ax15 and gears driveability

[shark]

I'm planning on putting an 8.8 in my MJ equipped with the ax15. 3.73's are common. i want to run 31"s.

this chart http://jeeptalk.org/gear_chart.php indicates the combo will be very mild. that surprises me. with such an increase numerically in gear ratio over stock i imagined the combo would be borderline extreme even with the larger tires.

 

what do you guys think about this?

[Pete M]

I'd have no problem running 4.10s with 31s. stock 4bangers came with 4.10s and puny tires and I've never thought of them as extreme.

[shark]

I'd have no problem running 4.10s with 31s. stock 4bangers came with 4.10s and puny tires and I've never thought of them as extreme.

do the trannys behind those 4 bangers have simlilar gear ratios? i was hoping to get at least some sort of a performance benefit from them as in stock gear and tire size vs. 3.73 or 4.10 and 31"s. what was the stock tire size anyway? shouldnt i have 3.09 stock gears with my combo of 4.0/ax15?

[Eagle]

I'm planning on putting an 8.8 in my MJ equipped with the ax15. 3.73's are common. i want to run 31"s.

this chart http://jeeptalk.org/gear_chart.php indicates the combo will be very mild. that surprises me. with such an increase numerically in gear ratio over stock i imagined the combo would be borderline extreme even with the larger tires.

 

what do you guys think about this?

I have posted several times that the setup I had in my '88 MJ was 3.73 gears with 31x10.50-15 tires, and the overall final drive ratio (as proven by speed-to-RPM) was exactly the same as my wife's XJ automatic with the stock 3.55 gears and stock tires. IMHO 3.73s are better for 30" tires -- which was my plan when I bought the gears. I think 4.10s are a better choice for 31" tires. And even that isn't anything "extreme" -- that's for general purpose, combination daily driver and light trail use. For a dedicated trail rig I'd look at 4.56 gearing.

[Pete M]

I'd have no problem running 4.10s with 31s. stock 4bangers came with 4.10s and puny tires and I've never thought of them as extreme.

do the trannys behind those 4 bangers have simlilar gear ratios? i was hoping to get at least some sort of a performance benefit from them as in stock gear and tire size vs. 3.73 or 4.10 and 31"s. what was the stock tire size anyway? shouldnt i have 3.09 stock gears with my combo of 4.0/ax15?

 

 

yes they have similar gearing. I think what you're experiencing is simply "different" than what you're used to and not anything necessarily bad. :thumbsup: just gotta drive it more so your shift patterns adjust.

[shark]

I'm planning on putting an 8.8 in my MJ equipped with the ax15. 3.73's are common. i want to run 31"s.

this chart http://jeeptalk.org/gear_chart.php indicates the combo will be very mild. that surprises me. with such an increase numerically in gear ratio over stock i imagined the combo would be borderline extreme even with the larger tires.

 

what do you guys think about this?

I have posted several times that the setup I had in my '88 MJ was 3.73 gears with 31x10.50-15 tires, and the overall final drive ratio (as proven by speed-to-RPM) was exactly the same as my wife's XJ automatic with the stock 3.55 gears and stock tires. IMHO 3.73s are better for 30" tires -- which was my plan when I bought the gears. I think 4.10s are a better choice for 31" tires. And even that isn't anything "extreme" -- that's for general purpose, combination daily driver and light trail use. For a dedicated trail rig I'd look at 4.56 gearing.

i had 3.73's in mind at first until i saw that chart and read a post from someone on this forum. made me think i was missing something but i do see how on the chart that 4.10's and 31"s are in the green. i was under the impression that it would be more in the red. 4.10's are less common in those 8.8's but common enough. hope i can find one with with a "4L10" on the tag. limited slip would be nice.

[shark]

I'd have no problem running 4.10s with 31s. stock 4bangers came with 4.10s and puny tires and I've never thought of them as extreme.

do the trannys behind those 4 bangers have simlilar gear ratios? i was hoping to get at least some sort of a performance benefit from them as in stock gear and tire size vs. 3.73 or 4.10 and 31"s. what was the stock tire size anyway? shouldnt i have 3.09 stock gears with my combo of 4.0/ax15?

