Eaton HO52 Gear Set

[ChevyTruckGuy68]

Hi,
I recently put my 67 K20 on the road. I would like to change the rear end and front axle ratio from 4.56 to 4.10 Does anyone have any suggestions on where I can get a gear set for the Eaton HO52? I would prefer to go in this direction instead of swapping the guts from a corporate 14 like I have read about elsewhere. Any input is appreciated.

[airdale94]

I just took a suposedly 4.10 Eaton to scrap hours ago. I pretty sure they were 4.56. I diddn't even bother counting the teeth. You won't really notice much difference between the two any way. With all the work especially with 4wd you'd probably be better off going with a OD trans. Of course that may be a different can of worms being 4wd. Randy TeeItUp has parted quite a few of these trucks. But the shipping will probably get you.

[landy]

I've read that Eaton gear sets can be hard to come by. One possibility might be to replace the Eaton with a Dana 60, which I've read is the setup that the GMC k2500s of the era used instead of the Eatons. Also could be put taller tires on it, which would change the effective gear ratio.

[special-K]

Find a whole rear. The differentials are no-brainers to replace requiring no lash set-up. You will certainly notice the difference going to 4.10s. My '72 K2500 cruises right along at 65 with 4.10s and 235/75-16s. They are about a half a turn improvement on the ratio.

[71Dually]

Google, Craigslist, auto swap meet and junkyard searches. Also check old school newsprint classified ads for all the non techie / non internet sellers to.

I have an Eaton HO72 4.10 in my 71 C30.

From everything I've read the ring gears are no longer available. This only leaves the used parts market for a source.

With the exception of bearings, seals, gaskets, brake shoes and hardware Eaton parts are few and far between and desirable used parts usually sell real quick. Serviceable brake drums and gear sets are desirable parts.

Ryan from Hoopers Rear End Exchange in Sun Valley, CA has told me the used 4.10 gear sets sell real fast when they are able to get a hold of them. Give Hoopers a try, ask for Anthony, they will do their best to help or point you in the right direction. They helped me out big time when I was looking for parts for my HO72. Google the name, lots of results. They have a website too.

Of course please support the forum and check the members selling parts and the sponsor vendors for this site also.

Like special-K says, "Find a whole rear end", it's the cheapest way to go for parts. Keep searching craigslist for 20-30 series trucks (C&K), Vans (G), Step Vans (P) and motorhome part outs. From what I understand HO52's & HO72's use the same ring gears. There may be a difference between the "load bolt" and "non-load bolt" gear sets though but I'm not real sure about that.

I picked up a 4.57 HO72 a couple weeks ago at the local pickyourpart (to bad it wasn't a 4.10 posi). I did a 14BFF JB8 brake swap right there in the yard and bought it with the big 3-1/2" JB8 brakes for $130.

Once you get your 4.57's swapped to 4.10's you can sell the 4.57's to a 4x4 crowd and recoup some of your costs. Once you change gear sets and/or run taller tires remember to change the speedo gear to keep your speedometer / odometer accurate.

[nolimitssjca]

I found a 4.10 locker on craigslist about a month ago. Just keep looking they do pop up.

[special-K]

These rears were used by GM since the '40s. The spring mounts and brakes went through multiple changes but differential design is virtually timeless through '72. Not that there is bounty of older trucks and 4.10s will be all the more rare. But,knowing this will expand your search

[ChevyTruckGuy68]

Thanks for the input. I am glad to say this forum seems to be a place where many are willing to help others. I would like inform you guys that i am only a sixteen year old kid who is in love with these body style trucks. I will be scanning craigslist, eBay, and the local papers. If time is of the convenience, i'm going to visit a couple of local junk yards to look for some differentials. I was also wondering were and what identification numbers i should look for on any differential i find that would distinguish what gearing it consists of ( if it still has the original gears). Again i really appreciate the input and i am trying to figure out how to post pictures for you guys to see.

68ChevyTruckGuy

[mx289]

So,I have a set of rears I was gonna put on the parts board soon.

4:10,Eaton Ho52,dana 44 8 lug.

[71Dually]

ChevyTruckGuy68,

Welcome to the forum

I know you didn't ask this but it's good info to take to the junkyard to check gear ratios.

To check for a posi spin one tire or hub, if the opposite tire/hub spins the same direction then you have found a posi.

If the opposite tire/hub spins the other direction then you have found an open differential.

Now that you know if it's a posi or open differential you can figure the ratio. Eatons only have 3 ratios, 4.10, 4.57 & 5.13. The 5.13 is the rarest ratio as from what I've read online very few were made on one model Step Van or something like that for 1 year I believe. It's also reported that Randy's Ring and Pinion had a very limited number of custom 3.90 Eaton gear sets made. I believe the reported number of custom Randy's R&P 3.90 gear sets was 10 so I highly doubt you will ever find one in a junk yard but you never know.

Back to figuring the ratio. Place the pinion yoke in a designated position that you can keep track of the rotations. Mark a tire/hub so you will know when it has rotated one complete turn.

