The Stovebolt Site Forums The Shop Area Driveline 3600 Rear Axle

This was buried in another post regarding brake conversions so I thought I would highlight the need for information regarding the axle. Sorry for the duplication.

Doing more research on disk brake conversions and there are kits available for the HO52/72 rear axles that GM used from 1962 to 1972. I am wondering if anyone here know what the difference is between the earlier (47?-61) HO axles and the 62-72 that would affect the brake conversion?

Please check and make sure I'm correct.
1947 to 61 has the 8 lug hub behind the brake drum.
1962 to 72 has the 8 lug hub before the brake drum.
That's the reason the 62-72 conversion kit includes a very deep rotor.
I did not check the 3/4 ton axle lengths from 1947 to 72.
Eaton manufacturing ends in 1972.

That makes sense as one of the rear brake disk conversions I found asks if the drum slides on or is pressed on to the hub. Mine is outside of the hub (drum slides off the hub after the wheel and 2 flat head screws are removed). The location of the drum relative to the hub must translate into location of the disk relative to the hub affecting the needed depth of the rotor.

However, I would think the version with the drum outside the hub (like mine) would require a deeper rotor. Maybe the deep rotor for the 62-72 needs to be even deeper for the 47-62 version?

That shows you how little I know about this conversion.
Obviously the brake shoes got a lot wider over time.

Make some measurement of your rear axle then go to your FLAPS and ask to measure their Raybestos 5014R.
This rotor came up in discussions of a Dana conversion.
It would require replacing the old lugs with longer ones.

A little different flavor of the original question but really the same topic.

As I try to decide about my rear brake conversion it appears that I should also include evaluation of options to replace the Eaton HO52 (4.56 gears) with a more recent axle. The criteria being that I want to retain a full floating axle with the 8 bolt wheel. I know that there would be spring and shock perch changed required and possibly different back spacing on wheels but I have not sourced wheels, drive shaft, brake parts, etc. yet so I want to make an informed decision about the axle (keep or swap) before I make those decisions.

So Eaton is out. If you want to stay with Chevrolet then it would be the Corporate 14 bolt full float.
Is this what you want? This driveline forum is for "all things driveline related Pre-'73 GM truck".
I would reformulate a new post and post it in the 73-87 trucks, HiPo or Tons 'o Funs forums.

14 axle swap (stovebolt):
https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1249600/14-bolt-axle-swap-info.html

http://billavista.com/tech/Articles/14-Bolt_Bible/index.html
https://www.motortrend.com/how-to/129-1305-14-bolt-basics-inside-the-ultimate-junkyard-axle

If you are not good at fabrication, I would look for a kit and find a good welder.
Example, not a recommendation:
https://www.ruffstuffspecialties.com/14COMKT.html

If you go with a used 14 bolt be sure to determine the condition of the bearings (especially carrier and pinion) and ring & pinion gears.

If it was me, I would try to find a good rear axle shop near where I live.

Thanks for all of the insightfull links. I had done some searching but did not find nearly the number of resources that you provided.

I can empathize with your situation….I went around and around trying to find a way to keep my 8 bolt wheel setup. I ultimately decided that the best route for me was to put a hubcap over new 5 stud hubs & rear axle and keep it simple, knowing that I would never be towing a trailer or hauling anything heavy in my restored bed. Working to keep the 8 bolt wheels, even if they are under hubcaps, is commendable- just don’t let it drive you coockoo!

Norcal Dave, thanks for the encouragement.

I have read through some of the material about doing the swap to a 14 bolt and trying to determine the pros and cons of either staying with the Eaton or going to the 14 bolt. Assuming that I would stay with the Eaton and install the disk brake conversion the biggest drawback would be parts availability which may or may not be a problem depnding on what I may need (so far bearing seem good so seals are only known chnages required) and the fact I would retain my 4.56 ratio. If I go with the 14 bolt first I need to find the required version with a good ring & pinion, then do the work to relocate the spring perches, decide about brakes, etc. Depending on what ratio I find in the correct version I could have something lower numerically, 4.10, 3.90, 3.73 or? which would have some advantages.

The good news is that I can remount the Eaton when I get the frame back from paint and work on the decision process without slowing the overall project timeline as I have a lot of things to do.

I may have located a 14 bolt with a 4.10 ratio that would be a viable option for the swap, they are confirming the width. The reported mileage is low but I suspect that the odomter has rolled over putting it at roughly 137k miles in a 1986 stake bed truck running a 350 with a 4 speed manual transmission. I am guess a farm truck.