 

 

yes they have similar gearing. I think what you're experiencing is simply "different" than what you're used to and not anything necessarily bad. :thumbsup: just gotta drive it more so your shift patterns adjust.

not "experiencing" anything just yet. still in the planning stage. just trying to figure out what i want.

[Pete M]

whoops. :doh: that's what I get for having multiple posts open at once. :shake:

 

bottom line, I'd shoot for 4.10s with 31s, but 3.73 will be good also. Ive got 3.55s with 31s in my 90 and it drives just fine for a street truck. :D

[Eagle]

i had 3.73's in mind at first until i saw that chart and read a post from someone on this forum.

It doesn't sound like you really understood what I wrote. Yes, I ran the 3.73s with 31x10.50s. But it was NOT an optimum combination, and it was not done by prior intention. I bought the 3.73 gears to run in my XJ with 30" tires, but then the MJ came along with a lift and 31" tires (and stock 3.07 gears) before I had installed the gears, so I put them in the MJ.

 

As I said ... the end result was exactly (and I mean EXACTLY) the same as stock tires with 3.55 gears. Not bad on the street, but nothing to brag about. And not nearly enough crawl ratio off-road. IMHO there is no question at all that 4.10s would have been MUCH better.

[shark]

i had 3.73's in mind at first until i saw that chart and read a post from someone on this forum.

It doesn't sound like you really understood what I wrote. Yes, I ran the 3.73s with 31x10.50s. But it was NOT an optimum combination, and it was not done by prior intention. I bought the 3.73 gears to run in my XJ with 30" tires, but then the MJ came along with a lift and 31" tires (and stock 3.07 gears) before I had installed the gears, so I put them in the MJ.

 

As I said ... the end result was exactly (and I mean EXACTLY) the same as stock tires with 3.55 gears. Not bad on the street, but nothing to brag about. And not nearly enough crawl ratio off-road. IMHO there is no question at all that 4.10s would have been MUCH better.

Thanks for the info and clearing up my concerns. I'm definitely sold on 4.10's.

[jpnjim]

Not trying to change your mind,

 

but the 4.0L/5spd/3.73/31" combo was the absolute best daily driver XJ setup I ever had.

(87' XJ Laredo with swapped in 3.73's on old smooth riding-thin sidewall 31" GY MT's :thumbsup: :banana: )

 

I usually drive pretty fast on the highway, and the 3.73's/31's were a nice combo to do that with,

plus it lowered 1st gear enough to return the power off the line to where it should have been (vs' using the stock 3.07's with 31's :shake: ).

 

 

Opinions vary,

so I understand Eagle suggesting 4.10's instead, but I loved the 4.0L/5spd/3.73/31's combo in this Jeep for daily driving.

 

 

A couple years later I ran 4.10's in a 2wd MJ (89' 4.0L/5spd MJ pioneer with a swapped in YJ 4.10 rear & 31" Yoko MT's), and it was pretty similar

but I remember at the time preferring the 3.73 geared XJ for long trips (I had them both at the same time).

 

 

A few years after that I dropped the trail-MJ down, and daily drove it on 31's, (4.0L/5spd/4.56/31" combo).

 

Honestly, I hated it on the street.

 

At a stoplight I'd have to shift into second gear before I even cleared the other side of the intersection, and it was buzzier than I like at highway+ speeds.

 

I never wheeled it with 4.56's/31's (that I can remember anyway), but I can't imagine the trade off would be worth daily driving on 4.56/31's.

 

 

Again, this is just my opinion,

I prefer the tradeoff of a little less gear off the line, for lower RPM cruising on the highway.

 

Maybe that's because before XJ's my previous two daily drivers were:

(73 J4000 360/4spd) 4.10s' & 31's w/o overdrive

(71 Javelin 360/4spd) 3.91's & 27's w/o overdrive

 

both combo's = bring earplugs, and leave early.

