Rotational Noise.

[Dfmanley]

Hi all,

I have a 2007 Ford Explorer Sport Trac

When I am traveling at around 15 mph I get a rotational hum, it is sometimes worse, but does not increase proportionally to speed, and while it happens frequently it is not always there.

It happens with 4 wheel drive engaged or disengaged
It happens accelerating, decelerating, and coasting.
It does not stop when I apply brakes but will go away as my speed drops below 10 or goes over 20.

I did stop by a mechanic and he said he believes it is coming from the 4 wheel drive system but he would need to take apart the differential to tell me more.

I am mostly just doing some investigation to educate myself, and also seeing if I am able to work on this myself which I would prefer just for fun.

 

[Tech By Trade]

Do you have a match set of tires all the way around? What kind of shape is your front u-joint in?

 

[Dfmanley]

It actually started right after I bought one new tire so I dont have a match set.

And I inspected the u joint according to some other threads here. It seems really solid no movement at all. I did not take it apart to see if it is seized.

 

[Tech By Trade]

There is your problem. You need a match set or the RSS will engage the 4x4, without the light coming on. Get a match set all the way around and it will go away. The slightest variation in dimension will cause this, so even the same brand, with less ware will not work. I guess you could take that new one and put it on a real car and roll it until its the same size as the rest .

 

[Dfmanley]

Huh I will have to try all new tires then was just waiting a paycheck or two lol. And real car??? Lol just kicking me while I'm down nice.

 

[Tech By Trade]

By real car, I mean something that will roll the tires, none of this traction control garbage... Lol.

 

[Dfmanley]

ah ok ok, so what in the traction control would cause the rotational rubbing/humming I hear?

 

[Tech By Trade]

If one tire is spinning faster then the rest it applies the breaks, but the 4x4 also applies on to stop what the cpu thinks is a tire getting stuck. It uses the speed sensors for the ABS on each tire. There was a fellow on here who had the same thing happen on his explorer last month. his tires were father apart in size and it was actually grinding around corners.

 

[Dfmanley]

well yea that totally makes sense. thanks for all your quick answers!