Center Mounting a Front Diff

[4Running Daily]

This is an idea I've talked with my friend David Farmer about many a time. If you design a 4WD LT kit, your limiting factor will be CV's for travel. And even most aftermarket kits just use Tundra CV's which aren't that much stronger than the tripod inner. Replace those with $1k RCV's, and you'll blow the diff first. Probably good for 16"-18" of travel with Tundra RCV's and my 3.5" LT. But you still have that 7.5" front diff. So if you're a guy who likes having 4WD for sand, but is primarily a go-fast build, this thread isn't for you.

But for the rest of us that like the complexity of IFS and want an upgrade up front, I think it's time we come up with a solution.

So I started digging around on the internet and found the famous AAM 9.25. This is your IFS diff for 2500 trucks. Here is a compatibility chart:

PDF is attached to the end in case you can't read this.


Ok so continuing on, this is a 1 ton IFS diff with a 9.25" ring gear. All aftermarket ratios are available for it, as well as lockers like an ARB. But it needs to be center mounted.

Also it's a big fucking diff


As you can see, it's a driver diff offset. Which is already ideal for our setup, but I want center mount front diff, and equal length CV's.

I don't see any clear reason, without buying one, as to why you couldn't take a gasket, scan it, DXF, and laser cut it. Then machine a cup for the bearing, and plate your own side of the housing more or less so that the stub shaft from the driver side fit in the passenger side. Then you would have the perfect mating surface for 2 CV's.


This is all theoretical until I try it.

Obviously there are cons with this diff. The stock 7.5" diff without an extension tube is 44 pounds. This 9.25 is 100-125 pounds. But it is weight that is theoretically below the center of gravity at least. It's also fucking massive. Obviously it needs extensive modification before it can even be attempted to be mounted, and I have no idea how you would get it in there without raising the engine and possibly even a new/modified oil pan.

Someone will ask about hubs too, but I purposely designed my LT kit to work with a fully fab'd spindle without modification. So really just a hub selection, then measure for axles and send them off to RCV.

Notable links to 9.25 info:
https://www.dieselworldmag.com/gm/u...5-aam-front-axle-for-your-gm-or-dodge-part-2/
https://www.race-dezert.com/forum/threads/center-mount-aam-9-25-front-differential.126163/
https://www.pavementsucks.com/threads/aam-925-axle-specs.39358/
https://www.gmfullsize.com/threads/...ton-locked-aam-9-25-with-hydro-assist.215119/

Other diffs to consider:

Ford 8.8. They are super cheap ($250), and have slightly less aftermarket ability.

The case doesn't split though, so I don't know how you would be center mount it. Notable mention though.

And also the 9" from the 2nd and 3rd generation Tundra's. These seem cool, lots of aftermarket, you can't find a diff for shit though. You'll never see one in a junkyard, and the only one on eBay is $800. It's been proven that you can shorten the ADD tube. The case also splits, so theoretically it could work.



Other options considered:
IRS diffs. Supra, Mustang, anything big and common would be great. But low pinion diffs up front seem to be not strong and not a good idea.

Aftermarket options:
Currie F9 https://www.currieenterprises.com/CE-4305B ($5k with gears and an ARB)
Dynatrac ProRock XD60 https://www.dynatrac.com/prorock-xd60-ifs.html ($6k with gears and an ARB)


Haven't looked into the Dana 44 front diff. If it can be center mounted, it is an option as well.

 

[4Running Daily]

Post reserved for Dana 44 investigation

 

[AssBurns]

I'd say if you are doing this swap, don't waste your time with a D44. While it's certainly stronger than the Toyota 7.5" and 8", might as well go full beef with a Toyota 9" or AAM 9.25". That's my opinion at least. With RCV's and one of those, I doubt that the front end would ever be a weak link anymore. I'd want something that can handle 37's and some HP with absolute ease.

Center mounting one of those big fuckers is gonna probably be the biggest challenge. You'd definitely need to raise your engine way up and modify the oil pan to clear the pinion and driveshaft. Still doable, but gonna take some creativity.
With the center mount that you are considering, are you planning to do center mount IFS as well? Or are you just trying to make the CV's longer for less severe angles? If you are just doing the diff without center mount arms, then you'll have to consider the amount of CV plunge. In theory, you want your inner CV inline with the Upper and Lower Control Arm pivot points to prevent plunge. To much plunge and you'll have to worry about the inner CV's getting hot and wearing out prematurely. That's why you hear LT guys constantly talking about driveshaft plunge when pulling huge travel numbers. To much plunge can tear things up. Just something to consider.

