Axle Swap and Gearing Question

[ktmall07]

This summer I'm planning on swapping my D35 for a ford 8.8 from the JY. At the same time I'll lift the truck (SOA rear, undetermined lift front). This will all happen with the hopes that I can run 32~33" tires, but no bigger. 

 

I have a few questions about regearing. There are so many explorers at the JY, I'm almost sure I can find one with 4.10 gearing. I recognize I'll have to regear the front axle as well, so I'm wondering if 4.10 will still be too tall for 33" tires, and if I should not worry about the gearing currently in the 8.8 and just regear both to 4.56? If 4.10s is good enough for mild wheeling, then it would be mighty convenient to only have to regear 1 axle.

 

Also, I found regearing kits containing all the gears needed for a swap for D30/Chrysler 8.25 combo D30/D44 combo, but not one for the D30/Ford 8.8 combo. Is there any significant difference in strength between the Ford 8.8 and Chrysler 8.25? I thought there was, but now I'm wondering if the difference is small enough to not worry about it, and settle for the convenience of regearing from a kit that contains both sets.

 

Any advice would be appreciated!

[watchamakalit]

4.56 would be good with 33s. I just put 4.10 in mine with 31s and the seem about right.

[75sv1]

    I notice both poster have manuals. I have an XJ with 4.10 gears, Ford 8.8 rear with LS. Its an auto. A bit spunky on 31's. I'm on metric now. They are about 32.5" or so. Possibly about stock ratio. So, a bit 'under powered'. 

    I with my Comanche, I am going with 4.10's and 32-33's. Its a manual. I think I'll be OK. It would depend on location and intent of use. I notice OP is in Utah. I would think some mountain passes and such. Also, if a wheeler. Then I might think of going with 4.30's or 4.56. 

   I did wheel with my XJ. I was in 4W Hi. I didn't have any issues. I did get stuck once or twice. Lift and tire size. You could install the 8.8, and run as 2wd to see if the 4.10s are OK for you. Also, I doubt there is much strength difference between the Ford 8.8 and the Chrysler 8.25, if the 8.25 is a latter one, 97+ (??). Axles spines. 

[Pete M]

car-part.com miiiight be able to find you a dana 30 with 4.10s.   

[ktmall07]

I originally thought of getting an 8.8 because of the disk brakes in a 95+ (?) model, but correct me if I'm wrong, Explorer 8.8s never came with 4.56s did they? If they did they were extremely rare?

[89 MJ]

I have heard that you could get a Ranger with 4.56s in an 8.8, but I’ve never seen one. You may want to look at an 8.8 out of an Explorer Sport-Trac. They are about the same width as your current MJ rear axle (a regular Explorer 8.8 is over 1” narrower, IIRC) and they came with either 3.73s or 4.10s. They did have drum brakes though. 

[Pete M]

I chose 4.10s for my 33s because that's the deepest factory ratio in late 70s ford axles and a pair sorta dropped into my lap so the cash savings was large.  BUT, if I was to do it all again, I'd skip the heavier axles and go with a dana 30 and an '05+ Liberty 8.25 regeared to 4.56.  maybe 4.88.  the Liberty axle also has disks but is a couple inches wider than a dana 35 rather than narrower like the 8.8.  the better to fill out the MJ's wide butt.  

 

explorer axles came in 3.07, 3.31, and 3.55 ratios too.  more or less mirroring the various MJ ratios, which is strange but convenient. 

[ktmall07]

What are the differences between a liberty and a cherokee 8.25 (other than brakes and width)? Will a gearset for an XJ 8.25 fit correctly in a KJ 8.25?

[Smokeyyank]

4.10s with a manual will be fine for ~32ish and mild wheeling. 4.56 would be an all around great combo. One thing to keep in mind is the 8.8 is fairly large and on 31's you're killing your ground clearance. 33's+ is really a better combo. It is nice having factory disc and a LSD on the 8.8 though. I ran one on my XJ with 33's and was great. With 31's it would dig a trench on occasion.  

[Pete M]

diff is the same.   axles are of the 29 spline variety.  the snout has a flange on it so you'll need to either swap that out when regearing, or use a ujoint adapter afterwards.

[ktmall07]

I'd need to do that with a ford 8.8 as well I think. KJ 8.25 with 4.56s it is! 

 

Last question, LSD or Air Locker? For the type of wheeling I'll do with this (easier trails/crawling in Moab, plus washed out Colorado/Utah trails), is it worth having an air locker? Or would an LSD be sufficient? Only reason I ask is because one of those is significantly cheaper than the other, but both are still expensive, so I would hate to buy an LSD and then realize I need to upgrade to a full locker later.

[Pete M]

tough call.  if I had the budget, I'd probably go with a selectable locker because I prefer an open rear diff for snow.  there are other lockers to, electric and cable operated (at least I think they still exist).

[75sv1]

The Ford 8.8 does come with disc brakes in the later years. Both of mine did. As far as LS, I have LS on both of my XJs with the Ford 8.8. It did OK this last year, which I wheeled twice. If you are going to do a lot of wheeling and heavy wheeling, then no. My neighbor wheeled his ZJ a bit rough. He told be he burned out the LS clutches in the Ford 8.8 after 3 times wheeling.  He put in a Tru-Trac.

