The Stovebolt Site Forums The Shop Area Driveline 1947.2-55.1 One Ton Rear End Upgrade - New Tech Tip

With great anticipation I bring to you the completed article by non-other than our Editor-In-Chief himself Mr. John Milliman. He has written this article about the pumpkin swap that was performed on the Stovebolt flagship Sir Charlie himself.

The Need for Speed!

One-Ton 4:11 Gear Upgrade

Enjoy!

Nice article,
Thanks!

Grigg

Very informative, thanks John

That is a very nice addition to the Tech Tips. Now we need one on how to find those replacement pumpkins!

Fred! Your wish is our command! We've updated the Tech Tip with some excellent information provided by Barry Charon on finding axles with the desired pumpkin, which trucks to look for, etc. Also, an added benefit is some huge news about brake part interchangeability... meaning, if you grab the newer center carrier section, grab the brake parts, too, as they will bolt right up to your older HO52/72 housing!

John,
thanks, that is some listing. The news about the brakes is awesome. I have my drums but I worried a lot before I got them.

Fred

John. Are you saying that the rear we yanked the pumpkin out of sitting on the trailer has good brake parts on it ? Tell me yes tell me yes tell me yes!

That's what I was told, Joe. So .... they're good for *me* as that is a SRW axle. You need to find a DRW HO72 axle to grab both pumpkin and brake parts from. Maybe even the backing plate. That's what I was told.

John, great article. This is going to be a big help, thank you. Question, how do I find the part numbers for the pinion seal and packing? I wasn't able to find anything listed for my 1954 3600. I did find and SKF Seal 25970 and National Felt Seal 5M89 listed for the Eaton HO52 in a 1969 C20 Chevy. Will those part numbers fit? Note, I asked for help on this in the Driveline forum and then reread this Tech Tip so I thought I'd ask you. Thanks.

Dusty - For the seals http://federalmogulmp.com/en-US/Pages/Search-Parts.aspx

If you are doing the pumpkin swap and keeping the old driveshaft you will probably have to keep your original pinion shaft. Even if you can use the shaft on the new pumpkin, it is a good time to replace the oil seal and install a sleeve on the shaft.

This requires some serious work. First use a center punch to mark the end of the pinion and the nut so you can return to the proper location of the nut. Then you can remove the cotter pin.

Now is where the wrenching gets serious. The pinion nut is 1-5/8" and needs a 12 point socket that will fit in the recess on the shaft. A heavy impact gun is most helpful in removing this nut, original torque spec was about 200 ft-lb. After removing the shaft replace the oil seal and install the sleeve on the shaft, using some loc-tite to secure the sleeve. The sleeve is used to maintain the smooth outer surface diameter against the oil seal.

Place the shaft back on the pinion and tighten the nut until the punch marks are aligned.

I don't think you will want to bother with the felt as that part is not needed with the new seal. Also the torque specs for the big nut are 160 ft/lbs to 280. So the procedure is to torque to 160 and then apply more to get the hole for the cotter pin to line up with a slot. I used a six point socket and I had to grind the outside to make it fit.

Great piece of information.
Already looking for a long time to change the gears of my 1948 Chevy 3600.
Now the only challenge is to find an Eaton HO52 center section, from a ’68-’72 GM 3/4-ton with automatic transmission.
And in the country where I live (Nl) there are no junkyard where you could find something like this.
So, need to find it in the US.
If there is someone out there who could help me on that then please send me a PM. New or used, as long as it is re-usable. Thanks.

Nobody? I'll need some help to find the parts in the US.
Can anyone give me a lead?
Thanks for any support.
JP

Hi I would to know if the brake system from a 73-2006 14 bolt will work on my 52 3600 getting ready to do the diff. swap when it gets here thanks

I have a 58 3800 Apache that i am trying to update the rear gear. I have found a 55 1/2 ton rear axle with a 3:90 gear. Does anyone know if this rear differential will swap with my axle?
Thanks in advance. Dan

I have another question: what is the difference between an AD dual rear axle and a single tire rear axle?
My 1950 dually has a neat little spacer that bolts to the single wheel thus giving dual tires. I'm not sure if I have a dual or single rear axle. Was this a factory option or is this spacer a farmer idea?