I think we need a separate thread about hubs for this beef setup. I'll link it back here when I post it up.

 

[4Running Daily]

I'd say if you are doing this swap, don't waste your time with a D44. While it's certainly stronger than the Toyota 7.5" and 8", might as well go full beef with a Toyota 9" or AAM 9.25". That's my opinion at least. With RCV's and one of those, I doubt that the front end would ever be a weak link anymore. I'd want something that can handle 37's and some HP with absolute ease.

Center mounting one of those big fuckers is gonna probably be the biggest challenge. You'd definitely need to raise your engine way up and modify the oil pan to clear the pinion and driveshaft. Still doable, but gonna take some creativity.
With the center mount that you are considering, are you planning to do center mount IFS as well? Or are you just trying to make the CV's longer for less severe angles? If you are just doing the diff without center mount arms, then you'll have to consider the amount of CV plunge. In theory, you want your inner CV inline with the Upper and Lower Control Arm pivot points to prevent plunge. To much plunge and you'll have to worry about the inner CV's getting hot and wearing out prematurely. That's why you hear LT guys constantly talking about driveshaft plunge when pulling huge travel numbers. To much plunge can tear things up. Just something to consider.

I think we need a separate thread about hubs for this beef setup. I'll link it back here when I post it up.

So that was actually my next point really. I don't know how far I want to take my 4runner given that it's been in my family since new and I enjoy it as it is now. So I'm considering building a 1st gen Tundra with the 9.25 AAM, full hydro, center pivot, and 40's. They're getting cheaper in AZ, to the point it would be ok ish. Plus V8. I don't know, just playing around. But I'd definitely be ok with my truck staying with the 7.5", and ARB, LT, and 37's.

 

[AssBurns]

So that was actually my next point really. I don't know how far I want to take my 4runner given that it's been in my family since new and I enjoy it as it is now. So I'm considering building a 1st gen Tundra with the 9.25 AAM, full hydro, center pivot, and 40's. They're getting cheaper in AZ, to the point it would be ok ish. Plus V8. I don't know, just playing around. But I'd definitely be ok with my truck staying with the 7.5", and ARB, LT, and 37's.

The only issue I have with tundras is that the body is so much wider than the 4runner's. That 8-9" would be a bitch in a lot of places, then you gotta consider the added length. At that point I'd just do a D44 TTB Bronco. WAY cheaper to pull huge travel numbers out of, comes with a V8, and you can beef up the D44 with RCV's to make it pretty badass.

 

[stumbles]

I think while doing all this work, one way to not worry about the oil pan as much would be to do some sort of dry sump setup.

 

[Hank]

How do you plan on running the drive shaft down the center to the diff? Oil pan, transmission pan and tcase?

The best option for ease of set up is clearly going to be the Currie or a Spider trax housing. It's just Expensive as all hell for a front diff. $4,890. Also at that point you're going to be paying at lease $2,500 for a pair of RCV's to match up with it. This is getting in the neighborhood of $8000 to get a center mounted diff.

RCV's are clearly needed at this point so the only area you're going to save money is going with a different front diff.

Tundra front Diff $300-$500 (Used)
Gears and bearings Kit $300
ARB $1,000
So call it $1,700 for the front diff.

Now you have to to figure out how to delete the add tube and put a stub shaft in there. Realistically, you might be saving $2,000 or so by going with a tundra diff or AAM 9.25 and a whole lot of headache. When you could order the front diff from Currie, they will set it all up. Then call up RCV, tell them you have a Currie front diff going to 3rd gen hub's and you need axles X length. Then at that point its all bolt in once you fab up the mounts for the diff and clearance for the drive shaft.

At this point, do you just build a tube chassis buggy? lol it really depends on how far you want to take your 4runner.

If you remove the idea of center mounting the diff (I Totally understand the idea of the center mount), then look into a tundra front diff swap and figuring out how to make that work. the figure out how to put tundra spindles and hubs on the 4 runner.

 

[4Running Daily]

The only issue I have with tundras is that the body is so much wider than the 4runner's. That 8-9" would be a bitch in a lot of places, then you gotta consider the added length. At that point I'd just do a D44 TTB Bronco. WAY cheaper to pull huge travel numbers out of, comes with a V8, and you can beef up the D44 with RCV's to make it pretty badass.

