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  #16  
Old November 9th, 2018, 20:19
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Re: Move up to 4.10 or 3.73 on 235s?

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
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2000 XJ: OME 2" lift, trimmed fenders, 265-75-16 Cooper AT3s, extended shock mounts, JKS swaybar disconnect, 4.56, Ox locker rear, trutrack front, Dirtbound Bumpers, warn winch, rocker skids. 1996 XJ Bone stock daily driver.
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  #17  
Old November 9th, 2018, 20:32
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Re: Move up to 4.10 or 3.73 on 235s?

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.

Quote:
Originally Posted by lazyxj View Post
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.
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  #18  
Old November 9th, 2018, 22:05
JeepNoob JeepNoob is offline
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Re: Move up to 4.10 or 3.73 on 235s?

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...
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  #19  
Old November 10th, 2018, 06:33
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Re: Move up to 4.10 or 3.73 on 235s?

Quote:
Originally Posted by cal View Post
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.
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Last edited by Tim_MN; November 10th, 2018 at 06:37.
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  #20  
Old November 10th, 2018, 07:44
RCP Phx RCP Phx is offline
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Re: Move up to 4.10 or 3.73 on 235s?

Quote:
Originally Posted by devildog0 View Post
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.
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  #21  
Old November 10th, 2018, 10:50
md21722 md21722 is offline
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Re: Move up to 4.10 or 3.73 on 235s?

The comments about just needing new shafts to go 29 spline in the 8.25 are correct.

My 01 XJ has run over 300,000 miles on BFG A/T 235/75R15 with the stock axle gearing and I never considered changing the gear ratio.

When I installed lockers in my 97 XJ which runs BFG A/T 30x9" I went with 3.73 because I didn't want to buy a 3.55 locker for the front D30. On that Jeep going 4.10's may have been a better idea.

Incidentally, my 97 XJ came with the UpCountry package and it had 3.55 axles.

Both Jeeps are automatic transmission.
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  #22  
Old November 11th, 2018, 14:58
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Move up to 4.10 or 3.73 on 235s?

I wouldn't do any of this for a negligible gain in gearing

If you're going to do it, at least go 4.56

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  #23  
Old November 11th, 2018, 20:52
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kastein kastein is offline
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Re: Move up to 4.10 or 3.73 on 235s?

Quote:
Originally Posted by cal View Post
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.
Same here. My 98 had a factory installed hitch and came with 3.55s.

XJ axles with 3.73 factory installed do exist in the parts catalog. I've just never ever seen them nor have I been able to find when they would be optioned.

Quote:
Originally Posted by Tim_MN View Post
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.
I thought it was the 3.30s they got rid of, and the 4.56s when they ditched the 4 speed aw4 2.5L option and went back to the 3spd Chrysler trans previously used 86 down because it was one of their products, which would mean you'd want 3.55s again. I could be wrong.
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Please do not PM me about the AW4 info thread unless you have a truly unique question that is not covered by it or info to add. I do not respond to questions answered by the thread.
Definitely do not hunt down my phone number at 3AM, text me about it, and then threaten violence when I am not helpful. It will not get you what you want.
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Last edited by kastein; November 11th, 2018 at 20:58.
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  #24  
Old Yesterday, 05:29
RCP Phx RCP Phx is offline
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Re: Move up to 4.10 or 3.73 on 235s?

Quote:
Originally Posted by denverd1 View Post
I wouldn't do any of this for a negligible gain in gearing

If you're going to do it, at least go 4.56

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That would spin up the 4.0 to high for any practical use.
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  #25  
Old Yesterday, 17:15
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Re: Move up to 4.10 or 3.73 on 235s?

4.56 with an auto and 235s would be... 3000rpm at 75 in overdrive. I dunno, it'll eat more gas but that's not too bad really.
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My yard looks like Sanford & Sons.
Please do not PM me about the AW4 info thread unless you have a truly unique question that is not covered by it or info to add. I do not respond to questions answered by the thread.
Definitely do not hunt down my phone number at 3AM, text me about it, and then threaten violence when I am not helpful. It will not get you what you want.
CTeunuch: Sometimes I really wonder if this sport makes you insane, or it just attracts the mentally unstable.
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  #26  
Old Yesterday, 17:17
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Re: Move up to 4.10 or 3.73 on 235s?

James drove on 4.56 and 235's with an ax-15 for 2 years before we finally lifted him.

I can't say that it hurt his mileage at all.
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  #27  
Old Yesterday, 19:56
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Re: Move up to 4.10 or 3.73 on 235s?

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2000 XJ: OME 2" lift, trimmed fenders, 265-75-16 Cooper AT3s, extended shock mounts, JKS swaybar disconnect, 4.56, Ox locker rear, trutrack front, Dirtbound Bumpers, warn winch, rocker skids. 1996 XJ Bone stock daily driver.
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  #28  
Old Yesterday, 20:30
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Re: Move up to 4.10 or 3.73 on 235s?

Quote:
Originally Posted by cal View Post
James drove on 4.56 and 235's with an ax-15 for 2 years before we finally lifted him.

I can't say that it hurt his mileage at all.
Efficient use of torque can't be a bad thing

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