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720 King Cab 2WD Rear end noise


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Hello everyone, I'm looking for a little advice before I get into too much of a mess. I bought my truck real cheap from a friend last year, it has 280,000 miles on it. It needed a little work, leaky vacuum hoses, tune up, that kind of thing, easy stuff I fixed myself. But the guy had kept it up pretty good otherwise.


A few weeks ago, I noticed a metal on metal grinding sound and some vibration coming from the rear end. It only seems to do it under load, going up or down hills, but it is getting worse every time I drive. First thing I checked was the u-joints but they all seem fine. I'm not sure how to tell if the carrier bearing is okay. When I push and pull on the drive shaft, the rubber around it seems fairly stiff, there is not a lot of play. I checked the oil level in the differential, it's topped off. The next thing I am thinking of doing is checking the wheel bearings. I'm really hoping that there is nothing wrong with the differential itself, I am trying to rule out everything else before messing with that.


If anyone has some suggestions or has had a similar problem, tips will be greatly appreciated. I'm too cheap and stubborn to take it to a shop just yet, I'm a DIY kind of guy.

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What color was the differential oil?

If it is a clear yellow color, then that is not the issue.

I also tell people that you have to remove the driveline to check the U-joints, it's really tough to check them in the truck unless they are really bad, like falling apart bad.

Are you positive it is in the rear, what happens when you are sitting still while idling with the clutch pushed in, and you let the clutch out in neutral, is it quite while the clutch is pushed in, but then makes noise when you let the clutch out?


BTW, Welcome :)

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Thanks wayno, the differential oil was dark brown, almost black. I will change that. I did not remove the drive shaft, but i did disconnect it at the differential to check the u-joints on the rear half and they seemed okay. I think i will check them again, a little more thoroughly. As far as when the noise happens, it doesn't  make any noise when idling in neutral or with the clutch in. It only seems to do it when i'm moving and it is louder under load. When it's moving on level ground at constant speed, it doesn't make much noise, if any at all. I did notice that the metal grinding sound seems to speed up when vehicle speed increases. That is what makes me think its something past the transmission.

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OK, I have had a few rear ends wear out, the faster I went, the more noise it made, when you change the oil in the diff, if it has a silver look in all the black, then you likely need a new one, and it's a waste of money to put new gear oil in it.

Do you have another gearset?

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The drain bung also has a magnet on it. A fine black paste is normal wear. Metal chips, flakes and chunks are not.


Wipe the bung clean so you can examine the next time the oil is changed.... usually every 30K miles. GL-5 80 or 90W. About 1 1/2 liters or just over 2 1/2 US pints.

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Thanks for the help guys. I do not have another gear set, so if the differential is bad, I'm gonna have to buy a new one I guess. I will drain and check the the gear oil, see if there are any metal chunks like you said datzenmike.

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