DodgenIt

Hey guys.
So I have a Mag Hytec cover on my rear dif, and about to put one on my front dif.
Figured while I was puttin the new one on, might as well change the fluid in the back as well.
My question is, how do I know if I have a limited slip dif or not?

I have a paper from a dealership that says eveything the truck came from the factory with according to my VIN #.
It says under axles..

Axle- Front, Dana M60
Axle Ratio- 3.55
Axle- Rear, Dana M70
Axle- Rear, Anti-Spin Differential.

Words tell me the differance between 'Limited slip Diff' and 'Anti-Slip Diff'.
I just wanna double check.
Is there something on the dif or axle I could look for that would reassure me?
TIA!

upersleder

with both rear tires off the ground and it in park you will not be able to rotate the tires by hand with a limited slip. open diffs one will rotate one direction, the other opposite.

DodgenIt

Perfect!
Just the answere I needed. I have an open dif, Both tires spun opposite ways.
Thanks Upersleder much appreciated!

totalloser

I think that is incorrect information. A tight limited slip MIGHT not turn as readily, but looser preloaded posis WILL spin the other tire backwards. You might very well have a positraction. Especially if it's in the truck manifest. The amount of force to get the other wheel turning backwards is entirely reliant on the preload springs in the posi. Some can be quite tight, others so loose as to appear to be open diffs.

The looser ones will still lock up tight as long as both tires have some traction to begin with since most of the lockup of a posi is from the engine torque deflecting the spiders against the sidegears which in turn push the clutchpacks to snug up the posi.

Usually you can feel a positraction before the clutchpacks begin to slip though. There will be a slight resistance that "breaks" and then the other wheel will turn backwards.

Most the posis in our trucks are preloaded light. The only real way to be certain would be to pull the diff cover and look at the carrier. But it's somewhat unlikely that someone pulled out the carrier, switched the ring gear onto an open carrier, and reshimmed the new carrier.

Either way, the oil won't hurt anything. If you put regular gear oil in the rear diff and it starts chattering and getting "grabby" all you need to do is add some "friction modifier". And if you put the posi oil in it really won't hurt anything.

Oh and the "antispin" is a positraction. I believe a conventional clutchpack type.

DodgenIt

So what exactly are you saying? In fewer words please?
Im getting mixed up between.. limited slip, open dif, posi lock, anti lock.

Manifest says "anti-lock"... They spun opposite yes, it wasnt "easy" though. Not super hard either, just kinda tuff.

RowJ

Limited Slip and Posi Lock are basically the same thing. Open Differential is no connection between two rear wheels.
Based in your build sheet, you have a Dana 70, Pwr-Lok rear end. It is a limited slip and does need some load to activate.
Best test... one wheel on dry pavement... one on wet grass, snow or gravel.
Then go, fairly quickly. You will feel the slip (maybe 3/4 rotation), then the grab.

For positive confirmation, pull cover and look on the side, for this oval with floating pin.......

Power Lok's are more expensive and prefered over the Trac-Lok by most.
Do a search for more info on the differences between Pwr-Lok's and Trac Lok's (which come on the D80 rear ends).

RJ

NCLandscaper

hoping more will chime in. I have a Dana 80 and need a new diff soon.

lgp9999

Posi/Positraction is a GM brand name for a Limited Slip Differential. With both tires off the ground you can always turn the wheels by hand, LSD or not (assuming the transmission is in Neutral, transfer case is in 2wd or neutral, and the parking brake is released). In general (99% of the time in my experience) LSD turns both wheels the same direction while open differentials turn in opposite directions.

justme-

here's the simple answer- the axle should have a metal tag on it that says it has a limited slip/anti spin diff and needs an additive- it may have corroded and fallen off tho. If the build papers say it has anti-spin, assume it does. Forget the how and why- the additive is not that expensive, besides if you've actually driven this truck you should know from experience if it has the limited spin diff or not.

The names is symantics- you either have
an open diff in which power goes to the wheel moving the fastest- the one on the outside of the curve when going around a corner. Simple wording- power goes to the wheel with the least traction.

Limited slip/anti-spin has some mechanism, be it clutches, ramps and *****, or whatever, that allow one wheel to spin a little faster than the other for a limited time/distance. In theory allowing a vehicle to turn a corner (as above with the open diff) but giving power to both wheels so the vehicle continues to drive when one wheel having less traction than the other. A limited slip can not ensure even power to both wheels 100% as there is some slipping allowed.

Locking diff/locker - the diff can be open or locked solid by mechanical means. Lockers can be active operated like an air locker (which locks the carrier when air is applied and releases it otherwise) or mechanical like the Detroit Locker which is a dog style that opens to allow cornering (not to the same degree as a limited slip) and locks otherwise. In locking, the difference to a locker is it will never allow either wheel to spin slower than the diff carrier- so a wheel with no traction may spin, but the wheel with traction will still be driven as fast as the carrier turns. Aside from air lockers which can be turned off and effect an open diff, mechanical lockers tend to be very aggressive in locking/unloking on the street and can cause quite a bit of stress to components and tire wear.

dguru

You can take out the fill plug and feel the edge of the diff with your finger. If you feel a sharp 90 degree corner like the pic above you have a power lock. You can also feel the bolt heads that hold the diff together as seen in the pic. An open diff has a rounded carrier not a sharp 90 and no bolts.

DodgenIt

K im still confused. RowJ and others say, "Based on your build sheet, you have a Dana 70, Pwr-Lok rear end. It is a limited slip and does need some load to activate."
My build sheet says "ANTI-SPIN Diff"
So is anti spin the same as limited slip?
Cause the wording doesnt make it seem that it is... Anti is the same as Limited?? (Anti= non.. limited= Just a little) ???

With my Trans in PARK, T case in 2wd, no parking break, both rear tires off the gound, I was able to spin by hand, and they spun opposite ways. This I am sure of. It was a little hard, not free spin, but not cranking on em either.

Russ Roth

Yes. All just different names for a limited slip differential.

k-bit

The trans should be in neutral when trying to turn the wheels.
Jack

RowJ

My dealers build sheet also says "Anti-spin Differential". Just another way of saying Limited Slip!
Also says Dana M70 267mm. If yours says that and Anti-Spin Diff....... you have Power Lok Dana 70.

The 5 speeds, 6 speeds and all duallys (I believe) have Dana 80's with 286 mm and Trac Lok Anti Slip.

RJ

DodgenIt

Right on pefect! Just what I needed to know.
Yep mine says the same thing on my build sheet.
Cool thanks Rowland.
Thanks guys!