Noise when cruising

[kata]

I have a 2000 XLT with the 5.0 engine and AWD. It has 53000 miles on it. There is a waaaa noise from under the truck at highway speeds. Its not super loud but definate. If I accelerate or decelerate it goes away. I only hear it when cruising. I had the tranny serviced and saw nothing that looked bad. The diffs were a bit dirty (the rear being the worse) so I had the fluid changed. The tranfer fluid was fine. I haven't had the truck long. Is this normal or a sign of things to come...

Thanks

 

[shifty1]

wheel bearings??

 

[kata]

I dont know, I know waaa is kinda vague. It actually sounds like a transmission in a heavy duty truck. You know that gear noise that you hear. I didnt know if that was normal in a v8 or not.

 

[the_tool_man]

Hi kata:

From your description, I think it's the backlash (gear tooth clearance) in your rear differential. A tiny amount of backlash is necessary, and there is an allowable range. Under load, the backlash is taken up, and the gears run quietly. When not loaded, the gear teeth generate noise. The higher the backlash, the louder the noise. I've had brand new vehicles have that problem, and the mechanics at Ford told me it was normal. My '93 was like that for the entire 140000 miles I owned it, without any other problems.

I would bet that a competent rearend builder could rebuild your rear differential and reduce the backlash enough to improve the noise, but you have to decide if it's worth the cost. Of course, if the noise gets louder, or changes significantly in character, you should have it looked at right away.

Regards,
John.

 

[kata]

Hey John,

That makes sense and had crossed my mind. Its not that bad, just one of those things you hear while driving and wonder about. I like the idea of the it being the rear diff as opposed to the transmission. Anyway, I had pretty much decided that I will drive it until I can't drive it ( or there is an obvious problem ) which hopefully wont be for a long time. Thanks for the reply.