Liberty KJ vs XJ 8.25

[TeKdo]

Hey guys, been playing around with some thoughts about an axle swap in my '86 2.5.

 

My '86 feels like it desperately needs a regear after doing my AX15 swap. First gear feels way too tall for the power I make and 5th gear is borderline unusable on the freeway.

 

I thought I would just regear my factory D35 non-c-clip since it has a factory limited slip and I should be able to find some kind of alloy axles to swap into it. Well...turns out alloy axles for the D35 NON-C-CLIP are virtually non-existent anymore in a 27 spline. Definitely don't feel like dropping the cash on a new limited slip 30 spline soooo looking at an axle swap because y'all make me paranoid of having this axle long term.

 

Not concerned with having a locker in the back because just having a limited slip meets my needs more than a locker. Would like to run 4.56s and a current max tire size of 31s.

 

I'm just wondering if anyone has used the Liberty 8.25s instead of the XJ 8.25s. I tha people use Liberty disc brakes to convert the XJs but is there anything else that's different besides that? Mainly because if I have to hack all the suspension mounts to weld on spring perches for spring under axle, why wouldn't I just grab a Liberty one instead of an XJ one?

 

My main concern for the Liberty 8.25 is if it's compatible with the same limited slips that are available for the XJ ones, if the parking brake works good enough to park on hills since my jeep is manual, and if it has 29 spline axle shafts for that said diff compatibility.

 

 

.....also liberty axles are cheaper than XJ axles near me.

 

[watchamakalit]

4.56 will be really deep with 31's. I would suggest no more than 4.11's if you want something highway driveable.   If memory serves 4.10's and 31's are very close to stock final drive ratio.

[Billabob]

If re-welding leaf perches isn't a deterrent, I would highly consider using an 8.8 out of an explorer. 31 spline, disc brakes, and many come with a limited slip.

[ghetdjc320]

KJ 8.25 is about 2.5” wider than the XJ model. Fits the rear of an MJ very well since it is a bit wider at the bed. Lots of brackets to remove but that’s not any real issue. Fairly easy to re-gear since it has side adjusters and a crush sleeve. 
That being said, rock auto has your bolt in d35 1541 axles around $150/ea. Also check with revolution axle and gear. They still had them last I checked. 
I’d stay away from an 8.8 for only 31’s. Too narrow on an MJ and with its large pumpkin, you might as well run 29’s on a d35.  
As for what ratio to run, plug your numbers into grimmjeeper gear calc and see what your rpm’s will be. And measure your actual tire size to use as your number. It’s likely 29”-30” true size

[89 MJ]

4 hours ago, watchamakalit said:

4.56 will be really deep with 31's. I would suggest no more than 4.11's if you want something highway driveable.   If memory serves 4.10's and 31's are very close to stock final drive ratio.

It would make it fairly close to a 4.0 ratio, which probably wouldn’t be much good with the 2.5L. 
 

3 hours ago, Billabob said:

If re-welding leaf perches isn't a deterrent, I would highly consider using an 8.8 out of an explorer. 31 spline, disc brakes, and many come with a limited slip.

In my opinion, there’s a couple of issues with the 8.8. Firstly, they are too narrow for the rear of MJs unless you get one from an Explorer Sport Trac. The other issue is the ground clearance lost. My MJ has an 8.8 and 31s, and I hit the diff when o did some very minor trails. 

[Billabob]

The 8.8 has a 58” WMS to WMS as opposed to the MJ’s 60”. If you plan on beefing it up even more, the semi-float kit puts you right where you need to be. The Liberty 8.25 has a 62” WMS to WMS, which IMO is more problematic. A narrower axle can cause clearance issues, a wider axle will cause handling issues. 
 

This is my first time hearing about pumpkin clearance issues kn the ford axle. How much more does it droop than a D35/8.25?

[Pete M]

a wider rear axe will not cause handling issues.    guys have been adding spacers to the rear axle (without adding them to the front) for years now with no ill effects. 

