I tested the breakaway torque on my posi, and it was less than specified (110-140 ft-lbs). It was working fine on the street and strip. But since I'm putting in new bushings, lowering the suspension, etc., now seemed the time to open up the rear axle, reset/shim the clutches, and give it new seals.

So, I dropped the rear end. Opened it up. Took it apart. Bearings are all in great shape. Everything tight and smooth.

Then I made my mistake.
I didn't look closely enough at the gear case. I glanced at it and thought "Eaton," and pulled the spring cage out, so I could check the clutches and add shims or do replacements. Then I rotated the gears out and discovered....

It's an Auburn cone-type posi. In looking at my manual, it says these are "non-serviceable. Only service possible is replacement."

Oops. Eaton clutch-type and Auburn cone-type look very much the same. You have to look closely to see the difference. It's my own fault. I made an assumption and didn't look closely enough.

The problem comes when trying to press the cones into the case enough to be able to rotate the pinion gears back in. Just a few thousandths of an inch, but it's enough that the pinion gears won't clear the side gears' rims and rotate into place. But if it can be taken apart so easily, you should be able to put it back together.

Has anyone had one of these apart and put it back together? I'm open to suggestions. I really don't want to buy a new one, 'cuz I don't need it. (The 100-140 ft-lb test is for clutch-type posi, not cone-type. This unit is in great condition.)

 

I don't understand why it won't go back together. They usually go together easy. The springs are the hard part to get back in.

 

The side gears have a rim, a lip, around the outside that overlaps the bottoms between the gear teeth. When the pinion gears are in place, they will not lift out of the case because their gear teeth tips are locked in under this rim.

There is a spot on the side gear where three teeth do not have this rim. To remove the pinion gears, you must rotate one of the side gears around with an axle shaft, to line up this spot with the window of the case. Then you rotate the other side gear until the pinion gear comes to this spot on the side gear. Then you can lift the pinion gear out.

The problem with reassembly is that the pinion gear's teeth won't slip under this rim, as if the side gears (on the cones) must be pressed in somehow. But there's nothing there to compress as you push the side gears in, so I'm a bit at a loss.

I'll post a picture or two in a little bit.

 

Here are some pictures.

1> The red arrows show the "lip" in the side gears that I was talking about. Notice there's a dip in it at one point.




2> This is the side gear installed in the case. Notice how the dip in the "lip" is made to line up with the shape of the case window.




3> This is the pinion gear set in the case, and rotated trying to put it in. See how the next tooth of the pinion gear hits the lip, preventing the gear from rotating in.



It's as if the pinion gear won't set down deep enough into the side gears, so it can be rotated into position. If the side gears were pressed into the case even slightly, then the pinion gear should drop in. But I don't see any "give" in the cones that would let them go in any deeper.

I've got to missing something.

 

The cones and gears don't press in. They should just fall in place enough to get everything assembled. I've put several of these together with no problems. I noticed that it looks like there is dirt or something on the parts. It's also going to be very hard to assemble this with the ring gear still bolted on. Maybe some of the dirt has got into the cone bore and is keeping the cone from going in all the way. Are you trying to do this with the differential still in the rear end?

 

When I took it apart, it was all very tight. To turn the gears for disassembly, I had to turn them using the axles with wrenches on them.

The dirt is because I just put the pieces together in a hurry to take the pictures. When I tried to do actual assembly, I had everything clean. I wiped down the cones and the bores with lint-free cloth before trying.

The only problem I have had with the ring gear being in place was manipulating the cones at just the right angle to get them to slide in or out. I can't see how the ring gear could be a problem just trying to rotate the pinion bearings in. But if you think it will help, I'll take it off. Since there is nothing wrong with it, I didn't take it off, thinking there was no need.

No. The differential is out of the rear end, as I wanted to check the bearings with my bare hands, even though they turned smooth as silk with the diff in the pumpkin.

I'll blow everything out with air, then wipe it all down with solvent and clean cloth. If you think it will matter that much, I'll also take the ring gear off.

 

The ring gear is going to be in the way when you try to get the springs back in. As far as putting the gears in the ring gear should be fine. Be sure to lube the cones when you put them in. I use GM limited slip oil additive on them when I put them in. I have axle stubs that I put in my vice to hold the differential and turn the gears. You could bolt and axle into a wheel and stand it up on the floor to help you work.

 

OK. Thanks for the input. I'll clean and clean and clean, then lube the pieces with quality oil, and see how it goes. I hope it's just a matter of clean and lube.

 

I still don't have it together. Just working in spare time, and not in a hurry lest I damage a shim. I'm using very thin amounts of Mellube assembly lube, by the way.

At one time, I fumble-fingered the cones and thought maybe I had switched them left to right. So I decided to try swapping them. Apparently, I did switch them earlier, because I can now get the pinion gears in without forcing them, but they are still very tight. So tight that I cannot get the shims to go in.

With gentle prying, I have observed that I can make the pinion gears settle in just a bit more. The split in the cone compresses just a bit, though still not enough to get the shims in.

It's more and more obvious that there was no reason to take this unit apart, except for my failure to recognize it as an Auburn instead of an Eaton.

