And we're ready to start!

[backcountryislife]

Took a while, but I've got my new diff carrier, and new diff, and new steering rack, rack sleeve, flex lines custom made for the rack (with enough slack in them to handle a snapped rack)


New, IRON F. diff carrier

New donor diff thanks to Reaper!!!
and new rack

Both hard lines being replaced with flex, then both rubber bushings being replaced with custom ABS bushings (my guy has TONS of spare ABS if anyone wants some of them made, if you're going to hard mount one side... no point in allowing flex on the other side. If one side is stiff, and the other moves, you'll crack just like before IMO.

Between this, the Hunner sleeve, and an extra added mount in there, this thing BETTER last a while.

4:1 t-case had some difficulties getting here, but should be here soon. Waiting for that so we can do T-case & diff at the same time.

I can tell you, I'll be hammering on it as we get closer to fall, to see if it's going to break, so that I don't get stuck without a rig for 2 months again... this SUCKED. I got screwed right in the middle of summer.
Honestly, I think if it snaps again, I'm probably just going to sell it & buy a RZR... next door neighbor runs the Same trails as me, 2x as fast, has a blast, and has yet to break ANYTHING!!!!:whaa: I hate the idea of hauling it, but most of the trails I do I can just drive it to without getting pulled over (they're not legal on the street here).

 

[06 H3]

Ill take some ABS bushings! How tough is it to add flex lines?

 

[Zach]

Saw that diff a few days ago. Glad it finally showed up

 

[4speedfunk]

I'll be hammering on it as we get closer to fall, to see if it's going to break,

"hammering?" Oh yeah...You'll be back in the shop before winter. :giggle:

BTW...did you look into replacing the axle mount bushings with something less flexy? Those two outboard bushings along with the crossmember bushing are really soft. The cast iron case is certainly an improvement but, its still subject to getting pulled apart if you have soft bushings. Obviously a lot of people have issues with the crossmember bushing but, Nugget was the only guy I'm aware of that upgraded the outboard ones. The outboard bushings are largely overlooked but, I think they play a big roll in diff failure....maybe bigger than the crossmember bushing. The spongy outboard bushings allow the bolt-on tube (on the drivers-side) to move way too much. This movement sort of "levers" the carrier out of its cradle (inside the case). Hopefully the CI version will keep things seated.

You're doing such a thorough job, you should look into some new urethane bushings...all three of em. Maybe some skateboard wheels and a lathe? Probably have to burn the old ones out with a torch. All the mods you're doing are pretty much the best you can do without major fab work. Good luck.

 

[4speedfunk]

PS...

Not sure if you are simply swapping guts or not but, the ring gear bolts are LH thread. Don't find out the hard way. They are special bolts too and I'm sure you would have to order them. Just thought I would mention it to save you some more down-time waiting for parts. Been there...not a good way to spend the summer.

 

[06 H3]

You may have to go to custom route for the bushings. I pm'ed nugget asking about it and directed me to trail duty. I sent them a message without ever getting a response back. Nugget may have gotten his from Phil...either way I'd upgrade them if possible

 

[backcountryislife]

Just swapping guts, plus a shim & seal kit.

I'll look into the other mounts, while it's out I should be able to find something. My guy could likely machine me some if nothing else.


And by hammering it... I mean driving like every other IFS guy out there instead of babying it like I do. At this point, the FJ guys drive easier then the solid axle guys... but way harder than me, and I have yet to see any of them break anything except front diff's (their diff is just as weak as the aam7 it seems like)

 

[Hunner]

You may have to go to custom route for the bushings. I pm'ed nugget asking about it and directed me to trail duty. I sent them a message without ever getting a response back. Nugget may have gotten his from Phil...either way I'd upgrade them if possible

If they made some and Trail Duty is carrying them, call on the old land line. In most cases Phil will be the one to answer or ask for him.

 

[4speedfunk]

Hey backcountry...I have an email address of a guy with some Canyon (double-ear) mounting plates for sale. You would have to add a second nut to the frame rail but, I think it would be a great upgrade. Anything you can do to further stabilize the front axle is gonna help you out. This mod would be very easy to do while disassembled and nearly impossible to do later on, so now is the time...



Who knows? Maybe if there were (4) bushings instead of only (2)...you could get away with stock rubber material, and forego making new urethane bushings. Shoot me a PM if interested, and I can hook you up with the guy.

 

[backcountryislife]

Shot a PM, I think that would be a great idea, and pretty easy to implement.


Out of curiosity, how many people have had damage to the iron diff?

 

[cgalpha08]

I think 4 speed found a new project for thor parts!! If this 4 mounting solution really works, then i think me and a lot of others would be interested in doing a mod like that.

