Ford 78 Bronco gear questions

[MPM]

Hey guys,

I have a question. I am in a 78 Bronco on 37s. Right now it has 4.56 gears in them with lockers. A couple of weekends ago I was out with some friends doing some crawling and started loosing teeth in my front end ring and pinon.

I am considering going to a bigger gear and was wondering if anyone has had success installing a 5.13 or 5.39 in the ford 9" rear. I don't think going that big is a problem in the front end, but I have been warned that the gears might not fit in the rear end.

I just feel like my 4.56s aren't low enough for a good crawl ratio.

Any info is greatly appreciated!

 

[ChestonScout]

I know for a fact the 5.13s fit with no issues. I dont have any experience with the 5.39s in the 9"

 

[BCGPER]

Keep in mind the lower gear ratio you go, the weaker the pinion will get. If it's just your crawl ratio your concerned about, and you like the 4.56's otherwise, you may want to look into some transfer case changes.

 

[4554x4]

Doubler!

I did a doubler transfercase in my Blazer. Instead of just a 2 to 1 ratio, I can also choose 4 to 1. I also converted it to where I can select front dig also. Your Bronco should have either a 205 or a 203 transfercase. You would need one of each, and the kit. Off Road Design makes the kit, as well as some others.

I am currently running 4.10 gears, 38.5 tires and a weak 350. It hardly gets out of its own way in high gear, but in double low it is awesome!

I would repair the diff with 4.56 gears so it matches the rear, and build the doubler. You will have normal power and fuel milage for on the road, and awesome gearing for crawling.

 

[Coreshot]

yup, I have 5.13s in my BB 9" rear. No issues yet.

 

[broncomitch]

i got 5.13's in mine with no problems as of yet. i wanted to go 5.38's but herd there is not much difference between the two.

I'm running about the same set up as you

c6,np205,78 axles on 38's.

its not been on a trail yet but goofing around in a field with some dirt obsticals in twd and driving around the harbor hood. i think the 5.13 are good. the 205 is so high geared i went from 3.00's to 5.13's there was not a huge diffrence in low gearing.

dont get me wrong, it helped allot with speed,power,and what not.
but going from 4.10's to 5.13's wont make a HUGE difference for ya.

 

[iamsparticus]

tranfer case upgrade

i would replace the front diff and gear the transfer case to like 6.5 to1 so you still will have all the gas milage and normal driveing but have amazing crawl ratio, or do a doubler kit, either way what you really want is lower gearing on the transfer case side of things not axles, especially if your already taking teeth off the gears lower gearing will just make your gear teeth weaker, and if you don't change the transfer case gears the same strain will be put on the new weaker 5.13 gears, lower transfer case gears will take alot of strain off the axles and axle shafts