Ya I'm against scissor arms. I don't like the issues associated with them and much prefer A-Arms. But I was more so thinking 4500 class 1st gen Tundra

I think while doing all this work, one way to not worry about the oil pan as much would be to do some sort of dry sump setup.

True, especially if you had an LS-variety as an engine.

How do you plan on running the drive shaft down the center to the diff? Oil pan, transmission pan and tcase?

The best option for ease of set up is clearly going to be the Currie or a Spider trax housing. It's just Expensive as all hell for a front diff. $4,890. Also at that point you're going to be paying at lease $2,500 for a pair of RCV's to match up with it. This is getting in the neighborhood of $8000 to get a center mounted diff.

RCV's are clearly needed at this point so the only area you're going to save money is going with a different front diff.

Tundra front Diff $300-$500 (Used)
Gears and bearings Kit $300
ARB $1,000
So call it $1,700 for the front diff.

Now you have to to figure out how to delete the add tube and put a stub shaft in there. Realistically, you might be saving $2,000 or so by going with a tundra diff or AAM 9.25 and a whole lot of headache. When you could order the front diff from Currie, they will set it all up. Then call up RCV, tell them you have a Currie front diff going to 3rd gen hub's and you need axles X length. Then at that point its all bolt in once you fab up the mounts for the diff and clearance for the drive shaft.

At this point, do you just build a tube chassis buggy? lol it really depends on how far you want to take your 4runner.

If you remove the idea of center mounting the diff (I Totally understand the idea of the center mount), then look into a tundra front diff swap and figuring out how to make that work. the figure out how to put tundra spindles and hubs on the 4 runner.

I'm pretty sure raising the drivetrain and having a manual transmission would give adequate driveshaft clearance. If you only get shafts from RCV, it would only be around $1,000. The only reason you get joints from RCV is for misalignment, but if your CV is 10" longer than stock, it doesn't matter.

I would never, ever spend $5k on a Currie front diff and keep 3rd gen hubs haha. 3rd gen 4Runner hubs suck cock. Buying Dana 60 unit bearings and getting a stub shaft for those would be much much easier and way stronger for 37"+ tires.

But I completely agree with you, how far do you want to go? Hence this thread. Taking collective minds and forming an opinion of what is the best option given the type of wheeling each of us do.

 

[Hank]

Ya I'm against scissor arms. I don't like the issues associated with them and much prefer A-Arms. But I was more so thinking 4500 class 1st gen Tundra

True, especially if you had an LS-variety as an engine.

I'm pretty sure raising the drivetrain and having a manual transmission would give adequate driveshaft clearance. If you only get shafts from RCV, it would only be around $1,000. The only reason you get joints from RCV is for misalignment, but if your CV is 10" longer than stock, it doesn't matter.

I would never, ever spend $5k on a Currie front diff and keep 3rd gen hubs haha. 3rd gen 4Runner hubs suck cock. Buying Dana 60 unit bearings and getting a stub shaft for those would be much much easier and way stronger for 37"+ tires.

But I completely agree with you, how far do you want to go? Hence this thread. Taking collective minds and forming an opinion of what is the best option given the type of wheeling each of us do.

Sounds like we should figure out a way to put a tundra front diff and spindles in the 3rd gens then... Buy the parts, then @AssBurns and I will come out for a weekend and figure it all out with you lol.

 

[AssBurns]

How do you plan on running the drive shaft down the center to the diff? Oil pan, transmission pan and tcase?

The best option for ease of set up is clearly going to be the Currie or a Spider trax housing. It's just Expensive as all hell for a front diff. $4,890. Also at that point you're going to be paying at lease $2,500 for a pair of RCV's to match up with it. This is getting in the neighborhood of $8000 to get a center mounted diff.

RCV's are clearly needed at this point so the only area you're going to save money is going with a different front diff.

Tundra front Diff $300-$500 (Used)
Gears and bearings Kit $300
ARB $1,000
So call it $1,700 for the front diff.

Now you have to to figure out how to delete the add tube and put a stub shaft in there. Realistically, you might be saving $2,000 or so by going with a tundra diff or AAM 9.25 and a whole lot of headache. When you could order the front diff from Currie, they will set it all up. Then call up RCV, tell them you have a Currie front diff going to 3rd gen hub's and you need axles X length. Then at that point its all bolt in once you fab up the mounts for the diff and clearance for the drive shaft.

