The dreaded "whump-wump" sound

[ganchan]

[font=verdana, geneva, lucida,]I have a (4x2) 2000 Ford Expedition with 197K on it. I've been getting a quiet "whump-whump" sound that gets faster with speed, resembling the choppy sound of helicopter blades up around 30-40 mph. It becomes unnoticeable (or maybe too fast to discern) at higher speeds, and doesn't seem affected by turning. It hasn't gotten any worse in the 8 months that I've owned the car. The previous owner apparently heard it too, but I think he just stopped investigating beyond the tires and cranked the radio up.    [/font][img=18x18]http://www.expeditionforum.com/styles/default/xenforo/clear.png[/img]

[font=verdana, geneva, lucida,]The other day I gave the car recommended maintenance to the tune of 2 new rear tires, alignment adjustment, and front wheel bearing repack. Haven't really driven it since then (ice storm), but am not counting on any of these changes actually solving the problem. If I discover that the sound is still there, what's the next thing to have the mechanic look at? All I can tell from my online research is that the issue could be rear wheel bearing, U-joints, pinion, hubs, loose wheel.... [/font]

[font=verdana, geneva, lucida,]I need to figure out the least costly way to troubleshoot the problem, especially if the solution turns out to be some kind of massive rear-end rebuild. The car is past due for a rear differential fluid change, so maybe we just try that first?...[/font]

 

[Motrukdriver]

At almost 200k it is probably due for a number of things to be replaced if they are all original. I have maybe 150k on my little Ranger 4x4, dunno since the little worm gear that operates the odometer broke some time ago, and I'll be replacing the U-joints and shocks when I get back home. Maybe I'll even replace that little worm gear so I can count miles again. I'm always checking tire wear to make sure it is even and nothing odd is happening. I've had the front hub bearings pulled, repacked and re-installed 3 times already and so far I was able to catch them before the bearings were toast. Rear wheel bearings repacked twice just because. Do you have any plastic trim pieces that might be loose and flapping slightly?

 

[ganchan]

Actually, I'm kind of lucky in that this car was a "project" for my mechanic, who worked on it for its previous owner. So it's had new shocks, struts, AC, bushings, ball joints, brakes, manifold, even an engine rebuild -- there's probably more new stuff than original stuff by now. But I suspect that the rear differential service got lost in the shuffle somewhere along the line... my records are curiously silent on that point....

Loose bits of plastic are always a possibility on an old beast like this. But I fear I may be facing a wallet-buster of a problem. On the other hand, I also fear having an axle break or a wheel seize up while I'm going down I-35 at rush hour.

 

[Motrukdriver]

Can you have your mechanic put it up on a rack and then put it in gear so everything turns as you rev the engine up and letting it fall back to idle. Might can catch some unusual sounds that way. I had to replace the diff gears on an old Ford pickup I had years ago. Pretty easy job but it was the old hog head differential. Just picked up a used chunk from the junk yard, swapped it out and took the old chunk back for scrap. Dunno how easy or difficult that would be on a newer Expedition. I say newer because my old truck was a 66. Heck, I even swapped the old 240 with a spun main bearing issue for a 300 I picked up from the junk yard. Rented a cherry picker, took everything off that was in the way, yanked the old mill and dropped the replacement mill in and bolt everything back on. That was a 2 day job in the front yard. My Ranger is a 96 and I wouldn't hesitate to wrench on it if needed and time allowed. If you do decide to wrench on it yourself be sure to take pictures before you do anything so you have a visual on how it goes back together.

 

[ganchan]

If it needs a whole new rear end, I'm definitely asking my mechanic to pick something out of the junkyard for me. I'm financially challenged.

 

[jonyjoe303]

It sounds like the front bearings that you replaced. If it still does it, it can be the rotor. On my car I replaced the bearings on one of my front tires but it was still making that noise, I found out that the original bearing had overheated and wore into the rotor. The rotor had too much play and was making that noise. 
I didnt catch it when I originally replaced the bearing, drove it for a while and it kept getting louder. Like your situation the faster I drove the faster the noise went. You can also feel it when you let go of the gas to slow down. 
If the work you had done doesnt fix it, check the rotors, its a easy fix, the new rotor wasnt that expensive for my car.

If you had a differential problem you will hear chirping type of noises when turning, also you may feel like one side of your front brakes is sticking. Sometimes you might hear clicking type noises when slowing down. No one ever changes the diffferential fluid, its a major job but you can get a good look at the gears, when I fixed my differential, as soon as I opened it I could see the damage, there was alot of bubbles on the oil (sign of water) in the fluid which probably was what cause the gears to fail.   

The u-joints is more of a clunking noise everytime you change gears.

