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I put in a 9" truck rear a few months back. At 60 or so MPH I got a slight but noticible vibration. I did a number of checks per your suggestions (driveshaft angle, U-joint issues, etc) and feel pretty confident the noise is due to the axle bearings. I talked to the guy that narrowed the rear-end, and he was not terribly concerned. He said I could drive it and put up with the noise for a while, or pull the axles and buy the bearings and he'd press them on free of charge. Well, I drove the car for several months with the usual vibration above 60 (the highest speed limit on the roads I usually drive is 55, so no big deal).

Fast forward several months, and I began having some brake problems, due in large part to me pulling a dufus and riding my brakes to help seat the front shoes, and as a result glazed the rear shoes. So this weekend I replace the rear shoes and go for a drive. I get the same type of vibration, but it is MUCH more severe and comes in around 40 MPH now. I pulled the drums and checked to make sure everything is kosher with the brakes, no problems noted. I was hopefull I just had one of the sides adjusted out too much, but I ran them both in almost all the way (until the adjuster was about to fall out), and the problem is still there! I also checked to make sure the shoes were centered on the backing plate, and they appear to be perfectly centered.

While I was replacing the shoes I noticed a thick liquid that had apparently drained from the axle seal at some point. It was thick and black (probably due to brake dust, I guess). This liquid was also around the back groove on the drums (the part that mates with the backing plate), and there was a ring of it around the inside of my wheels on each side. I cleaned this off very well with brake cleaner, and I'm wondering if the end seals are leaking, and I blast brake cleaner in there, could that de-lube the bearings and make things much worse? I have a hard time imagining I got that much brake fluid in there, but I dont' know what else to think. When I raise the rear on jack stands, I can hear what sounds like the bearings makeing some noise when I rotate the axles.

Another possibility is that I leaked enough rear end dope to make the bearings run dry, but again the amount of leaking is very minimal and looks like it happened weeks ago. I can't get the drain nut to budge, so I can't check the level. I can add more fluid through the vent hose hole, but I don't want to do that if I have plenty of fluid in there already.

I guess the part that frustrates me the most is that the only thing that has changed since early in the week (no noise/vibration at 40 MPH) to now is new shoes and a thorough cleaning with brake fluid. I even thought it might be the tranny somehow, so I checked and added about a quart of fluid (it was on the low end of the cross-hatch, so I figured I might as well. I have a slow pan leak but that's another post in itself...). That didn't help either. Do you guys have any insight into what I'm seeing? I know wheel bearings are inevitable, but I'd rather tackle what is making the vibration first if it isn't the wheel bearings. Thanks guys /forums/images/icons/smile.gif

Shane
 

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I had something similar, thought it was a worn ring gear. The svc mngr. at the local Ford place told me how to check the axil berring. Pull the axil, put the berring in a vice and tighten down on it enough to out some force in the berring race. Then turn the axil. If there is more resistance at some point the berring is bad. I replacerd mine then sent the new ring and pinion gear back to Summit.
 
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