2000 Expedition bearing noise stumper

Hey guys!

2000 Expedition AWD, 4.6l
150K on car, 50K on trans, 150k on transfer case and most else.

The problem is, under load, there is a intermittent bearing vibration noise...it sounds like a roller bearing that has too much tolerance so it vibrates in and out under acceleration. You can feel it in the gas pedal and chassis, you can hear it, and it robs a little power when the sound it pronounced. The sound is 10x worst when towing my 6000lb boat. Gear doesn't seem to matter, but it is hard to make it happen in 3rd gear.

Diagnostics so far:
-Can't reproduce sound on rack or out of gear
-Stethoscoped all accessories - good
-added Lucas oil additive to engine oil - no change
-added Duralube high mileage goop to trans - no change/slight change?
-Aamco said it was transfer case, tear down and inspection revealed nothing, they said it was mostly pristine for a car with 150K on it.
-Inspected U-joints - all tight

The duralube in the transmission may have made a slight difference in the frequency of the sound...but it could be my imagination, it wasn't significant enough a change to be determinate.

I am stumped on this one, so is Aamco.

I have never had an issue I could diagnose like this and really don't know where to go from here....any suggestions would be awesome!!!

I think I could isolate the issue with a diagnostic tool that doesn't exist as far as I know...it would be a handheld device with 4 magnetic mic sensors you could stick in various locations and watch the waveform output on the handheld...you would simply move the mic's around until you got the highest amplitude on the readout.

At this point the only thing I can think of:
-Aamco missed something
-Main bearings, cam bearings, or possibly oil pump
-Transmission bearing (Aamco says "NOT")

Please help, I am at a loss....

Derek

BUMP!

Come on guy, someone must have an idea....even if it's "Take it to your Ford dealership" Will they charge me if that can't diagnose it? Ammco didn't charge me anything and they removed and inspected the whole x-fer case....

I would guess they would charge you for labor.

I would check the u-joints and wheel bearings.
Make sure the front diff has fluid in it. Go in a parking lot and put it in "N" and push it. See if it is dragging or if it makes a noise.

When it does make the noise when driving pop it in N and see if it makes the noise when it is coasting.

Sounds like driveline to me. Does this Expedition have a two piece driveshaft? If so could very well be the center bearing,( aka hanger bearing). Thats the bearing that it passes through half way down the driveshaft. Lift the driveshaft up and down and see if the center bearing has excessive play. Other things to check is the transmission tailshaft bushing, where the driveshaft goes into the transmission. Lift the d/shaft up and down there too and check for excessive play. Although there's usually a leak there too. Check the engine and transmission mounts for looseness,cracks and rubber to metal delamination. Hope this helps.

I'd lean toward the drive line also. To try and eliminate the engine, I'd put it in gear, put on the brakes hard so that it won't move, then slowly increase pressure on the gas pedal to see how the engine reacts under extreme load while the vehicle isn't moving.

Whats the behavior when a carrier bearing goes out and how do you diagnose it physically? Will play in the bearing be obvious and evident? Can the noise come and go?

Check the center bearing like I said. The best way is to drop the driveshafts and check bearing for rotational roughness and side play. U joints can be bad and not show excessive play. They can be very tight when you twist them and show rust streaks coming out of the trunnions. Slip yokes can be worn. The driveshafts must be in proper phase to each other. Check for welded on balance weights that might have broke off. Check the engine mounts like I said. Yes all these can cause your symptoms. Yes it can come and go. Harmonic vibrations rise and fall with speed changes. Put the car up on jackstands and take it out of park before checking.

So, I got my car back from Aamco after they cracked the transfer case and said it was pristine and not the problem. They basically just put it back together and put new fluid in it...funny thing is, now the noise is gone! Or at least undetectable....I am going to tow my boat tomorrow, so it will see how it does under extreme load. Obviously there is a worn part in there, at this point I am considering just buying the master rebuild kit for $124 and rebuilding it myself. I just can't figure out how Aamco missed something like that. I'm guessing that once the assembly lube wears off the thrust bearings, the noise will return, but I guess it could also be one of the cage bearings...this is pretty frustrating!

Deltap, thanks for the info, I will inspect all that stuff. Can you elaborate on the shafts being in phase? I assume that means I should make sure the needle bearing cups are lined up? That's just for the split shaft, not all 3 correct? And cool screen name BTW, it tells me you have a background in science.


Thanks, Deek

Phasing the driveshafts means the 2nd shaft slip yoke would be installed on the splines of the first shaft so that its in the same orientation as the yoke just behind the trans and not 45 or 90 degrees to it.
I'm sure hauling that 6k boat at hiway speeds has taken it's toll on a 150k driveline. Time for maintenance.

Thanks all for the advice, it was the transfer case. Now, can anyone recommend a QUALITY rebuild kit? How about rebuild guide for a Borg warrner 4406 transfer case? After seeing it all opened up, looks super simple to rebuild, I am going to do it myself. I already own a snap ring tool and a blind bearing puller tool, assuming I have the correct size collets....Is there anything else I am going to need? Thanks again!

Did you ever get this issue resolved?
Mine was/is exactly the same. To test it I actually had to put it on a lift and run all 4 wheels until things got heated up and isolated the noise from the transfer case. Changed fluid and got another 10K miles and then the problem came back worse.
Problem was in the magnesium case halves. 3 Problems
(1) The 2 holes in the case that the shift rails seats into gets wallerd out of round causing shift rail to have excessive play.
(2) Rear bearing hole in the case that the bearing sits in gets out of round causing uneven pressure on bearing
(3) The tab on the pump slams into the case and over time causing a groove in the case caused by the impact of the pump tab

To me the best option is to get new case halves from Omega Machine in California, but it was expensive because of my distance and core charges. They put new bushings on all these troubled holes and a pin where the pump seats in the case. Better than new in my opinion.
I ended up just getting a low mileage used Transfer Case from a salvage yard, but its a crap shoot that it won't have the same problems that these cases are noted for. The first one I got used with 115K miles was worse than my original. I am hopeful that this 2nd used one with 72K miles will be better.