Eaton HO72/HO52 vs. 14 Bolt FF

[jbclassix]

This thread is dedicated to answering all the questions about the Eaton axles and comparing it to the more readily available Corporate 14 bolt.

Please post questions you have and I will do my best to answer them in this thread.

Please post any errors you see with this info and I will correct it.

[jbclassix]

Interchangeability... Sop far, only the brakes are interchangeable between the 14 bolt and the Eaton. I have seen a lot of requests for part numbers and how-to's for the Eaton brakes. Well, here is my how-to rebuild the brakes on the HO72 and HO52. NOTE: for the 71 and 72 HO72/52 axles this is a direct swap. 70 and earlier use smaller wheel studs and will require a hub swap, or the holes on the hub to be enlarged.

Eaton left 14 bolt right


13 inch 14 bolt backing plate assembled and bolted to HO72. Perfect fit.


This is the one issue with this swap if you are performing it on a 70 or earlier axle. from left to right early Eaton stud, 71-72 Eaton stud, 14 bolt stud.


I went ahead and installed the 13 inch drum on a 69 hub with the small studs for this demo. you will notice the that flanges of the larger drums are also thicker. The studs stick out just 13/16". The drum center fits perfectly over the hub. I would not recommend running the brakes this way without using a spacer between the studs and drum, or enlarging the hub to use the larger studs.


Bam!

[vectorit]

I'm all over this like stink!
Thanks for this, since I have 13" drum brakes off a 14FF.
Getting out of the not so common 12" system is going to be a relief.

I want to keep my original diameter wheel studs, so I'm gonna have to search for longer ones to work in this application.

Now, what to do with a 14FF axle with out it's brake system...

[jbclassix]

Chris,

Here is what I was talking about for the studs being smaller...
The I.D. of the holes on the 14 bolt brakes are roughly .552" and the I.D. on the early Eaton is .490" So you are looking at roughly a .030 gap around the studs. Those measurements aren't perfect because of the knurls.

[vectorit]

Ahh, I see what you mean.

[jbclassix]

Chris,

I am thinking now that running the drums with new stock studs will be OK. Every one of the slide on disc brakes I have done today has a much larger hole than the studs they slide over! As for the length, you are running steel wheels, right? You should have plenty of stud if you have steel wheels.

[DOUBLE-DINGO]

Originally Posted by jbclassix

Chris,

Here is what I was talking about for the studs being smaller...
The I.D. of the holes on the 14 bolt brakes are roughly .552" and the I.D. on the early Eaton is .490" So you are looking at roughly a .030 gap around the studs. Those measurements aren't perfect because of the knurls.

To make sure I have this straight, either bore out the Pre-70 hubs to accept the bigger 9/16 14 Bolt studs, or use longer 1/2 Pre-70 studs? Was there any issues running the smaller studs with the 14 bolt drums? Does the clamping force of the wheel being torqued down hold the drum in place and not slide fore or aft depending on the direction the wheels are turning upon applying the brakes?

I have the backing plates, just need to get the drums, shoes, hardware kit, and lug studs. In my research I swore I read in a thread on this subject that 14 Bolt hubs were required, and that with some creative interchanging of inner bearings and races, that the 14 bolt hubs would work. I then re-read this thread exclusively, as I cannot find the other threads I previously found on the subject, and discovered 14 bolt hubs only work with some machining to accept the Eaton inner bearing race. I did buy some 14 bolt hubs, but will most likely use the Eaton hubs for my swap to 14 bolt brakes.

Any information you guys can provide on the subject that I am missing will be much appreciated.

[Vanblindguy]

[QUOTE=jbclassix;5512266]Interchangeability... Sop far, only the brakes are interchangeable between the 14 bolt and the Eaton. I have seen a lot of requests for part numbers and how-to's for the Eaton brakes. Well, here is my how-to rebuild the brakes on the HO72 and HO52. NOTE: for the 71 and 72 HO72/52 axles this is a direct swap. 70 and earlier use smaller wheel studs and will require a hub swap, or the holes on the hub to be enlarged.


