Eaton HO72 Tech Thread

[06h3]

The old site had a ton of tech and info on the HO72.

I will just give a short recap on the axle.
-Axles were used from 1947 to 1972.
-The difference between the HO72 and HO52 is the factory load bolt.
-Axle shafts are 1.5in coarse 17 spline. Many argue whether if they are stronger or weaker then 14 bolt shafts.
-14 bolt axle shafts and the drop in (detroit, grizzly) locker fits in the HO72. There are some exceptions, on some older open carriers they are a tad narrower and do not let the 14 bolt locker unlock. Some have fixed this with washers between the carrier or machining a few thousandths off the side gear. I machined .008 off each side gear for a total of .016 and it now locks/unlocks like it should.
-some carriers are a few thousandths tight and the 14 bolt shaft wont fit. Bore it out a few thousandths to fit….it seems newer (closer to 1970 HO72s have larger IDs and 14 bolt shafts fit with ease
-14 bolt disc brake kits work
-Diff covers, I have found mine on ebay. Some guy makes a HD diff cover. Ruffstuff made a short run of them
-Some did come with factory 17 spline detroit lockers
-Factory gear ratios are 4.10, 4.57 and 5.14. Supposedly there is an elusive 5.86 and if I can get my damn hands on one I would.
-No gear sets are available from the aftermarket
-pinon bearings are expensive.
-Pinion shaft is BEEF at almost 2in in diameter with zero neckdown.
-Ring gear size is 10 1/8 (some conflicting info on this but its between 10 and 10.5)
-Yoke is 1350
-I havent weighed an Eaton HO72 but they are much easier and lighter to move around compared to a 14 bolt.
-Ground clearance is better when comparing unshaved 14 bolts to unshaved Eatons.
-WMS is 63 or 65in and determined by the hub
-2 types of pinion bearings, ball bearing and tapered roller bearing, the tapered roller is better.

I have seen many comments on the HO72 thread at the old place like
"I ran 44in tires and 400HP with no problem"
"I filled it with mud and the thing didnt care"

I had concerns with the axle handling highway speeds since the axle first came out in 1947...when speed limits were much less than today but I can report that I have logged 25k miles at freeway speeds between 70-80 all day long in 100* plus weather and in colder winter temps.

Carnage that I had....I havent had much carnage. I currently run 43s and used to run 40s. I had this bizarre twisted shaft that happened on 40s, this was bouncing around on the east coast in muddy rocks.

Then I had this shaft break on 43s in Moab. This was pure studity though, I have a 6500 lb rig, fully loaded probably near 7k lbs. Most of the weight was on that one tire in a hole much bigger then a 43. 3 tires were rotating and that one wasnt....POP. I wouldnt have been surprised if I popped a 300M shaft in there. To my surprise, the detroit held up.

As a whole I have enjoyed this axle, it is pretty stout....the detroit and R&P have been flawless.

I did just buy a spicer 1410 yoke for it when I redo my drivelines but I am on the fence from changing it. The 1410 yoke is a strap style with threaded holes for bolts and it appears to be some crappy cast. The 1350 from the factory seems forged....or they did a great job hiding the fact that it is cast.

Post up your tech on the HO72!

 

[ridered3]

Glad to see the Eaton tech thread over here. Had one in my old CJ7 and it was such a cool/neat axle. Swapped mine to disk breaks and welded the 3rd member.

Found a company in Nashville, TN area that still had bearings and races in stock for these old axles (as of 8 years ago anyway).

 

[ScottRS]

It is possible to use 14b wheel hubs to get 67" WMS width but outer wheel bearing screwaround will be necessary, either open up the hub to fit the Eaton bearing, or turn down the journal on the spindle to fit the 14b bearing. Inner wheel bearing to race fitup can be mix-n-match'd, but the outer bearing you'd need for that crossover doesn't exist (or at least didn't 20ish years ago when I last tried). Wheel bearing nuts are same thread as 14b and D60, can use any of the assorted wheel bearing nuts out there.

Using either the 14b or Eaton hub, it's possible (though a bit of a PITA) to shave down the snout to 4.25" and redrill the pattern to any of the popular 5.5" bolt circle patterns. Socket cap screws or some other small head fastener for the axle shafts will be necessary to clear the wheel bore if going that route.

Shaved ground clearance is comparable to that of a stock Ford 9", weight with discs on it is about 250lb, quite a bit more than a 9" but about as light as you'll get a rear 60 and much lighter than you're likely to get a 14b.

