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Eaton HO72 Tech Thread

Bearings are going to last forever if you continue to keep good clean oil in them. Debris and water are the real killers almost always.

As for bench testing a detroit, I was able to bench test the one in my front steering third by holding the third in a little setup stand I have, bolted to my work bench, and then used some bolts through a shaft end (that was also supported with a V block on the bench to keep it straight and from deflecting) and it took a hard "yank" with a long pry bar to get it to "pop" and then once in motion it would ratchet but the initial breaking force was quite a bit. Once installed in the front axle, the tires seemingly did it much more easily given the inertia I could give one with a quick spin.
 
AlxJ64 said:
Bearings are going to last forever if you continue to keep good clean oil in them. Debris and water are the real killers almost always.

As for bench testing a detroit, I was able to bench test the one in my front steering third by holding the third in a little setup stand I have, bolted to my work bench, and then used some bolts through a shaft end (that was also supported with a V block on the bench to keep it straight and from deflecting) and it took a hard "yank" with a long pry bar to get it to "pop" and then once in motion it would ratchet but the initial breaking force was quite a bit. Once installed in the front axle, the tires seemingly did it much more easily given the inertia I could give one with a quick spin.
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I’m gonna give that bearing a run for its money and see how it does. Hell, it’s been in there for 6 plus years just fine.

I did notice the shop that set it up last didn’t have much carrier bearing preload on it. It was like they cranked the spanners until it met the slightest resistance then stopped. I definitely gave it a good shot with a hammer and punch to increase carrier bearing preload. Maybe I shouldn’t have since they are so old.

I got the 3rd in yesterday. Just gotta install shafts and the cover. Since the cover is still off I can back off the carrier bearing preload if necessary

Progress has been mind numbing slow….my wedding is Saturday so that’s been taking all my time but the hummer is my ride to my wedding (for momento sake) so it’s going whether it’s working like a spool or correctly.
 
06h3 said:
I’m gonna give that bearing a run for its money and see how it does. Hell, it’s been in there for 6 plus years just fine.

I did notice the shop that set it up last didn’t have much carrier bearing preload on it. It was like they cranked the spanners until it met the slightest resistance then stopped. I definitely gave it a good shot with a hammer and punch to increase carrier bearing preload. Maybe I shouldn’t have since they are so old.

I got the 3rd in yesterday. Just gotta install shafts and the cover. Since the cover is still off I can back off the carrier bearing preload if necessary

Progress has been mind numbing slow….my wedding is Saturday so that’s been taking all my time but the hummer is my ride to my wedding (for momento sake) so it’s going whether it’s working like a spool or correctly.
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The spanners on a Toyota 3rd get torqued regularly 100 to 150 ft lbs. Used 3rds get torqued to 100. New 3rds get torqued to 150. You could crank the fuck out of them and not worry about anything.
 
Test drove the H3… .003-.004 on each side is not enough. It’s almost enough. It does unlock but it’s bangin and clankin! I think there’s just enough for it to disengage but I think there’s teeth interference. Hopefully it didn’t fuck up the locker.
 
06h3 said:
I called up hoopers and asked him what he thought. He said they usually setup HO72s at .010-.015. I was at .020 but he said make sure the pinion isn’t moving when you rock it back and forth. Normally on new diffs the pinion is tight enough to not have any pinion movement and you can just rock the ring gear back and forth. On these older HO72s he said you may be picking up another .005 if your not holding the pinion down tight. Admittedly, I didn’t do that and it’s apart now. So who knows….I’ll set it back up to .011ish while holding the pinion.

How does one “bench test” a Detroit locker? I wanna bench test mine before slapping it all back together.

Here are some pics of my bearings/races.
1A4BCC01-E59C-4C1E-B0DF-3556562DBA21.jpeg
EB61F54A-9D2D-4454-B4B7-DAC7FA78DFAE.jpeg
E8F29FB8-1911-4B46-A220-746B984097F4.jpeg




First pic is the worst. You can feel the ridges in the roller. That’s the only roller like that between both bearings.

2nd pic is light pitting. Maybe 3-4 are light that between both bearings.

3rd pic is some small imperfections in the race.

This diff didn’t make noise when it was pulled. It’s been in for 6 years and about 30k miles. It’s been up to 90 mph. It has spent many 8-12 hour days at 70-80 mph in 100+ degree heat.

It’s been under a 7k lb rig on 40-43s dragging dead U4 cars, heavy rigs, light rigs, etc. the diff has seen some abuse.

The only reason it was pulled was to test 14 bolt shafts/locker and it’s the first time I pulled the 3rd since install in 2016.

So, run it? Find new tapered roller bearings from orielly? Or try and pull a better condition bearing off another one of my HO72s and put it on this one?
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Are they pitted and ridged 6 years ago?

Bearing preload will be lost when bearings start to put from what I’ve seen.

I’ll replace them.
 
06h3 said:
Test drove the H3… .003-.004 on each side is not enough. It’s almost enough. It does unlock but it’s bangin and clankin! I think there’s just enough for it to disengage but I think there’s teeth interference. Hopefully it didn’t fuck up the locker.
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I’d imagine a slightly bent housing can cause a ‘tight’ locker problems. I’d like to try rule that out before get carried away with re-machining anything.
 
My 17 spline Detroit locker in it before worked perfectly so I can’t imagine it being a housing issue.
 
Got the 3rd tore back down and disassembled. So .04 per side isn’t enough. It was enough to technically unlock but it was BANGING every time it unlocked. Like it barely had enough to unlock. Wish I had a video of the noise.

So gtxracer2 said he did .065 per side but his unlocks hard. I know I should take an extra .025 off to get that that .065 like gtx but I’m fearful his locking/unlocking hard is the same thing I had. So maybe I go with .13 like AlxJ64 did and move on.