Sent from my DROID BIONIC using Tapatalk 2

 

[alrock]

The only diff mounts I saw from Trail Duty were beta test units that did not fit the metal bracket.

 

[4speedfunk]

Not to be a snob...but I'm probably done for good with the AAM-7 stuff! I had a bunch of prototype ideas in the works...some bracketry and such to try and beef it up. But the deeper I got into it, the more I realized I was whippin a dead horse. The final nail was the realization that even if I did get it stronger...I was still limited to 4.56 gearing and a teeny-tiny ring gear. No 5600lb truck should ever leave the pavement with a 7" ring gear! I don't care what opinions there are on that subject...math is math, and I just don't feel the AAM-7 is large enough for the application, especially with 35" tires.

As we all know...there is no easy replacement, so beefing up the stocker is really the only true "low cost" option. Its either: Get by on what you got...or drop $5000 on something custom. I really don't want to waste any more time on the AAM but, I would certainly help out anybody that wanted to pursue beef-up options. I feel its a viable idea compared to full replacement. After all...what have you got to lose? If you're sitting there staring at bunch of shattered parts, and the thing is already torn apart...I say: GO FOR IT! You certainly aren't going to give up any strength by stiffening the assembly. I've always thought that AAM-7 is probably much stronger on a test bench than it is under a chassis. Get it to quit flexin and floppin around and it might be as durable as a Dana 30. Only one way to find out!

:wink:

p.s. CG...that would be a 5-point mounting system (still keep the crossmember bushing).

 

[backcountryislife]

Next part just showed...

as soon as the case 1/2 to replace the broken tab get here I'll be throwing it in!(guys who shipped it to Zach were less than prudent in their methods... he was good enough to put it in this tub for me so it didn't end up even worse!)

Just got to swap 1/2's, then install... hoping to be up & running by next weekend!

 

[reaper]

Now bring down your front output shaft and I'll give you one of Alex's custom rubbers!!! Oh wait a minute, that SO did not come out right...

 

[Bigunit]

Now bring down your front output shaft and I'll give you one of Alex's custom rubbers!!! Oh wait a minute, that SO did not come out right...

:lmfao:

 

[backcountryislife]

Ok... swapping guts, pulling apart the alum. diff today.

Got the flex lines, not quite what I was hoping for, but hoping they work out as planned. They were made with 1" of extra slack, so really hope they will do the job we're shooting for.

 

[backcountryislife]

By the way, what is the limiting factor in not being able to go bigger on the gearing?

We're seeing a little clearance in the carrier, and thinking that 4.88's could fit with some minor clearancing, and with the steel diff, you could actually get away with that as long as it was minor.

My guy is thinking that we'd be looking at only needing to cut about 1/8" max, but I'm wondering if gear circumference is the only factor, or if we're missing something else. Obviously there's a reason nobody has done this... just trying to figure out why.

 

[jakesz28]

They just don't offer other gear ratios for that axle. Unless you found a source we don't know about.

 

[jakesz28]

Take pics of the pieces when you pull out the pinion gear. My parts break down says crushable spacer. I want to see it before I'm in that deep.

 

[4speedfunk]

Physical size has nothing to do with lower gears actually "fitting" inside the case. All of the gear ratios are the same basic size for any differential...the gearset does not get bigger or smaller with a ratio change. The only thing that changes is the ratio of teeth between the ring gear and the pinion gear. Highway gears (such as 2.73) may have 41 teeth on the ring and 15 on the pinion, while low gears (such as 4.56) will have 41 and 9 teeth. Both gearsets will use the same diameter ring gear...but you will notice that the pinion gears look drastically different. Lower gears have smaller pinions with less teeth....and there is a limit to how small you can go. That limit is usually around 7 or 8 teeth for most differentials, regardless of the make/model/size. This is not "theory" or "opinion" but, rather an absolute engineering limit...and the AAM-7 comes off the showroom floor already at that limit.

As the gear ratio gets lower...the pinion gets smaller. Smaller pinions have less teeth. Less teeth means less contact area between the pinion gear and the ring gear at any one time. The designers will adjust the pitch and cut of the teeth to get as much contact patch as possible, but there are limits. As you go lower and lower...you lessen the area of metal you've got in contact, and eventually you will surpass the point where the tooth size is too small to handle the power being put to it. That's the point when you need to go to a larger ring gear (ie = larger differential), to get more "tooth". The AAM-7's itty-bitty ring gear allows for a very compact size but, the trade-off is this limitation on gearing and the power it can handle. A lower ratio is not offered...and it will never be offered. It has nothing to do with Hummer's market share or popularity...its simply an engineering limit. If you want lower gearing...you need a larger diameter ring gear, to get more contact patch where the teeth mesh. There are many other forces that dictate a diff size but, that's the main reason an axle is the size it is. These rules apply to ANY hypoid-cut differential...from an MG Midget to a Tri-axle dump truck.

