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Old 03-18-2017, 11:08 PM   #1
MASTERBrian
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1960 Eaton rear diff?

Finally got around to draining the fluid on my rear diff this evening. It came out looking good, which is a bonus as this burb sat for fifteen years.

I'm debating whether or not to pull the cover and reseal it our just go with it. Being as it's a two piece, I'm in a bit of unfamiliar territory. Will both sides come of and will rtv work to seal it or do I just leave well enough alone?

The other question is what do I used to fill it and how much will I need? Any chance it could be posi, I tried testing it once and got a result I wasn't sure about. I'll check it out again when I Jack the rear up to do the springs and work on the rear brakes.

I'm pretty certain it's a 3:90 and previous owner claimed posi, but I'm doubting the posi. My understanding is if it is posi, I'll need a special additive, which I can add once I find out.

I thought I'd asked some if this before but can't figure out where and I need to refill her....Thought some things said 80 weight, some said tranny fluid....I run royal purple in my other trucks, not sure about this old truck though.
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Old 04-02-2017, 09:56 PM   #2
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Re: 1960 Eaton rear diff?

Any suggestions on if I should pull the cover and check. Can I do this with the driveshaft back in place?
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Old 04-02-2017, 11:15 PM   #3
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Re: 1960 Eaton rear diff?

If you didn't pull the cover to drain it, what did you do? just remove one of the lower bolts? Personally I always pull the covers on diffs and have a look. I like to know the condition of the internals and to verify the gear ratio. I always reseal the cover with the correct gasket, although no one else seems to. They typically use silicone. Fill it back up with some 75W90 or similar gear oil. If you do have a posi, you will want to add a bottle of the friction modifier.
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Old 04-02-2017, 11:25 PM   #4
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Re: 1960 Eaton rear diff?

Mine has a drain plug at the bottom, I just removed that. On these two piece diffs, if I remove the cover from the back I'm dosing I have to reseal the front as well? That's kind of my delima on removing the cover. As for the gasket, I've been told numerous times forget the gasket and use silicone.
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Old 04-02-2017, 11:58 PM   #5
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Re: 1960 Eaton rear diff?

If the front does not leak, you can leave it alone Most common on the gears, was 4.10/4.57...on the big trucks 5.14. When you pull the cover, you can do a count on the gears, & the math....then you will know for sure on the ratio....best of fun, Longhorn
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Old 04-03-2017, 11:24 PM   #6
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Re: 1960 Eaton rear diff?

If you have a Eaton HO32/33 differential, the most common gear ratio is 3.90. The only other option was 3.38 which was rare.
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Old 04-04-2017, 04:09 PM   #7
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Re: 1960 Eaton rear diff?

Quote:
Originally Posted by Captainfab View Post
If you have a Eaton HO32/33 differential, the most common gear ratio is 3.90. The only other option was 3.38 which was rare.
Can you tell me where this should be stamped on my diff? I've looked and can't seem to find it anywhere.
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Old 04-04-2017, 04:18 PM   #8
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Re: 1960 Eaton rear diff?

Quote:
Originally Posted by Captainfab View Post
If you didn't pull the cover to drain it, what did you do? just remove one of the lower bolts? Personally I always pull the covers on diffs and have a look. I like to know the condition of the internals and to verify the gear ratio. I always reseal the cover with the correct gasket, although no one else seems to. They typically use silicone. Fill it back up with some 75W90 or similar gear oil. If you do have a posi, you will want to add a bottle of the friction modifier.
Anything wrong with a synthetic or would you run conventional? Also about how many quarts? 2-1/2? I've run Royal Purple in my other trucks, wonder if that is good to use....I've also thought about something cheaper, running it and then drain and change it again at 1st oil change.
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Old 04-04-2017, 06:04 PM   #9
crazy longhorn
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Re: 1960 Eaton rear diff?

Quote:
Originally Posted by Captainfab View Post
If you have a Eaton HO32/33 differential, the most common gear ratio is 3.90. The only other option was 3.38 which was rare.
Thanks Captain fab....I was thinking 3/4 ton , we all keep it in check Still, to the OP, pull the cover & do a tooth count/ math & you will have your ratio? longhorn....keep on truckin
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Old 04-04-2017, 08:14 PM   #10
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Re: 1960 Eaton rear diff?

I'm pretty sure it's the 3.90. Just need to know how much fluid and if synthetic or conventional.

Thanks!
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Old 04-04-2017, 08:50 PM   #11
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Re: 1960 Eaton rear diff?

I would go conventional lube on that one...(75/85, or 80/90), & add the limited slip lube , if you need it. I cant say on the amount to fill....but if it is like the old 3/4 ton Eatons, it should have a fill hole....just fill to the bottom edge of the hole Longhorn
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Old 04-05-2017, 12:20 AM   #12
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Re: 1960 Eaton rear diff?

