Ok,riddle me this...

2004 F150 SCAB 4WD with 150K miles and it has developed a rythmic mild rubbing/thumping sound from the front end. The noise is definitely in time with the wheel speed, and if I do a slalom down the road, when curving left it is present, but when curving right, it goes away.

To me, this sure sounds like the right front wheel bearing is on the fritz, so this afternoon I replaced the unit (&*&@!*&# Ford and their integrated hub/bearing module).

SOUND STILL THERE!

So here's what I know:
- Unload right suspension, sound goes away.
- Load on right suspension, sound present.
- Sound present in both 4WD and 2WD
- Sound present when accelerating.
- Sound present under light & heavy braking.

 

When was the last time your front diff fluid change? Do you notice anything different when you are on the gas (drive) vs when you let of the gas and coast?

 

Front diff fluid hasn't been changed in quite a while, but with the truck in 2WD shouldn't there not really be anything moving in the front diff?

Not really much difference when accelerating vs coasting.

 

Regarding the front diff...I just went back out to the truck to check on some more stuff. How much rotational play should there be in the front axles when the truck is sitting on the ground and in 2WD?

My right front axle has about 1/2" of rotation at the inboard flange bolts and the left front axle has about 3/8" of rotation at the inboard flange bolts.

My guess is that this isn't good, and there should be zero rotational play.

 

You are right with the diff shouldn't rotate in 2wd (I forget which car I am thinking about). Could be your hubs? I would think if you are in 2wd and your truck is on, aka providing vac to the hubs then you should have infinite rotation because if you roate the flange, it's just going to spin the spiders in the carrier which will spin the other side drive axle. I think in you test you are testing the amount of rotation before the locking hub grabs.

 

Finally able to resolve this issue today. My original analysis was correct...it was the wheel bearing. Only problem was I thought it was the right front but it was actually the left front. I would have bet $100 the noise was coming from the right side (in fact I did bet $200 with the new wheel bearing!) So I pretty much just confirmed that I need to do a diagnostics and not just go with my gut feeling about what is wrong.

Unfortunately, I also discovered that both IWE's are shot while changing the bearings.