Deciphering My Rear End

[bddcustoms]

Hey,

I've got a '69 C20 with a full float rear end (on coils), and 4.57 gears. It's either an HO52 or HO72. I've read (mainly from posts) that HO52 was for 3/4 tons, while 1 tons got HO 72s. But Randy's Ring and Pinion says 3/4 tons got HO72s also. Here's what I've been able to visually verify about the axle under my truck:
- 10 bolts
- 3rd member
- pinion bearing bolt
- "HU" stamp (4.57 gears)

Other visual ques are undecipherable by me, and I'm hoping for some help and feedback from ChevyNation. Specifically, next to the pinion bearing bolt appears a 7-digit number, a six-spoke wheel icon, the letter "D", and the number "2" (see image). What the hell?

Ultimately, I want to swap in disc brakes, which I believe I can using 14-bolt kits. I would also love to get highway gears. This is a cruiser. I've read a few places that the aftermarket offers 3.90s but I can't find them on the web. Any hints? What about lockers or limited slips?

I purposely chose a 3/4 ton LB because everyone on the custom scene is doing C10 SB. I want the this big boy to be sexy and trick but still true to itself.

Any direction or perspective you might offer is welcome and appreciated.

David

[El Jay]

I can't help you with the rear end question, but what I can do is say, "Welcome to the boards!"

Hang in there; somebody will come along and chime in with an answer to your question.

[Sinister]

I'm pretty sure the only difference between the HO52 and HO72 are the brakes. Good luck finding gears or a limited slip. The only gears I could find for my HO52 were 5.14, which wouldn't help, and that was after searching a while.

[LONGHAIR]

You are probably better-off swapping to a different axle. A 14 bolt or even a Dana60 would keep the "heavy duty", yet give you far more options for gears, brakes, and differentials.

[special-K]

There are 4.10s all over if you look for them.Try to catch them before they all get junked.These rears are awesome.You can swap the gears out easier than any other 8-lug rear and the only coil housing you`ll find would be a Dana60 from a big block Chevy.That would be a 3.54 and the most hiway friendly rear.

[Longhorn Man]

randy's R&P is wrong. the HO72 didn't come in 3/4 ton trucks.
HO52 is 3/4 ton
HO72 is one ton.
3.90 gears were *reportedly* aftermarket only, and discontinued like 15 years ago.
4.10 was the tallest gear you could get originally.

[special-K]

I agree that Randy`s is wrong.Maybe they were saying they are no different,as from a differential stand point.

[STOCKISH]

Originally Posted by LONGHAIR

You are probably better-off swapping to a different axle. A 14 bolt or even a Dana60 would keep the "heavy duty", yet give you far more options for gears, brakes, and differentials.

The 14 bolt locker, axle shafts and brakes(backing plate and all) will swap to the HO52 axle. And yes, the HO72 was a one ton only. Ho52 in 3/4 ton.

[capev86]

so you are saying this is an early version or variation a 14 bolt. i just today realized the rear under my 72 3/4 ton suburban 2wd was not a regular 14 bolt but instead a 10 bolt just like in the picture. thats good news that i can swap out the guts with later 14 bolt axles. i like the look of this housing but i need a more highway friend rear gear than 4.57 (thinking a 3.54 or 3.73) and some day i want to add factory rear disc from a year 2000+ truck and perhaps also a lsd style locker.

what do we do for cover gaskets on these axles and how do you drain them and refill them? is there a fill on the top or the front? i plan to add some fluid for now or flush and replace with fresh fluid and go to royal purple synthetic gear oil when i swap the guts out! hope to hear back on this soon! i love my truck, just want to iron out all the loose ends so i can start using it for what it was inteneded....hauling people, cargo and trailers all the while lookin' pretty while doing it!

[Longhorn Man]

it's not an early 14 bolt at all... it is an eaton diff in a corperate axle. 14 bolt stuff fits in it though.
the gasket for the cover on the eaton/corp is napa p/n P39130, or a tube of good RTV... make sure you cover the lower bolts with RTV, they will seap. looking at this photo;

you can see the fill hole on the cover. Remove the plug, fill till it is barfing out the fill hole, and plug. To drain, remove the cover.

