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Center mount AAM 9.25 front differential

v7guy

Member
I keep reading references here and there about the AAM 9.25 IFS front diff found in 1 ton Chevy and Dodges being simple to center mount. Nothing specific though.

It looks like you could take the passenger side extension off, mill a plate to replace it that would bolt onto the case and hold a stub shaft bearing and seal and just use a drivers side stub shaft in the passenger side.

Do any of you know if that's the case? Is there anything else required?
 

Chris Tobin

Well-Known Member
It seems to me that something like that would work. I really see no reason it would not...
 

v7guy

Member
I've read converting it to center mount was done fairly regularly back in the early buggy days when there weren't any high dollar front diffs. But I haven't been able to find specifics and I was hoping I could get a confirmation of the process without pulling it out of my trailblazer to mock it up.
 

Chris Tobin

Well-Known Member
I think you need to go with a 2500 HD or 3500 HD differential to get the 9.25-inch. I think the 1/2-ton and smaller trucks and SUVs used an 8.5-inch model that is not near as strong.

Get one out of an HD truck not a Trailblazer if you want max strength...

Here is an article I wrote for Diesel World magazine on beefing up the 9.25 IFS... http://www.dieselworldmag.com/ultimate-axle-build-building-a-super-strong-9-25-aam-front-axle-for-your-gm-or-dodge-part-2/

You may even want to contact Fleece Performance Engineering as they may be able to build you the shorter length passenger side tube and they sell better shafts as well.

EDIT: Looking over my article again. I don't think you will be able to make it short enough to use the same length shaft on each side. I think the passenger side shaft will still be longer, but going through someone like Fleece to have a custom shaft and center axle disconnect delete tube might be one way to go to make a much narrower 9.25 IFS center section even if it isn't exactly centered.
 

v7guy

Member
Currently the diff has 5.13s and an ARB in it. For a temporary solution I extended the CV by cutting and sleeving them, it works for now, but I'd prefer to order some RCV shafts like mentioned in the article you wrote.

After driving it around a bit I'd like to narrow it some and figured I'd best do it before I ordered some CV shafts.

I hadn't thought about contacting fleece about a shorter extension, I'll shoot em a message and see what they have to say.

I did run across an old thread on pirate where the poster "mosebilt" narrowed one of these, apparently you have to mill about 3" off the case to use the drivers side short shaft on the passenger side. It's doable for me, but I haven't got the Bridgeport running yet, should probably stop being lazy and get that vfd on there
 

Chris Tobin

Well-Known Member
10-4, I understand. The truck in the article is mine, I have thought about running a narrowed one in there to get more travel as well.

By the way, Branik Motorsports has the drawings for the stock replacement CV axle shafts and can do 300M axle shafts for you to use factory ends in any length you need. They did the shafts for me when we installed the suspension as it required 3-inch longer axle lengths. The RCV ends are more robust than the factory ends though. RCV can also do the assembly in any length you need.

Even if Fleece wont do a custom shorter extension, they may sell you the stock length one (not sure if it is still in production or not, as I believe they now do the center axle disconnect delete by just replacing the axle assembly) and you could cut it down then have a custom length axle made...

I wonder what material would be left for mounting the plate to a housing with 3-inches milled off???

You also need to consider your driveshaft routing if you center mount. In my truck with the Duramax I would have to go to a dry sump setup for sure to try to clear a centered driveshaft...
 

v7guy

Member
I've included the only picture I've found. It looks to be not that serious. I can't TIG it closed in the garage, but everything else I can do. I'm just not entirely sure if dropping it below the fabbed rear sump oil pan is worth it, or if the general decreased belly clearance is worth it.

As you've mentioned, routing the driveshaft is an issue as is the steering and keeping it in line to limit bumpsteer. All things I've wrestled with. Narrowing everything further complicates it.

I've blocked off the disconnect with a machined slug so it's permanently locked in. Generally, as is, everything works well with over 16" of travel, but living with it day to day is cumbersome at this width. Especially in a major city.


I'll look at Branik, that sounds like exactly what I was looking for, much thanks.

I appreciate you taking the time.
 

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Chris Tobin

Well-Known Member
I've included the only picture I've found. It looks to be not that serious. I can't TIG it closed in the garage, but everything else I can do. I'm just not entirely sure if dropping it below the fabbed rear sump oil pan is worth it, or if the general decreased belly clearance is worth it.

As you've mentioned, routing the driveshaft is an issue as is the steering and keeping it in line to limit bumpsteer. All things I've wrestled with. Narrowing everything further complicates it.

I've blocked off the disconnect with a machined slug so it's permanently locked in. Generally, as is, everything works well with over 16" of travel, but living with it day to day is cumbersome at this width. Especially in a major city.


I'll look at Branik, that sounds like exactly what I was looking for, much thanks.

I appreciate you taking the time.
If you keep it at stock width I would definitely recommend going with the Fleece internal shafts. The center axle disconnect is COMPLETELY done away with by installing a solid shaft in its place so you do not have to worry about the multi-piece shaft breaking. They also build a stronger short (driver side) shaft but they are a little less prone to breakage. In diesel truck sled pulling guys are putting quite a load on these with the right upgrades like what I did to mine in the article...

Branik can do just about anything!!! They are great guys and their prices are very competitive, in most cases I've seen they are quite a bit cheaper than their competitors.

That looks like a lot of work to the diff and packaging difficulties I would think narrowing the assembly a few inches and cheating the driveshaft over an inch or two (maybe even 3 if you have the room) and using a custom length passenger side shaft with a bolt on axle tube like the Fleece one would be a better option in a front engine vehicle to gain some more CV length and travel than to do a true center mount 9.25.
 

v7guy

Member
Packaging everything was "interesting" as I'm sure you can imagine. I've contacted fleece, it does appear they only offer the axle shaft now and not the whole housing.

I wonder if I could just cut a few inches out of the stock extension housing, slide a tube in it to line everything up and then weld it back together. It's cast, so I'm a lil skeptical it would hold up. Still not entirely sure losing 5"of clearance at the belly directly under the diff is worth it, not to mention I have no idea what I'd do with steering unless I went for some kinda swing set setup.
A dry sump setup would be pretty fantastic, but I'm not sure I'm ready to drop a few more grand into this thing and I'm not entirely sure how I'd go about mounting it all. Something to read up on, maybe it's doable without spending a fortune. It's starting to look like maybe this is gonna have to wait till next summer.

Hopefully I hear back from fleece and branik soon. I really appreciate the recommendations.
 
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