Eaton rear axle

[72-396]

I have a 72 3/4 ton 4x4 with an eaton rear axle. I am not sure what model it is and I am having trouble finding info on it.
Please help? I tried to atach a piture ut it did not work
Thanks

[75-K5]

ho52 i believe, or ho72, but i think the ho72's were in 1-tons.

[72-396]

Do you know if it is refered to as a 14 bolt or someting like that.

[75-K5]

nope, the 14 bolt full floater is a GM Corporate axle like the 12 bolt. They started coming around in 73 I think. The Eatons are totally different.

[72-396]

Thanks

[kiley]

If you've got an eaton it will be round, about the size of a basket ball. Everything is expensive to replace. You can't find ring and pinion or lockers new. Save yourself some money and swap it out. I love mine because it is tough as nails but if I had to do it again I would replace it with a 14 bolt.

[72-396]

I will take your advice. I want to change gears due to the fact it has 4.56. But I have heard that eatons are strong as nails so I was comtemplating keeping it. I will start looking for a 14 bolt.
thanks

[Longhorn Man]

Other than being expensive, there is nothing wrong with the eaton differental. It is in fact tough as nails.
If you were to locate a V8 automatic powered C/20, it should have 4.10 gears in it onles otherwise optioned.
The pic I posted here is an Eaton differantal under a c/20 longhorn. ho52 is the 3/4 ton version, while one tons got ho72. Some ppl think they have a one ton rear in there truck, but if it is suspended by coils, you can automaticly call B.S. since one tons never came with coils. (onless some one modified a leaf rear) I only mention this becouse I hear so many 3/4 tons with a supposed one ton rear)

[72-396]

Is there a # on thhe rear end some where I can find out if it is a h52 or h72. If I was to keep this rear end and rebuild it. it would probably last for onother 30 years.

[Rod]

What do you think is wrong with it... not much goes wrong with these... they last a long time. You can drop a whole different pumpkin in with a different gear ratio even, without even lifting the truck.

As for differenecs between h52 to h72... not much - all parts interchange... the difference would be in the drums and stud sizes possible depending if you had a dually rear wheel set up.

[72-396]

There is nothing wrong with it but the gears are to low for me. I have wanted to put higher gear in it that's all. Some people are telling me I might be better off swapping it out with a 14 bolt.

[72-396]

Here are the #s I took off the third member 3934695 257 D 2

[Rod]

4.10 you find pretty easy... 3.90 is availble after market... expensive.... and they may have been an elusive 3.73 made by some company decades ago ...only heard decent rumor of that one....never seen one.


hey if you got $995 here the place to buy new.

http://www.rearman.com/truck.htm

Anyway... I didnt think so.

If you have a BB in your truck would it not have come with a dana rear with 3.54 ratio.... which brings up another suggestion... if not... ask around here for a dana diff ... for leaf or coils depending what you have and maybew you'll get someone selling a 3.54 ratio rear diff in the dana series.


You could still swap to a newer 14 bolt also. Other have done that swap here already and can help you more. Rod

edit note.. whoops didnt remember the 4x4 in your first post... OK... so it probaly is 410 already if it was a 72 with a V8.... probably easier to find bigger tires, that a drop the ratio.

[1969 GMC]

it seems split, i have heard some board members say they hate the axle cuz its too expensive to fix, and some say its no biggie to fix. i want to get one for the optional detroit locker.

[Vince M]

If your looking to just change the ring and pinion..someone here might have the 3rd member complete and it would be an easy swap. If your looking to buy new ring and pinion it would be cheaper to find the 14 bolt. That's what I did. The 14 bolt is a better axle in my opinion and has parts readily available and a wide assortment of ratio's. Remeber whatever you do to the rear you'll have to do to the front also. Finding matching ratios for the Dana 44 front might determine which way you'll want to go. Along with ring and pinion changes many times the carrier has to be changed also. I went with 3.73 in my 14 bolt and swapped the front to 3.73 out of a later model. It seemed to be a good match for my 3/4 ton.

[72-396]

Thanks for all your help ! if I decide to go to a 14 bolt is there any specifice trucks out there that would make a smooth swap.

[1969 GMC]

i think the 14 bolt from the '73 up C/K 30 will bolt right in to a 67-72, but i'm not sure. maybe someone else can help.

[Longhorn Man]

There will be a few issues, the shock location being one. One shock perch needs to be relocated to the other side of the axle.
There may be spring perch issues too, but that I am unsure of.

[mikep684x4]

Shock perches and the E brake cables where all I changed with my 14 bolt from a 75. Three days later and a snaped axel and the eaton went right back in. Haven't had a problem since. I did what Rod said and incresed my tire size. Still blows the tires loose but now I've got some highway speed too.

