Currie axle

[Jakedog]

Which calculator are you guys using?

 

[KyddsPly]

Which calculator are you guys using?

http://www.grimmjeeper.com/gears.html




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[bax]

http://www.grimmjeeper.com/gears.html




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Thats a pretty good one.

 

[DirtDonk]

Thought I posted mine yesterday, but guess it didn't take.
I use the one from Yukon here: https://www.yukongear.com/calc_rpm.aspx

If you notice, there are different links to different types of calculators on their site. They have some that are basically giving the same answer, but coming from it at a different angle.
Some might just like the other formats better. I like 'em all, but tend to stay on the page I linked to most of the time.

Paul

 

[Jakedog]

I think my choices have narrowed down to the 4.30 or the 4.56. Not a huge change from rpm between the two, so I'm leaning more towards the 4.56. I think the 4.88 will be a little to low for the hwy for me.
If I cruise on the hwy between 60-70 with the 4.56 that should keep me in the 2600 to 3000 rpm range.

I'll let you guys know what I go with.

 

[DirtDonk]

If your tires are actually 35" tall, then yes that's the case.
Never hurts to measure to know for sure, so you have all the data for making your decision final.

See you at the Roundup!

Paul

 

[Jakedog]

If your tires are actually 35" tall, then yes that's the case.
Never hurts to measure to know for sure, so you have all the data for making your decision final.

See you at the Roundup!

Paul

I measured my tires at 33.5" tall. This might come down to a coin toss between the 4.30 & 4.56.
I have bfg AT tires and it seems bfg tires run on the short side. Definitely something to consider if I plan to run this same tire next go around.

 

[KyddsPly]

I’d say 4:56’s. A bit more fun for a small RPM climb.


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[Bukin 67]

I got a custom Currie 9" in '15 and have been very happy with it. 35 spline, 4.56. It's been bulletproof in Baja. I've got around 4000 racing miles on it.

 

[DirtDonk]

I measured my tires at 33.5" tall. I have bfg AT tires and it seems bfg tires run on the short side.

Probably 90% of the tires we can normally purchase do run short.
Don't know all the reason, but at least a big part of this is that the sizes listed by the companies are probably still the "mold size" and tires shrink down a fair amount when they cool after being made.
My BFG old-school Mud T/A's (circa '96) were 34" on the truck. The 35" General Mud Grabbers they replaced were barely 33.5" on the truck. The 255x85x16 Dunlop Mud Rovers (also old-school from approx. '99 maybe?) are just about in-between those other two.
So equivalent to a tall-ish, skinny 35.

Paul

 

[Jakedog]

Should I factor in the weight of the Bronco as well? My future plans are HD rear bumper with full size spare, cooler rack, and fuel can rack.
Front bumper will be the Bobcat 8274 winch bumper. I have an 8 pt family cage in it which is also fairly heavy.

I will not be running a hardtop at all. Especially since I sold it to another CB member.

Edit: now that I've been mulling it over and re-reading all the replies, and reading everything I can find on the internet, I think 4:56 would be a good choice. The weight factor has to play a part in this. I know there are much heavier Broncos than mine but it is definitely heavier than stock.

 

[DirtDonk]

Yes it should be at least a small part of the equation.
Different weights have no effect on engine rpm obviously, but a heavier truck is harder to get rolling and harder to push through the wind too, so a little more power available through the use of lower gears can be a benefit.
Does not sound like your weight will be excessive, but it's still worth keeping in the back of your mind.

Paul

 

[Jakedog]

DirtDonk,
Just for curiosity sake, If this were your rig you were re-gearing what would you go with?

 

[DirtDonk]

Well crap, I just knew you were going to ask that!
I'm right with you're previous decisions in fact. If I wanted just that little bit of extra pull off-road or when fully (over)loaded for a weekend trip, I'd go with the 4.56 and freeway rpm be damned.
If I was spending more time on the highway and it was a driver (maybe even a daily driver) and a lot of that was out on good ole I-5, I'd stick with 4.11's.
If I just wasn't sure, I'd compromise with the 4.30 and just decide to be happy everywhere.

But for my own case the answer is pretty straightforward because an overdrive transmission was always in the cards. Whether an NV3550 for the '71, or the 4R70W in the '68. With the 4R70 I actually do have 4.56 gears with tiny 30" tires, but can still roll along the highway comfortably at 2600 rpm. Very stout off-road, hard pulling from a standstill, but still somewhat freeway friendly.
With yours remaining a 1:1 top gear, you're more interested in the compromise.

So here's one take on it in your case. Basically saying the same things we've all said over the last 30+ posts. If you're going to travel up the highway occasionally and willing to not try to hit 75mph each time, stick with the 4.56 and be happy on the trail.
If you really do like to travel in fast company, that little bit lower rpm the 4.30 offers may be just the key to your sanity.
The 4.11 is out for now I think because you said you wanted it biased more to off-road than the street and did not have the whole setup done.

So with all that you've said so far, I'd go with the 4.56 and be done.
And if you ever decide to run a larger tire, or an overdrive transmission, you're set and never have to think about gearing again.

See? I can still do wishy-washy with the best of them!%)

Paul

 

[EricLar80]

Quick performance seems to have competitive pricing, and a lot of options:
https://www.quickperformance.com/

 

[EricLar80]

Also, so you are aware - the 9" is relatively easy to assemble. The bearings and gear setup is all contained within the 3rd member. You just need a competent shop to do that work, and you pretty much just assemble the rest of it if the axle perches are in the right spots.

Hoopers in Sun Valley could set you up with whatever assembly you need, and they are pretty affordable.

 

[68ford]

Another great priced option. 31 spline full float with disc brakes $975

http://9inchfloater.com/CompleteRrEnd/CmplteRrEnd_28_31.htm

 

[fordguy]

My Currie housing shipped yesterday

 

[bax]

I am currently running the currie housing. it's a nice piece. I don't think I will ever have troubles with it or a need to upgrade.

 

[Jakedog]

I finally made up my mind back in February and ordered a Currie 9". It showed up today and my boys helped me bolt it up.
I now need to get the brakes and the drive line hooked up.