swapping a rear diff with the rear end?

2014 FORD F-150
212,000 MILES • 3.7L • 4WD • AUTOMATIC
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SUSPECCTT27
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Hi, my question is about swapping a rear diff with the rear end. I'm looking to swap out the entire rear end bc the rear differential is howling. My truck is 4x4 with an open differential, 3.73 ratio and 8.8 ring gear.
The question becomes do I need to get a differential that came off another 4x4 truck with the same ratio and ring gear size of course? Idk if this matters but I'm looking at junkyard parts, trying to save some money. There's one im looking at but it's in OK. Which is a 2 hr drive and I don't want to go there for nothing.

Thanks
May 27, 2026 at 12:57 PM
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STRAILER
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Hello,

The main rule is: match the rear axle ratio to the front differential

Since your truck is 4WD, the rear axle ratio must match the front differential ratio.

Your truck has 3.73 gears, so the replacement rear end also needs to be 3.73.

If you install a rear axle with 3.55, 3.31, 4.10, etc., the truck may drive okay in 2WD, but the moment 4WD is engaged, the front and rear axles will fight each other. That can damage the transfer case, differential, tires, or driveline. Let me know if you need anything else.
May 27, 2026 at 4:02 PM
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SUSPECCTT27
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@STRAILER the junkyard folks im gonna buy it from said the diff they have matches for both ratio and ring gear, it's just not sure that it's a 4x4 truck that it's coming out of. So I was wondering if that was important. I attached a Google AI screenshot of it saying to stick to 4x4 donor trucks
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May 27, 2026 at 9:59 PM
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STRAILER
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Those are some good points, I would look at the doner rear end and see if there are differences. Check the mounts, drive shaft yoke, sensor locations and if everything looks the same and the gear ratio is correct I would go for it.
May 28, 2026 at 4:41 PM
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