I started getting a Groan at any speed (0-75mph) coming from the Rear end. Never did it until I went on a road trip this past week, and now seems to be getting worse. Its a 2002 F-150 screw 4x4.

Gunna have the fluid checked in the morning, if not it, is the Diff going (gone) bad, and if so any one know how long it will last before it falls apart?

 

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Could be your pinion or carrier bearings are on their way out. The longer you wait to have this checked out, the more damage it'll cause. Have it looked at as soon as you can. Dont drain the fluid to inspect it yourself, you'll just waste money in filling it back up only so they can drain it again.

Mine did the same thing (9.75 axle) and groaned..more like a howled whenever I gave it gas. Most noticable above 40+ mph when was at its loudest. Carrier, pinion and wheel bearings were shot. When one fails, it releases bits and pieces of metal that flow into the others and cause damage. I neglected it for too long and had to have all the bearings replaced.

 

My 2000 groans only under acceleration and turns. It has done this since new, as does my friend's '99 Mustang. It reminded me of the groans limited slip rearends make. I might check my rear just to see if there is anything wrong with the bearings. I do have the limited slip axle though.

 

A limited slip might make some noise going around a turn while accelerating, not when going in a straight line.

If your LSD makes noise when accelerating around a turn, change the oil and add the reccomended amount of limited slip additive (it'll tell you how much to add on the bottle( it differs by brand) and it should cure that problem. but if it continues groaning when going in a straight line, your pinion or carrier bearings need to be checked. Or if you just recently had new gears installed, they were not set correctly.

 

Sorry for the misunderstanding, it does not groan under straightline acceleraion, nor in dirt. It is worse when accelerating and turning with a trailer on. Thanks for the info.