have effectivly a locked diff.

All this is the opposite of what you want.

The effect of oil friction modifiers is the same as in automatic transmissions. It's a "fix" to get around the grabby static friction characteristics of wet clutches. Deleting the modifier will make the clutches engage *slightly* better and is unlikely to cause chattering (on the X) as the preload is so low.

I've found the Xterra's LSD to work exactly as I expected.

Improvements to an LSD are tradionally made by adding clutch plates or by using stronger springs, both of which increase the preload only, which is what you what. The downside is possible chattering on corners.
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-Paul
2007 Nissan X-Trail
New Zealand (ex San Diego)

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#48485 - 24/04/02 01:26 PM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
Cygnus-X1 Offline
Member

Registered: 15/02/01
Posts: 1976
Loc: Alexandria, Virginia
Quote:
Originally posted by *paul:


I've found the Xterra's LSD to work exactly as I expected.

Ditto. I know it's not the greatest, and I can't blame Brent for trying to improve its function. But it does work. It just takes a lot of spin to get it work where you can feel it.

A wet boat ramp with a bit of an incline is the best situation I have found where I notice it working. Upon heading up the ramp from the water there is slippage initially and then a slight jolt/gabbing feeling - and then the X motors right on up the remainder of th ramp.

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#48486 - 24/04/02 07:18 PM Re: LSD friction modifier makes the LSD LESS EFFECTIVE!
OffroadX Offline
Member

Registered: 17/08/00
Posts: 13692
Loc: Baltimore, MD
Our friend McSoo from the 4x4parts.com board said that adding an extra clutch disc would make a difference, "just like the ones in Mexico"
Seems to think the ones sold in Mexico have a tighter diff from the factory. Weird, but I'm not going to pull mine apart to add a disc. For that much trouble I'll go ahead and get a locker in there.

Brent
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