Used gears a good idea or bad idea?

[Eagle]

3.55s with my 31's will bring me slightly lower than stock 3.07's with stock 215's. 99% on road driving, some offroading, but mostly just logging trails to good fishin holes. I don't think I want to go any lower. Got any reasons I should think otherwise?...cuz I'm still in the planning stages here.
B.

I've been running 31s and 3.73 gears. The overall final drive ration (as indicated by MPH per RPM) comes out exactly the same as a stock XJ with automatic. It didn't hurt gas mileage at all -- in an MJ running on the highway with the tailgate up I still got 19 to 21 MPG. That compares to my XJ which gets 21 to 23. About the only vehicle on the road that's less aerodynamic than an XJ is a pickup with the tailgate up, so I'd call it even.

By all means, if you can find them go for the 3.73s. I actually bought the gears intending to run them with 30" tires. The 31s sort of happened by coincidence. I think 4.10s would be even better with 31s.

 

[MrShoeBoy]

I got a set of used 4.10s for my front axle and have not had any problems with installing them or for the last 8,000miles I have driven on them. If you can gear setup labor for free and only have to pay for parts, run a used set. If they blow up, your only out $50 or less for a set.

I have a set of 3.55s with an open carrier for sale. They came out of my HP dana 30 and are in good condition. PM me if you want them.

AARON

 

[XJ_ranger]

I have wondered about this. Would you indulge me with a bit more detail? What else comes into play? As I posted above, I am still in the planning stages, and am open to advice.
Thanks,
B.

Rotational Inirtia - the larger the tire, the more weight that has to spin, and that makes it harder on acceleration. I have no expierence, but have heard of this and see why this would matter...

 

[Beej]

Rotational Inertia - the larger the tire, the more weight that has to spin, and that makes it harder on acceleration. I have no expierence, but have heard of this and see why this would matter...

Good point, I am leaning more and more towards at least 3.73s and possibly 4.10s now.
B.

 

[BrettM]

Rotational Inirtia - the larger the tire, the more weight that has to spin, and that makes it harder on acceleration. I have no expierence, but have heard of this and see why this would matter...

also added wind resistance of being higher, especially if you have a basket type roof rack

 

[XJ_ranger]

i also remember reading about contact patch size, and the bigger the tire the bigger the patch. something about rolling friction and rolling resistance

AND lower (numericaly higher) gears give you a better crawl ratio in 4 low - something i wsh that i had this weekend. My 3.07's are a lil more than annoying with my tires because my crawl speed isnt as low as i would like...

working on it tho...

 

[cLAYH]

PS, clay, I have a manual tranny, and hence am starting out with 3.07s. 4.10s would be way to low for what I want. 4.10s would be the stock ratio equivalent with 37s! Way too low for my usage.

I was where you are now about 4 years ago. I went from stock tires with 3.07s to 31s with 4.10s. There is no problem running on the highway with 31s and 4.10s. I could easily do 120+kPH. I think you will actually like the way 4.10s pull off the line. I know I do. Don't forget you are also compensating for a now heavier tire and incresed rolling resistance and reduced aero-dynamics. Most people in AB running 37" tires are running atleast 4.88 gears. A member of my club was running an XJ with 35's and 4.88s. He towed his tent trailer everywhere with it. From Calgary to Radium on more than one occasion. BUT if you REALLY want a set of 3.55s I have a complete front and rear diff in my back yard.

Check out thses sites

www.fourwheelstampeders.ca
www.calgaryjeep.com
www.4wheeler.ca
www.island4x4.com

 

[Beej]

Check out thses sites
www.fourwheelstampeders.ca
www.calgaryjeep.com
www.4wheeler.ca
www.island4x4.com

already bookmarked!
Thanks again for the help everyone. I know I can get 3.73's but I'm keeping my eyes peeled for 4.10s.
Jeep on,
Brent.

 

[flexjay87]

i agree with Brett, if you go to the junk yard, just get the whole axle, and go at least 4.10, my .02

 

[Beej]

i agree with Brett, if you go to the junk yard, just get the whole axle, and go at least 4.10, my .02

I already explained why that is a less viable option. Used gears = 65.00 per set, Used axle = $600~$1000. I can see how it would be a better option in the US, you have over ten times the population!
B.

 

[Slo-Sho]

wow, axles are $20 on the weekends!