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Diff oil?

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Deano1481 View Drop Down
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    Posted: 18 Apr. 2019 at 6:07am
im going to be changing my diff oil this weekend in my 51 m38. I have the gaskets coming for both front and rear. My question is what kind of oil should i be getting? 
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willyt View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote willyt Quote  Post ReplyReply Direct Link To This Post Posted: 18 Apr. 2019 at 1:00pm
I think most use GL4 OR 5 in a 90 weight.
1952 CJ3A (Lil'Green)
early M38A1(Ole Green)
1970 Jeepster Commando
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Oldpappy Quote  Post ReplyReply Direct Link To This Post Posted: 18 Apr. 2019 at 5:49pm
I don't know whether the M38 had them, but the M38 A1 axles I have are limited slip (Power loc).

So, you need to research the M38 to find out what it used because while the lube suggested "GL4 OR 5 in a 90 weight" is fine for an open differential, it is not what you need for a limited slip differential. 

If you can't determine that by research, you should pull the cover off and take a look.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gunslinger Quote  Post ReplyReply Direct Link To This Post Posted: 19 Apr. 2019 at 7:20pm
I understand that the GL4 or GL5 is supposed to be compatible with these old trucks, however I used GL5 in my Tranny one time, it was supposed to be compatible, it wasn't, I had yellow metal in the lube when I drained it.  Since then I only use GL1 in a 80-90 weight, get it from NAPA.
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50 CJ3A, M38A1
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TateC Quote  Post ReplyReply Direct Link To This Post Posted: 19 Apr. 2019 at 7:24pm
From my experience GL1 in the transmission/transfer case, GL5 in the differentials. I think the only issue with GL5 being used in old cars is eating away at brass synchros and shims in the transmission and transfer case.
Tate Christensen
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1943 Willys MB #263100
1944 Ford GPW #234613
1945 Willys CJ2A #10226
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Ol' Unreliable View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ol' Unreliable Quote  Post ReplyReply Direct Link To This Post Posted: 20 Apr. 2019 at 7:44pm
Back when my now-30-year-old YJ was new, I was changing the tranny oil every year and I used Mobil 1 gear lube.  I saved the old oil in empty Pepsi 2-liter bottles and let the junk settle out.  I used this oil in all the gearboxes of Ol' Unreliable and never had a problem.  The oil never stuck around in the tranny and X-fer case long enough to cause trouble there.  Wacko
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Post Options Post Options   Thanks (0) Thanks(0)   Quote RA472A Quote  Post ReplyReply Direct Link To This Post Posted: 21 Apr. 2019 at 3:34pm
I've been using GL 4 Hypoid for many years.  STA-LUBE still makes it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deano1481 Quote  Post ReplyReply Direct Link To This Post Posted: 22 Apr. 2019 at 1:43pm
now i have a bigger problem. Opened up my rear diff and my spider gear spacer is cracked. Now my dilemma is do i just fix it or drop in a lock right locker? I want to lock up the front but am unsure if i want to lock the rear as well. I will be doing some offroad driving with it but will manly be old logging roads and trail rides not rock crawling or anything. Decisions decisions

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Post Options Post Options   Thanks (0) Thanks(0)   Quote RA472A Quote  Post ReplyReply Direct Link To This Post Posted: 22 Apr. 2019 at 2:26pm
Sounds like my kind of jeepin'.  My stock unit has performed very well for a long time.  Puttin' up Hell's Revenge in Moab was a head turner for folks there. I would keep it simple FWIW
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deano1481 Quote  Post ReplyReply Direct Link To This Post Posted: 23 Apr. 2019 at 6:47am
ive been thinking about it and i think im going to just fix the rear diff and lock the front. Some of the old logging trails around the farm get pretty muddy and lots of trucks get buried back there.
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