I have not been able to determine prices for all of the conversion parts required but it appears I could likely obtain and modify the 14 bolt for less than the cost of the disk brake conversion for the Eaton. The 14 bolt would provide a better final drive ratio (4.10 vs. 4.56) as well as better parts availability so even at a wash in cost it may be a better choice but I would appreciate feedback from others.

There IS a 4.10 gear set available for the HO52/72. I forget what years, but something like a 66 K20 I think. I found a whole axle through my connections for $100 and yanked the center section to put in my truck's axle. If all you want is a 4.10, I'd do that long before swapping in some other axle. Now if you want something in the 3.xx range, then yes, you must swap to something else.

BLSully, I understand that the 4.10 for the HO52/72 exists in theory but they are apparently extremely rare in today's market. The other aspect is parts availability for the HOs as they were last produced in 1972 (roughly 50 years ago). My goal is to end up with a good drive train that can be serviced for as long as the rest of the restored truck is viable. That may be the HO52 with a disk brake conversion but at the moment I am leaning toward the 14 bolt conversion, staying with drum brakes.

One of the reasons the 4.10 third members are so scarce is the fact that us dirt track racers scavenged up every set we could find back in the 1970's to run on 1/4 mile tracks behind Muncie 4 speed transmissions with a 1.88 ratio 2nd gear. That setup was ideal for running a "long quarter"- - - -a track that mesured a quarter mile around the infield. A "short quarter", measured around the outside, needed a 4.56 gear.
Jerry

FWIW -- Here is our own Stovebolt.com Tech Tip on changing out the gearing in an HO52/72 rear axle. Maybe it will help the OP:

HO52/72 gearing upgrade article

Shouldn't that be the other way around? Inside - short quarter / outside - long quarter? Or were the measurements staggered to make them equal?

Nope- - - -the "long" track measured 1320 feet around the infield. The outside dimension was considerably further. With an overall gear ratio approaching 9:1 with a 4.56 gear working with a 1.88 second gear, those "short track" engines stayed wound up all the time. 3K RPM coming off the turns and close to 7K at the end of the straightaway was pretty much the norm. Add a little wheel spin, and a rev limiter set at 7500 would get activated occasionally. Some guys liked the short stroke engines, the 283's and 302's with a 3"" crankshaft. Those engines loved to run 8K or so, and stayed together if they had stiff enough valve springs. Then there were the 289 Fords with the 2 7/8" stroke- - - -they sounded like a bumblebee on steroids!
Jerry

The high pitched sound is like the Demolition Derby of young fire department drivers driving no-exhaust junkyard "Rice Burners" full throttle at the Galax, Virginia fairgrounds. Don't laugh. It brings in a crowd of young folk and the money is used to buy needed equipment for the fire department.

I guess I'm missing something. How can the distance around the inside track be longer than the distance around the outside track? And if the outside dimension was considerably further, as you say (which makes sense), why would it be called the short track. Or does short and long refer to something other than distance? I'm confused.

I believe he said the long quarter the 1/4 was measured at the inside, while the short quarter the 1/4 was measured at the outside. Depending on the width of the track the actual center of the track distance would be longer for the long quarter because it would the 1/4 plus the addition required to get to the center whereas the short 1/4 would be less reduced by the amount required to get to the center.

I have verified that the 14 bolt axle I located is the correct width wheel mtg to wheel mounting so now I need to decide if I am going to pull the trigger and head down the swap path. As I understand the swap would involve relocating the spring perches, moving the brake backing plates outward, and installing new shallower offset brake drums.

The 14 bolt is still in the truck so I would appreciate any advice regarding how to determine it's condition prior to agreeing to purchase. Pinion backlash, at least a general idea from the input free movement should be an indicator as well as indicatoins of fluid leaks from either pinion area or axle shafts. I believe that they have a time limited warranty period but given my project timing I don't know that provides any real value.

The benefits of the swap being a better gear ratio (4.10 vs. 4.56) and better parts availability. I have not been able to determine if bearings and seals for the HO52 axle are in fact hard to find/expensive but given the axle was last produced in 1972 (50 years ago) I can easily see that being the case and only getting worse going forward.

If I stay with the HO52 I plan to do a disk brake conversion but if I go to the 14 bolt I plan to stay with drum brakes (front is going to be disk brake conversion regardless). The HO rear disk brake conversion price is a factor as it appears I can buy and convert the 14 bolt for less than the HO brake conversion.