Beefing up the Crap for Cheap

[Schwarttzy]

I'm reading this tread about the 10bolt, which has me thinking about another option... one that's not quite so expensive. I find the number one reason differentials fail is because of deflection, in-particular the diff housing flexing. Which I see no reason why with a few modifications we couldn't help push this turd the little bit further that the majority of us only need to get out of it. So I'm hoping to get some glorified destruction photos posted up here so we can see exactly whats happening to these thing when they go kaboom.

I just know in my heart that I could make a heavy duty aftermarket differential cover and replace that tube #22 with some incredibly thick stuff making a night and day difference in strength. Hell, my Dana 30 I had on my grand Cherokee survived some really stupid abuse and that vehicle weighed a ton with everything on it. And these parts wouldn't cost much to make either. If you're asking, "Why build a heavy differential cover?" The answer is simply to provide more strength to the housing. If you have ever installed a Ring & Pinion you might learn about a device the stretches the housing so you can easily slide the bearings and all in. Basically we want the opposite, we want to prevent that from happening.

I am however in complete opposition to locking down the axle with heavier duty mounts because I know your just going send more force into the housing, which is exactly opposite of what we want.

So bring on the destruction photos!

 

[06 H3]

**** I gotta see if I have a pic of mine when it broke. The pinion gear got shredded up but not too bad, just a few teeth were gone lol

This is interesting

http://www.hummer4x4offroad.com/forum/showthread.php?3333-Front-axle-beef-up

I agree that the housing flexes too much, one of the 3 bushings go bad you slowly will flex the housing out and when you throw it on a tough obstacle where your spinning or you hit something the wrong way BAM!

 

[4speedfunk]

The AAM-7 fails in one of two ways...both caused by the same problem. The main issue is that the driver's-side outboard mounting bushing (#9) allows WAY too much lateral movement in certain conditions. Because its out on a 20" long lever...any movement out at the end of axle tube (#22) applies leverage to the side of the main case (#?). The main case is also held to the frame by (#54) and another bushing (missing from your diagram) on the snout of the case. Even though all three bushings are equally "squishy"...its the one on the drivers-side that causes the problem, due to it being out on a 20" lever. Many times I have witnessed a tremendous amount of fore/aft movement at the mounting plate (#10)...especially during spin-and-grab situations. In a split second...a sudden bite of traction will allow the end of the axle tube to be violently jerked forward...sometimes up to a 1/2". If the jerk pulse is strong enough...it will transform the axle shaft (#21) into a giant lever, and it takes the tube (#22) with it. It basically acts like a claw-hammer pulling a nail. Remember...the main case is held in position by two other bushings much closer to the center of its mass, and those are not going to move...but bushing (#9) is left out there by itself and its allowing the end of the tube to flop all over the place. And that is the problem in a nut shell. Inside the case, one of two scenarios happens:

1. Stub axle (#21) stays in one piece and pulls the diff carrier (#50) out of alignment or completely off of its saddles inside the case. Boom!
2. Stub axle (#21) fractures in half right where it plugs into the carrier. Usually not a boom...but definately stops forward motion, and launches metal debris into the case.

We're talking about thousandths of an inch, here. These parts are spinning at a high rate of speed, and it only takes .010" of internal movement to completely mis-align the teeth between the ring & pinion. It happens in a split second but, that's all it takes. Here's what scenario 2 looks like...



I'm convinced that if you could clamp the entire AAM-7 assembly firmly onto a test bench and apply normal torque and load to it...it would hold up to more than most of us expect. Brute force does not seem to be the culprit...its an alignment issue. Imagine you take that same AAM-7 on the same test bench, and while is running...you place a bottle jack sideways and start slowly jacking the end of axle tube (#21) forward. What you're gonna see is that cast iron tube applying lateral torque on the side of the aluminum case, (with parts spinning inside it). At a 1/4" of deflection, you'll start to hear things inside going very wrong. At 3/8", it will be screaming. Jack it too far and BANG!...you will induce one of the two failures above. This is exactly what happens in a fraction of a second when off-roading. I'll bet my nuts on it!

The problem is that the three mounting points are independent of each other, and this allows the excessive flex. The solution is to add a truss between the axle assembly and the truck's frame. You bolt the axle assembly rigidly to the truss...then suspend the truss to the frame with bushings. This way you're not relying on the axle assembly itself to absorb the jerking motion that pulls it apart. Instead...the 3-piece AAM-7 is held together, cradled as one rigid unit, and the bushing-mounted truss is allowed to these absorb shock loads. The axle assembly is still allowed to flop around...but it moves a single unit. I have a prototype drawn up on CAD and also a cardboard mock-up....



I shelved the whole idea for one basic reason: The AAM-7 cannot be re-geared. I feel a 7.25" ring gear is too small for 35" tires...regardless of the design. So, that sealed the deal for me and I didn't see the point of pursuing it. I like the other idea (the 10-bolt) better.

