Anyone hear of Ford having problems with the rear ends on the last body style F150's? My uncle has an 05 with 70k on it and its had two front pinion seals, now the axle seals just went, and the cover is always a bit damp. Its like WTF I wonder if they screwed up the casting at the factory? My dads 07's dry.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

The two piece driveshafts have a habit of vibrating due to not being well balanced. I'd search for a replacement drive shaft, and have the front pinion seal replaced. Since the rearends didn't come with cover gaskets, use a high temp RTV to make one, after cleaning the mating surfaces with brake cleaner. When you have the cover off, look for metallic shavings on the magnet. if they are present, look for a replacement axle as well. Replacing with a yard find would be cheaper than a rebuild...generally.

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1987 560SL
85,000 miles

This has nothing to do with your question, but the rear end on my wife's 2000 F350 went out at about 100,000 miles. She pulls a heavy trailer, but I don't think she stresses the truck beyond what it is supposed to handle. The truck has been maintained by the book (better than the book, actually). It did not have a seal problem. The differential just wore out, which was disappointing. It is the only problem we've had with the truck beyond the usually stuff. Cost about $2,500 to fix.

This truck doesn't tow, my dads does but only a light boat, which maybe weighs 800 pounds wet so that doesn't really count. Its almost like Ford figured something out between 05 and 07 with the rear ends on these.

The pinion seal was replaced on the 05 when it was new at around 12k miles, and it just went out 5k miles ago and was changed again. I'm usually pretty sensitive to drive shaft vibrations, I went through quite a bit fixing them on my SDL. This truck drives smooth I can't believe the drive shaft is that far out of balance from the factory.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

It can vibrate without you knowing it. Even a small amount, over time and during longer trips, will cause the issue you explained. Pull the drive shaft and see how much play there is at the sleeve.

I had the same issue with my '06 150. My final fix, after dickering with it 5 times in a 12 month period, was to swap the drive shaft. I ended up selling to a buddy who still drives it without issue.

I prefer the brick nose styling of the late 80s/early 90s...I have two 89 150s and a 89 250 now. One of the 89s is a parts truck, and the other is a work in progress. The 250 is the only 4X4 in the group, and is used primarily in the winter months and for hauling.

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1987 560SL
85,000 miles

if the pinion then the axle seals went,check the vent.

^^^
This.

Hmm good idea, maybe its clogged.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200