Please describe the HO52 and HO72 axles

[nu2-72]

I need a side by side comparison. What is the same and what is different. What is direct bolt in and not so direct.
If I am understaning correctly, the only difference is from the backing plate out through the brakes. I assume the rest is identical?
Meaning I could make one or the other by swapping the entire brake set, backing plate from the 4 bolt flange out and there would be no other changes?

[Longhorn Man]

The HO72 was only avalible in leaf spring.
most HO52 were coil.

I THINK the HO72 had bigger bearings.
The HO72 has provisions for adjusting the preload on teh pinion where the HO52 does not.

[special-K]

Was the HO72 1 ton(leaf)?Weren`t HO52s in K/20s?

[69oldie]

Actually the HO52 has the provision also depending on the year of the truck the axle came from. Another difference would be the size of the wheel studs...either 1/2" or 9/16". You would think that the 1/2" would be the 3/4 ton and the 9/16" would be the 1ton but that is NOT what it always is!! Earlier 1 tons (Pre 1971), had 1/2" Dual or single rear wheel, and 3/4 ton 4x4 1971-72's has 9/16"!!!!!!! Now that really didn't ever make sence to me..but GM products did things that always didn't make sence! Another difference is the size of the wheel cylinders for the brakes...the 71-72 had smaller ones than the pre-71's this is due to the fact front disc brakes were introduced in 71. So you need to be sure that its compatible with what type of brakes you have in front of your truck. Otherwise you will need to modify your brake proportioning valve to compensate the difference. You will have braking problems like the rear tires locking up too soon or not braking enough and the front brake will be doing ALL the work which is bad also! Another difference would be the size of the hub...Longer for the duals and shorter for the single rear wheels. I would explain the reasoning behind that but this post is getting already too wordy and long.
I think I said too much......... but I hope this helps!
Good Luck
Jim "69oldie"

[69oldie]

HO52 were not only for K20. Example......3/4 ton Longhorns had HO52 and 1 ton Longhorns had HO72.....both leaf sprung

[special-K]

1/2"studs/Drums on front(pre-71).9/16"studs/Discs on front.Went to chamfered-type lugs on dual-wheel in`71(w/spreader ring).Flat castle-type on pre-71 drum with 1/2" studs.

[Longhorn Man]

I guess it was never said that the HO52 was 3/4 ton and HO72 was one ton. And I THINK the one ton trucks all had the 1/2 inch stud untill 71... I know mine does.... I'm also talking single rear wheels...not talking duallies.

[Maximum Overdrive]

I cant give a side by side comparison but my 70 GMC 3/4 is leaf spring and a HO72 rearend.

[72MARIO]

Anyone know if I can take the locker out of my 71 C20 and use it in my 73 3/4 ton with a 14 bolt ? Think I have read about it before ?

[JIMs70GMC]

yes, but you'll have to use the axles out of the 71. because the H052/H072 had 17 splines and the 14 bolt has 30 or something like that. Supposedly the H052/072 detroit and 14 bolt detroit are identical except for the splines. Detroits for a 14bolt are only about $325.

[4x4Poet]

Mario, you could probably sell the Eaton locker for more than you could purchase a 14bFF Detroit locker. Also, the Eaton's axles would be 1/4 inch shorter than the 14bFF axles, so the Eaton axles would have less side gear engagement if installed in a 14bFF. I don't know if the lessoned spline engagement would be a strength problem. And I've forgotten whether the Eaton axles have the same flange bolt pattern as 14bFF axles. Overall, you're going the wrong direction, but they're your trucks.

[72MARIO]

I know it's worth a alot. Just a hassle trying to ship it out. I am not sure what I am going to do.

[D.PASSMORE]

FYI,
I had a my HO72 rebuilt with a newer Detroit No-Spin and new axles. Axles were referenced as, I believe, '78, 14 bolt, C-20. I'm away from home but, I can check the paperwork this weekend. No problems and no other modifications needed. Let me know...

[4x4Poet]

Yeah, D.Pass, the 14bFF axles should have had 1/4 inch cut off the splined end to not stick too far into the Eaton diff.

[Rod]

Well..as you know GM was all over the place in years where things changed.

I obseve 1 ton duallies using 9/16 studs as of 1970 in a dually with 133 inch wheel base.

Have seen many 1 ton duallies with the 157 inch wheel base use either stud 9/16 or 1/2 inch ..but mostly the 1/2 inch stud in a longer wheel base. The 9/16 seems to start 1970... but I dint often see the 9/16 in longer 157 inch wheel base models.

My take on it..is if you had the heavy duty spring option on a 1 ton duallie you got the 9/16 studs if it was 1 ton with a 133 inch wheel base as of 1970.
Otherwise most anything else being 3/4 ton a 1 ton single wheel you got 1/2 inch stud.


The spreader flanges and the tapered stud appeared in 1973 to my thinking. That was untill I came across a 1976 motor home with a 1972 grill in it with9/16 studs using the flat washer type base lug nuts. I saw that grill and thought I found a 72 P body
motor home...I'll take my camera with me for a pic of that.
It has a 454 also...so its not a 72. Couldn't find a vin but the camper body serial number said made in 1976. Had a 14 bolt rear also.

I had to order lug nuts for mine and they were not easy to find...9/16 flat type.. I have spares in someone wants to buy some....original NOS GM...GM parts books says there 71-72 but I've seen them on a 70 also.

[4x4Poet]

Rod, I think you're on a whole 'nuther level than the rest of us.

[Rod]

Its not the only subject I'm full of either...LOL.