Wednesday, March 12, 2008

Rebuilding a 9 Bolt, 7.75” Borg Warner Cone Style Posi

This is basically a cleaned up version of a post that I made on thirdgen.org, the title links to the original thread. Like in other cases, I got a number of requests to put it back together with pictures, so here it is.

As always, the pictures are all clickable for a larger version.




Rebuilding the posi: There are pretty good, detailed instructions in the FSM and in the tech section on this site ( thirdgen.org ). Look them up, they’re a good start.

I’ll add a quick nutshell description and note where I did things differently/suggestions:

Disassemble: unbolt the axle retainers, pull the axles, pull the center section cover, remove the bearing caps (make sure that you remember what side everything came from so you can put it back like it came out), pop the carrier/ring gear assembly out of the housing. Note, this will require some prying and turning and make sure you save the side preload washers/shims so you can reinstall them like they came out. Be careful with them, they are machined out of a cast piece and can be brittle.

To perform the rebuild you need some kind of fixture to hold an axle. I took a chunk of wood, cut 2 shoulders to sit on top of my vice jaws, drilled a hole through the middle and then sliced it in half on the table saw to make some clamp/vise pads for the job:



Through the whole deal use the axles as alignment tools.


Before you disassemble it check this spot out:


It’s hard to see in that pic, but if the end of the cone is contacting the end of the case there your case is worn out of spec and you’ll either have to do some machining to it to make it work or get a new case.


With it sitting on the bottom axle, housing bolts up, unbolt the smaller, center bolts and pull the end of the housing/ring gear off.

When you do that you’ll see this (except you’ll have it in the case side, not the ring gear side like in this pic):




If you lift the spider/cross/preload spring assembly off you’ll get this:



If you lift that side gear out of the end of the case you’ll see the pocket in the side cone where you put the shims, there will be one on each side of the case between the side gear and the cone (unfortunately I don’t have a good picture). You can use any shims that are small enough to drop into the machined area between the 2 and still fit around the axle. I usually use 10bolt or ford 8.8” pinion shims. Actually, the last time I think I just stopped by the local machine shop and got a stack of whatever left over shims they had approximately the right diameter.

* This is where I differ from the instructions on the site or in the FSM, forget measuring clearances or anything else, just load both pockets with as much shim as you can get in there and still reassemble the case completely. I’ve never seen one of these get so tight it doesn’t work right (if anything you’ll want it tighter, not looser) and you’ll be kicking yourself if you do any less and start spinning one wheel again sooner then you had to. The shim packs will probably have to be the same thickness on both sides.

From there the reassembly is the opposite of the disassembly, just make sure that you have both axles installed and fully bottomed before torquing all the bolts, if you don’t line up the splines in the side gears and cones before then it’ll be next to impossible to do with it assembled.

Now if the case is worn out of spec, you can still usually get some life out it. What happens is that there are some rings machined into the end of the cones and the case to contact if the case is worn down too far, if you cut them down you can get some extra life out of it.

This is what it looks like if the cone and case ends are worn to the point where they’re grinding into each other, case side. The numbered parts were originally put in for something else, but they do point out the points that are contacting and wearing that aren't supposed to:



Cone side:



What I’ve done before is machine those down till they no longer contact (as a matter of fact, I think I machined them down till I had over .125” clearance). Again, case side:

Cone side:

FWIW, I did the inside of the case on a drill press with a surfacing disk and I did the cone side with an angle grinder by hand, just played with them till I got them within about .005 of flat… If I remember right I ended up cutting close to 1/4" total to make sure that everything fit (yes, this thing was way outside of spec, and yes, it still worked well after all this).

Eventually, after a few more rebuilds the cones/case will wear enough that they get too thin, and I started getting cracking around the opening that I mentioned to check above to see if it’s worn past spec. When that happened I pulled it all apart, bevel ground the sides of the cones, centered them up in the housing using the axles and welded them in, like this:


Monday, March 10, 2008

Bending Box Sections

(as always, all the pictures are clickable)

So the Deker said onto me: “do you know of anyone that can bend box stock out of flat sheetmetal? Can you do it with your press brake?”

(pressbrake:

more on this later)

Without much thinking I responded something like “Sure, why not? Pressbrake, big steel 20ton crushy thing. Good tool of destruction and changing the shape of things that don’t like to change shape…” (I can be quite eloquent sometimes when I’m not mumbling something incoherently. I mostly do that at work because I they heard what I was mumbling…)

He went on to describe how when they’ve been making Damascus billets they’ve been putting the steel into a steel box, sealing it up to weld it together and if the box could be made of the same steel that they’re making the knife blade out of it would save them the hassle of cutting it off the blank after they forge weld/hammer it. Real metal fab/machine shops were mentioned…

Huh, this is starting to sound like a challenge. I end up doing a lot of things just because I can when someone else doesn’t think so or can’t…

So later when I got home I thought about it some more and I could think of a few ways to do it that seemed kind of ugly and brutish but wasn’t sure what would be the results. Of course, I have a way with ugly and brutish, (or is that dumb luck? I keep forgetting) and the first thing I tried that I really expected not to work too well came out quite acceptable:

All I did is mark 4 sections and threw it in the press brake, bent the two ends up first making a U twice as wide as it was high, then making the middle bend around the head of the press brake. The worst part about it is that I had to hammer the piece off of the head of the press brake when I was done.


That’s a 2.5” square, it looks like I could go as small as 1.5” or so with the dies that I have but with a smaller bottom die I could get sharper corners (those are roughly 3/16” radius). I have roughly 22.5” capacity, which is more than long enough.

Unfortunately in the process I broke my 4x6 horizontal/vertical band saw (more accurate, the blade guides that were threaded into the thinnest part of the casting stripped their threads out), so in the process of further modifying, redesigning and replacing bits of it (more on that later also) I ended up needing to test it so I cut some end pieces.

Next thing I know I found myself in the basement with this thing clamped down on the drill press and the wife shaking her head “you’re not actually…”

“Yep”

I even made patterns for it so I can reproduce it exactly ;)