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Axle selection

BruiserOutdoors

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Aug 22, 2013
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236
I've currently got a set of 1977 stock axles with 4.56 gears and lockers. I have not run them yet, as the bronco was sitting but I anticipate they will function fine.

I'm sticking in a 408w with roughly 425HP and 450+ TQ with a 4r70w/dana 20 combo and an end goal of 37s.

I anticipate some axle breakage but would like to avoid headaches on the trail.

This bronco will see mostly snow and sand, with some light trails. No major rock crawling (maybe moab?). Similar wheeling to NVRSTK.


What axles would you recommend? I need to be mindful of costs. Can I get away with CTM ujoints and chromoly axles in the stock dana 44 housing and big bearing 9"?

Whats most cost effective? My fab skills do not allow of welding on wedges so looking for something as bolt on as possible.

Thanks in advance for your advice!
 
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bigmuddy

Bronco Guru
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Dec 28, 2004
Messages
6,447
From what I have seen on the net, if your driving like NVRSTUK you will need to step up to customer dana 60's front and rear:)

Really though I would think you can get away with upgrading the axles and be ok with only occasional rocks thrown in with snow and sand.
 

DirtDonk

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Nov 3, 2003
Messages
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Well, even a stock engine will break rear 28-spline axles with a locker. So go light on the right foot if you plan to wheel that stock rear. Too bad when they changed the gears and differential they didn't upgrade the shafts too.
Or are they upgraded? Most manufacturers no longer offer 28 spline lockers, so if yours was done recently, I'm guessing the axle shafts are upgraded to at least 31-spline?
In which case the housing is stock, but which is usually not the problem anyway.
But lockers and 37's behind 450lbft are still very breakable if you try.

Fronts? Same story sort of. If you go in a straight line then the weakest link is the 4.56 pinion gear. If you put the power to the ground with the wheels turned, even the CTM joints and stronger axles can let go quickly.
That is, if the Dana 20 does not let go first of course.

I'm not sayin' that you're automatically going to break stuff. Just that it's going to be a lot easier than before so it's going to be entirely up to you and your self control.
Especially once you jump to the 37" tire part of the equation. In that case I'd say you don't have enough gear at only 4.56. Because of that, the Dana 20, the driveshafts, and whatever transmission you're using are put under a lot of stress.
What tire size will you be running initially?

paul
 
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BruiserOutdoors

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Aug 22, 2013
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Well, even a stock engine will break rear 28-spline axles with a locker. So go light on the right foot if you plan to wheel that stock rear. Too bad when they changed the gears and differential they didn't upgrade the shafts too.
Or are they upgraded? Most manufacturers no longer offer 28 spline lockers, so if yours was done recently, I'm guessing the axle shafts are upgraded to at least 31-spline?
In which case the housing is stock, but which is usually not the problem anyway.
But lockers and 37's behind 450lbft are still very breakable if you try.

Fronts? Same story sort of. If you go in a straight line then the weakest link is the 4.56 pinion gear. If you put the power to the ground with the wheels turned, even the CTM joints and stronger axles can let go quickly.
That is, if the Dana 20 does not let go first of course.

I'm not sayin' that you're automatically going to break stuff. Just that it's going to be a lot easier than before so it's going to be entirely up to you and your self control.
Especially once you jump to the 37" tire part of the equation. In that case I'd say you don't have enough gear at only 4.56. Because of that, the Dana 20, the driveshafts, and whatever transmission you're using are put under a lot of stress.
What tire size will you be running initially?

paul

I know the dana 20 is a weak link but its what the budget allowed for right now. I was initially going to start with 35s, Then 37s but im leaning towards 37s to begin with. My plan for the longest time was 35s, because of the current axle ratios.

The bronco was "built" in the 80-90s, meaning both that it had good solid parts with high horsepower (built 351w with Keith black pistons, previous owner and others locally claim that it would "pull the front tires on pavement", and to date the build. So i would assume they are at least 31 spline axles.