So if we were to go to, say, Napa and try to buy a backing plate, shoes, wheel cylinders to perform this swap What year would we ask for? 1973? 1974? 2WD or 4WD K20, or k30? or would any 14bolt 1973 -87 all work the same. I have a 2000 k2500 with a 14 bolt with drums would all the parts from it swap over? Seems like somewhere along the way the e-brake hook up is going to be different and so on.

[Aaron Burkemper]

I want to buy an OEM locker unit for the 52 under my 71 C20. Does the locker unit determine the ratio?

[jbclassix]

Nope! The locker goes inside the diff case halves. You will only find them used, or you can buy buy a detroit locker for a 14 bolt and use 14 bolt axle shafts. You will only need to turn about a 1/4 inch off the splines of the 14 bolt shafts. I have one done this way.
Posted via Mobile Device

[rustyburbin]

Originally Posted by Aaron Burkemper

I want to buy an OEM locker unit for the 52 under my 71 C20. Does the locker unit determine the ratio?

I know this is an incredibly old thread but I just thought I'd chime in... I have an old timer 4x4 shop owner who has some new old stock drop in Detroit lockers for the eaton. I got one from him for 100$ before we were buddies so I'm sure he'd do the same for someone else. I love it by the way, it was a great improvement and didn't effect my 70 K20 Suburban's road manners enough to be an issue.

Message me if you or any other reader I'd interested in one and I'll do my best to work something out for ya.

[Peanutbutter]

Hi, are you familiar with the bigger HO axles, 11000, 15000 and 17000. I have a 1966 C80 with Napco conversion, looking for 7.20 ring and pinion but still haven't determined which differential I have. Napco used their housing with GM carrier, the carrier is completely round opposed to oval. I think its the 11 or the 15 but not sure, one thing I can tell you is the ring gear is 12 1/4 inchs in dia. Do you need pics to see what I have?

[Peanutbutter]

Maybe this will help, others may be able to use this info.

[Longhorn 70]

Jeremy, first thanks for posting and accepting questions on this subject.

I have recently converted the front drum to disc on my 1970 C20. I would like to stop better and have the same size studs on the rear as well as install a locker. I take it from reading that I have an EATON FF rear. What would I need to change to go to 13" brakes and bigger stud hubs and have my brakes work? Would it be better to get a disk kit from someone like BlackBird and go to disc? Or should I look for a newer rear end with brakes, locker and all in it?

Thanks in advance,

Vince

[jbclassix]

Vince, I'm glad you asked these questions!

There are a few things that you need to know about your truck first. Does it have the Eaton axle or the Dana axle? And, does it have leaf spring rear suspension or coil spring with trailing arm rear suspension?

the Eaton and dana axles are easy to differentiate. the Eaton will have a round diff cover, along with a removeable 3rd member. There will also be 5 bolts around the yoke. the Dana axle will have a side-ways egg shaped cover with a square hump around the fill plug.

The reason I bring this up about what type of suspension you have, is you are looking at doing a locker and brakes. If you have the leaf style suspension, then you may want to look into a 14 bolt from a 1973 and up Chevy truck. 14 bolt parts are cheaper, and easier to come by. you will also have the option of 2 more gear ratios. 3.73, ad 3.42. you can swap a 14 bolt into the trailing arm set-up, but it will require welding new spring pads and fabricating, or relocating the panhard bar.

Now, if you do have the Eaton, and want to stay with it, The brake swap is straight forward. you will need the backing plate, fully assembled, and the brake drum from a 1973 and up 14 Bolt truck. They are interchangeable as I demonstrated. If you want to use the 9/16" studs, you can simply have the hubs bored out to accept them. the inner wheel seal is the same for the Eaton as it is for the 14 bolt.

On that, the bearings for the 14 bolt and the Eaton are DIFFERENT. The 14 bolt hubs will not swap dirrectly onto the Eaton without machine work for the inner bearing journal to accept the Eaton bearings. But it can be done.

