Hum at 70+ mph
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New User
Joined: Sep 2007
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Hum at 70+ mph
I recently installed a 2" suspension lift on my '05 5.4 F250 that is my work truck as well as my personal vehicle. Typically I drive w/ about 600lbs. of weight on the truck between the ladder rack, tool boxes and tools, and in the two weeks that the lift has been on, the truck has driven well. Today before I departed on a 300+ mi. trip I removed the rack, the boxes and tools from the truck. Initially everything was fine. Once I got on the highway I noticed that a humming noise and a slight vibration started at 70 mph and got worse as my speed increased. As soon as I took my foot off of the accelerator the humming stopped even though my speed stayed the same no matter how fast I was driving. The noise is the worst when have my foot on the gas just enough to maintain my speed without accelerating or losing speed. What might be causing this? Thank you in advance for any insight.
Fleet Mechanic
Joined: Aug 2005
Posts: 1,339
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From: NJ
I believe that it is the driveshaft angle. I also got this same noise/vibration after going from F250 to F350 rear blocks. I have not done anything about it as I rarely drive over 70 but I believe shimming the carrier bearing would help. This is of course assuming your truck has a 2 piece driveline.
Fleet Mechanic
Joined: Aug 2005
Posts: 1,339
Likes: 5
From: NJ
You could either buy premade shims from Ford or you can easily make them out of 1/4" flat stock, cut to size, drill some holes and install between the bearing and the mount. Try 1 and see how it is, if it is not gone you may need to add a second.
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I checked and Ford said that they do not make the shims, so I did what rwilimo said and cut them from 1/4" flat stock. I made two pieces 8" X 1 1/2" and installed both pieces above the carrier bearing shimming it down 1/2". It fixed the problem and eliminated an acceleration vibration that started after I put the lift in. Thanks a lot for the help.
