Low Pitch Hum from 03 Sport Trac 4x4

[gguerra]

I recently had my oil changed and the guy that did the work noticed a leak from the front differential. He topped it off but when I looked myself I noticed the leak was coming from the pinion seal. Well I figured I would fix it in due time and it would not be a big deal since (I thought) the truck was part time 4wd (or is it?) and as long as I did not engage the 4wd I would be OK. Well a few weeks after it started making a low pitch humming sound. It is a manual tranny. So what I did was while going down the road I stick in neutral and turn the engine off, well the low pitch hum continues until the truck comes to a stop. At this point I don't know if it's bearings or axle/s. It sounds to me like an axle (probably the front).

At this point I'm going to take it into the shop and have the fluid checked on the axles and tranny. I dont know what else to do. The truck still runs well except for the annoying low pitched hum.

Question: Is the truck part time 4wd or full-time (AWD). It does have the knob on the dash indicating 2wd, 4wd high and 4wd low. It's always in 2wd. Last time I went to the beach (after the leak was detected) the 4wd worked fine. (It was kind of an emergency)

 

[John_Rock]

It's a part-time 4wd system, but....

There is no disconnection of the front drive line at the hubs like you see on an F-250 4wd. So the CV axles are always spinning and in turn they spin the Ring and Pinion gears and that spins the front drive shaft. Hence that's why 4wd Explorers get worse gas mileage than the 2wd Explorers.

And your pinion seal could still be leaking.

But, I doubt it would go bone dry and cause a humming. You should still check the hub/wheel bearing assemblies.

 

[gguerra]

Thanks for the reply. Finally someone answered. I was going to call the ford dealer and ask them. I doubt it's the wheel bearings because while road testing it I quickly turn the wheels to either side and there is no change in the sound. Pinion seal doesn't leak (much) as there is only a small little stain on my driveway and it has since gone dry.

Are there any other bearings in the hub assembly besides the regular wheel bearings?

I'm going to have my mechanic replace the leaky pinion seal and and at the same type open up the front axle to inspect it. It really sounds to me like it's from the front of the vehicle. It could be the rear but I doubt it. Also from what I have heard when you have bad wheel bearing/s it is usually a higher pitch sound... I guess we'll see what the mechanic says. Oh and one more thing the sound is audible only when going less than 50 mph, really bad from 20 to 40 mph

 

[John_Rock]

Are there any other bearings in the hub assembly besides the regular wheel bearings?

No.

I'm going to have my mechanic replace the leaky pinion seal and and at the same type open up the front axle to inspect it.

To take the front cover off and look at it, he will need to remove the CV axles on both sides and drop the axle down out of the truck.

Sometimes they make noise when going bad and sometimes not in my experience. My latest one is not making noise but is going bad. An alignment shop caught it and would not do the alignment until I fixed it.

 

[gguerra]

I'm about to take it to the mechanic today. Can't stand the sound anymore as it's getting loder. I'm just wondering, could it it be something with the CV axles since they are always spinning. Do they go bad?