   My plans are to keep the LS in my '00XJ and add a front selectable locker. Probably an electric OX. For another build, I'll probably end up with True Trac in the rear and a slectable in the front. On the MJ, ???. I think the Dana 44 out of the ISUZU has limited slip.  Since I don't plan to wheel it, it will probably be kept LS. Front??? I might see about cost. I'll need to regear it. I have a Waggy PSD being done.

[ktmall07]

My reasoning for an Air Locker as opposed to an e locker is that (at least with Eaton's e locker, it takes a quarter or half rotation of wheel in order to engage fully, which is fine when you're moving, not so good when you stop and start in really technical spots. As for which is more reliable,  I'd just like the locker to engage and disengage right when I press a button, not have it disengage every time I stop, leaving me with the potential of getting stuck. Maybe my worries are unfounded, and I'm sure that someone who knows more than me has the right answer, but that's just my thought process!

[derf]

I had an XJ with limited slip front and rear.  It did fine on trails rated up to about a 6-7 in Moab.  Went all over hell's revenge with it.  No problems.  I did bypass the harder lines on the obstacles.  As soon as you get a tire or two in the air, you're not going very far.  So I couldn't tackle everything in that Jeep.  My old J10 had Eaton E-Lockers front and rear.  My 2012 JK had them as well.  My new Rubicon has factory selectable lockers.

 

I love having selectable lockers.  They are easy to drive with and lock up quickly when you push the button.  And then you can get yourself into all sorts of trouble fun.

 

Unlimited budget, I'd do selectables front and rear.  And I'd probably do Eaton E-Lockers instead of ARB since I don't need an air source (saves several hundred).    That tire rotation time really doesn't make a big difference on the trails in the real world.

 

Next step down would be TrueTrac front, Eaton back.

 

From there, TrueTracs front and rear.

 

Below that, TrueTrac rear, open front.

 

Last choice, open front and rear.

[Jesse J]

when you get it in lets wheel!

[ktmall07]

Unfortunately, Eaton doesn't make a locker for the Chrysler 8.25. It seems like the only place I can find that does is OX, does anyone have any experience with them? They cost hardly anything more than a TrueTrac, so if they work well, I'll just get one for front and rear since they make one for a D30 as well. Thanks for all the help guys.

 

@Jesse J For sure man! All major projects will have to wait until the semester ends, but hopefully I'll have most of this done in time for summer. We'll have to go then! How goes your build? I've been trying to catch up on it and it's giving me so many ideas haha 

[derf]

Just on anecdotal experience, I'd prefer an ARB locker over an OX.  But I have no direct experience with either of them.

[Smokeyyank]

Trutrac rear selectable up front is a nice combo. I have that in one of my MJs. Others prefer selectable in the rear and trutrac up front. When I build my WJ axles I'm going zip lockers front and rear. If budget allows I'd go selectable. If you can only lock one do the front. 

[omega_rugal]

most exploders came with 3.73, only a few packages came with 4.10 so don't be dissapoinetd if you can't find one

[Parei_doll_ia]

6 hours ago, ktmall07 said:

Unfortunately, Eaton doesn't make a locker for the Chrysler 8.25. It seems like the only place I can find that does is OX, does anyone have any experience with them? 

I had Ox lockers in my JK that worked great. I had the air adapter for them too, so they worked basically the same as ARB. I didn't like how ARB's have you run a pressurized line inside the diff and have it seal on the axle shaft. Ox uses a shift fork in the cover kinda like the CAD, but if you lose air pressure, they have a backup you can screw in to lock it over.

[Eagle]

https://docs.google.com/spreadsheets/d/1pHFuhGgj6dQDfzyfFJH5z7NCDLW2KX3ABQgAJr3lBvM/edit#gid=0

[ktmall07]

Thanks, Eagle. I looked at that when deciding between 4.10 and 4.56. As of now this will still be a DD so I probably won't go higher for now. The goal is to make the perfect "go anywhere" truck.

[75sv1]

Gear Ratio Calculator (grimmjeeper.com)

That's the one I reference. For a stock gearing, 55 is 1800 rpm, 60 is 2000 rpm and 70 is 2200 rpm. 

[Eagle]

4 hours ago, 75sv1 said:

Gear Ratio Calculator (grimmjeeper.com)

That's the one I reference. For a stock gearing, 55 is 1800 rpm, 60 is 2000 rpm and 70 is 2200 rpm. 

 

Those numbers aren't too far off (for an automatic), but they're off. But the OP has a 5-speed, so stock axle gearing is 3.08, not 3.54.

 

The problem with every on-line gear ratio/speed calculator I've seen is that they use the nominal diameter of the tire. In reality, 31" tires are typically about 30.5" in diameter, 32s are typically about 31.5", and 33s are typically about 32.5". Then you put weight on them and the sidewalls flex, so the actual rolling radius is less than half the diameter of the tire. I made up my chart to allow for this, as much as possible. Wherever I could find data, I used a manufacturer's actual published rolling diameter or published revolutions-per-mile (the best number) for doing my calculations.

 

For the OP, 60 MPH with stock tires and stock gearing is going to be just 1676 RPM in 5th gear. Jumping to 33" tires with 4.10 gears, 60 MPH will be 1974 RPM. So the overall gearing will be a slight improvement, but only a tiny bit better than stock tires with 3.54 gears. That's not bad at all for general driving with some mild to moderate wheeling. I was able to do a lot of trails at Paragon in my '88 Cherokee on 30" tires with the stock 3.08 gears.