 

[Netter]

[font=verdana, geneva, lucida,]I have a (4x2) 2000 Ford Expedition with 197K on it. I've been getting a quiet "whump-whump" sound that gets faster with speed, resembling the choppy sound of helicopter blades up around 30-40 mph. It becomes unnoticeable (or maybe too fast to discern) at higher speeds, and doesn't seem affected by turning. It hasn't gotten any worse in the 8 months that I've owned the car. The previous owner apparently heard it too, but I think he just stopped investigating beyond the tires and cranked the radio up.    [/font][img=18x18]http://www.expeditionforum.com/styles/default/xenforo/clear.png[/img]

[font=verdana, geneva, lucida,]The other day I gave the car recommended maintenance to the tune of 2 new rear tires, alignment adjustment, and front wheel bearing repack. Haven't really driven it since then (ice storm), but am not counting on any of these changes actually solving the problem. If I discover that the sound is still there, what's the next thing to have the mechanic look at? All I can tell from my online research is that the issue could be rear wheel bearing, U-joints, pinion, hubs, loose wheel.... [/font]

[font=verdana, geneva, lucida,]I need to figure out the least costly way to troubleshoot the problem, especially if the solution turns out to be some kind of massive rear-end rebuild. The car is past due for a rear differential fluid change, so maybe we just try that first?...[/font]

could be either a unbalanced tire or a bent rim. Maybe a bent axle.

 

[mr_elijah_gardner]

Any idea where the sound is coming from? Front or Back of the car? left or right? or is it at the transmission tunnel? Let someone else drive so you can move around and try to get a general idea of where the sound is coming from. That's what I usually do to help track down funny noises.

 

[ganchan]

I think it's coming from the back, but it's really hard to tell. I supposedly had a rotor resurfaced during my last brake pad replacement -- but I'm not actually seeing the rotor work noted on the service record, and the sound didn't change afterward. (It did solve a "crunching" noise I was getting on braking, fortunately.) I could have that double-checked.

I thought differential fluid had to be changed every 90,000 miles or something. But you're right, nobody ever seems to make a point of it.

 

[ganchan]

I looked under the car and I see what looks like an oil stain on the differential. So I can safely assume that my differential is leaking fluid? Sigh.

 

[jonyjoe303]

When they open up the differential to replace the fluid, they will be able to tell if there is any damage. There are some big gears in there, not easily damaged. 
The differential fluid is very thick, will leak very slowly if the cover is coming loose.
I be very surprise if the differential is the one making the noise. I think the differential just needs fresh fluid and new cover gasket since it hasn't been done previously.
But also check around the front of the differential the seal where it connects to the driveshaft, if its leaking from there, its major work to replace it.
Myself I would try a stopleak product first before I replace the seals.

 

[ganchan]

Drove with a mechanic this morning, and he discovered that the e-brake appears useless. He's looking at that issue, and he's also going to check the u-joints. Believes that a failing differential would present different/additional symptoms such as howling noise. He also says that the noise feels like it's centralized, not coming from the right or left side.

Well, we'll see what happens.

 

[ganchan]

Update: Well, the differential, u-joints and axles are shot, from what I'm told. I don;t know whether to authorize the repairs or just drive this thing to nearest used car lot and try my luck on something else....

 

[ganchan]

Fortunately, the shop has a couple of preferred "recyclers" that it can pick parts from, so they can get me a used diff instead of a rear one. So I guess I'll come down off the ledge and invest some more dough in this car, since it's doing such a good job for me in other respects and it seems to be in good health otherwise.

 

[ganchan]

Update: Amazingly, the rear axle bearings were OK after all. Replaced the rear diff and u-joints (and balanced the drive shaft). Runs perfectly now! Let's hope this is the last big thing I need to do for a while.....

 

[Riverman]

Glad you got it fixed.

 

[Varmint]

I've had this "whump-whump" sound on a couple of vehicles, and it was caused every time by either:

a) Broken or torn belt in a tire. Not noticable by wheel-balancing, it is only detected by driving on it. Replacing the tire with another new one is the only cure. This is always my last resort for some reason. I've had to go through several tires to get one that doesn't have this problem, as being "new" means nothing. I think it's just a manufacturing glitch.

b) Having a window open on only one side of the vehicle, usually in back. The sound is caused by pressurizing of the cabin followed by a sudden release of said pressure, hence the "whump-whump" sound. Opening or cracking two windows, usually in the rear, will relieve this, as the air pressure can equalize smoothly.

I'd try the window thing before spending cash on the others, and the tire replacement is a last resort after the other options fail to cure the problem. Like I said, buying a new tire isn't necessarily a cure-all, as I've seen the problem on brand new tires.