Cheap re-gear/more speed on 31's?

[gw204]

Sure, and I see where you're coming from on that. However:

Long-term, the savings of doing the gears makes more sense from the financial, livability, and wear-and-tear standpoints. I'm in a 2000 on 4.10s with 31" tyres, and ran 3.55s for about a year after putting the 31s on; the 4.10s have more than paid for themselves by now just in fuel savings. While the cost of recouping the gears (or axles) won't be made back on his 1000-mile trip, it'll be a good start at offsetting it, and will have him taken care of for the foreseeable future given the tyres he's running.

Agreed. Long term solution is definitely to regear as is definitely what I will do if I even do a lift and tires on my 2000. I got the impression that his trip was coming up soon and figured a little time in "3" was better than rushing into axle work. :cheers:

 

[89xj]

how was the performance before the 31" tires? the 88 renix is a fairly strong(good torque at low rpms) engine, but what condition is the engine in?

i didnt like the performance when i went with 31's on my 89 5spd, but it wasnt bad enough to not take a 1k mile road trip. i did eventually regear, but as long as the engine and driveline are in good working condition, a 1k trip should not be a problem with 31's.

you only need to regear front and rear if you use 4wd. if you decide to regear and dont have enough cash for both axles, do the rear first and not use 4wd.

 

[stroked88]

gearing up like every one is suggesting is not going to give you more speed. it is going to make you be able to take off faster but you will not go faster it will be slower top speed due to the steeper ratios

 

[Lightfoot]

I have a 99 5spd that I bought stock (3:07), I went up to 31's, and the power loss was significant, but not something that cant be lived with. (drove it from CT to CO) When I went to a 4.6 stroker (stock intake/ exhaust), I would say it returned to maybe a little better than stock, however there is still alot more stress on the transmission and engine mounts. Low gears are very long, and it feels like your pulling a trailer until about three grand. I can use fifth, but only If im doing 70+ because otherwise rpms are too low to sustain speed. Any significant hill and I am in 4th, and going up I70 through the mountains I run 3rd at over 3k up the big hills, and can pass pretty easily. My setup works, but I am definitely planning on going to 4:10's. According to my math, the feeling of 4th gear now, will be about the same as 5th when I change my rear end.
I know the 5speed is a bit different than the aw4, but hopefully my experiences can help you with your decision. You can absolutely run 31's on 3.55's, but you may find yourself in the slow lane more often than you would like, and in 3rd at higher rpm's.
As far as the "more speed" argument, lower gears will effectively lower your top speed, however, to me, this is irrelevant. Your jeep on 31's ( if it had the power) would do at red line in 4th about 190mph, and in 3rd 136mph.With 4:10's, these numbers drop to 170, and 125 respectively. I have had my jeep to just over 100, and I dont plan on doing it again. This combined with the fact that most jeeps lack the power to hit these numbers anyways makes this unimportant to me. What I look at as far as top end is the rpm's ill be turning at 70. With 4:10's, you'll be at about 2260rpm in 4th which is right in the middle of where you want to be for good mileage with a 4.0. On the low end, you will change gears sooner, but who cares, its an automatic. as far as more power, you will have about 15.5% more torque at the rear wheels with 4:10's. This translates to faster acceleration.
Its really your call if you regear or not, but I would say go with 31's, and regear when you can afford it. Many people have had no problem doing this, including myself.
I made this chart a while back for gears vs tire size and rpm vs speed if you want to have a look for yourself http://lightfootxj.webs.com/index.htm
Hopefully this gives you an idea of what to expect.
~Lightfoot

 

[HenryKrinkle]

The engine only has 156k or something even though it's an '88. It ran fine on stock tires. I could do 70-75 all day. The problem now is really just acceleration, not speed on the 31's. I have a feeling the manifold leak is robbing some power. There shouldn't be anything wrong with starting off in 3, letting off the gas and putting in D right?
I've never really gotten on it. I doubt it's been above 3k rpm's more than a few times. I like to take it easy on her, but after some more maintenance it'll be easier for me not to worry so much about that. I'll do new wires/cap, trans flush, alignment, maybe have someone try to balance the tires again, etc.

 

[old_man]

Here we go again...:doh:

4.10s were only found in 2.5L / AX5 XJs. Meaning if it has an AX4 it does NOT have 4.10s (and yes there were 2.5L / AX4s). I've never heard of the "off-highway vehicle" package. Not saying it doesn't exist, but who here owns or has seen one? If it was an elusive 2.5L / AW4 it had 4.56s.

I've seen a few examples of either of these first hand. I've PERSONALLY pulled a D30/8.25 set from a rolled '94 2.5L/AX5 XJ that had 4.10s at a JY. I've also PERSONALLY popped the covers off TWO sets of D30/D35s from 2.5L/AW4 XJs that had 4.56s at a different JY.

I hate to contradict you but the dealer could order what ever gear ratios they wanted. My 85 2.5L with an AX4 came with 4.10's from the factory. It also came with manual steering and rubber mats. It turns out there was a dealer in AZ that liked the 4.56's and you tend to find a higher percentage there.

 

[Bdiddy11]

Ford 8.8 has the same bolt pattern as a Cherokee axle correct? So I can use my Moab wheels.

And the 410 gearing will show on the diff cover? Or possibly the striker on the door panel? Read that on a Ford site that it's sometimes on the door sticker.

And for a D30 4cyl axle with 410 gears, do I need to look for a specific style?

 

[MoparManiac]

I hate to contradict you but the dealer could order what ever gear ratios they wanted. My 85 2.5L with an AX4 came with 4.10's from the factory. It also came with manual steering and rubber mats. It turns out there was a dealer in AZ that liked the 4.56's and you tend to find a higher percentage there.

No worries, this is the kind of input needed. People with ACTUAL experience. Not someone regurgitating wikipedia.

 

[FlexdXJ]

Ford 8.8 has the same bolt pattern as a Cherokee axle correct? So I can use my Moab wheels.

And the 410 gearing will show on the diff cover? Or possibly the striker on the door panel? Read that on a Ford site that it's sometimes on the door sticker.

And for a D30 4cyl axle with 410 gears, do I need to look for a specific style?

Yes same bolt pattern, thats why its a good swap.

not sure if it will be on the cover. Its stamped on the ring gear though.

Anything past 91 i think is what you want. They have the 297 u-joints that are much stronger than the older vacuum disconnect axle.

 

[kastein]

It'll be on a tag hanging off the diff cover bolts, but that's not that reliable, someone could have had it regeared and put the tag back on. Pull the cover and look on the side of the ring gear like Flexd said, that's 100% reliable.

As for the d30, 91-up (iirc) is non vacuum disconnect, anything with ABS is going to have the larger U-joints, and anything 95/96/97 (unsure, and do not want to put out bad info) up will have the larger 29-size U-joints that can be swapped for 297s or 760s. Mid 99 and up have a different unit bearing size, so make sure to verify that yours are the same - you can tell by the height of the centering ring/hub around the axle shaft nut.

 

[austinaubinoe]

no not bolt in, but very simple on a cherokee. If I was only running 31's I would definitely go for a 4 cyl D30 (TJ, YJ, XJ) and a rear 4.10 8.8 LSD.

All YJ's had that disconnect shit I think, but you could just snag solid axles out of any d30 (even WJ I think) and an install kit.

I have personally never seen a 4cyl XJ, though there is not many good junk yard near me.

 

[kastein]

YJs are leaf sprung all around, so putting a YJ d30 into an XJ is a bit more of a project than you'll want probably. TJs are the same Quadra-Link setup, but I'm pretty sure they are all LP...