 

[YotaAtieToo]

Anyone know who built a crew cab first gen Toyota with ruffstuff ho72's f&r? I know the guy who bought it and was wondering who built it. I remember a blazer that never got finished. Maybe those were the axles?

I really love these axles, but have always been shy of stuff with low (no ) parts availability. Good to hear the one in the H3 has been lasting on the highway. I knew they were strong, but always wondered about longevity of bearings and whatnot.

It's too bad they weren't used for just a bit longer.

 

[06h3]

That is great to hear on hub matching. I have seen a lot of discussion on it but haven’t seen one actually done or if it’s even “possible” most said the bearing you need doesn’t exist and never mentioned the bearing journal or hub turndown.

parts availability has been an iffy topic. The only thing I can say I have personal experience with is the wheel bearings. I changed those out when I did mine. I ordered them in the AM and they were at the parts store that afternoon. I forgot which one, but the inner or outer wheel bearing is the same as the carrier bearing. From a carrier bearing and wheel bearing/seal standpoint I have had no issues getting parts. (This was 5 years ago though)

pinion bearings are a different story, I never had to order them. For shits and giggles I called around one day and I was told a warehouse in LA had some. They were expensive (like $300) but they had em....But who knows if that’s just the last one on the shelf, never to be made again type of scenario, or they can get more.

you cant get new R&P’s but they don’t break and come in offroad friendly ratios.

I have the utmost confidence in saying they can handle highway speeds all day long. I was nervous and felt like a test dummy for a while but it’s worked out

 

[TTMotorsports]

I had one that came stock in a 1964 K20 BUT it needed a few bearings and such to fix leaking pinion seal and such, so along with the D44 closed knuckle drum brake front end was given away to Dirt Every Day Fred and I have no idea what he did with it. We swapped axles for a 8 lug D44 and a 14 Bolt from an 80's Chevy truck and went with 4 wheel disc brakes. Works much better for street driving and servicability than the HO72 axle and drum closed knuckle D44 front end. Truck is far from original with a 6.0L 4l80E LS swap and a divorced dodge NP205 t-case, full autometer gauges etc. No help or input on them but I did own one and it was a cool axle with diff cover and drop out 3rd.

 

[TTMotorsports]

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One I just saw on Facebook Marketplace as well if someone is in Juneau, Wisconsin and wants one. Or wants it Shipped or dirt cheap since people are stupid and don't know that's an option when listing stuff on there for sale.

 

[AK_F250]

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One I just saw on Facebook Marketplace as well if someone is in Alaska and wants one. Or wants it Shipped or dirt cheap since people are stupid and don't know that's an option when listing stuff on there for sale.

Wrong Juneau

 

[TTMotorsports]

Oops my bad Juneau, Wisconsin

 

[arse_sidewards]

How would people rate the HO72 compared to the D80 and Sterling 10.25?

Did the HO52 ever come in semi-float or is the load bolt really the only difference?

 

[rockmup]

Found a company in Nashville, TN area that still had bearings and races in stock for these old axles (as of 8 years ago anyway).

Well don't share a link for the place in a thread about info.

 

[06h3]

How would people rate the HO72 compared to the D80 and Sterling 10.25?

Did the HO52 ever come in semi-float or is the load bolt really the only difference?

I would say the fair comparison is comparing a dana 70, 14 bolt, HO72 and Sterling 10.25/10.5

they all have similar sized ring gears where the Dana 80 is much larger then all the axles listed above.

if I was to put them in order I would say with 100% confidence, Sterling, Dana 70 and then idk where to put the 14 bolt and HO72.

I think they are all good axles and will live a healthy life under most 4x4s running 40s-42s, under extreme abuse I have seen Sterlings and 70s let go. Fully warranted failure with the abuse seen and I didn’t blame the axle. The 14 bolt and HO72 have the 3rd bearing support to prevent deflection and the HO72 has a load bolt to prevent it even more.

If I was building a rig and wanted lower then 5.38s I’d go with the Dana 70. That’s the main benefit, you can go down to 7.17s. If I’m stopping at 5.13-5.38 I’d go 14 bolt or eaton.

HO52 is full float. Only difference is load bolt

 

[ridered3]

Well don't share a link for the place in a thread about info.

Good point! I didn't share the company name and contact info since I wasn't sure if they still had these items in stock. But here's the company info, but your mileage may vary since my info is from 8 years ago.

ALLIED BEARINGS AND SUPPLY

SURE WE CAN DO THAT!!!!

www.alliedbearingsnashville.com

 

[arse_sidewards]

I should have clarified, entire axle comparison not just ring and pinion set.

