Front and rear gear changes

[H20rider]

Currently: 302 with nv3550 and 4.11 open diff. With Dana 20 (30” tires). Mainly (almost exclusively) street use.
Pretty sure it is still 28 spline
Want to convert to 3.70 posi in rear. What front diff gear should I be looking at? 3.70 also?

I know I could just ignore the front and not go to FWD, but that seems a lazy choice with a big sacrifice.
Thoughts?

 

[jamesroney]

Currently: 302 with nv3550 and 4.11 open diff. With Dana 20 (30” tires). Mainly (almost exclusively) street use.
Pretty sure it is still 28 spline
Want to convert to 3.70 posi in rear. What front diff gear should I be looking at? 3.70 also?

I know I could just ignore the front and not go to FWD, but that seems a lazy choice with a big sacrifice.
Thoughts?

The nearest match for the Dana axle is 3.73. It was available in the Dana 44 in the Chevy, and in the Dana 30 in the Jeep. The Dana 44 will require a Carrier change.

I'm not here to tell you what you want. But the change from 4.09 to 3.73 is hardly worthwhile. Put a set of 32 inch tires on it, and it's basically the same effect.

A Bronco with 190HP, a 3550 and 4.11's on 30 inch tires is just about perfect. You call it a 2003 Jeep Wrangler Rubicon.

 

[bigmuddy]

I agree with James. 4.10 would also allow you to go to a larger tire down road if you wanted it. Don't fear the gear!

 

[Apogee]

Closest ratio to 3.70 for a standard rotation D44 would be 3.73 if I'm not mistaken, but that seems like a lot of effort/cost for a 9% gear ratio change...3.54 would be about a 14% difference. With the .78:1 OD transmission and Ø30" tires, I would think the 4.11's would work well. What RPM do you prefer to shift at? What about the current setup do you not like?

 

[Broncobowsher]

Thoughts? Leave it alone. Next time you need tires, go up a size.
Broncos have a lot of natural drag and like a little more gear.
You are looking at maybe 200 RPM drop at highway speeds? I don't see the value in that.

 

[cbunas]

Which rear end do you have? Dana or Ford 9"?

What is your low and cruising gear in your trans? With the current non oem trans you kind of need to start your calculations from the beginning but you need to know your trans gearing with the rest of your info. Call Yukon for advice once you get all your info.

You can also adjust based on your rpm at cruising speed and what you want it to be. It sounds like road driving and efficiency may be important based on your entire post. 2 of my Brocos came with 3.50s in the rear, not the optional 4.11s. The stock tires were about 29.5" and stock 3 speeds. The 3rd Bronc came with a 6cyl and the 4.11s in the rear although that one has new axles and coyote swap happening now.

The formula with all OEM engine, trans and tires if you want bigger tires (ie 33") is OEM Gear x New tie / OEM tire (3.50x33)/29.5 = 3.92 to go to 33in tires - pick the standard ratio above or below that number. 4.11 would be fine with 33s.

 

[H20rider]

Man, am I glad I came on and asked!!
This really all started with wanting a limited slip differential. The gearing change was a “Well, while I am at it….”
I have put gear idea to bed.
I hope this strand also helps some other beknighted soul.
Any reaction to the limited slip?
Thank you all.

 

[jeffncs]

Personally, I’d skip the LSD if you’re strictly cruising for ice cream. Off road or performance driving? Sure - change out the carrier. Otherwise, I’d just run it and be happy.

 

[Yeller]

installing a limited slip is easy and has minimal special tools needed. Me, I would install a true track and a set of 31 spline axles and call it done. If just street driving, you can even forgo the 31 spline axles. I dispise the "one wheel peel"

 

[Broncobowsher]

+1 on a helical gear limited slip design. True Trak has been around a long time, Torson is the original, heard good things about Torque Worm from my axle guy. Probably more out there. For what you describe, any will be good.
I avoid clutch based limited slips, worst of both worlds. Slips when you really need it to hook up, hooks up when you really need it to slip.

I would pull the 28 spline axles and inspect. Do you have excessive wear on the seal surface? Do the splines have excessive wear? Anything shy of perfect axles is the time to consider 31-spline as part of the upgrade. More of a service item with better parts.