Thanks John; Just bought my EATON 4.10 and This will give me some Reference as We do the Swap.......
Jim.

did you find a set of 4.10 gears yet? I might be able to help.

Hi , new member here and want to do a "ring and pinion swap" on my one ton axle.
after reading the article it says "The desired (for this upgrade) 4.10 ratio is only found in the HO52 axles
used 1968-1972 (3/4-ton trucks with the 350/auto trans combo) "
My question is does the auto/396 combo have 4:10 gears?

I have a 1950 ; 3/4 ton GMC with a '56 235 chevy motor ,HEI dist. , live in Northern Gulf Islands
"Wanna drive to town and get some gravel"

Quick (I hope) question. I have a guy offering me a rear axle with torque tube out of a 3100 that he says has a 4.10 gear in it. Will the gear swap into my 3600? The article only really suggests to look for the 68-72ish axles and not the half-tons.

No, the 1/2 ton (3100) gears will not fit the 3600 housing. They're much smaller and nothing matches up.
Jerry

So I just found a vendor who sells new ring and pinions for the HO52-72 Eatons. I'm not very well versed in differentials and will be following the Tech Tip very closely. Since this isn't coming out of an existing rear-end, other than the gaskets and fluid are there any other parts that I need to make sure are in the box?

You might want to purchase new carrier bearings and races, possibly pinion bearings as well, all depending on condition. Pinion seal, wheel seals too if needed.
Follow your standard practices/tolerances for "might as well while I'm in there"

[quote=Goach2]So I just found a vendor who sells new ring and pinions for the HO52-72 Eatons.


Goach2 , would you please share the contact information for the vendor who sells ring and pinions for the HO52 and HO72 Eaton rear differentials ? PM me if that is your preferred method of communication and thank your for the post. This is great news.

Well, I just confirmed with the vendor that they DO NOT carry these parts. Sorry to get everyone's hopes up. The search continues...

Thanks for doing all the leg work. It wasn't the answer everyone was needing but you didn't leave us hanging.

I have been a lurker and never had an account until now... This site has been a valuable source of info and I thank you all. Now for the question. Several years back, I bought a 1950 3600. It was in multiple boxes in multiple locations and finally got it kind of assembled and running. I dropped in a 350 SBC and 700R4... I know sacrilege but the motor was shot and we (wife) needed an auto trans. I figured the .70 Overdrive would help but it was not enough. Well after a couple years of searching I found a donor 4.10 3rd member and picked it up. It looks good and the gears look fine, however I found that I have about .016 backlash. How important is it to get that down to .008? I am afraid of screwing it up and have not had historically good luck with differentials in general. Years of wheeling old jeeps etc...

My guess is if the contact pattern looks good (should, as it wore to where it is now) then just keep on running it.

If gear pattern looks like it could be corrected then you might be able to do so while also reducing backlash.

Also check that bearings are in good shape and snug enough per the manual. Might need adjustment if they're worn but appear in good useable shape.

55 years of setting up rear end gears has taught me one basic fact. When dealing with gears with an established wear pattern:

DO
NOT
MESS
WITH
BACKLASH!

You will create a howl that would make a banshee blush with shame! It's far better to have quiet-running gears and a little more backlash than specified, than to try to create a new running relationship between the ring and pinion gears.
Jerry

Ok, I will slap it in and see how it goes. Thank you for confirming my thoughts. I was quite afraid of messing with it and changing the mating surfaces. I will let you know how it sounds when I get it done. Thanks

Jerry , thanks for that post on back lash. After experimenting with different ratios I finally decided on the one I should use . I had it in the truck in the past for a while with only minor gear noise . Before reinstalling it I took it to a rear end guy to go over it at which point he adjusted the lash and anything else that might be adjusted in it .
I installed it happily thinking this would be my last pumpkin change . WRONG . This thing screams big time but only on acceleration , the harder I press on the gas the louder it screams. The rear end guy suggests the pinion bearings might need tightening but this hasn't been attempted yet.
Jerry whats your thoughts, can this be corrected or should I search out another 4:57 rear for a HO 72.

