My X has a pronounced rumbling in drivetrain upon deceleration. It sounds kind of like the strips they cut into the edge of the pavement to let you know you are running off the road. For instance, if I'm going 75 and encounter a hill, it rumbles when I let my foot off the gas to maintain speed. It goes away if I accelerate, or take my foot off the gas entirely. It happens at 55, but is more pronounced at higher speeds.

Any ideas?

 

Sounds like pinion bearing preload.......hhow lond since the new gears ?

 

About 25,000 miles.

 

Is your pinion seal good ??

 

I think so. I had it replaced once because it threw oil on the exhaust. It has done this to some extent since I bought the truck at 92,000 miles. It seems to be getting worse. I thought it was tires, until I bought my new Michelins last winter. I had one rear end rebuild with my old 3.73's, (bad pinion seal replacement) and my 4.30's.

 

Sounds like it ran low on oil at one time. Tighten the nut on the yoke until there is a little drag and replace the oil for starters. Try it.

 

When they replaced the gears with 4.30's in Florida, they apparently set it with NO backlash, causing premature wearing of the ring and pinion gear. Looks like another ring and pinion set.