[capev86]

awesome.....

can i swap in a 14 bolt carrier and keep my drive axles? i want to get a 3.73 FD setup and possibly a street friendly lsd......should i go with corporate/eaton parts or 14 bolt stuff? i know the whole carrier has to go because the 4.56 and up and 4.10 and down are two different setups atleast with the 14 bolt. anyway....thanks for helping me spiff up my new baby and get her ready for reliable towing duties!

[Longhorn Man]

I have no clue. I only hear the talk on the swapping guts. Never paid much attention honestly, the 14 bolt is a better rear than the eaton, you can still get parts for the brakes on a 14 bolt, only some of them are avalible on the eaton, and I don't see the point in mixing and matching old to new on a single component.
I say swap in a 14 bolt and be done. That's my plan on the longhorn.

[capev86]

oh well...i will keep looking into this as i don't want to have to do all the fab work to put in another axle. the eaton is prettier looking than the 14 bolt in my opinon and the truck already has it.....i just want to change the gear ratio for something that is dual purpose (a 3.73 is a good compromise for highway and towing)

[LONGHAIR]

Originally Posted by capev86

awesome.....

can i swap in a 14 bolt carrier and keep my drive axles?

I don't think so....I'm pretty sure that the splines are different. You have to swap the axles too...or so I have heard. I have never done this swap.

The biggest problem I see with this, over swapping in the entire housing, is that you are looking at having to set-up gears. That is going to co$t you.

Where as an entire housing swap leaves the gears intact with no set-up involved.

Changing gears is not a job for the average guy. There are special tools required and a lot of patience is needed too. It is not worth the the effort for what is, in most cases, a once in a lifetime job.

[capev86]

i have a mechanic who is competent at this. my dad swapped the rear axle from his 84 burb 1/2T 2wd into his present 87 burb 1/2T 2wd because he wanted a 3.73 instead of 3.08 and the original rear end was having troubles. the mechanic used the best parts from both axles. i thought the big axles were supposed to be easier. if i swap in axles, i'd spend a LOT of money having things fabbed up....all those mounts that are already on the housing. if this was a leaf spring truck then swapping axles would be very straight forward. i guess i will have to swap the drive axles too. what years are compatable in terms of track width?

[capev86]

i was right when i said the eaton was a variation/precursor to the 14 bolt.....found some good info here:

http://www.4wheeloffroad.com/techart...rts/index.html

[Longhorn Man]

While it IS a precursor.... so is the model T ford.
It isn't a variation of the 14 bolt.
They are both rock solid light duty rear axles. They both have full floating hubs, and were used in GM trucks... thats about it.

[capev86]

i mean, some of the design features were carried over into the 14 bolt and with work you can use the 14BFF guts in the eaton so there is some -extreme- compatibility between the two. i may see if i can find the 3.54 gear that my 72 burb dealer brochure mentions as an option on the 3/4T 2wd trucks and put the overdrive unit i just learned about on the back end of my saginaw 3 speed on the column. it would be slightly better for highway cruising than a 3.08 w/ no overdrive (3.54 x .85 = 3.00) AND i'd have almost the get up and go of a 3.73 for towing and hill climbs.....

[1969 GMC]

Originally Posted by capev86

so you are saying this is an early version or variation a 14 bolt. i just today realized the rear under my 72 3/4 ton suburban 2wd was not a regular 14 bolt but instead a 10 bolt just like in the picture. thats good news that i can swap out the guts with later 14 bolt axles. i like the look of this housing but i need a more highway friend rear gear than 4.57 (thinking a 3.54 or 3.73) and some day i want to add factory rear disc from a year 2000+ truck and perhaps also a lsd style locker.

the highest gears for the eaton are the aftermarket 3.90's, and good luck finding them. Your best bet is oem 4.11's and an overdrive. if you want a higher ratio than that, you have to swap in a different axle (14 bolt goes to 3.23 iirc).

also, there is no 'lsd' for the eaton. options are: open and no-spin (detroit locker).

Originally Posted by Longhorn Man

While it IS a precursor.... so is the model T ford.
It isn't a variation of the 14 bolt.
They are both rock solid light duty rear axles. They both have full floating hubs, and were used in GM trucks... thats about it.