So.... I have worked out a way to "pull" the cone on the ring gear side deeper into its socket. Basically putting a half-inch bolt through from the inside, hooked to the C-clip, and through a steel plate on the outside at the ring gear end. I haven't tried it yet, but see no reason why it should not work. I only need to gain about half the thickness of the shim to get them in there.

I tried pressing them out from the middle using a short bolt and nut, but then I could not turn them to rotate the pinions and shims into place.

I now know that if the torque breakaway test is not up to spec, be sure to confirm that it's actually a clutch-type before taking it apart. I'm kicking myself, as this thing did NOT need to come apart. It's in near-perfect condition.

Oh, well.... One should never stop learning.

 

I've put this aside for a bit, 'cuz it's been too hot to work in the garage. It's cooled off now, and I'm back at it.

I can get the spider gears in, and rotate them into place. It's tight. But I CANNOT get the shims in on top of the spiders. There's not enough space between the spider gears and the case. Maybe one or two thousandths. If I shine a light in through the crosspin hole, I can just barely see light over the tops of the spiders. No matter what I do, as I try to rotate them in, the shim is pushed off the top of the spider. There's no getting it in there.

I got an assembly sheet from Auburn's web site. It just says to rotate everything into place, so this tightness may mean something is wrong..

It also says that if there is any sign of galling, the unit must be replaced. Everything looks smooth. Nothing like any galling that I have seen before. But this is about the only explanation I can think of for why this unit was so tight coming apart, and why I can't get it back together. Perhaps it's galled, and some metal build-up from that is on the cones/tapers?

I'd sure hate to have to spend money for a new differential unit.

 

In case anyone is following this thread....

I have come up with a possible solution for this "unserviceable" posi differential. As I said earlier, it appears my problem is galling, that somehow made the cones sit higher in the funnels.

I figured that I have nothing to lose, and everything to gain, and could save about 400 bucks.

I picked up some 150-grit grinding compound at my local NAPA. Then I worked out a way to spin the cones in their funnels with my drill. It also lets me vary the pressure as I spin the cone.

I set the cones in place, and measured how deep they were sitting with a depth micrometer calipre. Then I applied the compound and spun them in place for about 5 minutes each. I reversed the direction about every minute, and added more compound as needed.

Then I cleaned them off, and put them back in place. One cone set in about .015" deeper. The other about 0.020" deeper. I set a spider gear in place and was actually able to rotate it in without force. I still could not get the shim in, but there is more room now, and I can clearly see light through the gap now.

Another side benefit is that the cones are fitting their funnels closer. I can tell this because there is more friction now when they are in place. If this works, I think this will bring the test specs back into line.

It's going to take probably a half hour or hour more grinding. I actually think that I'm not only going to get the thing back together, but I will have restored it in the process.

Whether this procedure will work for other tired Auburn posi units, I can't say. But it appears to be working on mine.

I'll report the final result when I'm done in a few more days.

 

If im reading this right your sanding the walls where the cones sit? Your effectivly wearing it down quicker if thats the case...making the cones sit in deeper. An auburn works by putting pressure on the cones against the case so sanding it and making it sit deeper in will mean that spring is not pushing on it as hard anymore and it will not hold as well.

 

The problem with mine is that somehow, for reasons I can't explain, the cones were actually sitting higher in the case than they were supposed to. Normally, when an Auburn wears out, the cones have settled in deeper just as you describe, and the spider gears and shims get loose. I don't know if it was some sort of galling, or what, but mine came apart very hard, and it was impossible to reassemble because there was no clearance for the shims.

As I have worked on this, I can see how it was originally machined. I can tell that I am just putting the cones back down into the proper original position. For instance, the little crescent cuts on the top edges of the cone now match the crescents in the case. Once they matched in that way, magically I could assemble it, and the shims now fit like new. Snug, but easy to get in.

I'll post a couple of pics to illustrate what I'm talking about.

I can tell from the grind marking from the compound, and from the feel of the cones in their bores, that I have possibly restored the original fit. Before I started, I could turn the cone easily in the bore, even when dry. Now, they stick like they're glued in place. Very hard to turn without lube.

I am going to assemble it now, and then test it according to the manual. If the breakaway torque is in spec, I'm gonna say it's good. Worst case, I have to replace it. Best case, I've save over 400 bucks.

It's an unusual case, which is why I was asking for advice on it. The wear just wasn't "normal."

 

Well, I did it. And it worked!

It only took about 30 minutes of grinding, and the cones settled into the bores far enough to assemble it. As the cones settled in, the friction to turn them increased dramatically, indicating the fit was being fixed. As I ground them, I was able to see how the surfaces started out being uneven, then matched up with each other.

I took this picture just after I started grinding. See the red arrow, showing how the "dips" in the gear and casting did not match up. As I spun the cones in the bores with grinding compound, I checked regularly. I found that when these "dips" matched, the fit became "perfect."

After grinding, the surfaces were a uniform grey colour. I finished the cones and bores by hand rubbing with medium-grit emory cloth, giving the surfaces a nice silver cross-hatch surface. The cones still have the needed spiral lube grooves.

When I assembled the differential, all the pieces went in with no problems. Using "Mellube" engine assembly lube, I was able to turn the spiders and shims in. The whole assembly has some preload without the springs and plates, but turns smoothly with some effort.

Of course, time will tell how it all works out. But I'm bettin' I just got a good-as-new rebuild.