Move up to 4.10 or 3.73 on 235s?

[devildog0]

I have no plans to go on past 235s as this Jeep will not be a trail rig. It's a family/exploration XJ, that will see some light duty towing, it is also be a daily driver seeing use to and from work about 100 mile round trip so fuel mileage is a bit of a concern as well.

Currently have 3.55s but the axles could use a rebuild (lots of play in the rear axle) and I figured if I'm going to do that might as well have a set of gears put in at the same time.

Rock Auto lists 3.73s and 4.10s (4.11 for the 8.25) and either way is about the same price. Was also leaning towards LSD in the rear but as far as I can tell no one carries anything but the factory type trac lock for the 27 spline 8.25 axle, I'd rather have a TrueTrac but only see them for 29spl 8.25s.

NOt sure what I'm going to do up front yet. I've already got a Powertrax No-Slip in there so leaning towards just keeping the stock carrier and going to different gears but have also considered the TrueTrac up front. It would add about 400 dollars to the overall cost.

If you had to choose gearing for a mostly stock XJ would you stay 3.55? Or go to 3.73 or 4.10s?

 

[smccollamjr]

If you want a truetrac in the back I think you just need a set of 29 spline axle shafts for the 8.25. For gears, I’m not real familiar with AW-4 gearing, but I doubt you’ll feel much of a difference going from 3.55 to 3.73.

 

[devildog0]

I think it's more involved than that since the axleshafts have a larger diameter. So I'd think you'd need a new diff carrier, which the truetrac woudl take care of and possibly new outer axle bearings but not sure if they would fit int he existing axle housing.

Might be worth the effort to just find a 29spl 8.25 and rebuild it to what I want. They're still pretty avaliable out there.

 

[Empty_Pockets]

I would swap to the 29 spline with the true track, I prefer the gear style posi over the clutch style, it's nice not to have wear parts to worry about. I had 31's with 4:10 gears and an auto and love it. Was a great combo and got good gas mileage.

 

[devildog0]

I had 31's with 4:10 gears and an auto and love it. Was a great combo and got good gas mileage.

Keep in mind I'll be staying at 235 sized tires.

 

[RCP Phx]

I'd see if you could find some Tow package/Up-country axles as they came with 3.73's, you would be happy with that.

 

[Empty_Pockets]

I have 235's on my 5 speed now and I would be putting 4:10's in. I would probably run 3:73 with the auto since you use it to commute.

 

[devildog0]

I'd see if you could find some Tow package/Up-country axles as they came with 3.73's, you would be happy with that.

Pick and pulls are pretty rare around here. At least I haven't found any looking around. I had a tow package XJ previously (according to equipment installed and Jeep build sheet) and still had 3.55 gears in it Seems to be hit and miss on what tow package XJs got 3.73s

 

[lazyxj]

I rebuilt my 1997's 27-spline 8.25, using alloy 29-spline axles and a TrueTrac.
Since it's staying on 235s, I stayed with a 3.55 gear, knowing that 3.73 wouldn't be enough of a change to make a significant difference and didn't want to spend the money or time involved to regear the front axle.
Inchitis can strike at any time, I would consider 4.10s, especially if going through the both front and rear axles.

 

[Tim_MN]

….. staying at 235 sized tires.

Then there is no point at all in investing in the parts for a gear ratio change and the necessary labor cost. I would simply find a suitable low mileage junkyard replacement axle. Even with shipping costs you would save 60 % or more. You can go through a whole stack of junkyard axles for the less than the cost of parts and labor for re-gearing. It would take a lot of additional miles to make a slight increase in gas mpg's pay for new gears.

 

[kastein]

I'd put in used axles rather than regearing as well. It's not really that big a difference tire size, I ran 235s for years on stock axles and I'm not convinced I could actually tell the difference from 225s in a double blind test.

FTR, if you don't mind low vs high pinion, a ZJ front 30 from a V8 equipped vehicle will almost certainly have 3.73s. You can swap your U-joint axle shafts and everything else over, the only downsides are the slotted LCA mounts (ZJs use axle side caster adjustment with a cam bolt, XJ uses frame side with an adjustment shoe and shims) and the fact that it's a low pinion axle. Neither is that big a deal if you're only running 235s and not rock crawling.

The rear axle you gotta do yourself or find a pregeared axle from an XJ, though.

Still, I'm not sure it's really worth it. It is your money but I wouldn't even consider regearing until 30s or 31s.

 

[smccollamjr]

Even though he doesn’t need an 8.8, it might be easier/cheaper to find one of those with the correct gearing. Depending on wheels you may need spacers too.


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[Tim_MN]

The difference in diameter between 215 or 225-75-R15 and 235-75-R15 is not great enough to require, much less even benefit from, deeper gears.


As a matter of random curiosity, ask anybody with a lifted XJ running 30x9.5 tires or 31x10.5 tires if they have axle gears other than what the Jeep factory installed.

 

[cal]

I'd see if you could find some Tow package/Up-country axles as they came with 3.73's, you would be happy with that.

I've been trying to find proof a pair of these were ever made for about 10 years. I've managed to find the alleged south american HP44 front, japanese right hand drives XJ's, factory 4.56 4 cylinder XJ's.

But I've never found an up country / tow package 3.73 XJ.

 

[cal]

If you had to choose gearing for a mostly stock XJ would you stay 3.55? Or go to 3.73 or 4.10s?

If you're giving this serious thought, I'd go ahead and consider the 3.73 gears. 4.10 maybe, but that may be more that you want for the highway.