At this point, do you just build a tube chassis buggy? lol it really depends on how far you want to take your 4runner.

If you remove the idea of center mounting the diff (I Totally understand the idea of the center mount), then look into a tundra front diff swap and figuring out how to make that work. the figure out how to put tundra spindles and hubs on the 4 runner.

I personally am not set on having a center mount setup on the 4runner. It would be super cool, but I'd need much more HP to really take advantage of all that travel.

Either way with whatever diff we do, we'd have to ditch the ADD tube and make a shortened intermediate shaft to narrow the width to match the vehicles control arm pivot points. So again, doing custom work there. Probably not cheap however you look at it.

The problem with going with Tundra hubs is they are only 5 lug. So that makes things complicated there. Got ditch the stock rear axle anyways, so you could do a huge tundra rear axle but I think I'd rather do a Currie 9" at that point. So then we go back to front axles and hubs. Since you'll be deleting the ADD system, you'd really want manual hubs. Stock Tacoma manual hubs are crap when considering the strength we are going for. So now we need to look into something strong for spindles/hubs. Skip D44 hubs, we need real BEEF. Here comes Super Duty Unit Bearing Manual Hubs. Now I know you'll all say "Well those are 8 lug!". Well Trail Gear makes 6 lug Super Duty D60 hubs. Now you just gotta make a fully fabricated spindle and get brakes and locking hubs. Cheap, I know But it's the BEEF we are looking for, while also being manual hubs.

This is getting to the point of questionability with the amount of work and money involved for a 4Runner, but when has that stopped us before?

 

[Hank]

I personally am not set on having a center mount setup on the 4runner. It would be super cool, but I'd need much more HP to really take advantage of all that travel.

Either way with whatever diff we do, we'd have to ditch the ADD tube and make a shortened intermediate shaft to narrow the width to match the vehicles control arm pivot points. So again, doing custom work there. Probably not cheap however you look at it.

The problem with going with Tundra hubs is they are only 5 lug. So that makes things complicated there. Got ditch the stock rear axle anyways, so you could do a huge tundra rear axle but I think I'd rather do a Currie 9" at that point. So then we go back to front axles and hubs. Since you'll be deleting the ADD system, you'd really want manual hubs. Stock Tacoma manual hubs are crap when considering the strength we are going for. So now we need to look into something strong for spindles/hubs. Skip D44 hubs, we need real BEEF. Here comes Super Duty Unit Bearing Manual Hubs. Now I know you'll all say "Well those are 8 lug!". Well Trail Gear makes 6 lug Super Duty D60 hubs. Now you just gotta make a fully fabricated spindle and get brakes and locking hubs. Cheap, I know But it's the BEEF we are looking for, while also being manual hubs.

This is getting to the point of questionability with the amount of work and money involved for a 4Runner, but when has that stopped us before?

Jesus Christ this rabbit hole got deep quick. I'm gonna stick with building a 4800 car instead. you boys have fun with the Stock class and fighting the 4 runner platform. ahahahaha

 

[4Running Daily]

Jesus Christ this rabbit hole got deep quick. I'm gonna stick with building a 4800 car instead. you boys have fun with the Stock class and fighting the 4 runner platform. ahahahaha

Ya my point really is fuck the 4Runner platform. Too much body to wheel. I love mine though and I’ll keep it around, but if my wheeling is going up one more level, then I’m going for it.

 

[4Running Daily]

This thread already defies all logic because if you want strength in rocks you SAS. Which can be built to go fast.

 

[Hank]

This thread already defies all logic because if you want strength in rocks you SAS. Which can be built to go fast.

The last few years of the 4400 cars, have proven that IFS can handle the big rocks.... if you throw $15K in front diff, axles, and hubs.

 

[4Running Daily]

The last few years of the 4400 cars, have proven that IFS can handle the big rocks.... if you throw $15K in front diff, axles, and hubs.

More than that. A PROformance front diff starts at $30k

 

[Hank]

More than that. A PROformance front diff starts at $30k

Alright alright, if you don't run 900 HP then maybe you can get away with a more economical front diff. lol

 

[AssBurns]

I'd love to do a little extended cab taco, centermount IFS, LS swap, trailing arms, etc. But I got kids that need a back seat. No way they would be willing to sit back at camp while I'm bombing through the desert. They love this shit as much as I do haha.

#4seaterwhoopeater