To be fair, with the third pinion bearing, it is quite a bit like the 14 bolt. Most other axles (dana and aam) only use two. but they are two totally different styles of axle (drop-out vs. salisbury).

Originally Posted by capev86

i mean, some of the design features were carried over into the 14 bolt and with work you can use the 14BFF guts in the eaton so there is some -extreme- compatibility between the two. i may see if i can find the 3.54 gear that my 72 burb dealer brochure mentions as an option on the 3/4T 2wd trucks and put the overdrive unit i just learned about on the back end of my saginaw 3 speed on the column. it would be slightly better for highway cruising than a 3.08 w/ no overdrive (3.54 x .85 = 3.00) AND i'd have almost the get up and go of a 3.73 for towing and hill climbs.....

The 3.54 ratio mentioned is for a Dana 60 FF rearend.

Originally Posted by capev86

awesome.....

can i swap in a 14 bolt carrier and keep my drive axles? i want to get a 3.73 FD setup and possibly a street friendly lsd......should i go with corporate/eaton parts or 14 bolt stuff? i know the whole carrier has to go because the 4.56 and up and 4.10 and down are two different setups atleast with the 14 bolt. anyway....thanks for helping me spiff up my new baby and get her ready for reliable towing duties!

The only 14 bolt parts that swap into the eatons are the diffs themselves and the corresponding axleshafts. The carriers and gears do not. This opens up the aftermarket only a bit. You can get a lock-rite, detroit, or mini-spool for a 14 bolt which would all work in the eaton. I am not sure if there is an aftermarket clutch type posi for the 14 bolt, but if there is, then it will fit. (the stock 14 bolt gov-lock will not work in the eaton because it is an entirely different carrier)

[capev86]

so no way to put the dana 60 3.54 into the eaton? guess i will have to hope i can find a 3.90 or atleast the 4.10 (still an improvement over the 4.56)....any ideas on sources? maybe someone looking to do rock crawling or mud bogging wants to swap?!

[1969 GMC]

no, the eaton and dana 60 can't interchange gears.

i'm pretty sure 4.11 was the standard ratio in a 3/4 or 1 ton with the eaton (52 or 72) with the 327 or 350, so at least in theory they shouldn't be that hard to find. the aftermarket gears would probably be hard to locate, since i am pretty sure they don't make them any more.

[capev86]

on the suburban 3/4 ton.....only available (standard equipment) with a 350, 4 wheel drive and an automatic or 4 speed. pickups may have been optioned differently. i will have to find a place to pilfer the parts.....wish me luck!

[Longhorn Man]

You'll want to look for small block automatic trucks... they had the 4.10 as base equipmnt (not sure on K/20 trucks though)
Daul rear wheels will have the 5.13.

[sdcfish]

I have the same Eaton rear end from a 65 C-20 4 speed. Been doing a LOT of homework and also have found that 390's are the best I can do. I have actually already purchased a 14 bolt new rear end with 373 gears, but am opting to just switch out the gears to the 390's. Too expensive to switch out the rear end and I hope I will be comfortable with the 390's......now have the 457's which runs the truck at 45 mph cruising in 4th. Pretty lame.

I didn't find out about the 390 option until I found out how much it was gonna REALLY cost to swap rear ends.....I was originally told that 411's or 410's were the best I could do and was also told $600 to swap em.....but that reality became $1500 when I met with the real dude who knew what he was doing......2 days to fully swap and 1 day to re-do the brake lines and e-brake stuff. It's a job!

[capev86]

4.11/4.56 are in more modern axles like (1/2 ton) 10 bolt, 12 bolt, and 14 bolt.

3.90's were an aftermarket gear set and therefore no longer available when it's been 40 years since this axle was used in a truck.

i swapped out the original 4.57 for 4.10 third member in my 72 Suburban C20 (307, 3 on the tree). fuel mileage improved from 10/11 to 14/15 with that 10% reduction in rpm. i also put a Q-jet on in place of the 2bbl so i'm sure the small primaries help around town. truck turns 3,000 rpm at 60 with stock rims/tires. i keep it at a steady 50mph/2500rpm on long highway trips which nets good mpg (considering) and cuts down on the racket. even once i get my saginaw/borg warner overdrive installed and have the truck sound insulated, i will still keep it at 60-65. i tend to speed only in the car.