Also, some folks assume a gear swap will get you more "strength". In fact the opposite is true...lower gearing will actually amplify other weakness's in your axle (shafts!). The differential is nothing more than a torque-multiplier, and whatever power you send to the input side gets increased (by the ratio you are running) to the output side. If you send 400 ft-lbs to a 4.56-geared diff...you'll get 1824 ft-lbs out of it. If you send the same 400 ft-lbs to a 5.13 diff...you'll get 2052 ft-lbs. Lower gearing applies tremendous amounts of torque to the axle shafts, which is why most SA guys running lower that 4.11s are also running alloy shafts.

 

[cbetts]

Thanks for that education. I never got into drivetrain mods this is completely new territory for me.

 

[atvspeed4]

Physical size has nothing to do with lower gears actually "fitting" inside the case. All of the gear ratios are the same basic size for any differential...the gearset does not get bigger or smaller with a ratio change. The only thing that changes is the ratio of teeth between the ring gear and the pinion gear. Highway gears (such as 2.73) may have 41 teeth on the ring and 15 on the pinion, while low gears (such as 4.56) will have 41 and 9 teeth. Both gearsets will use the same diameter ring gear...but you will notice that the pinion gears look drastically different. Lower gears have smaller pinions with less teeth....and there is a limit to how small you can go. That limit is usually around 7 or 8 teeth for most differentials, regardless of the make/model/size. This is not "theory" or "opinion" but, rather an absolute engineering limit...and the AAM-7 comes off the showroom floor already at that limit.

As the gear ratio gets lower...the pinion gets smaller. Smaller pinions have less teeth. Less teeth means less contact area between the pinion gear and the ring gear at any one time. The designers will adjust the pitch and cut of the teeth to get as much contact patch as possible, but there are limits. As you go lower and lower...you lessen the area of metal you've got in contact, and eventually you will surpass the point where the tooth size is too small to handle the power being put to it. That's the point when you need to go to a larger ring gear (ie = larger differential), to get more "tooth". The AAM-7's itty-bitty ring gear allows for a very compact size but, the trade-off is this limitation on gearing and the power it can handle. A lower ratio is not offered...and it will never be offered. It has nothing to do with Hummer's market share or popularity...its simply an engineering limit. If you want lower gearing...you need a larger diameter ring gear, to get more contact patch where the teeth mesh. There are many other forces that dictate a diff size but, that's the main reason an axle is the size it is. These rules apply to ANY hypoid-cut differential...from an MG Midget to a Tri-axle dump truck.

Also, some folks assume a gear swap will get you more "strength". In fact the opposite is true...lower gearing will actually amplify other weakness's in your axle (shafts!). The differential is nothing more than a torque-multiplier, and whatever power you send to the input side gets increased (by the ratio you are running) to the output side. If you send 400 ft-lbs to a 4.56-geared diff...you'll get 1824 ft-lbs out of it. If you send the same 400 ft-lbs to a 5.13 diff...you'll get 2052 ft-lbs. Lower gearing applies tremendous amounts of torque to the axle shafts, which is why most SA guys running lower that 4.11s are also running alloy shafts.

I completely understand what you are saying but always have found it strange that the dana 30 with the same ring gear size has options down to 5.38 for standard rotation and 4.88 for reverse cut (high pinion). A standard rotation dana 30 is low pinion just like our front diff. Not sure how the heck they get away with that!

 

[backcountryislife]

I completely understand what you are saying but always have found it strange that the dana 30 with the same ring gear size has options down to 5.38 for standard rotation and 4.88 for reverse cut (high pinion). A standard rotation dana 30 is low pinion just like our front diff. Not sure how the heck they get away with that!

That was what my buddy was saying, was that it was the same size as a 30, so we should be able to go lower... if we can't we can't though, at least I'll have the 4:1 when I'm in 4L though.

 

[atvspeed4]

Thats the tough spot im in. My plan next is the 1" body lift, extend the rear bump stops down 1.5" and do the extended bumps in the front. That along with the 2" shackles I have in the rear should let me clear 37s. But as far as gearing I wish I was lower for on road. For offroad I have the 4:1 transfercase and feel its geared plenty low even with the 37s. I rather have a larger pinion gear with 4.56 vs 5.13 etc.