Lastly. I want to make sure that the machinist is machining the right side. I told him to machine the first pic…the portion that sits against the inside face of the carrier.


C1F5533D-CC5D-4BE0-89B0-339C925D1252.jpeg


I’m fearful he machined this portion that faces away from the carrier (faces the other side gear on the other side)

BB5A7F76-B0DE-4527-BBF7-3D7D4A961252.jpeg


So does it matter what side he machines?
 
I machined the end clearance on mine, the end that faces the other side gear, that way it doesn't change the surface finish. The issue I had was that the ends of the gears just ran into each other when trying to ride over the ratchet teeth. Mine is in the front and the few times I've had it engaged it runs around and clicks the way an Aussie locker sounds in a Dana 30.

Finally found some of my old photos of the process.

Carrier gap when locker was installed.
0602181336a.jpg


0602181702.jpg


Meat off the end to close the gap, but bench testing it wasn't enough room still so I took some more off each side and it works fine.

0602181702a.jpg


0602181703.jpg
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IMG_20180603_184536_791.jpg
 
I got the side gears back with another .004 off on each side. So now I’m at .008 per each side and .016 total.

I’m gonna let the RTV dry overnight and see if it works tomorrow! I’m hoping this is it
 
Ok, she works!!! No more noises and it works like it did with the 17 spline Detroit! So now the real testing begins, are 17 spline shafts stronger or weaker than 14 bolt 30 spline shafts?

Diameter is the same…but now we wait and see

.008 per side gear did the trick for a total of .016 machined off
 
06h3 said:
Ok, she works!!! No more noises and it works like it did with the 17 spline Detroit! So now the real testing begins, are 17 spline shafts stronger or weaker than 14 bolt 30 spline shafts?

Diameter is the same…but now we wait and see

.008 per side gear did the trick for a total of .016 machined off
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Stellar that it works!

0.016" or 0.160"? Wheres that zero go?

The jury is still out on the shaft strengh comparison. The 30 spline roots are by mechanical design comparison, in fact "stronger" due to pressure angles and spline contact area, but when it comes down to metalurgy, who really knows. Some of the books on these axles say that 4100 series steel was used for a number of years in the forging of the axles which would give a good bit more yield curve before the ultimate snap... I've seen more snapped stock 14B shafts in my days wheeling and only the few pics on here of snapped Eatons; but there are a far greater number of 14Bs out there.

If its a real concern, get you some double float RCVs and we can all find out where the next weak point is in these cool old axles.
 
AlxJ64 said:
Stellar that it works!

0.016" or 0.160"? Wheres that zero go?

The jury is still out on the shaft strengh comparison. The 30 spline roots are by mechanical design comparison, in fact "stronger" due to pressure angles and spline contact area, but when it comes down to metalurgy, who really knows. Some of the books on these axles say that 4100 series steel was used for a number of years in the forging of the axles which would give a good bit more yield curve before the ultimate snap... I've seen more snapped stock 14B shafts in my days wheeling and only the few pics on here of snapped Eatons; but there are a far greater number of 14Bs out there.

If its a real concern, get you some double float RCVs and we can all find out where the next weak point is in these cool old axles.
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I was told it’s .016. The machinist said 8 thousandths total per side. So that’s .008 right?

If I wanted to fix the problem and move on I would have gotten 300M double splined RCV shafts, 17 spline on the inner and whatever RCV spline count uses on the outer but I wanted to put theories on shaft strength between the 2 shafts into some real world testing.

I can confidently say that Eaton 17 spline Detroits are stronger than 30 spline grizzly/Detroit’s. I know many people personally who take out a grizzly or Detroit EVERY SINGLE TIME a shaft breaks. This has been in 14 bolts, ford 8.8s, Toyota 8in, dana 44, etc. I know one guy who broke 3 grizzlys in his 14 bolt. Broke 2 stock shafts, then Yukon “chromoly” shafts and then is now on RCVs and has been problem free but anytime a shaft broke, the grizzly went with it. Grizzly claims theirs don’t break when a shaft breaks but I’ve seen it happen multiple times. The benefit to grizzly is customer service. Trying to get replacement parts from Eaton is like trying to pull teeth.

With that said, I have broken 3 shafts, all in very different ways, and never broke the Detroit. The old school Detroit is hands down stronger.
 
so i found a 456 third today for 100 bucks, gonna stop by on sunday and give it look. its close to my house so why not, then i too may start down the HO72 rabbit hole of awesome ness......:beer::beer::beer:
 
No idea what the value of it or that truck would even be. It had a 6 cyl and manual trans. Basically complete truck and only some visible rot
 
Someone who's interested shoot me a DM with a serious offer and I'd consider it since I'm going back down early next year and have owners info to negotiate. Will have a friend translate for me to make a deal. Also complicated with having to get a USA title before bringing it across the boarder too, unless someone knows any easier way to make that happen b
 
TTMotorsports said:
I saw a 57 GMC napco down in Baja last week with a Eaton front axle.
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6 lug or 8 lug?

My step dad had a 59 chevy with a neapco 4x4 conversion. It was 6 lug and the diffs looked more like an old land cruiser than the Eaton iirc.

Either way, sure the truck is worth far more complete than for dumb rock driver over parts.
 
Didn’t someone on the old forum have housings made? I have been considering widening one of my housings to 67-68 WMS.
 
YotaAtieToo said:
I want to say ruffstuff made a handful. Not sure if they'd be willing to make another one or not if you called.
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I doubt it, ruffstuff has become a bunch of cocksuckers in the past couple years. Dan is cool but their service has gone to shit
 
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