 

[MTUH3]

I am on 4speed a bit with this, though stronger would be better, I am more concerned with being able to regear. Call it luck, or being a pansy, but I have yet to break a half shaft or differential.

 

[4speedfunk]

Don't jinx yourself!

:giggle:

 

[06 H3]

I broke one half shaft and one axle and that was at the same time. That was before I learned to drive the way cbetts and crew taught me. Bounced the front end on a steep hill came down on a rock and the pinion sheered and the half shaft went. I also had those dumb diff drop spacers in at the time and I didn't know this then but now I realize how they messed with the rear crossmember bushing and left tons of play. That was a big factor IMO. Since then I have done much tougher trails and kept it all in one piece

 

[4speedfunk]

Yeah...it took me a couple axles to figure out the H3, too. The tried and true "gun & go" (Jeep method) usually results in broken parts. The H3 is a creepy-crawler. It must be finessed, and you have to trust the electronics and take full advantage of them. When the TC is working correctly, and the driver knows how to use it...the H3 can be a stunning off-roader (even if it doesn't look as impressive as a full-throttle assault). At the end of the day...the H3 will arrive at the same remote campsite as other vehicles, (often with twice the articulation and ground clearance). So its definitely capable...just a little fragile in the front axle department.

 

[MTUH3]

Don't jinx yourself!

:giggle:

I was thinking that when I was typing, but figured... what the hell. I have a couple spare half shafts anyway. And whether it is a totally new diff, or just a reason to put in a front locker... oh well

 

[MTUH3]

Yeah...it took me a couple axles to figure out the H3, too. The tried and true "gun & go" (Jeep method) usually results in broken parts. The H3 is a creepy-crawler. It must be finessed, and you have to trust the electronics and take full advantage of them. When the TC is working correctly, and the driver knows how to use it...the H3 can be a stunning off-roader (even if it doesn't look as impressive as a full-throttle assault). At the end of the day...the H3 will arrive at the same remote campsite as other vehicles, (often with twice the articulation and ground clearance). So its definitely capable...just a little fragile in the front axle department.

I completely agree. Lucky for me I never owned a Jeep. The 3 is the truck I learned to wheel in, so I paid extra attention and learned some lessons from others, both in the forms of good advice and their mistakes. I just wish that others would listen to me sometimes. It would save them from repairs

 

[bebe]

You can go all the way back to my and Neos "ebola" days to find this discussion.

They don't break in ways that you can put a collar or saddle on it to stiffen it up. The only thing I could reasonably devise was a 1/2" steel ring and longer cover bolts to make the whole pumpkin more rigid , but then you could run into an electrolysis problem and a steering rack is in the way.

I'm not taking credit for it - but between F5 and my "Letter to the H3 Brand Quality Manager" is why we eventually got the AAM760 in CI in. That was in October of 07.

 

[Schwarttzy]

Well for me 35's will be plenty big, especially with this idea of cutting off the cross members and clocking the transfer-case, should have ample ground clearance if I do that. I don't agree that slop in the mounts will allow for leverage, but I got no way to prove it.

 

[bebe]

What was consistent about the diff issue was the 1st time it broke it usually deflected enough to allow the pinion to ride up the ring gear and peel off a few teeth. The dealerships almost always just replaced the internals, then the next failure would be the R&P, and the case would crack/split in a saddle like fashion from the drain plug.

 

[Schwarttzy]

What was consistent about the diff issue was the 1st time it broke it usually deflected enough to allow the pinion to ride up the ring gear and peel off a few teeth. The dealerships almost always just replaced the internals, then the next failure would be the R&P, and the case would crack/split in a saddle like fashion from the drain plug.

Got any pictures?

 

[06 H3]

I completely agree. Lucky for me I never owned a Jeep. The 3 is the truck I learned to wheel in, so I paid extra attention and learned some lessons from others, both in the forms of good advice and their mistakes. I just wish that others would listen to me sometimes. It would save them from repairs

Heeps are way too common and you wont see me in one. lol I know jeepers who will wheel cautiously like us and I know some who hammer down and they replace parts a lot! I know one guy on Dana60s, an I6 (not even a V8 with big power!) and 39s which are totally ok for dana 60s and he has broken over 6 shafts and his excuse is that they are stock shafts. Who cares! lol He has done some tough trails but nothing that much tougher then what I do..A lot is driver. Recently dynatrac came out with a Dana80 that is compatible with the JK electronics...Why? Some of there users have been breaking dana60 full floats. HOW!?!?! Its usually drivers, if I was dynatrac I'd be happy. Consumer error/abuse puts money in their pockets.

 

[Schwarttzy]

That's why I want just a bit more strength for cheap and I'll be happy.

 

[bebe]

Got any pictures?

Yes, what of?

You can also use your google foo...(H3 broken front differential) and click images

 

[4speedfunk]

Caution Bebe....doing that might crash Google!

:giggle:

 

[Schwarttzy]

I can google picture all day long but I don't get much on story or information on whether bearings gave or what.

But it doesn't matter, after sleeping on it, building 10 bolts seems much smarter.