my FX4 has developed a knocking sound in the rear somewhere over the last few days. Only happens on bumpy roads so I figured it was suspension related. Well after having a friend shake it from side to side while I rolled around under it, it was immediate that the noise was coming from the rear end housing. It sounds like that axles are banging around in there and at the hubs. Not good.....

I have taken apart many 9 inch and Winters style quick change rear ends in race cars but never checked into this unit before. Are these full floating axles that may be banging around like that due to possibly low fluid? Other than banging on bumpy roads, the rear end is smooth and quiet. Any thoughts before I pull the back cover off?

Figured now is the time to change/add fluid (obviously)and possibly change the pinion seal.

 

That side to side "clunk" is normal for any rear drive housing that has any real miles on it. It's the play between the groove in the end of the axle and the "C" clip and the cross pin that keeps the axles out in place. You probably hear it on rough roads because there is a tendency for the axles to slip sideways that small amount as well as be pummeled up and down. It's nothing to worry about and easy to take a look at while you have the cover off. Normal wear in the inter-relation of those parts. I wouldn't even take it apart (cross pin and "C" clips). Just have someone shake it from side to side while you watch that with the cover off.

 

thanks for the info, makes me feel a little better but the banging is loud now that I can hear it really well in the cabin with the windows up. Fluid level is okay as it dribbled out when I removed the fill plug but I am going to change that anyway. Can these C clips come off or break? Or are they considered a wearable item that sometimes do need to be replaced? They don't look too terrible to change. I understand that some noise is acceptable but I feel this is excessive and fear I find something major when I pull the rear cover off. Truck just clocked 130k.

I'll get a video and imbed later

 

C clips can break but if they do your axle would fall out. So doubt that's the problem. I doubt the pinion nut would back out... Other than that most times a rear axle will whine if something is wrong. I would go back thinking something with suspension or a body mount is loose. Or check the spare time, never know.

 

A.desisto is correct. The axle would be doin' a "wide track" if one of the clips broke. I suppose they could, though I've never personally seen it happen. When wear happens (normal in enough miles) it would likely be the "C" clip AND the groove it sits in, in the inner end of the axle. That means to get rid of it IF that is the cause of the noise, you'd likely have to replace the axles, clips and the cross pin. Obviously the noise could be something unrelated to the rear axle, that needs to be thoroughly checked out BEFORE you go into the rear end. 130K mi. shouldn't be a problem unless those parts weren't hardened properly, and I doubt they'd last NEAR that long if they weren't. The reason I told you to have someone rock the truck back and forth when you have the cover off is then you can lay under there and SEE how much movement there is in the "C" clip, end of the axle and the cross pin. You said it was quiet on the open highway, the reason I said it was likely the normal wear in those parts. If the cross pin wasn't hardened properly it could wear and allow the excessive inward play.

 

If you're really worried pull the cover. Look at the oil, if you see signs of metal in the oil then you have problem. No metal = no problem. At 130k wouldn't hurt to change the gear oil anyways.
I had the spider gears in mine grind up at 60k. So stuff can happen to the rear.

 

Well I removed the tailgate, checked spare tire, banged around underneath with my palm to see if anything was loose. Took off the gas tank protector and any thing else I could think of that might cause the noise. Checked all nuts, bolts, fasteners, bushings etc. Its definitely inside the axle housing, more so on the drivers side.

Fingers crossed.....

 

Check out this link https://www.f150online.com/forums/ar...lots-pics.html It is not quite your problem but might give you some idea of what you should be looking at.