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Old Feb 4, 2025 | 09:53 AM
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Rear Axle Code

Hey guys, does anyone have an idea as to the rear axle code on my "73 F100 4X4 of H2J ? Trying to determine if I can tow an 18 ft boat / trailer. Has 3.50 gears, 9 inch ring and 31 splined shaft. I did upgrade the motors a number of years ago from the 360 to a 428. GVW 5600 with a factory Ford fiberglass topper shell. Another concern are the standard shoed brakes. Thanks!
 
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Old Feb 4, 2025 | 01:28 PM
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You will be fine. People have used half ton pickups (or less) for generations to tow boats and campers and we're still around to tell the tale.

How did people originally tow big vintage Airstreams? : airstream
 
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Old Feb 4, 2025 | 02:12 PM
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Thanks for the reassurance! Moving forward now.
 
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Old Feb 4, 2025 | 04:42 PM
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One thing you should absolutely do, though!
Any time you’re towing with an old truck with an unknown number of miles on the rear wheel bearings, is to either service them, or replace them.
Chances are pretty good that you have the tapered roller bearings, which were the heavier duty version for the Ford 9 inch rear end.
But chances are still good with the 73, possibly even with 31 spline axles, you have the sealed ball bearings.
Those were perfectly fine when new, but have a finite life expectancy of about 100,000 miles. And even if not mileage, after 50 years, I’m sure the grease has done its job well.
Definitely check, or have them checked. If in doubt, replace them.

I have a book that should tell us what type of bearing your truck uses, given the GVWR that you stated.
But do you also have the rear axle GAWR handy?
 
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Old Feb 4, 2025 | 05:12 PM
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Great idea about the bearings. Last time I had a bearing issue was when traveling through Salt Lake in the early 90s!

Pillar sticker below. Sorry for the large size. Just scroll it down for the placard info. Thanks!!

 
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Old Feb 4, 2025 | 05:24 PM
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Perfect. So 3110 it is.
If nobody else comes up with more info on the bearings, I’ll try to get the info later when I get home.

In the meantime, can you verify that it is indeed a Ford 9 inch differential? There were some trucks that got the Dana 44 rear.
Although I think those were only 2 Wheel drive trucks, it wouldn’t hurt to confirm.
 
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Old Feb 4, 2025 | 05:41 PM
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Thanks....

Yes, rear diff is coded: WFE-F. My understanding is that it's a F3600 rear case. The raised code on top of the hognose is "N". Other numbers: 3FA, 3L50 9 358A.
The front diff is D318F. Then other numbers are: D3TA-AA, 3 54, 603394. My understanding is that this is a Dana case set.

Jim
 
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Old Feb 4, 2025 | 06:18 PM
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Originally Posted by 75M
Thanks....

Yes, rear diff is coded: WFE-F. My understanding is that it's a F3600 rear case. The raised code on top of the hognose is "N". Other numbers: 3FA, 3L50 9 358A.
So you're saying your 9" center section has the N case marking, as seen here, denoting the nodular iron HD piece? 3L50 is 3.50 ratio Traction Loc. It doesn't get much more heavy duty than that in a F100.

Ford N Case 9

Even with all this, you're only going to have a few hundred pounds of tongue weight on the hitch, or about as much as a good load of trash to the dump or a small load of lumber from Home Depot. Still not a big deal.
 
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Old Feb 4, 2025 | 06:25 PM
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Great! Thanks for the thoughts about the bearings. I'll take action on that.

Jim
 
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Old Feb 4, 2025 | 07:27 PM
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As soon as you said “hognose” we knew it was a Ford 9 inch.
Dana differentials don’t have removable center sections. Just a bolt on rear cover to access the gears.
and yes, an N-case is a real find in a truck!

At least I think they were semi rare in pickup trucks. Maybe not as rare as I think, but they were often found in Boss Mustangs and things like that.
Maybe in some of the bigger heavy duty cars with big engines too?
 
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Old Feb 4, 2025 | 07:35 PM
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Great information. I appreciate it very much.
 
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