HO52 Rear Axle for general use
 

Now that I have the title in hand for my '67 C-20, the time to start getting my butt in gear is upon me. And I'm looking of guidance from collective, starting with the rear axle...

But first, I do want to stay 3/4 ton and have ZERO desire to convert to 5 lug pattern. I'd rather stay 8 lug.

I have the Eaton HO52 with 4.56 (open) diff. That coupled with the SM420 transmission makes for a relatively high rpm drivetrain, especially with today's highway speeds.

I'm inclined to keep the HO52 and build around it. Why? Good question, but I think I'd rather drive a Prius than do a "belly button mod" (350+auto+14 bolt). And I would never own a Prius - not even if it was free.

And of course, this will lead to the engine discussion and what really gets under my skin. Every single thread (here and elsewhere) seems to follow the tractor beam thought of more cubes the better. Sorry, had to vent a bit.

So first, is today's highway speeds detrimental to a vintage 4.56 diff? Specifically the HO52, which doesn't have the load bolt as I understand it. If prolonged highway speeds is truly an issue, then I will look at the alternatives.

Thanks in advance.

Z

Re: HO52 Rear Axle for general use
 

14 bolt! Only way to go!!

Re: HO52 Rear Axle for general use
 

You're not going to hurt a HO52 by driving it on the highway at 60-75mph, other than wear it out quicker. Repair parts are $$$ if you can find them. If you plan to drive your truck on the highway much with the SM420 and those 4.57 gears, you should plan on an engine that will hold up to the high RPM's for extended periods. Something like a 283. An alternative to lower the RPM's would be an OD trans, but that can get expensive depending on which one you choose. It is much less $$ top just swap the Eaton HO52 for a 14 bolt or a Dana 60 with 3.73 or 3.54 gears.

Re: HO52 Rear Axle for general use
 

I have run my HO52 with 4.10s at 75MPH for 400 miles straight trips. No issue there. You may want to keep an eye out for someone junking a 4.10 center chunk. The most common donor is a K20 with a factory 350 and 4spd.

Capt is right about the 283 but I can tell you that they cost to much to build now. A properly setup 350 would cost alot less. Piston and head choices for a 283 suck these days.

Re: HO52 Rear Axle for general use
 

I believe when these trucks were built the highway speed limits where about the 5+same as they are today. 65/70. I just verified it, Nixon lowered the speed limits to 55 in 1974. I know my dad drove my truck at 70+ all the time with the 4.10 gears TH350 and a 350 engine. Never seemed to bother anyone then. It's just what trucks did then. Fast forward to today and everyone is used to 2K engine speed at 75+ and much better sound isolation. If you want to lower the hwy RPM an overdrive unit might just be the way to go.

Re: HO52 Rear Axle for general use
 

Yup, we've been spoiled with modern O/D transmissions and modern fuel injection. The engines/transmissions/rear ends of yore held up just fine to a little bit of RPM's. :)

Gary

Re: HO52 Rear Axle for general use
 

Thanks all. I think I’ll look for a 4.10 chunk and delve a bit deeper into the motor next.

Re: HO52 Rear Axle for general use
 

I plan on adding a gear vendors overdrive to the SM420 and getting a good balance on the driveshaft. It's not the best economic solution, but I like my SM420 and HO52.

Re: HO52 Rear Axle for general use
 

I've read somewhere that Randy's did a limited run of 3.90 gear sets for the HO52. I wonder if they would consider doing it again. Has to be enough demand for a limited run...

Re: HO52 Rear Axle for general use
 

GV OD is pretty expensive. I've scrounged parts for an NV4500/rrange box/NP205 4x4 swap on the K10 but I got lucky parting a sub.

Re: HO52 Rear Axle for general use
 

Glad to see your sticking with the HO. Should be cheaper in the long run.
I think you will be happy with this choice. I daily drove an HO 52 with 457 gears and an SM 420 for several decades with zero problems. A few years ago found an HO72 center with 4:10s and love them.
Now a word about parts and reliability. I doubt you will break it ( I have tried) they are very stout. The only way to ware one out is to let it go dry or keep driving it with that 50 year old mixture of water and tar that's in most of them. Find one in good shape that has not been sitting in a field. The best thing you can do is drill a drain hole in the housing when you have the chunk out, and then change the lube every couple of years-cheap insurance!
I know this is kind of an old thread, but hope this helps.
Good luck with your project, sounds fun,
Tom

Re: HO52 Rear Axle for general use
 

I'm glad your keeping it genuine. Just drop in a 327 and let it spin (only 4.88/5.13's would require a 283..lol) !
I drove a '70 chevelle with 4.56 gears and a TH350 / 350 combo and only about 27" tire height, but not at 70+ mph sustained. It really just wanted more cam at highway speeds.

I get a chuckle when folks worry so much about turning 3,000 rpm, just hurts at the pump alot.

Re: HO52 Rear Axle for general use
 

It’s funny (or sad, depending on your point of view) because that was my thought also. I was getting excited about making a high revving engine, perhaps even with a modern long block for efficiency. But when you start reading up on the 327 vs 350 debate, the modest lb-ft difference suddenly takes on enormous, practically biblical proportions. Hell, I was going to go one step further and build a modern 307. I might still, even if the 350 club thinks it’ll drop my IQ and shorten my ....well you get the idea.

Sorry to vent.

Z

Re: HO52 Rear Axle for general use
 

Maybe a ranger overdrive would work. Here is a photo. The case is now aluminium and curently made by AdvanceAdapters. Chevy Ranger Torque Splitter Overdrive 27%

Re: HO52 Rear Axle for general use
 

I've considered the Ranger. The only thing holding me back is the shifter relocation. Maybe bucket seats solves that. Any idea what the length of it is?

EDIT: It's 7-1/2". I'll have to look at what that does to the seat/shifter.

Re: HO52 Rear Axle for general use
 

Freeway speed limits in 67 were probably around the same as they are now. I remember a 4 lane undivided road (route 20) in Ohio with a speed limit of 70 when I was a kid.

Re: HO52 Rear Axle for general use
 

LOL.. that was the speed limit when I took Drivers Ed....err..a long time ago...lol