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Discussion Starter · #1 ·
I know this will sound like a silly question to most of you, but I need to know what POSI (sure grip) is. If I spin one tire the other tire rotates the opposite direction, and when I do a burn out BOTH my tires turn in the same direction-is this Posi?
 

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Posi-Trak is GM's name.

Sure-Grip is Chryslers.

anyways both wheels spin the same way all the time,reverse,forwards and when you twist the driveshaft.

an open unit does the funky action.
 

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And you can alway do a few burnouts, especially around corners, to find out if your Sure-grip is still working properly, as traction devices do wear/burn-out over time. There should also be a factory aluminum tag, probably on the passenger side of the differential pumpkin that states "Sure-grip," and there should be a warning tag referencing the Mopar fluid that must be used for your traction unit.
 

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Just what fuluid is that? I've just installed a brand new 3.91 sure grip in my 73Swinger but haven't filled the pumpkin up yet. I was waiting till I found out what additive to use?

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Should be mopar P/N 04318060AB comes in a 4 OZ plastic bottle. It's called Limited Slip Additive, friction modifier.
 

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You can buy generic friction modifier from Summit or your local part store, but I would use what your nearest Chrysler dealership recommends. Usually they'll sell you 80 or 90 weight fluid and a small bottle of friction modifier. Mopar P/N 04318060AB sounds right, but just go to your dealership and they'll have it right behind the counter.
 

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With a limited slip (posi-trac, sure grip, traction loc, twin grip, whatever) the axles are locked together with spring loaded clutches kinda like a motorcycle clutch. Both wheels turn the same unless you overcome the clutch/spring pressure.
Lockers can fool you. They need pinion twist to activate. They lock like a ratchet.
 

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I don't wanna be a jerk but I think you're wrong about the lockers. they are totally locked all the time unless you are going around a corner and the wheels turn at differnet speeds. The outer axle shaft floats outwards slightly (from going around the corner) and unlocks the rear usually accompanied by a ratcheting or clicking sound as the dogs slip by each other

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Every "limited slip" from the factory works slightly differently, but they all do the same same thing, which is provide traction by locking up the wheels when the base power wheel slips. No locker or limited slip locks up both wheels at all times, hence allowing differentiation of the axles. Spools or "Lincoln Specials" which are differentials home welded, often with a Lincoln welder, do NOT allow differentiation, and DO lock the axles together at all times. Aftermarket limited slip units like the Detroit Locker keep the axles in sync most of the time, which make for jerky street driving, especially when they're new. Factory units like the "Sure-Grip" allow more more slippage than their aftermarket components. The Ford units ( Trac-Loc ), also used in AMC rears, burn their clutches after 100,000 miles and have to be replaced. I've never owned a GM vehicle, but I know the Chrysler limited slip is known to last. And yes, if you turn the wheel one direction, the opposing wheel will rotate the opposite direction when the vehicle is up in the air. If you turn the wheel one direction, and the other turns the same direction, then you have an aftermarket unit like the Detroit, or a Spool/Lincoln.
 
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Discussion Starter · #10 ·
When i spin the tire the other tire rotates OPPOSITE. Which I am told is LIMITED SLIP. So I did multiple burnouts and BOTH tires smoked. So i was told that it is probably welded in the differentials to make a "wanna-be" sure grip. I am looking for a third member,should I buy an open unit? I have a 440 in my car, and I sure would like to wear both back tires evenly.
 

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if it is in gear or park when you spin it this is the only way they can turn(opposite) but if it is in nuetral or out of park they will spin the same direction.

limited slip is again a trademark name for a non open differential.
 

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phade said:
When i spin the tire the other tire rotates OPPOSITE. Which I am told is LIMITED SLIP. So I did multiple burnouts and BOTH tires smoked. So i was told that it is probably welded in the differentials to make a "wanna-be" sure grip. I am looking for a third member,should I buy an open unit? I have a 440 in my car, and I sure would like to wear both back tires evenly.
Dude, if you burn both tires when you mat it, what's the problem? It's a sure-grip. If you only burn one tire when you mat it it's either an open diff or a worn out sure-grip. what you said about the welded spiders is wrong. if they were welded, the axles would act like one piece (not move seperately), like a spool, no matter what you do. We used to do this on bush buggies, because we didn't give a shit about them. we called them "lincoln lockers". get it..... lincoln welders? LOL I definately don't recommend that on anything you care about especially for something you drive on the street.


Don't buy a open unit , keep what you've got..... what's the problem with it?

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I have had open diffs burn both tires, it is all a matter of available traction and how much power is being applied. They will not consistantly burn both tires at the same time though, and looking at the burn out marks, you will see they don't start and stop at the same time.


The spin the tire trick works.
Opposite directions - open or broken LSD
Same direction - LSD or locker

Real lockers do try to force the axles together - and spools are absolute. http://store.summitracing.com/partdetail.asp?autofilter=1&part=MSR-5S9F31&N=700+115&autoview=sku
 
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Discussion Starter · #15 ·
The problem with the diff i have now is that I blew a bearing seal driving it 1000 miles back home and wore them out, they are singin real good o[ow!
 
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