One of my concerns is, I dont want to invest in stock bronco axles if I will continue to break parts even with upgraded axles and joints. I can use these axles in another rig, if it makes more sense going that route.
 

sprdv1

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Mar 8, 2007
Messages
79,319
37s here w/302 explorer.. RCVs up front.. I just try not to get to skinny pedal happy lol

Dana 44 and 9"
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,702
worry about the Dana 20 output shaft too. you will want to control axle wrap too. might be better to sell what you have and start over to recoup some costs. You need to think about axle tube thickness. 37" tires 400 pounds torque and proper gearing and then some form of compound gearing you need good stuff. moderate trails you not going to break it but the combo will take you to places where if you break it your in trouble. I have been watching what the jeep guys in the 4 doors have been doing. they throw everything out and start over making a fortune for Currie. tire sizes have gotten ridicules and common place but cant run them with stock stuff.
 

snipes243

Bronco Guru
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Oct 12, 2006
Messages
1,241
Loc.
Huntersville, NC
SO I might be the crazy outliner, But my 393w runs about the same numbers. I'm running "stock axles" they are built the front is 4.88 arb with RCV's and the rear is a 35 spline unit with a shaved and trussed housing. I'm in the south so we are constantly bumming up obstacles and playing on the rev limiter. Now hubs that's a different story the warn 30 spline units with out the 300m inserts have spiral retaining clip that like to deform. Which causes the hub to disengage.

Its possible but the dana 20 would ultimately be your weak point.
 
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BruiserOutdoors

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Aug 22, 2013
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Well I can ditch the d20 without too much heart ache even though I have one clean, rebuilt and repainted, I can use it in a different rig.

So then what are my best bang for the buck Trasnfer Case options. Np205 seems like an OK option but rather not have the extra weight and mounting issues. Will an ATLAS limit my wheel speed? Was hoping for higher wheel speed for sand and snow. Altas not really in the current budget!
 

sprdv1

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Well I can ditch the d20 without too much heart ache even though I have one clean, rebuilt and repainted, I can use it in a different rig.

So then what are my best bang for the buck Trasnfer Case options. Np205 seems like an OK option but rather not have the extra weight and mounting issues. Will an ATLAS limit my wheel speed? Was hoping for higher wheel speed for sand and snow. Altas not really in the current budget!

just save up for that atlas :) lol

I have the same dilemma though, spending that $ on the atlas LOL

KNOCK ON WOOD

D20 here, stock radius arms, 37s, RCVs in front, D44, Ford 9, and still going strong.. All about that skinny pedal really
 

Broncobowsher

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Total hack
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Jun 4, 2002
Messages
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With the power and tire size, and conditions where you can actually use that power, 35 spline for the back. Being a '77 you already have a big banjo housing or else I would suggest upgrading the housing as well.

RCVs will let you put power down while turning.
 

ntsqd

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Jan 30, 2005
Messages
2,863
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Upper SoKA
I'd say that the 300M D20 output shaft is the bare minimum and that you really should be eating Cup of Noodles (student diet) so that you can keep putting pennies in the Atlas Fund. They have several different low range ratio options, don't have to buy the 4.3:1. I bought a 3:1 and I think there may be at least one taller low range ratio offered.

At some point in the past NVRSTK had about the combo that you're building. Might look to see what he was running then that worked and lived.

The weak points that I see:
Axle spline size, F/R (31's are bare min, 35's would be better)
Front turning joint size/strength (CTM's or RCV's are only going to get you so far, maybe that's enough and maybe not)
Flanged rear axle shafts (eventually likely to need to go floater)

A friend with a JK is making 37's work with D44's without excessive parts breakage, but he's only got (as he calls it) "that mini van V6" for power. Search for the mag feature on the "Yeticon" if you think he doesn't wheel it hard.
 

LSharpNM

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Mar 9, 2020
Messages
164
So for the people saying CTMs (or and bushing-style aftermarket chromoly joint for that matter) aren't enough, have any of you seen a 760X-size version fail? I haven't; it is always the shafts that let go first in my experience. RCVs are good axles, but I think they are over-hyped and they do break contrary to how they are advertised. I don't think RCVs are any stronger than a set of 300M shafts with CTM (or equivalent) U-joints.