Thanks John .

Exciting to see new additions to the how to dos.
Hoping to see new additions to the gallery too, hopefully in the near future, we love this stuff.

Once the contact pattern has been disturbed, there's very little that can be done to correct the whine, especially if you're paying someone to experiment on it. If I had that situation with a vehicle I owned, I'd just drop the differential out and try to get the backlash back to where it started. All that costs is a little time and some gasket sealer if you're doing the labor yourself. The two big spanner nuts at the carrier bearings control backlash, so try turning the left one CCW one notch and tightening the right one the same amount. You'll need to loosen the big bolts holding the bearing cups in place before adjusting, and torque them afterwards to about 100 FT/LBS. Of course, since the first rear end I set up was done in 1964, I probably wouldn't have tinkered with the adjustments in the first place. What's happening there is that a relatively unworn part of the ring gear teeth is climbing over the pinion gear teeth, and trying to establish a new running fit. The gears aren't likely to fail, but they will be noisy. Invest in a set of earplugs and be patient- - - -in a few thousand miles the noise will subside somewhat, but it's not likely to ever go away entirely.

Fortunately, 4.57 gear units aren't scarce or expensive- - - -it's the 4.10 gearsets that are like hen's teeth! That's partially the fault of us dirt track racers, who bought up and wore out every 4.10 3/4 ton rear end we could find back in the late 1970's!
Jerry

Thanks a bunch Jerry, that's the best info I've got so far. I have a number of rear ends here and I will practice taking one apart before attempting it on the one I need.
That being said I do have a 4.10 here that I'm told needs bearings that I would trade for a unmolested 4.57.
If the O.D.S.S. group will be attending the Manchester VA. event in Sept. I hope to join them there , I can bring it with Me.

Is this posted in the wrong forum?????? should it be in the parts wanted forum ??

John

If you're planning to disassemble a used differential, try to get a good gear contact pattern before changing any adjustments or removing any parts. The traditional way to check tooth contact is with a mixture of white lead (lead carbonate powder) and linseed oil. Anything with the word "lead" in it gives snowflakes a case of the vapors, so finding white lead these days is almost a lost cause. It's also possible to check tooth contact patterns with Prussian blue. Paint several teeth with the indicator dye, have a helper grab the input yoke with a pair of heavy gloves to provide some resistance, and spin the ring gear back and forth rapidly to spread the dye. The tooth contact pattern will be obvious by the places where the dye is wiped away. Also check the backlash before disassembly. There's no guarantee you'll get it back together in the previous relationship, but at least you'll have a pattern to shoot for!
Jerry

Thanks again Jerry, I hope to get at it soon .

John .

One pretty good substitute for white lead would be to go to an artists' supply store and buy a small tube of white oil paint pigment. A 2-ounce tube would be a lifetime supply unless you're building several rear ends a day. The idea is to have a thick, slow-drying or non-drying indicator dye that allows you to visually check the contact patch between gear teeth. It's also useful for checking seat width while doing a valve job.
Jerry

The first rear end I put together, I didn't know what to use. I did have a tube of yellow ochre oil paint. it worked like a champ! This type of oil paint is used by painters using the spatula method of painting. No brushes. It is like a paste. In the right hands, this technique results in some amazing interpretations of landscape scenes.
I would bet money that this paint contains lead.

Thank you for all the details. Stovebolt is truly a blessing for those of us getting started in this hobby of AD trucks

How can I identify an HO52 differential out of the vehicle?
I have one located on the shelf, supposedly 68-72 vintage,
has 10-41 on the ring gear