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Discussion Starter · #1 ·
Has a growl at about 55 and above, only when under power. If I let off the accelerator, it stops. Has a new auto tranny, so that isn’t likely. Wouldn’t be a wheel bearing, because that would be constant, and I don’t think they sound like that going out. Possibly carrier bearing? or rear end input shaft bearing? This is in 4high, with hubs out, so it’s not the front end. I’ve only had it a few weeks. Any ideas from someone who has more experience with these?
 

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Check to see what rpm gives you the growl. Then park the vehicle in park and rev the engine to that rpm and see if you get the growl from the engine while the vehicle is not moving. This test will identify whether the growl is coming from the engine, or from somewhere else.
 

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Discussion Starter · #3 ·
Well, I found out the problem. Noticed the rearend getting hot to the touch, so checked the oil level. Usually, I would have done it already, but just got the truck and hadn’t. It was half a quart low and had a foamy gunk on the back of the plug with metal particles in it. Rear ujoint is also sloppy. What is the best way forward? change of gears or look for a used rear axle? I’ve never replaced rearend gears, but probably can do it. I am assuming that with rotors on the back, that nasty oil didn’t get into the wheel bearings. They are hopefully packed, not fed with oil from the rearend.
 

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A little metal dust isn't unusual. I would pull the cover and see what's up. The u-joint may be the cause of your growl. Is the pinion seal leaking, and is there any play in the pinion shaft? If so, then the bearings are shot and the gears may be worn enough to need replacing.
If if's not a dually, it will have a Ford axle, which does lube the wheel bearings from the differential lube.
If you've never replaced rear end gears, I would recommend you have someone do it for you. It takes some care in getting the gear pattern and backlash set up correctly, as well as bearing preload. If you can find one, a used axle might be your best option.
 
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