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Message: [QUOTE="me2, post: 386916, member: 3825"] My truck is a 08 F350 6.4 5R110 4x4 LB CC. I bought it with 82K on it last fall. Its now got 110ish on it. Its a very clean truck. The previous owner never towed with it as far as I can tell. Its given me zero problems other than engine issues covered under warranty. A month ago I pulled our 13K 5er about 450 miles in some hills. When I got to the campground I noticed that the rear diff chattered going around corners, especially with the 5er hooked up. My '99 F250 does the same thing, but not nearly as hard. I also noticed a bad vibration from the rear axle area under hard acceleration in the lower gears with the 5er hooked up, like when you are accelerating away from a stoplight. This happens when driving in a straight line. I put a couple thousand miles on the truck and then we went camping again. This time I pulled the trailer about 600 miles. A couple times I noticed some vibration in the rear when accelerating. Once it was after an OD to 4th downshift. One day I was driving up a 5% grade, slowly accelerating. I was going around a bit of a curve. The transmission tried to upshift into OD, but there was a horrible chatter and it wouldn't complete the shift until I backed off the throttle. Our house is at the top of a hill. There is a steep section about 3 blocks long to get to it. It has a slight curve. When I pulled our trailer up it at about 15 MPH, the rear axle chattered hard the whole way up. It was shaking the entire truck. The transmission was not trying to shift. The truck also has a slight vibration at highway speeds on smooth roads. It shakes/vibrates an empty child seat sitting on the back seat. Tonight I dropped the driveshaft on the differential end. My truck has a steady bearing. The steady bearing seems OK. The slip joint works, but its a bit stiff. The differential U joints seem to move fine in all directions. I opened the diff and drained the oil. It appeared to me to be the first time it was opened. The oil is a bit dark but does not smell burnt. There was about 1/8" of debris on the diff drain plug. The ring gear pattern looks good. The volume of oil drained out seems about right. Prior to pulling the 5er the chatter going around corners was slight. Now it is much more pronounced. Other than the mentioned transmission incidents, it seems to work great. What is causing my truck to chatter ? [/QUOTE]