Let's ignore ground clearance for a minute...

Of course the D80 has a massive ring gear but the Dodges variants have nothing special in terms of tubes/housing and spindles. Dana housings are known for being kinda floppy (leading to more gear failure) relative to the others so I dunno how that affects things. Of course the 450/4500 sided truck D80 housings may be better (I've never seen a comparison, they certainly have much better tubes) but they have odd hubs you can't adapt to 8x6.5/170 easily because of the shaft bolt pattern diameter. D80 shaft is a standard 35spl shaft unless you have one of the larger truck 37spl ones which don't fit through a 8x6.5 or 8x170 center bore.

I'm not sure how to compare the carriers since barring a massive size difference a shitty LS carrier is going to be weaker than an open carrier which is going be weaker than a two-piece carrier in any application and the HO72/14B typically come with a two piece carrier.

I have no idea what the carrier bearing spread on these axles is but that does affect carrier strength a fair amount.

TL;DR the D80 in the Dodge truck form that we'll usually use it in has a lot of shit counting against it and I'm wondering if in practice it adds up to being a wash compared to the HO72 which has a lot of stuff going for it.

 

[YotaAtieToo]

Hard to not put sterling at the top when they are still building them.

I think everyone knows what the 14b is capable of.

D70 is all good except for the small pinion spline diameter, it's not weak, but I don't think it quite belongs with the others. Although if you want a cheap axle with a ridiculous big housing, an old D70 HD (4x500 wall tubes) is hard to beat. Probably would be great for something where wieght carrying is priority over ring gear strength

D80, like mentioned, wins over all ring gear size. They seem to hold up well in the diesel bros. Does seem wierd they "only" use 35 spline in the dodge application.

Ho72 is hard to compare. At this point, it could have been under a truck being used for 60-70+ years, and could be stressed close to failure. Could be sitting, and ready to be beat on. Hard to say.

 

[ScottRS]

That is great to hear on hub matching. I have seen a lot of discussion on it but haven’t seen one actually done or if it’s even “possible” most said the bearing you need doesn’t exist and never mentioned the bearing journal or hub turndown.

Opening up the hub ID is a bit of a pain because of how GM did the snap ring outer wheel bearing seat deal, but not too bad for a machinist with tooling appropriate. I took the spindle OD down on mine when I did it, worked fine for as long as I used it, IIRC, it was only maybe 1/16-1/8" diameter difference from the 14b to the Eaton outer wheel bearing. I did horrible things with 44" tires to that axle and couldn't hurt it, but I also only had four cylinders of naturally aspirated fury at the time. Lots of crawler gearing though.

 

[06h3]

Speaking of the 1.625 small pinion diameter on the 60s/70s I’m shocked someone hasn’t made a bigger pinon and yoke available in the aftermarket

 

[YotaAtieToo]

Speaking of the 1.625 small pinion diameter on the 60s/70s I’m shocked someone hasn’t made a bigger pinon and yoke available in the aftermarket

70s are a pain in the ass, there are way to many different versions of everything.

Plus no 5.38s.

It's just so much easier to grab a 14b or sterling.

Or an HO72

 

[AlxJ64]

Glad to see this over here now too. I'll dig up some more of my tech. I have a pile of these axles still and will be willing to sell a few, and some thirds if need be.

One of the big things about these axles that gives them the strength and durability is the original use of hemispherical style cone bearings, ie the Hyatt stuff that is machined in an orbital. This allows deformation of various surfaces under high load but doesn't alter the surface area of the bearing in contact with the race, ie, no single pointing or shoulder loading a square edge modern style taper bearing because the orbital match of the bearing makes up for the changes. There is information from GM regarding factory chromoly shaft materials in various different years. There is an elusive 70" WMS axle as well found under some P30 Vans but only in two or 3 years of production. The same P30 series vans are where the mythical 5.89 is to be found as well.

Something else not mentioned is the ability to flip the third 4 different ways in the housing as the cover and third are symmetrical front to back and upside down as well. This allowed the use in all kinds of other interesting equipment and even the h110s (GM 2.5 ton) of WW2 and Korea use this concept as the front and rear shafts for the 4x4 application had wrong hand rotation. Rear engine applications are managable with this housing flip also.

I've run one of these with the gears so pitted that you'd swear someone was arc -gouging the teeth of the ring, and it never let me down.

For the weight to strength ratio, and clearance gains from shaving. Disc brake options, etc... I'd put this as one of the best built axles ever. The quality of the machine and casting work in most of the ones I've opened is far far superior to anything Dana I've been into.

