Zusez3

Hello all, I rebuilt my police package XJ (Project Protection below) with jy parts over a year ago and a few months. I used a donor differential and haven’t used the 4wd due to them being different sized gearing more than likely.

I need recommendations on gears and parts needed to complete the work. What is a ballpark estimate on the price for parts and average shop time hours for this work?

I also have a matching set of diffs on a parts Cherokee, would you regear what’s on the Jeep or swap the diffs and add new suspension parts?

all equipment is stock configuration and in need of some love. It’s time for a new suspension but I need a regear also. Kinda stuck on what to do. Any info is appropriated!

00t444e

What size tires do you plan on running?

Zusez3

stock AT tires. No plans for lift for larger tires at the moment

agreen

On stock size tires, 3.55 ratio is perfect.

I don't know what the police package had as a ratio, but 3.55 is pretty much the most available ratio available. If you can't find the numbers on the axle tags (usually on the diff cover bolts) then pull the covers and count teeth. Or the tooth count might be stamped on the gears. You should probably go ahead and pull the covers and take a look/ inspect anyway.

robsjeep

I dont know about the xj, but my old ford exploder 🤣 had the factory tow package, which meant a slightly lower ratio was installed. So there maybe different factory gears, certainly Id think that for the 4 cylinder engined xj's. So as other wiser folks said, check the tags and or count the teeth on both sets of axles you got. The standard stock six cylinder axle ratio is ok for some people up to about a 29 inch tire, after which you really need to regear if you drive highways, and want to keep up speed on hills, and have passing power. some folks will not even put up with that, and prefer a regear even for less than a 29 tire, depends on your driving style. I was used to an old under powered VW Bus in the mountains, so even a poorly geared jeep seemed fine to me, even if I had it down shifted in 2nd to make it over highway 50 in the Sierra's as that old bus had to be in first to make it over that pass! I got, or my 4.0 liter six jeep got 4.11 on 33 tires, not ideal, but useable, I also have a 4.11 transfercase low. The 4.11 diff gears is better suited for 30 tires which is what prior owner had, 30 inch, then later he raised the jeep more, and went to 33 tires, but couldn't justify the cost a regearing again. So my gears, for my tires are about 10% to low ratio, (33 inch tire is 10% more bigger than a 30 inch tire) so instead of 4.11 which is good for 30 inch tires, I should get 10% more gear ratio and go to the next gear size, 4.56. That will restore my jeep to stock,overall ratio. but I can live with it, there are far more important things I want to do on the jeep first, given my limited budget, and time. But I am considerably slower on mountain highways than my friend with a correctly geared cherokee, thats the fact. I must down shift when he can stay in OD, and by the time he shifts down to 3rd on steep highways, I am already in 2nd, engine screaming fast to keep up with him. Likewise on downhill highway, I must down shift lower for more engine braking. Some down grades require first gear ( Old Priest grade highway 120, near Yosemite) with my not ideal gearing, I dont have as much engine braking as then as if I had stock over all ratio. so I need to ride the brakes a bit more than my friend does in his correctly geared jeep. Basically your jeep gets more gutless the more the ratio gets out of wack verses stock, 10% is kind of the limit for me, if mine was 15% off Id definitely regear, if mine was 5% off, id not consider regear, but 10% I am on the fence, yeah it would be a nice upgrade, but it costs a lot of dough in parts, and it would be a big project (and I have done this kind of job several times in the past, not a quick job for me, I rather drive my jeep)
Moral of that is, if you regear, plan ahead, are the tires you are converting too the ultimate size, or might you decide to go bigger still? Regear once, not twice.

Anyway around a 10% or more change in tire diameter from stock is around the limit where a gear change is warranted to satisfy most drivers. You want to be able to keep the engine in the power band, 300 or 400 rpm less can make an engine be weak, effects your ability to climb grades without down shifting out of over drive.

Also larger tires dont stop as well with tiny stock brakes. Disc conversion in rear, larger brakes over all are a consideration, if you get new rims for big tires, consider rim diameter as the limit of how big diameter brake you can install.

for stock tires, a minor lift can help with offroad, dont go too high, else you get into big drive line angle changes, different shackles, shocks, spring, steering, brake hoses and all sorts of other considerations, the higher you go the more the other changes need be made. Again, increased lift means more things need get changed, and if you want more lift still later, some of those other changes you made will have to be redone, so plan ahead. If you think you want a big lift eventually, you don't want to spend a whole lot of money on some mid size lift, only to have to do it all again shortly after for the great big lift. it will cost you less money to do it once to the big lift, specially since you might be paying for the labor. plan ahead

For costs, consult your local shops. the labor costs vary so much by locality, that many of the responces from out of area will be incorrect for you. Parts cost is on the interweb.

I have bought from these folks, west coast differential, legit company as near as I can tell, good phone advice too...

https://www.differentials.com/

cruiser54

Good rule of thumb once the XJs were equipped with the 4.0

Auto trans 3.55 and manual trans 3.07.