Lockers. You have the option of one locker. The Detroit No-Spin. There is an original factory Detroit that usually sells for 400 and up. Then you have the "other" No-Spin option. The Detroit locker for the 14 Bolt is a direct fit for the differential of the Eaton. These lockers are readily available, and can be had used for around 200 and up. There is one catch to this though Swapping a 14 bolt locker into an Eaton requires the use of the 14 bolt axle shafts, and machining about 0.250" off of the splined ends. Otherwise it is a direct bolt in. I have pictures somewhere of my 14 bolt locker installed in my Eaton. I will have to load them to the computer.

I hope this little bit helps. If you want, post up a picture of your axle if you are unsure what you have.

[jbclassix]

Found them.

That is a 14 bolt carrier on the left, Eaton on the right. I swapped the guts.


Bolted together

[truckeez]

Originally Posted by Longhorn 70

Jeremy, first thanks for posting and accepting questions on this subject.

I have recently converted the front drum to disc on my 1970 C20. I would like to stop better and have the same size studs on the rear as well as install a locker. I take it from reading that I have an EATON FF rear. What would I need to change to go to 13" brakes and bigger stud hubs and have my brakes work? Would it be better to get a disk kit from someone like BlackBird and go to disc? Or should I look for a newer rear end with brakes, locker and all in it?

Thanks in advance,

Vince

i just knoticed someone roughstuff, or roughcountry selling disc brackets for the 14 bolt /and eaton for $50 the kit - uses slide on rotors/ calipers from 75 up 3/4 ton

http://www.ruffstuffspecialties.com/...g/EHO5272.html

[Longhorn 70]

Mine is basically a round slightly ovate cover on the rear. I haven't looked at the front of the diff, yet.
I'll try to get under the truck with a camera tonight.

Thanks for taking the time and effor to post this stuff. It is really appreciated.

[Longhorn 70]

Here is a pic of the cover on my rear end.

Next, a pic of the front of the differential.

[jbclassix]

That would be the Eaton on leafs! the only welding that would be required if you wanted to swap in a 14 bolt would be relocating the shock hangers on the axle.

[SmirchIs#1]

Originally Posted by jbclassix

That would be the Eaton on leafs! the only welding that would be required if you wanted to swap in a 14 bolt would be relocating the shock hangers on the axle.

It should be mentioned that if you want to put a 14 bolt FF rear in the 72' & older leaf spring truck with out modifying spring perches,it has to be from a one ton.3/4 ton perches are in the wrong location

[SS Tim]

That would be an HO52 then and very likely the stock axle. Now you need to decide if you want to upgrade the brakes or just put in a locker. Couple of things I would do the help the decision process would to be pull the pumpkin and take a look around and see if it has worn or damaged parts. Rebuild parts exist but are more difficult to find. Another would be to measure the front track now that you have disc brakes and match it to the rear. From the pictures it looks like you gain about an inch on either side swapping brake parts.

[jbclassix]

Thank you Longhorn 70 for posting that picture of an Eaton rear axle. I don't have any that are still bolted under a truck!

Just for reference, I am posting a picture of a Dana 60 from under a 67-72 GM truck. Notice the square part of the cover. This would be how you would differentiate the Dana 60 from the Dana 44. Other manufacturers used 5 Lug Dana 60 semi floating axles under half-ton trucks and SUV's. And I am only referring to back-in-the-day vehicles, not modern ones.

Dana 60


Here are some pictures of a 14 bolt Full float 10.5"

14 Bolt




Anyone have a picture of a stock diff covered 14 bolt? I don't have a straight on one.

SS Tim, you bring up a good point about track width, I didn't even think about that with his new front end! I want to say the TW on the Eatons I have measured have been 67". I will have to double check my notes tonight.

[Longhorn 70]

After I get the front end aligned, I'll measure the track width. Do I really want it the same? I remember Pontiac made it a big deal when they had a wider track on one end.

[jbclassix]

You won't get a factory rear end wider than the front end, I think what SS Tim is talking about is the track width on the rear might be 2+ inches narrower than the front.