[Billabob]

I’m sure people have been getting away with it just fine, an inch on each side is hardly cause for concern. However, if the argument here is that the 8.8 is the wrong width then the 8.25 is equally wrong.. and the general rule of thumb is that the front axle should be equal to or wider than the rear. 
 

As for pumpkin clearance, I won’t have time to get my own measurements till next week but I can’t imagine it is significant. If ring gear diameter is any indicator then the 8.8 only sits 1/4” lower than the 8.25. 
 

I’m not sure what OP’s priorities are with this axle swap and they are free to do their own research but the 8.8 should certainly be a contender. 

[schardein]

I agree the rule of thumb is the front track width is usually equal to or wider than the rear.  Use and priorities definitely plays a role:

daily driver- reliability

just want to make it drivable- ease of swap/installation

max effort off road- strength and ground clearance

 

Pumpkin clearance might not be a concern for a daily driver, but 1/4" difference on a off-roader can be the difference between stuck and not stuck.

[Pete M]

being a slightly different track than the front is not the issue here with either axle. 

 

the 8.8 is theoretically wrong because it pulls the tires in towards the bed and can cause rubbing.  plus the bed is already wider than it should be relative to the front and this exacerbates the visual issue.

 

the "same width" is more myth than rule of thumb.   plenty of regular cars/trucks have done it over the years.  like, every dually for example. 

[Ωhm]

Wouldn't rear axle length affect the front tire scuffing, when cornering?

[Pete M]

do dually trucks have an issue with front tire scuffing vs single rear wheel trucks? 

 

 

[Billabob]

Duallys aren’t exactly known for their exceptional handling. An extreme example would be a trike, would you prefer to ride a trike with two front wheels or two back wheels? 
 

Can’t say I’ve ever encountered an Ackermann denier before, lets agree to disagree. 

[Pete M]

we're talking about a whole inch and change difference per side.  taken to extremes (both in large track differences as well as in high speed maneuvering) I'm sure there are things to consider, but I'd wager a large sum that none of us are going to see or feel a change with an inch and a half offset. 

 

I wish Don was around to chip in.   he was one of the first to add spacers to the rear only. 

 

 

[ghetdjc320]

The 8.8 housing is a decent bit larger than the ring gear and, compared to a D35, will loose significant clearance. Normally in the order of two tire sizes. So if you’re getting an 8.8 to run 33’s, vs 31’s on your existing d35, it’s a zero sum game. The 8.25 is also larger than it needs to be but does provide more room to shave the bottom of the pumpkin than the 8.8. 

Other than that, they tend to be higher priced and harder to find now than liberty axles. They are narrower and can rub on the frame rails of an MJ, the tubes are prone to spinning with large tires, they max out at about a 35 in stock form, still have c clips, still need shims to setup the gears. They’re not horrible axles but they just aren’t as good of a swap candidate for an MJ. And they come with a hefty weight penalty. If you’re running 31’s there’s a solid argument for keeping a d35. Up to 35’s and there a solid argument for the 8.25. The argument for the 8.8 just isn’t as convincing as it was 10+ years ago and more so for an MJ. 

[gogmorgo]

265 wide tires on stock wheels on a stock axle are real close to the inner fenders. Close enough I can’t get chains on anyhow. That’s nominally a 10.5” wide tire, which is what most 31’s are. I’d rather have it a little wider. I definitely wouldn’t want it to be narrower than stock either. 

 

The MJ isn’t exactly a precision handling machine. For one thing the steering geometry is set up for the XJ’s much shorter wheelbase. Rear axle width doesn’t generally factor into Ackerman steering, but the MJ is out to lunch there already, especially with a long wheelbase.
I doubt most of us would notice the difference in rear track width. We’re talking about handling at the limits of grip, which really isn’t something we should be approaching on public roads anyhow. And the effect of a wider rear axle would tend towards understeer too, which is generally considered to be safer on a road vehicle.