If you have a posi both tires will rotate in the same direction as you spin the pinion yoke. A 4.10 ratio will take approximately 4-1/8 turns to spin both tires together one full revolution. A 4.57 will take just over 4-1/2 turns of the pinion. The 5.13 will take just over 5 turns of the pinion yoke.

Open differentials are a little different but still easy to figure out. The gear ratio is the number of turns of the pinion to rotate both tires one full revolution. A posi will rotate both tires at the same time, an open will only rotate one tire. Since a posi rotates both tires/hubs at once and an open differential only rotates one you will have to rotate the open diffs one tire/hub, two rotations, to match the 2 tires/hubs one full rotation formula.

So with an open diff and a 4.10 ratio approximately 4-1/8 revolutions of the pinion yoke will rotate the single tire/hub 2 revolutions. A 4.57 takes just over 4-1/2 etc... But you don't really need to rotate the open diff tire/hub two full revolutions. A single tire/hub rotation will do. With an open diff 4.10 ratio just over 2 rotations of the pinion yoke will spin the one tire/hub one revolution. For the 4.57 its just over 2-1/4 pinion revolutions. The 5.13 is 2-1/2 pinion revolutions. With open diffs it provides more accuracy if one tire/hub is prevented from rotating by wedging a tire under it, having a helper hold it so it wont turn etc...

Of course there are code numbers stamped on the normally heavily dirt caked carrier housings that can be deciphered once you clean the dirt off. Numbers are also stamped on the ring gear inside but that requires removal of the rear cover.

For a quick check the pinion tire/hub spin is an easy way to tell. If that quick check points to the ratio you are looking for then if desired pull the rear cover to check and verify the actual stamped ratio on the ring gear.

Each of these ratios had a certain number of gear teeth on the pinion and on ring gear. These "teeth" numbers may be stamped in lieu of an actual ratio like 4.10. The tooth count can also be stamped on the gear along with the ratio number (4.10). This methodology also applies to the codes stamped on the outside of the carrier. I don't recall all the teeth counts per ratio but a search in the forums for "Eaton Gear Ratio" should bring that information to light.

FYI, these Eatons do pop up fairly regularly. Look at all 72 & prior pickups, Suburbans, GMC's, Vans, 4X4's, step vans, flat beds etc... I believe the 1/2 ton models didn't use Eatons (but not really sure). I always look at 3/4 & 1-ton vehicles (and the 1/2 tons just in case). Don't forget to look at motorhomes also, HO52's & HO72's were put under a lot of GM vehicles over a period of what? 30 years?

Earlier today in a pick-a-part yard I spotted a 4.10 open diff Eaton in a 72 Cheyenne C20 but I didn't pull it. It was pretty loose but some eBay speculator will probably pull it anyway as the gear sets are just not available at the local parts houses anymore. Although it's showing wear it should sell fairly quickly at a decent profit. If it was a posi there would be unwanted carrier parts all over the ground and my wallet would be little lighter.

Good luck in your search.

[ChevyTruckGuy68]

nolimitssjca I would most definitely be interested in that gear set. I sent you a message to call me but here's my number. If I don't pick up leave a message and I'll get back as soon as possible. 860-256-1858

[bigrigpardo]

I have a complete eaton ho52 out of my k20. it has new shoes wheel cylinders hardware. bearings seals and re surfaced drums. I would like 350. I am 2 hours away in nj. parts for these are getting expensive. I am basically giving it to you for less than it cost me to service it all.

[dhandiman]

Hi All... I'm in what seems to be a familiar situation to some of you... I have an HO5200 rear axle in a 72 3/4 ton 2WD... looking for a gearset in the low to mid 4's instead of the 5.10's currently in the axle. Any suggestions would be welcome. Cheers.

[special-K]

Find a 4.10 unit and pop it in. These rears are the "drop-out" type. Drain fluid, unbolt axle flange bolts on hub, slide axles out, disconnect driveshaft at rear yoke, remove bolts that hold differential into axle housing, and remove. Repeat in reverse steps and fill with fluid.

[dhandiman]

Hi Special-K... thanks for the info... but my issue isn't so much in doing the work as it is finding the parts.... I can't seem to find anything in the way of replacements... I'm almost to the point of looking into a different axle all together... which I'd prefer not to do as I'd like to keep the HO5200 . You'd think with all of the interest in these rear ends, someone would have produced some replacement gear sets...

[dhandiman]

Hi special-K,
Don't know what I was thinking.... I mis-spoke, I have 4.10 in the truck currently... looking to go to mid 3's... finding that range of gearset is the issue...
Sorry for the confusion...
so again - anyone with a lead on mid 3's gearset for an HO5200...??

[RedRoad]

The highest gear ratio ever produced for HO52/72 was 3.90, they have been out of production for quite some time. Best bet is to go with a Dana 60 and run 3.54s or FF 14 bolt 3.73s. I too have been doing all I can to keep the 72 in my K20 but finding a usable set of 4.10s has been difficult and quite expensive. There seem to be a lot of guys out there like K that hoard them for future use and wont let them go.

[dhandiman]

Hey Red... well if I decide to go with a Dana, I'll let you know and maybe we can make some kind of deal for my 410 axle... I'd just like to drive it on the open road without revving the crap out of it...!!