[shark]

ok, now I'm really torn :(

[jpnjim]

ok, now I'm really torn :(

 

 

4.10's are better if:

you're ever going to go past 31's

you're trying to find a ft axle to swap in (and not buy/swap gears).

- XJ 3.73 geared HP D30's are tough to find

you don't mind trading a small amount of highway RPM for a small amount of more power off the line

you do a lot of technical 'work' when wheeling, and could use the extra control of 4.10/1st gear/low range vs 3.73/1st gear/low range.

 

 

3.73's are better if:

you rack up miles, and could stand to drop some cruise RPM

30-31's are all you're looking for

(I didn't mind it with 32's either, but if you 'need' 33's, you'd probably 'need' 4.10-4.56+'s then too)

you have 3.73 axles handy (that's why I originally swapped them in)

once I tried it, I realized how much perfect they were for me in a 4.0L/5spd XJ.

[shark]

ok, now I'm really torn :(

 

 

4.10's are better if:

you don't mind trading a small amount of highway RPM for a small amount of more power off the line

i think this might be the key right here. i do most of my driving in town. i see very limited highway mileage. if i do see highway mileage its to the junyard on the other side of the bay or down south to the good beaches and during football season. go gators!

[Eagle]

Let's put this in perspective (again). The gentleman is talking about running 31" tires.

 

With 3.73 gears, 70 MPH would be 2881 RPM in 4th gear and 2161 RPM in 5th.

 

With 4.10 gears, 70 MPH would be 3167 RPM in 4th gear and 2375 RPM in 5th.

 

Guys ... 2400 RPM at highway speed is NOT going to burn up the engine. I know I have posted before that this basic engine was designed long before overdrive transmissions were commonplace. Top gear used to be 1:1 (what 4th gear is in our vehicles), and we routinely cruised for long distances at 3,000+ RPM. My brother's '72 Gremlin went over 350,000 miles with no engine work, with the basic 3-speed manual tranny.

[shark]

Let's put this in perspective (again). The gentleman is talking about running 31" tires.

 

With 3.73 gears, 70 MPH would be 2881 RPM in 4th gear and 2161 RPM in 5th.

 

With 4.10 gears, 70 MPH would be 3167 RPM in 4th gear and 2375 RPM in 5th.

 

Guys ... 2400 RPM at highway speed is NOT going to burn up the engine. I know I have posted before that this basic engine was designed long before overdrive transmissions were commonplace. Top gear used to be 1:1 (what 4th gear is in our vehicles), and we routinely cruised for long distances at 3,000+ RPM. My brother's '72 Gremlin went over 350,000 miles with no engine work, with the basic 3-speed manual tranny.

the voice of reason has spoken, folks. thank you, sir.

 

i think i can live live with that difference in rpm. we are talking about a very small difference in rpm but if youre talking about long distances that could be a huge differece in mileage. as i said, i don't do a huge amount of interstate driving. conversely, I'm not building a trail rig here either. I'm building what could be called a resto-mod(itll have a an 8.8 and a 97+clip, etc.) but it will also be a daily driver. i couldnt afford a new truck(i wanted a dakota) so I'm building the next best thing. i would like to build a stroker for this truck at some point too but that is another story.

[comanche09]

I am running an AX-15 on 31" BFG ATs with 3.55 gears behind a stock Renix 4.0 with 104k miles on a 3" lift.

 

1st gear is pretty deep, no problems pulling off the line and keeping up with traffic. Never really have a need to go past 2.5k RPM anytime.

 

Can't use 5th gear at 70 on the hwy when pulling my 5x10 utility trailer loaded with my 4wheeler unless the road is flat.

 

I think 4.10s would be nice for a DD.

[Justin_k]

I think 3:55's would be the best. I'm still running the stock 3:07's with 31's and don't mind it. I don't do much offroad and for the 4x4ing I do I use 4lo. The only time I want deeper gears is for towing my quad trailer. (It would also be nice to use 5th at speeds around 100 kph, I like being able to do 125 kph in 3rd though )