[ghetdjc320]

24 minutes ago, gogmorgo said:

Rear axle width doesn’t generally factor into Ackerman steering

This . Rear axle width doesn’t play into the equation. Front axle pivot points and wheelbase are the factors here. It is perfectly acceptable to have a slightly wider rear axle or front axle. It will be one of a great many factors that determine the handling characteristics of a vehicle. 

[TeKdo]

9 hours ago, ghetdjc320 said:

KJ 8.25 is about 2.5” wider than the XJ model. Fits the rear of an MJ very well since it is a bit wider at the bed. Lots of brackets to remove but that’s not any real issue. Fairly easy to re-gear since it has side adjusters and a crush sleeve. 
That being said, rock auto has your bolt in d35 1541 axles around $150/ea. Also check with revolution axle and gear. They still had them last I checked. 
I’d stay away from an 8.8 for only 31’s. Too narrow on an MJ and with its large pumpkin, you might as well run 29’s on a d35.  
As for what ratio to run, plug your numbers into grimmjeeper gear calc and see what your rpm’s will be. And measure your actual tire size to use as your number. It’s likely 29”-30” true size

Interesting. When I checked Revolution Gear for alloy axles for the D35 they only had axles for C-Clip D35s now. The only other companies I saw that made them for the non C-Clip axles were Ten Factory (which only comes in 30 spline applications) and Alloy USA (which is only selling drivers side axles for some reason). I'll take a look at rock auto though, didn't think too check them for axles.

 

I'm definitely staying away from the 8.8 for my application though, I've heard the parking brake is really weak and I need the parking brake.

[TeKdo]

11 hours ago, watchamakalit said:

4.56 will be really deep with 31's. I would suggest no more than 4.11's if you want something highway driveable.   If memory serves 4.10's and 31's are very close to stock final drive ratio.

Interesting. When I was running the math with the Spicer gear calculator, 31s and 4.56s actually brought me back closer to the stock AX5 and 28s cruising speed.

 

With 28.8" or 29" tall tires it really feels like it wants more rpm to cruise comfortably with the AX15. AX5s stock fifth gear is 0.85 vs the ax15s 0.79 ratio which is about 6mph difference at 2800rpm (where the AX5 would have been sitting in fifth gear at 65 mph). To cruise at the same rpm as stock where the engine feels like it isn't being lugged id have to be going about 75mph with the AX15.

 

If I swap to 4.56s and 31s I can bring down the cruising speed to 71mph or if I did 4.88s I can cruise back down at the stock speed of 67mph at 2800rpm.

 

I think 4.56s and 31s would feel like too much with an automatic and a 4.0, but with the stock 4.10 gearing the 2.5 feels way underpowered, even with just an inch taller tire....and the math says I should shorten up the gearing a lot to bring it back to stock. Especially first gear going uphill, the AX15 feels way gutless compared to the AX5 (AX15 first gear is 3.83 and AX5 is 3.92), a little help from the final drive would be awesome for my application.

[Comanche SS]

On 12/23/2024 at 4:00 PM, ghetdjc320 said:

This . Rear axle width doesn’t play into the equation. Front axle pivot points and wheelbase are the factors here. It is perfectly acceptable to have a slightly wider rear axle or front axle. It will be one of a great many factors that determine the handling characteristics of a vehicle. 

 

 

FWIW, my MJ on 35s with a wider front track width feels far more stable than my XJ on 35s felt (with similar width axles) I can comfortably pitch it sideways without fear of rolling, without any sway bars. Albeit, my suspension design and arcs are FAR different than any solid axle rig would have. So take with some salt ...

 

The MJ is 69" WMS front, 60" rear.

[ghetdjc320]

8 hours ago, Comanche SS said:

 

 

FWIW, my MJ on 35s with a wider front track width feels far more stable than my XJ on 35s felt (with similar width axles) I can comfortably pitch it sideways without fear of rolling, without any sway bars. Albeit, my suspension design and arcs are FAR different than any solid axle rig would have. So take with some salt ...

 

The MJ is 69" WMS front, 60" rear.

Makes sense. Lots of factors at play when it comes to handling and an ifs MJ would have a whole new set of equations I’m sure.