[Blazer1970]

Originally posted by 1969 GMC
i think the 14 bolt from the '73 up C/K 30 will bolt right in to a 67-72, but i'm not sure. maybe someone else can help.

The spring perches on the K30 axle are correct if it is a single rear wheel truck. The vast majority of 14 bolts are 4.10 ratio, some are 4.56, and a few are 3.73. If you have to regear the 14 bolt, and do any brake work (very likely), it will cost more than you think to swap one in. Randy's ring and pinion does sell 3.90 gears for HO72 axles. Their catalog says they are for the axles with the pinion load bolt only. Randy's does sell overhaul kits for all the HO72 axles.

[Dean]

I personally wouldn't change the Eaton out for a 14 bolt ever unless that was all I had. The Eaton is much stronger and parts are not that hard to find. Plenty in junkyards around here. They used this same rearend way back till like the 50's. Lockers can be found also. I've found several of them. And don't just look in 67-72 trucks. I bought my last one out of a yard's 65 boom truck. Only disadvantage I see it the low gears. I wish my 85 C20 with the 14 bolt had the 4.10/4.56. 3.73 just isn't the best for my towing but it gets by.

Bearings are available with no problem. I have the part number for the pinion seal if anyone needs it. I also just put new brake cylinders and shoes on mine with no issues.

[crazy4chevs]

72-396, You could go with a dana 60. I just sold a coil rear 60 with 3.54 gears for $50 two months ago. I told the guy $50 before I knew it was the hard to find 3.54 gears though so I had to stick to my word. There out there you just have to look.

[COBALT]

I'm one of the guys who had my HO52 (3/4 ton coil sprung axle under a '69 C20) rebuilt before I knew anything about these trucks. Short version: don't bother unless you have spare parts. Swap it out if it's not in good shape.

It had 4.10 gears in a standard carrier. After sitting in a hay field for several years moisture invaded the housing. The carrier bearings pitted, and led to the slow destruction. One of the spider gears siezed, and welded itself to the cross pin. The rest tore the teeth off and kept turning.

The moaning and vibration was evident when I first bought the truck. I had Randy's Ring & Pinion (http://www.ring-pinion.com) take a look at it for me. I forsaw difficulties with getting parts, so I had them swap out the 4.10s for 3.90s (that are still available) and a detroit locker. Here's what the damage was:

3.90 gears - $250.00
New Locker - $550.00
Complete bearing set - $500.00
Labor - $300

Total - $1600.00 + tax

You can still get 3.90 gears, but aparently you can't get new lockers for them, so unless the carrier is still in good shape I'd say its time to either look for a carrier in good shape or plan on swapping it out.

The whole HO52/HO72 debate is a common misconception which starts when someone with a flashlight and some cleaner starts looking for numbers on the axle. First, the numbers on the housing mean almost NOTHING. I haven't found any reliable sources that can decode the numbers. Second, you can find "HO72" stamped in parts in and out of the axle (pinion nut for example). This leads people to think they have a 1 ton axle under a 3/4 ton frame. Some of these parts are interchangeable! Most shops will absolutely SWEAR they're all HO72 axles, but the chassis manual speaks for itself. The presumed history behind these axles is that the housing made by the GM corporation, the carriers were made by Eaton, and the axles were made by Spicer. Therefore, the axle is nick-named an Eaton axle, but usually it's called a Corporate Axle, with 10 bolts on the cover and supplies an 8 lug axle. Two options were available once-upon-a-time for these axles: an eaton posi unit (which are still around but hard to find in good shape), and the ever-ghostly 3.73 gear set. I've seen a set of these, so I know they exist, but they're impossible to find. My only guess is that sometime in the '70s you could by an aftermarket set for this axle, and some people got them, OR it was a dealership thing that people opted to swap out their 4.10s for 3.73s before the truck left the dealership.

Finally, the only real liability of these axles is if dirt/moisture gets in the housing. That means good axle seals, and a good seal on the diff. cover. Gaskets for this axle is impossible to find, so most places just use some RTV or Silicone II Window/Door sealer to seal the cover (seriously).

I've been running mine for a few years now, and I love it. I've had 3 people request to buy it once I tear the truck apart. I've had it out of the truck once when I rebuilt the rear suspension, and it was a heavy bastard. I probably won't keep it when I restore the truck...

[kiley]

I called them a few months back and they don't sell new ring and pinions anymore, especially for 3.90 gears. They said they might have some used 4.10's but were out at the time I called.

[COBALT]

You should still be able to get them direct through Yukon.