So I've read in a few places, jack one wheel up, test how much torque it takes to turn. 35 or better and you're ok. ....is that basically just taking a torque wrench to one of the lugs, setting it to 35 foot pounds and see if that'll turn/slip the wheel, or if it clicks, in which case it would essentially take MORE torque than 35 foot pounds to slip?

 

That would be from the center of the axle, not from the lug nut. That would require an adapter that would bolt to the axle with a hole in the center for the torque wrench. Using a lug nut is going to change the leverage ratio and not give an accurate reading.

I wouldn't worry with all of that, just jack it up and grab the wheel and see how hard it is to turn it. You can also remove the cover and look in the slots and see if the cones have bottomed out in the holes.

 

Or you could just do a burnout..... see if one mark is longer than the other......

 

I'm glad you said that. I thought it needed to be from the center of the axle, but didn't exactly "how" to do that.

....burnouts are currently 2 legged, but I was trying to gauge the condition of the posi.

 

on the later posi's from GM in the 9 bolts, they will usually last longer than the rear end will, you will blow apart the carrier before the posi goes.

 

"Testing" the posi will only tell you if it's working NOW; won't tell you how much life it has left in it, which is the usual question you want the answer to.

Using a lug nut is plenty accurate enough for most purposes. It's not like, if it takes 35.37 ft-lbs it's OK, but at only 35.36 it's bad. It's a whole lot more of a yes/no type of test than a "how much" one.

9-bolts are NOTORIOUS for the cones being wore out. It's unusual to come across one nowadays that has much, if any, life left in it. The posi almost always is dead long before anything else about it is used up.

Pop the cover off and look at it. It's the ONLY way to know for sure what you've got.

 

Great pic of the 9-bolt POSI carrier 'clearance window'.....


http://9bolt.com/technical.html

Little / No gap in the window means cones (POSI) are really worn out or soon will be !

 

Average person ....reasonable amount of effort That's pretty technical, lol.

Thanks for the responses guys.

 

I agree Sofa, the only way to truly know is to inspect it but a "weak" by (torque specs) usually indicates cones getting to the end of the housing where a "'tight" by torque specs would indicate one with more clearance- right?
I found a "new in 92" spare posi a race team sold a few years ago that had plenty of cone depth to go. I shimmed the play out and sorted and installed the "strongest" springs in my inventory. After a few years of running it measures ~65 lb/ft to slip it at the lug nut. I would think 35# is a minimum.
Another thought regarding center vs lug nut torque. Since the lug nut is 2+ inches from center it would have an advantage. Therefore, a 35# reading at the lug would be "something more" than 35# if taken at the center, right? Also remember, these are cone type LSD not clutch so it is mostly the force of the planetary gears working against the side gear that "locks" the cones to the carrier. Otherwise a 35# or even my 65# torque reading would be weak compared to a Trac-loc's 150-200# break away torque.
I think the 35# torque reading just tells you "the cones are probably not bottomed out yet".

 

That's really about it...

The degree to which a 2" radius difference would affect the torque reading, would depend on how long the rest of the radius is. For example if your torque wrench was 15" long, the 2" addition would affect it by a factor of about 2/(2+15)... or, right about 4 ft-lbs error @ 35 ft-lbs. IOW when the wrench reads 35 the actual torque is 39.

The question then is, if a "nice" one reads about 65 ft-lbs and a "normal" one reads, say, 60, is there really any difference between a reading of 35 and one of 39? Really? Or have we merely descended into "measure with micrometer, mark with chalk, cut with axe" hell?

In any case, NO torque reading can possibly tell you that it's going to work even 1 more time. It might be on the hairy edge of bottoming out and will fail utterly when the very next layer of atoms gets peeled off of something. The ONLY WAY to know whether it has any life left in it, is to take off the cover and look.

 

Lol yeah that's the only way to know how much is left.

I was really meaning the "break away torque" isn't really a measure of how well it'll pull both tires in a straight line since it's the action of the gears in the diff that really locks it all together. My posi with a higher break away torque will still spin an inside tire in turns from time to time or even in straight line when the traction differential is great.

We agree on "what the torque reading means".