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4.10 or 4.56 gears

S

Stubbs

NAXJA Forum User
Location
Aztec, New Mexico
I have searched and thought, and thought and searched, and I cannot come to a conclusion.

I've got a 96 xj Country, 3.55 gears on a 4-speed auto tranny, Chryco 8.25 rear, Dana 30 front, with a recently installed 3" RC lift, 31x10.50's, and I'm pleased with the whole thing except for the gearing. My RPM's are far too low to produce substantial power, especially in the mountains, and especially towing. Towing in the mountains is atrocious.

I want to run 60 MPH at 2800-ish RPM's in 3 for towing, and I want to run about the same RPM's in overdrive at 75 not towing on the interstate. I find all kinds of gear ratio calculators on the net and NAXJA, and I find mention of the XJ auto having a low overdrive around .69-.73, but I cannot seem to find ratios for the rest of the gears, especially 3rd.

If I "assume" 3rd is 1.0, and OD is .73, 4.56 gears seem to be where I want to be, but I'm about to place a lot of money on that assumption. All of the FAQ's say go with 4.10's on 31's, but my research has left me completely confused.

Can any of you steer me in the right direction?

TIA

Stubbs.

:wow:

P1010032.jpg
 
If you're doing a lot of towing, especially in the mountains, I'd go with the 4.56's. Normal for 31's is 4.10's, but that's not including towing regularly. What size and weight are you towing with it first of all? If it's anything kinda heavy, I'd have no problems going 4.56's with it. That's just my opinion though.
 
the only problem that you would possibly come across with 4.56's..especially with tires as small as 31's...is that you will have no top end speed. meaning something like 75 tops with high RPM.

I think 4.10's would suffice for the application...
 
Im runing a 87 aith auto and have 31 with 4:10 gears not bad but in the moitain with a trailer there no power go with 4:56 with i did
 
Planning on adding any armor, skidplates, aftermarket bumpers, carry a lot of stuff camping?

Go w/ the 4.56 gears.

A lot of highway driving, no off-road use, no passengers?

Go with the 4.10's
 
jeepcomj said:
the only problem that you would possibly come across with 4.56's..especially with tires as small as 31's...is that you will have no top end speed. meaning something like 75 tops with high RPM..
Click to expand...

I used to run 75 with this combo all the time with no ill effects at all. 100 was possible( I never pushed it father than that) but I wouldn't run that for any distance. JIM.
 
beaterjeepjoe said:
If you're doing a lot of towing, especially in the mountains, I'd go with the 4.56's. Normal for 31's is 4.10's, but that's not including towing regularly. What size and weight are you towing with it first of all? If it's anything kinda heavy, I'd have no problems going 4.56's with it. That's just my opinion though.
Click to expand...

^^^what he said.

I have never read a post that said after the fact "Man those gears were JUST too low. i wish i hadn't bought them"
 
I am running 4.56's and 31"s and I absolutely love it. I can run 75 all day long at just under 3000 rpms. I pull a small motorcycle trailer or boat almost every weekend and it tows really nice. I go to Colorado every year and the 4.56's are perfect, espescially with power loss from the higher altitude. The first year I did it on 3.55's and I never used OD. I thought about 4.10's when i did my swap but I am glad I went with the 4.56's instead. I also did not notice much difference in fuel economy when I went with the deeper gears. In fact, my in town mileage increased slightly and I still get over 18mpg on the highway if I can keep my foot out of it. Also 4.56's will work well if you decide to run larger than a 31" tire in the future.
 
another vote for 4.56
if you don't like it, the next set of tires can be 32's and you will love it.
 
First off, the gear ratio for third is 1:1. I'm running 4.10's and 33's, but with a five speed, and 4:1 low range...around 65-70, I'm at 2500 rpm. For what you want to do I would suggest the 4.56's you won't be dissapointed.

Justin
 
jeepcomj said:
the only problem that you would possibly come across with 4.56's..especially with tires as small as 31's...is that you will have no top end speed. meaning something like 75 tops with high RPM.

I think 4.10's would suffice for the application...
Click to expand...

Meh, I use to ride on 31s and 4.56s and it was like 3k rpms at 70, no biggie.
 
I'm towing a 4400 lb wet camp trailer. I know that's pretty heavy, but I've upgraded the brakes to high end rotors, semi-metallic pads, and the trailer has brakes on both axles. I've also added a tranny cooler. I'm trying to build a light trail vehicle (not a rock crawler) that can tow the camper into places like Silverton, CO, and unhitch and go jeeping from there. I wasn't able to make it all of the way up the pass last weekend, the tranny got pretty hot, just barely into the red on my gauge, and I chickened out and camped up in the forest service area above Purgatory.

I'm hoping if I take it easy, and maybe add a second tranny cooler and disable the path through the radiator I can pull it off. If I can make it to 9600 feet on the current gears surely the new ones will help.

I think from what you guys have said I'm going to go with the 3.56's, and yes, I do plan a roof rack and front bumper at some point.

I just know all of you guys are going to call me crazy for this idea, and I guess I'll just have to burn up a transmission to find out for sure.

Thanks for all of your advice.

Stubbs.
 
Interco tires has a chart which you can use for refrence. It shows tire size, gearing and approximate rpms. But there's no black and white as to what you should use, only grey. While you'll hear alot of opinions remember they're just that. I've got a friend who races baja and swears by the 4.10's he's running with 31s. Therefore 4.56's would seem too high, but that's just my opinion.

Cheers
 
I've got 4.56's in mine with the same lift/tire set up plus lots of armor/cage and more crap to add weight, I'm glad I have 4:56's. I tow a Jayco Baja camping trailer fully loaded through the hills and have no problems...other than engine temp when its 100+ outside.

*edit* I actually get better MPH now (~22 mpg) than when I have same setup running 3:55's
 
JoesXJ said:
I've got 4.56's in mine with the same lift/tire set up plus lots of armor/cage and more crap to add weight, I'm glad I have 4:56's. I tow a Jayco Baja camping trailer fully loaded through the hills and have no problems...other than engine temp when its 100+ outside.

*edit* I actually get better MPH now (~22 mpg) than when I have same setup running 3:55's
Click to expand...

22mpg. That's awesome! Have you checked your miles using a gps? That tire to gear ratio may be giving you a false read on the odometer.

But to the question at hand.......I have 96 auto with 4.56 and 33's........not sure I like that on a set of 31's. But I'm on the highway quite a bit, and not pulling 4500 lbs. Tough call really.
 
Another vote for 4.56 gears with 31's. I'll trade top speed for torque any day.
 
tdr1213 said:
22mpg. That's awesome! Have you checked your miles using a gps? That tire to gear ratio may be giving you a false read on the odometer.
Click to expand...

Yup, changed the speedo gear and then checked everything with the Garmin GPS, my average MPG now is 22 (up from ~12)....I do drive mosty with a light foot though.
 
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