For your limited slip, look at Motive's "Grip Pro" which is a similar gear drive limited slip to the trutrac, but a lot cheaper. I have them front and rear on my current build. You can get one of those and some aftermarket 29 spline shafts for the 8.25 and it would all just bolt together.

For gearing considerations; the left below is 3.73 and 235's, the right is 4.10.

 

[bridgerx]

I run slightly bigger tires than yours on my offroad-xj... 265-75-16's with 4.56 gearing, and my final drive is a little lower than you'd be with 235's and 4.11's. The tacomaworld tire size gearing calculator isn't dead on for your final drive, but is great for comparative analysis.

This is going to bring your highway rpm's up a bit, and exacerbate any nascent vibration issues you may have. I'm also running several hundred extra lbs of bumpers, armor, winch, tools, gear, kids etc... and often tow a small trailer or have a canoe on top etc. With the cruise control on 85 (as high as it goes) I'm going 72 mph by the gps... and thats about as fast as I want to go for any amount of time.This is not my sole daily driver, but I do take it to the grocery store frequently enough. I live in an area with 80 mph speed limits on the interstates... but honestly we do a lot more up and down on 65 mph mountain roads. I also have an XJ on 235's with stock gears. I prefer the lower geared jeep offroad, around town, and anywhere the speed limit is less than 80. It gives the jeep a quicker feel around town and reduces the need to downshift in the mountains. All that said, driving home from Moab last month I took the front driveshaft out for the highway drive home and am now seriously looking at a free spin hub kit for the front. The vibes really weren't bad, but their absence was noticeable enough I want them gone.

Whether this all is worth the cost of regearing... pretty questionable

I also have a 2008 Subaru with a 5-speed and tires smaller than any XJ ever came with and it has 4.11 gears. Granted, that motor is more meant to spin and the drivetrain is unmodified and well designed, but it is spinning substatnially faster than the jeep is on the highway. If your jeep isn't lifted the minor vibrations I notice may not affect you at all.

Hope this helps

 

[devildog0]

Just upcountry equivalent suspension pieces so about an inch to 1.5 inches higher than stock.

I appreciate everyone's input so far. I'm leaning towards staying with 3.55s to save some money, unless I find some 3.73s used on one of the forums. I just figured when I started this thread if I'm going to rebuild the diffs with new bearings the gears were going to have to be reset anyway so why not go to a lower set in the process.

Keep the suggestions/experiences coming. No matter what I do it's going to take a while to gather the parts/money to get it done. I don't have the precision measuring gear to install gears so I was going to farm it out to a well known independent mech int he area.

I rebuilt my 1997's 27-spline 8.25, using alloy 29-spline axles and a TrueTrac.
Since it's staying on 235s, I stayed with a 3.55 gear, knowing that 3.73 wouldn't be enough of a change to make a significant difference and didn't want to spend the money or time involved to regear the front axle.
Inchitis can strike at any time, I would consider 4.10s, especially if going through the both front and rear axles.

I haven't found any truetracs or any other locker so far that takes 3.55 gears. All of them I am finding are 3.73 or lower gears.

 

[JeepNoob]

I would stay with the stock gears. As others have pointed out, factory tire size is a 215 or 225 and a 235 really isn't much of a step up from that. I had no problems turning a 235 tire with a 4.0 5-speed and 3.07 gears. (Interesting side note- even with the 3.07 gears, an AX-15 XJ has lower gearing in first and higher gearing in 5th than an AW4 XJ with 3.55's, so if you're looking for the best of both worlds, that might be an option.)

All you're going to gain from going to a deeper gear on stock-ish size tires is a pre-maturely blown engine with lots of bad fuel mileage before that. 4.0's are torque-y, old-school luggers. If properly maintained, and kept below 3,000 rippums 99.9% of the time, they will live a long and happy life of being stuck into the highest gear that doesn't stall the engine out. Also, keep in mind that if you re-gear the rear axle, you'll have to re-gear the front as well. At least if you don't want the one of the axles to grenade itself in 4x4.

As far as traction devices go, I'd rather have a proper locker than LSD, but that's just me. If your preferred flavor of traction device isn't available in 27-spline, I'd just go with 29-spline axles. You're gonna have to pull them out to disassemble the diff anyways. While you're at it though, I would HIGHLY RECOMMEND making sure your vent tube is clean and clear of obstructions and installing a diff cover with a proper threaded fill.plug or modifying your factory cover to accept one. Seriously, I have no idea what the bean-counters were smoking when they thought that rubber push-in crap would be a good idea...

 

[Tim_MN]

I've been trying to find proof a pair of these were ever made for about 10 years. I've managed to find the alleged south american HP44 front, japanese right hand drives XJ's, factory 4.56 4 cylinder XJ's.

But I've never found an up country / tow package 3.73 XJ.

Some ( actually very few ) early 1980's AMC XJ's were built with the optional 3.73 gears. As a cost control measure, Chrysler eliminated the 3.73 and 4.56 gears shortly after buying Jeep in 1987. I have not seen an early 1980's XJ in the junkyard in many years.

 

[RCP Phx]

I think it's more involved than that since the axleshafts have a larger diameter. So I'd think you'd need a new diff carrier, which the truetrac woudl take care of and possibly new outer axle bearings but not sure if they would fit int he existing axle housing.

Might be worth the effort to just find a 29spl 8.25 and rebuild it to what I want. They're still pretty avaliable out there.

The housing and outer bearings are the same. You just need axles and a new carrier.