4.56 gears??

[88Bronco2EB]

I have some 31" BFG All Terrains and I want to know If running 4.56 gears in the diffs would make the highway RPMs to high??? or should I go with 4.10s I have an A4LD tranny by the way. I'm going to be swapping in a dana 35 and 8.8 rear end. I wanted to go with the 4.56s to have some extra torque so turn the larger axles along with the lager tire size.

Thanks!

 

[Bronco_Chuck]

i would go with 4.10's should be fine for 31's, and throw a tranny cooler in there so you can prolong the A4LD's life.

 

[88Bronco2EB]

well I did some searching in the tech library and I found the gear ratio chart its based on 1:1 ratio at 65mph (4th gear in a manual)

http://www.therangerstation.com/tech_library/gearandtirechart.html

It says that if you have OD the numbers on the chart are 15%-30% lower, so I crunched some numbers and if I run 31s with the 4.56 gears my RPMs would go up less then 250 RPMs, witch means that at 65mph I'm only at about 2500 RPMs

This sounds about right considering with my 215/75/15 (about 28") tires and 3.73 gears going 65MPH I'd be at about 2300 RPMs

I think I can sacrifice a few MPG for a little extra torque, what do you guys think.

oh and I already have a tranny cooler!

 

[holeshot]

I have 4.56's and an A4LD. With 33's, I am running about 2500 rpm at 65mph in OD.

 

[88_Eddie]

if your gonna be doin an 8.8/D35 swap, why bother puttin gears in your current axles?

 

[BlackBII]

if your gonna be doin an 8.8/D35 swap, why bother puttin gears in your current axles?

That's what I was thinkin' Maybe he is going to put the gears in his new axles.

Are you ever going to go to 33's? If so, I'd get 4.56's..

Buying a gear set and having a shop do it is rather expensive, I'd hate to see you get 4.10's and then just need lower gears later on when you get 33's.

4.10's can be found under BII's and Rangers in the junkyard, and the whole axles can be had for cheap

 

[trail B2]

I figure about 2400 RPMs and the OD is .74 if I remember right.Mine has 4.11 and 33s does a little over 2000 at 60 I think it is.I must really like my 4.11 cause half the time I wish they were higher the other half I wish they were lower.

 

[88Bronco2EB]

if your gonna be doin an 8.8/D35 swap, why bother puttin gears in your current axles?

lol, I,m putting new gears in the 8.8 and D35 because the guy Im getting them from has 3.27 in them, but he also has a lock right in the 8.8. Plus I'm getting a good deal on them. so I don't mind buying new gears.

and I will most likely want to get bigger rubber later on, doesn't everyone!! lol

I really don't mind the RPMs getting higher as long the motor doesn't get to hot.

 

[strvger]

my 4.56's go in this week and i'll be putting on 31" tires with them. i'm hoping to get a little more performance from them as well as a useful 5th gear, without a giving up too many mpg's.

 

[88Bronco2EB]

that's what my goal is. I just don't want to over rev the engine and cook it on long highway drives.

 

[4x4junkie]

Assuming you got the 2.9L, 4.56 is perfect for 31s. How long before the bigger rubber? You might even think about 4.88 gears.

 

[88Bronco2EB]

yes! I have the 2.9L. The new rubber want be for a long time seeing as, for right now, the 31's are my new rubber. lol

for right now I'm waiting until its warmer to do the lift and axle swap/ring and pinion swap(I'm putting the ring and pinion in the 8.8/D35 in case anyone is wondering)

so you recommend 4.56 gears for 31s cool. I think you're the first person to tell me that

thanks

 

[88Bronco2EB]

Ok guys, I did a ton of number crunching and found that 4.56 gears are perfect

I used a formula to determine your rpms after a tire change or gear change or both!

Its the formula TheRangerStation used to make there gear ratio chart http://www.therangerstation.com/tech_library/gearandtirechart.html

The formula is: MPH x Gear Ratio x 336 / Tire Size = RPM (The MPH are based on a 1:1 gear ratio, not your Over Drive Ratio)

and to figure out your Over Drive Ratio: Gear Ratio x Over Drive Gear Ratio

So... 65 x 4.56 x 336 / 31 = 3,212.5RPM or 3,213 RPM like the chart says! But since I have over drive I take 4.56 x 0.75 = 3.42 Then I take that and plug it into the formula, so... 65 x 3.42 x 336 / 31 = 2,409RPM

And I did this Formula with my stock tire size and gear ratio as well, and If you get the 4.56 gears with the 31" tires my rpms only go up a little over 100 at 65 in OD!!

This is awesome try it your self. I had a chart that listed all 1st-4th gear ratios for my transmission in case you wanted to know how I got the 0.75 OD gear ratio.

 

[mjonesjr]

Assuming you got the 2.9L, 4.56 is perfect for 31s. How long before the bigger rubber? You might even think about 4.88 gears.

Exactly.

I ran 31's and 4.56 gears in my Bronco II and loved it. I had plenty of low end power and it wasn't all that bad on the highway.

 

[88Bronco2EB]

Thanks a lot you guys.

I'm going with the 4.56s for sure. Now I cant wait to get everything and start building my Bronco up

I'll have to start a build thread in a month or so!!