 

[Grendel]

I like this thread, too.

Alex is building a set for my PW.

 

[YotaAtieToo]

So funny, my buddy was asking me about trading for the rig that I previously mentioned with them f&r in ruff stuff housings.

He said the guy who has it now thinks it needs lower axle gears and thinks it has 3.xx's. Google shows some people saying there was a 3.73 option, but it was rare. I'd find it hard to believe someone would go through all the trouble of building a pair of these with ruff stuff housings and only put 3.73s in it. But lets say it has 4.10s, what's the best route for rehearing to 5.xx? Find a FB group and offer a trade? I think the 2wd C20 guys are probably looking for the higher ratios.

 

[06h3]

So funny, my buddy was asking me about trading for the rig that I previously mentioned with them f&r in ruff stuff housings.

He said the guy who has it now thinks it needs lower axle gears and thinks it has 3.xx's. Google shows some people saying there was a 3.73 option, but it was rare. I'd find it hard to believe someone would go through all the trouble of building a pair of these with ruff stuff housings and only put 3.73s in it. But lets say it has 4.10s, what's the best route for rehearing to 5.xx? Find a FB group and offer a trade? I think the 2wd C20 guys are probably looking for the higher ratios.

I’d say trading with restoration guys or finding a junkyard with these axles. I surprisingly still find these axles in junkyards from time to time

 

[AlxJ64]

So funny, my buddy was asking me about trading for the rig that I previously mentioned with them f&r in ruff stuff housings.

He said the guy who has it now thinks it needs lower axle gears and thinks it has 3.xx's. Google shows some people saying there was a 3.73 option, but it was rare. I'd find it hard to believe someone would go through all the trouble of building a pair of these with ruff stuff housings and only put 3.73s in it. But lets say it has 4.10s, what's the best route for rehearing to 5.xx? Find a FB group and offer a trade? I think the 2wd C20 guys are probably looking for the higher ratios.

Where are ya located? If they are 4.10s or 3.73s even I will trade you a for two 5.14 thirds that I have here on hand. Located NW of Richmond, near Charlottesville.

 

[Grendel]

Where are ya located? If they are 4.10s or 3.73s even I will trade you a for two 5.14 thirds that I have here on hand. Located NW of Richmond, near Charlottesville.

Aren't those 5.14's for me?

 

[YotaAtieToo]

Where are ya located? If they are 4.10s or 3.73s even I will trade you a for two 5.14 thirds that I have here on hand. Located NW of Richmond, near Charlottesville.

They're in norcal, not sure what became of all that.

 

[gtxracer2]

Has anyone had a housing made? I knew Blazerboy built one from a RuffStuff housing back on the old board. I have one designed in CAD but don't really want to build two housings from scratch, I'd rather adapt an existing housing. I was thinking Branik might do it. This is a long term project for me, I want to retain these third members but push my WMS to about 70" front and rear. I also thought about cutting and sleeving my existing housings, which may be the best bet.

Glad to see this thread here

 

[SLOWPOKE693]

Has anyone had a housing made? I knew Blazerboy built one from a RuffStuff housing back on the old board. I have one designed in CAD but don't really want to build two housings from scratch, I'd rather adapt an existing housing. I was thinking Branik might do it. This is a long term project for me, I want to retain these third members but push my WMS to about 70" front and rear. I also thought about cutting and sleeving my existing housings, which may be the best bet.

Glad to see this thread here

How hard would it be to design a new faceplate that could be welded into an existing manufacturers fabricated housing so it accepts the Eaton chuck? Instead of building two from scratch just send the mfg a cad file of the faceplate and have them cut and build with that instead of the standard 9"/10" plate. In my head this seems easy...

 

[gtxracer2]

How hard would it be to design a new faceplate that could be welded into an existing manufacturers fabricated housing so it accepts the Eaton chuck? Instead of building two from scratch just send the mfg a cad file of the faceplate and have them cut and build with that instead of the standard 9"/10" plate. In my head this seems easy...

Yeah, we can design a faceplate, that's easy. The face of the third member to the axis of the axles is the part that's a mystery. I'd have to measure and draw it up in CAD then send off to the housing fabricator to compare the distance to their existing housing measurement. I can design whatever we want, that's the easy part, but making an affordable housing is the hard part.

 

[Boclatt]

I know a few years ago I contacted diamond axle, and they were willing to make one. He said he would need the face to the axle axis. I would assume he may be able to modify the Tundra 10.5 housing?

 

[06h3]

I’d be interested in a housing. I’d love to go from 65 WMS to 69-70