To answer the OP, anything can break if you abuse it badly enough, and just because you have 400+HP doesn't mean you have to use it. You need to take into account your driving style and what you expect out of the rig. If you want to play rock bouncer with 37" tires and 400+HP, nothing you do will make those axles live. On the flip-side, If you are a fairly conservative driver who isn't ashamed to pull cable instead driving with the "make it, or break it" mentality, you can get by on a lot less.

At a minimum, I would upgrade the rear to 31 spline and upgrade the front to some 4340 axles with 5-760X joints and full circle clips. This would cost well under $1000 (not counting gears and lockers) but should hold up to reasonable usage. You will just have to be cognizant of the fact that you are going to break something if you get throttle happy and start trying to bounce through obstacles.

If you have the coin and want the best guarantee against breakage, I would go 35 spline axles, an aftermarket third member, and seriously consider a "big pinion" (35 spline) gear set in the rear.

For the front, I would do a Jana K4 conversion (installs the stronger 8.9" JK Dana 44 ring and pinion in a low pinion Dana 44 housing), and run 300M axle shafts with 30 spline outers with drive slugs (RCV or traditional style with CTMs/equivalent U-joints).

Also, I would reconsider your gear ratio selection regardless of what you do. Deeper axle gears will take stress off your transfer case and driveshafts, and I think 4.56s are too high with 37" tires, even if you are planning on doing lots of highway driving. Personally, I would run 5.38s If you are planning on wheeling it hard, 5.13s as a good all around gear, and 4.88s only if you are planning on doing a lot of interstate driving.
 
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BruiserOutdoors

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Aug 22, 2013
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After more consideration, I will stick to 35s for now and upgrade along the way. I am contemplating an Atlas 2 now. So selling some parts that were unnecessary (beadlocks) to help fund the altas. Good move? Or could I snake by with an HD output shaft on the Dana 20?

I thought about going np205 but didn't love the mounting issues and clearance issues.
 

fishinman78

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Sr. Member
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Apr 28, 2017
Messages
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I have a NP205 in mine after a broken Dana 20. I couldn't justify an Atlas. I think you are going to find the Atlas and NP205 are close in size. If you get the right cross member mounting isn't bad. Gearing is better in the Atlas but I don't do any rock crawling so that wasn't a problem for me.

I paid $750.00 for my fully rebuilt twin sticked NP205
 
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BruiserOutdoors

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Aug 22, 2013
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I have a NP205 in mine after a broken Dana 20. I couldn't justify an Atlas. I think you are going to find the Atlas and NP205 are close in size. If you get the right cross member mounting isn't bad. Gearing is better in the Atlas but I don't do any rock crawling so that wasn't a problem for me.

I paid $750.00 for my fully rebuilt twin sticked NP205

If I got an atlas, it would be a 3.0 or 3.8. I dont want to give up wheel speed.

What cross member are you using? Probably going to be a little different since you're using the 6r vs 4r.

Did you find it "used" for $750 or thats what the total cost of everything came out to be? What year/model np205 is it and would everybody recommend? Cable shifted?
 
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BruiserOutdoors

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Aug 22, 2013
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A little update. I got the bug to go to a 6r80 after attending the northwest bronco roundup. So I sold my 4r70w and d20 setup and bought a 6r80.

I also ordered an atlas 3.0. Which will be a 19 week wait!



But my question still remains, in the long run, what axles make the most sense for my application?

408w stroker
6r80w
Atlas 3.0
Duff long arms
37s


I can use my current axles in another rig, and invest in better axles, but don't know where to start. I would like to stick with duff long arms and rear leafs, which likely limits my choices to a d44 and 9"?

Full width vs narrowed d44/9" vs factory EB d44/9" ? Are those my options? Best bang for your buck?
 

nvrstuk

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Just a Bronco driver for over 50 yrs!
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Jul 31, 2001
Messages
6,355
I don't abuse my rig but my rig is used-a LOT. Anybody that uses their Bronco will have stock parts fail- every part, not just a D30 frt. :)

I have some completely different outlooks on a few posts (like ujoint strength) here but that's ok. I've run 7 different tranny's, 2 different doublers, 3 different doubler combo's, and 3 different t-cases (not counting 4 grendaded D20's). Some good combo's, fun ones and now this one.