To my knowledge it is not stamped anywhere. The Eaton HO32/33 has 6 lug and the Eaton HO52/72 has 8 lugs for the wheels


Quote:
Originally Posted by MASTERBrian View Post
Can you tell me where this should be stamped on my diff? I've looked and can't seem to find it anywhere.
I do not know how much oil they take. Just fill it to the bottom of the fill hole just as crazy longhorn said.
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Old 04-05-2017, 12:25 AM   #13
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Re: 1960 Eaton rear diff?

Ok, then I'll stop looking...of course it'll be obvious when I pull the cover and reseal. It's 6 lug and I'm sure it's a 3:90. Was just shy of two revolutions when I tested a few months ago. The debate is if posi. Previous owner said it was, but I didn't get a good result when I tried testing it.

Thanks for the help, if it ever stops raining, I'll get the cover off and find out what I have for absolute certainty.
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Old 04-06-2017, 07:45 PM   #14
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Re: 1960 Eaton rear diff?

Here is a picture of what I have. I'm guessing to count properly I'll have to jack her up and spin her to count the teeth. I'll just go with my assumption of 3.90 and it's just limited slip...correct?

Everything looks nice!
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Old 04-06-2017, 11:17 PM   #15
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Re: 1960 Eaton rear diff?

May have spoken too soon. I decided to mop the thicker left over fluid out of the bottom of the pumpkin and I thought I heard something so I felt around and below is what I find....what the heck is it, is the question. I think at some point this truck had some axle work done as there is a big weld along the passenger side axle tube. Hopefully it's just something that is left over. I spun the wheels and all the gears look ok and I don't hear any bad noises except the brakes are tight and scratchy.

Figure I'll run the pieces by an axle shop tomorrow and see if they have suggestions. I also believe I fixed an axle on an old cj I had once. Seems like the ring gear broke and I didn't seem to have any issues, but I certainly am not set up for anything major.
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Old 04-06-2017, 11:18 PM   #16
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Re: 1960 Eaton rear diff?

I'll add I don't remember anything else seeming to be in the fluid when I drained it.
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Old 04-06-2017, 11:49 PM   #17
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Re: 1960 Eaton rear diff?

You don't have to physically count the teeth unless you just want to. The tooth count is stamped on the outside edge of the ring gear along with the date and part number.

I do not know what those pieces are from.
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Old 04-06-2017, 11:54 PM   #18
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Re: 1960 Eaton rear diff?

The larger piece is L shaped, so doesn't appear to be a bearing. I'm also wondering if, like I said, had work done. The yellow paint remind me of how salvage yard Mark used parts. It almost looks like it might have been the angle piece that is bolted to the center of what I'm guessing is a bearing assembly. The ones bolted are in good condition, so it's obviously not from them.
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Old 04-06-2017, 11:55 PM   #19
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Re: 1960 Eaton rear diff?

It also doesn't appear to have floated around in the teeth, because none of them have and scratches or marring.
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Old 04-07-2017, 02:06 PM   #20
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Re: 1960 Eaton rear diff?

I figured out where the metal came from and it did take a small chunk from a tooth on the ring gear, but see no other damage. I took the piece of metal and a few pics to shop that does rear diff work and he didn't know what that part does/importance of it. Looks to somewhat limit a disc movement but....

He said clean up the tooth with drimmel, that isn't a huge issue area. Other than that, he said ask around as to the importance of that part....if I can find the piece he can repair if necessary. Wouldn't mind new seals and bearings as well..
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Old 04-07-2017, 03:36 PM   #21
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Re: 1960 Eaton rear diff?

Here's the rest of the numbers. Trying to find out how to decipher.
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Old 04-07-2017, 11:33 PM   #22
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Re: 1960 Eaton rear diff?

Yes you do have a posi. Those are 3.90 gears. See where it says GM 10 39 8 60.........39 divided by 10 = 3.90 and those gears were made in August (8th month) of 1960.
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Old 04-07-2017, 11:45 PM   #23
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Re: 1960 Eaton rear diff?

Quote:
Originally Posted by Captainfab View Post
Yes you do have a posi. Those are 3.90 gears. See where it says GM 10 39 8 60.........39 divided by 10 = 3.90 and those gears were made in August (8th month) of 1960.
So the PO didn't lie about that. Not that he had a reason to, but....

Any idea how important that tab is or if it can be found and replaced? I think it's part of the thrust washer if my research is correct, but it doesn't appear most thrust washers have the ears. Maybe that is because it's posi....hmmm!
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Old 04-07-2017, 11:45 PM   #24
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Re: 1960 Eaton rear diff?

Oh, and I was starting to wonder if it was the 39/10 deal as it made sense, but wasn't sure.
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Old 04-08-2017, 12:37 AM   #25
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Re: 1960 Eaton rear diff?

I'm thinking it's a clutch guide. Newer ones apparently are a single C shaped piece. Would it take any special tools/knowledge to yank this apart and possibly get a good I've out and fabricate a new one without tons of effort?

I'm wondering if previous owner(s) didn't use posi additive.
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