Gearing Advice

[AeroNautical]

A topic that's been beaten to death, but I've got a more unique scenario I think:

 

     I have a 98 XJ 29 spline 8.25, and a 99 XJ HP Dana 30. Geared for 3.55, I grabbed them from auto XJs when I did my 2 to 4wd swap. I run 33s. I've got engine mods that boost my 4.0 30+ HP and torque, making it manageable, but not ideal. I pull a 1000+ lbs trailer, and I've gotta slip first. (AX-15)

 

     Quoted about $1200 for a re-gear either 4.10 or 4.56. I'm unsure which would suit me best. She's on the road alot, a DD, but crawls every other weekend. I want OK gas mileage (I get about 17MPG on my 3 1/2 hour drives to Raleigh as of now), but also want pretty good torque when pulling a trailer or crawling a rock. I can google all day long and get mixed feelings about either ratio. 

 

     It won't be easy, but if I choose 4.10, I could find an 8.8 with an LSD and weld perches on and just pay to regear the D30, save a butt load of money. Or, if I choose 4.56, I'd have to pay for 2 regears, I really doubt I'd find them in a JY, and invest in an overall weaker axle (29 spline 8.25), without an LSD or locker. 

 

     Also, if I'm paying to regear the D30 either way, how do you feel about a lunchbox locker in it? I've heard when power isn't applied, the locker is open. Pop it in 4-wheel, and chances are you have enough tire slippage for it to behave just fine.

 

     Opinions, thoughts, gripes and insults are all welcome. Comments about everything I've mentioned here will be most helpful. Thanks. 

[Pete M]

all costs being equal, I'd go with 4.56 without any hesitation. :thumbsup:  If 4.10s are cheaper, then that's up to you.  I've got 4.10s and 33s and I want a bit more gear for both highway and trail.

[HOrnbrod]

^^ This

 

My simple gear ratio vs. tire size rule of thumb compromise for combined on and off road driving:

 

31" tires - 4.10

32" tires - 4.10 for mostly street, 4.56 for mostly trail

33" tires - 4.56

[MrSimon]

I've been where you are.  Multiple times.

 

I'd highly recommend the 4.56s with 33s, especially since you wheel regularly and will be towing a trailer.  I wouldn't even consider 4.10s.

 

The HP30/8.25 is a good sturdy set of axles.  They would hold up just fine with 33s, even locked.  I wouldn't hesitate to put the money into them for new gears.

 

Regarding lockers, a lunchbox locker has good road manners and works well off-road.  They are a fine option.  HOWEVER, with deeper gears, 33s, manual trans .... you definitely up your risk of breaking shafts while wheeling.   Saving up for some chromolly shafts would be a good idea too.

 

But, with all that said .... I feel the best thing to do is be PATIENT and watch the forums/Craigslist for a set of used axles.  I've seen lots of D30/D44 axle sets with gears and full case lockers sell for less than $1000.  

 

And don't be afraid to buy an entire Jeep just for the axles.  I just picked up a two door XJ for $1,500 (it won't start) that has a D44/D30 combo with 4.56s and a rear ARB, not to mention a full 4" lift, York compressor, SYE, and lots of other goodies.  I can strip what I want and part out the rest.  Might even break even and end up with FREE axles. 

 

Think outside the box, and be patient.

[Eagle]

My rule of thumb has long been 3.73s for 30's and smaller, 4.10s for 31s and 32s, and 4.56 for anything larger. That said, either one will do you okay.

 

IIRC, the torque peak for the '88 Renix 4.0L engine was 2200 RPM. With 4.10s, at 70 MPH in overdrive your engine would be spinning at 2282 RPM. With 4.56s, it would be turning 2538 RPM. The 4.10s theoretically would put you right on the torque peak for highway cruising, but the 4.56s would be better for towing -- and since you shouldn't be towing at 70 MPH, the 4.56s would get you at the torque peak down to about 60 MPH, for better towing and better fuel economy when towing.

 

Plus, obviously, the 4.56s give you a better crawl ratio off-road.

 

IMHO 4.56s are the better choice, but if you can do the 4.10s for a lot less money, it wouldn't be a horrible choice.

[89eliminator]

I had 4.10s and 33s (with an auto).....get 4.56s.  i would but don't want to stick more money into my axles.  

[Lee21490]

 Might as well do 4.56 if you have the option.

 

I'm running 4.10's on 33x12.5's  it does just fine.  I wouldnt use larger tires with it though.

[AeroNautical]

     Great advice, 4.56 it is. As for the locker, I can't afford a selectable, so the lunchbox locker, or a Detroit Tru-Trac (LSD) for either the front or rear. Is there a benefit of having it in the front over the rear? Would the front ratchet in 2wd? I've found myself on more than one occasion getting stuck in mud, I've gotta have something. I hate mud, but it's a necessary evil getting some places. Thanks. 

[MJCARENA]

I have an 89 XJ  with an automatic trans  on 33's with 4:56 gears and it works good on and off road. I also have a Lock-Right in the rear and the Tru-Trac in the front. Works good in the rocks around here.  A lot of other guys have Lock-Rights front and rear with no issues on the road. They say it is like its not there in 2wd on the road. 

[Lee21490]

Aussie locker is what i was looking into awhile back.

 

Ended up just paying the extra for Yukon Grizzly front/Back.

[64 Cheyenne]

Lunch box lockers in the rear suck. Unless your truck sees way more dirt than pavement, I'd say OK, but for the street you'll hate it.

Matter of fact that's why I have one (8.8 lockright) for sale in the classifieds.....

[AeroNautical]

Alright, 4.56 and no Lunchbox (on the road more than off). Maybe I'll just grab a Detroit Trutrac for the rear and call it good. 

[MrSimon]

Lunchbox in the front will be fine for on-road driving.  You might hear some clicking at full turn in parking lots and stuff, but most of the time you won't know it's there.

 

Detroit tru-tracs are fantastic.  They have good road manners, and with a little two foot action on the pedals, you can get them to lock up just as good as any full locker.