I put off installing my D60 for almost 18 yrs and drove with EXTREME care with CTM's, and excellent aftermarket axles. Trying to never back up with the wheels turned- always worried about frt end carnage since guys were always blowing 760 joints- myself included, even with excellent quality alloy axles. Ujoints can not take the torque that RCV's can.

I spent some time to debunk several myths about D60's & NP205's. You'll see that it weighs a little more than a D44 when narrowed and different brakes are installed but is in a totally different league for durability, confidence and lower cost than a D44 (when trying to build a strong 44).

Do not spend all that money on building a D44. You will see on my build thread (and probably many others) the # of guys that built 44's years ago and kick themselves for not saving money and putting in a D60 from the start. Parts on built 44"s still break. You can never make it as strong as a stock D60. Build the 60 with a few inexpensive upgrades and you will be money ahead and dependability ahead and saving vacations from disappointment from broken parts.

RCV's are MUCH stronger than CTM's with excellent alloy axles. If you have a chance, do some research and see how much strength you lose when the ujoint is "turned". I used to post up a chart showing the strength that joints lose when turned. The chart totally convinces ya. Some say that a CTM and aftermarket axles are as strong as an RCV but they are not even close.

Installing the D60 when doing a 6r is an excellent time to do it because you will have clearance issues with the rear corner of the 6r case with the 1350 dbl carden & have clearance issues with the shift linkage- all avoided if you narrow the 60 and align it in under frt end properly.

I just wrote up a pretty comprehensive 6r build Tech Article that Jon (webmaster) is going to put on the site. It might help, 35+ pics.

The 6r should eliminate your doubler needs for wheel speed in snow/sand because of it's low first gear. I went Atlas 3.0 & with my stroker and it works great.

The 205 is another good option since you aren't doing rocks (I love rocks) but with the 4.17:1 first gear and the 205 you have GREAT ratios for trails, sand and snow. It is NOT that heavy and it's easy to mount.

In my build thread you will notice I have weights of D60's, 205's, the somewhat stronger '77 rear housing compared to much stronger aftermarket HD housings etc. After you bend a couple '77 housings or pickup housings you'll also convert to either aftermarket 9" housings or a 14 bolt.

Best of luck, you'll love the 6r. I bounced around a bit on this post. :)
 

Yeller

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Mar 27, 2012
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Long story but I think worth it.

I'm a 60 fan as well, the last 44 I built 20 years ago had every hizoot, cryoed “indestructible” part made at the time, including some prototype 4340 axles from a popular supplier. Went for my typical Sunday trail ride and 10 minutes in broke all 4 axles, ring and pinion and locker. Only thing not broken we're a set of CTM joints from the very 1st run of them. 3rd time in 6 weeks that I completely destroyed the front end. Came home and assembled a stock 60 I picked up from a military truck, put 35 spline outer shafts on it and ran it. Couple of years after that shaved that axle and cut/turned the c's for proper caster and pinion angle. Reassembled with the same parts except a new set of spicer ujoints. 10 years later changed to 4340 inner shafts, literally wore the originals out, could see daylight around the ujoint caps. Change the inner shafts and ujoints for a second time. Still running, and they have been abused and haven't touched it in 10 years. The cover has only been off twice, once for the shave and once to check it over when I did the inner axles. I was into my 44 after every trip even if nothing was obviously broken.

Doing more than streets and gentle fire roads with 37's don't spend a penny on a 44. Just because your buddy keeps his together don't assume you will. It costs zero dollars more to build a 60 than a 44 and one of them will be fantastic for the life of the vehicle.

PS: I'm still running the pre public release 4340 Yukon outer shafts that I put in in 2001. In those days they all new me by name when I called looking for better front axle parts. I could have paid cash for a new dually pick up with all the money I threw at a 44 over and over, it was insanity at it's finest, I was ready for a new hobby but loved it and still do.
 
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BruiserOutdoors

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Aug 22, 2013
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I figured as much, rather invest in the right axle once and avoid breakage.


What vehicle (model/years) would you source a d60 from?
 

nvrstuk

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Just a Bronco driver for over 50 yrs!
Joined
Jul 31, 2001
Messages
6,355
How close to stock WMS are you hoping for?

I think there are a couple choices out there that make them easier to narrow.
 
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