max,

You may have touched on this when I was asking about the ls, but I wanted to get some more info. As I was parooosing through my Ford service schedule manual, I noticed that the front and rear axle lubricant is not scheduled to be changed out until the 150,000 mile service. Interestingly enough in the back of the manual it says that the axles are considered lubricated for life (kind of contradicting itself, maybe Ford considers the life of its trucks to be 150,000 miles).

Anyway, can this be right? How can synthetic, as fine as it is, maintain itself for 150,000 miles? How often do you change out? And does the rear cover on the differential housing use a gasket? I was looking at mine and it seems like it is sealed rather than using a gasket. The reason I ask is that with my ls I think I might like to do my own change outs, so as not to forget the friction modifier. Even if I conducted a 5-minute lecture to all the techs on hand that I have a ls (although the tag of the diff says different), I'd say there's a 60% I'd drive away from a schedule service without friction modifier.

That actually reminds me of a tire situation I had on a Honda years ago, and I forget what the real deal was, but there was something wrong about the tire that made it pull more than a little to one side (although the tire dealer assured me there was nothing wrong safety wise and that the tire would correct itself the more it was driven). Anyway, the point was that tire could NEVER go on the front, because it was front-wheel drive and would pull the car one way or the other. Needless to say, I kept track of which tire it was, and played hell keeping ANYONE (Firestone, Allied Tires, or the Honda dealership) from rotating the darn thing to the front every time I had the tires rotated.
Eventually the pull went away with wear, but twice I told them not to put the right rear (or left rear whichever it was) up front, but they did. Finally on the last rotation I marked the tire, showed them the mark, and they STILL moved it up front, but I was able to see it the second I got there and they moved it.

 

Yes, this is what Ford recommends for changing synthetic gear oil. If you're interested in superior rear end care, you should change the gear oil more often in my opinion; oil is cheaper than repairs. Those who have severe uses should change more often too. An aftermarket cover can have advantages as well: easy servicing/drain plug, increased capacity, cooling fins, O-ring seal, etc. Synthetic fluids cannot remove metal particles and most additives do not meet "sealed for life" criteria. I agree with you on the self maintenance. I was always taught that if you want a job done right, do it yourself (you will know you get friction modifer then). The rear cover uses sealer, not a gasket. I've always changed my fluids early and often. It's overkill, but I'm going to change mine every 30,000 miles or so. SO, HOW'D YOUR LS INSTALLATION GO???

 

max,

Installation went oh-tay. Got them to rotate the tires too since they already had the rear two off to get to the axles. Yeah, I never thought of an aftermarket cover. That would make it alot easier. Otherwise, I'm going to have to unscrew all those bolts and use sealant every time. That's too much trouble. What do you have for a cover?

Speaking of the ls, it is odd that the Ford SOP decription was differential "locker". I presume that's referencing Traction-Lok, but it really isn't a locker in the true sense. I'm also a little confused on how the unit operates, as when I looked at it (when I picked it up at the Parts dept.) it appeared to be spring loaded with clutches. The way I remember "Positraction" working is this (no spring loaded clutches):

The axle side gears were driven by four differential pinion shafts (as opposed to the two on an open diff). The two shafts crossed but were free to move independently of each other. The shaft ends had two flat surfaces that formed a sort of V shape that slid up and down special ramps in the diff case. Clutch discs were splined to the diff case and the side gear thrust members (with the thrust memeber splined to the axle). The differential pinions would encounter resistance when they attempted to to turn the side gears, and this would force the pinion shafts to slide up the ramp surface, and thus pressed the side gears and forced them to lock up the clutches. When the vehicle turned, the pinion gears started turning on their shafts and walking around the slower shaft, causing the outer shaft to rotate faster, allowing the pinion shaft on the outer side to slide down the ramp (unclutching that side gear).

Apparently that isn't the case here, as it looks like the spring load does the locking. How exactly does this unit work? Is there some preset load at which the clutches will slip?

 

I'm glad that your installation went good. The Trac-lok uses spring loaded cluthes which are overpowered and slip during turns. I install a drain plug in my transmissions and rear ends as soon as possible. I really like the www.mag-hytec.com cover; I don't have it yet. There's more covers available for the 8.8" over the 9.75". There was a post a while back where several people posted pictures of their various models.

 

cpadpl,
Mag-Hytec is now offering a cover for the 9.75" Works great: Easy to chage fluid, no worse than changing engine oil. I can vouch for ~20F drop in operating temperature (in phoenix!). On a 2hr freeway run, the diff would rise towards 210F. After the cover, it rises to ~190F. I'm going to try the LE oil that Roy reccomended & see if it cools better.
I too, have the LS. Don't forget the friction modifier!

Tony

 

Max,

Just so I understand correctly, are the springs the sole cause of pressure on the clutches, or is it "preload" (a term I have heard). I thought the spider gears spread the side gears which also exterted force on the clutch plates (i.e. increased load increases the pressure against the plates). My thinking was that the purpose of preload was to assist in the limited slip in situations where "load" was not there yet (i.e. you are completely stopped and one wheel starts spinning in sand).

Re/ my earlier post about the operation of Positraction (which I confess was obtained during the 70s, so it may be outdated), I thought the carrier and the associated parts inside would have to be moving at a relatively decent rate to have full effect (i.e. the pinion gear, ring gear, and diff carrier would have to get up to a certain "speed" before the pinion shafts would fully slide up their ramps and lock the clutches up fully). It seems the preload spring would be a way to put pressure on those clutches and "limited slip" up until the Positraction function could step in and assist in the job.

Anyway, my question is (if I rambled too much), is the spring the only load on the clutches and is my understanding of the way Positraction works now defunct? It seems like if the spring is the only load, the effectiveness of the unit will go down rapidly with clutch wear.

By the way, wear do you get all your knowledge? Are you a mechanic?

 

The "preloaded" or spring loaded clutch packs transfer "some" ring gear torque to the tire with less traction. The stiffer the spring or higher the load, the less wheelspeed differentiation is allowed. Loss of traction causes the clutches to transfer power by driving the opposite side gear. As you mentioned, the spider gears spread the side gears, which secondarily provide additional force on the clutch plates. Increasing loads correlate to increased clutch plate pressure which transmits power to the wheel with traction.