Driveline goes "brrrt"

[Cherryriver]

Our very recently-acquired 2003 XLT 5.4 AWD, 185K miles in excellent condition, has a curious driveline shudder that's getting on my nerves.
It's very occasional, brief, and most people might not even notice it.
It comes across as if you've run over some of those road shoulder noise-maker cuts they put in to alert drivers they're off the road. Or maybe a couple of rough Botts Dots, or even a little patch of excessively-rain-grooved concrete.
Yet I'm sure it's not pavement defects, being an old-time motorcyclist; we spend a lot more time studying the pavement ahead than non-motorcyclists do. So I'm not seeing the culprit on the concrete.
It's short duration, one to at most, two seconds. There's a vibration to be felt in the steering wheel but it's pretty faint- I mostly notice the sound, which is not at all loud.
About the only time I can seem to discern it occurs, and this not reliably, is letting off the throttle for a bit, say, three-five seconds, then coming back on anything other than softly.
I have no illusions that a forum written description can serve for a diagnosis, but on the off-chance this is something that's a known thing (that I couldn't find exactly searching here for an hour), maybe I could get a clue as to where to begin to look.
My previous experience makes me think, completely without justification, that possibly the transfer case clutch is sticking and chattering, or there's a driveshaft slip joint dried out and binding. I had an early Blazer K-5 with a NP203 that would do the dry-splines thing with annoying regularity, and that's the basis of that wild guess.
Thanks
Bill

 

[whtbronco]

So you had pretty close to the same thought I did with the driveshaft. Look at the u-joints first. Assuming you have a 2wd setting as well you can remove the front driveshaft and drive around with no implications and isolate it entirely that way.

It's a long read, but I have been chasing vibrations for months now and this thread has some info on what I found, how I found it and what I did to resolve it.

https://www.expeditionforum.com/threads/not-so-good-vibrations.55319/

Man I loved that NP203, had one in my 78 Bronco and it was awesome.

 

[Cherryriver]

whtbronco, I went through that whole thread and it sure was fascinating. But it didn't seem to hit on what is going on with this one in my inexpert opinion.

 

[whtbronco]

Agreed, but it should have given you an idea of what to look at and maybe how to. I doubt anyone can say "here's the issue" without getting under it. Start by pushing/pulling on stuff looking for play and if that fails get it on jack stands. Start it up, put it drive and try to replicate the scenario while you watch and listen for the noise/vibration. I have found a mechanics stethoscope can be pretty useful, a wooden or metal dowel can suffice for this as well, but the stethoscope for $5 works better I think.

Another thing is don't discount any possible contributor just because it's unlikely, ya know like I did :-( and noted in that thread.

 

[Johnnyfinn]

I had an issue like this and I felt it on lockup. I replaced the trans fluid and the issue went away. I did end up having to rebuild the trans in about 50k, which for me is like 9months. I am not a big fan of the trans fluid change but in this case it worked. Good luck

 

[SafariGoneWrong]

Hey Bill, I keyed in on 3 things you said: (1) Yours is AWD, (2) It happens after off throttle then back on throttle anything but softly and (3) it's felt through the steering wheel. It got me thinking the Integrated Wheel Ends (IWEs) Ford uses to lock / unlock the front hubs to the half-shafts. They're vacuum actuated, so when you're in 2WD vacuum is applied and the hubs are disengaged from the half shafts. Maybe if one or both are weak or leaky, they want to engage or partially engage as engine vacuum drops with applied throttle. May be worth checking the vacuum system/lines aft of the battery and the condition of the vacuum reservoir and its line behind the battery box. I've read when the IWEs fail they can be heard... Hasn't happened to me so I have no first-hand experience (replaced mine pre-emptively in 2019 at 110K mi.). Also, the vacuum line set going to the IWE solenoid is replaceable as a set and includes a check valve. Until @whtbronco was going through his vibration troubleshooting, I didn't realize the front driveshaft is turning in 2WD...had to read the service manual...so these AWD systems aren't like the BW1356 in my Bronco or the NP203 I suspect. Good luck --Dave

 

[whtbronco]

@SafariGoneWrong well the IWE's is a good point, I sure had not considered a partially failed IWE scenario.

Yes, I would love to have a straight up 4wd transfer case like the BW1356, NP205 or my favorite the full-time 4wd NP203. I have never liked AWD and this Expedition has made me like it even less. Overly complicated system.

​

 

[Dustin Gebhardt]

My '01 had a similar noise at odd times and it went away after I replaced all 4 U-joints. It was a relatively easy job, once I obtained the 3 different u-joints, which required 3 trips to different parts stores.

Or, as others have said, it could be the IWE system. This system is easy to troubleshot with a handheld vacuum pump and gauge. I was able to find the broken tubing on my '07 within 20-30 minutes of easy diagnostic work.

 

[EngineerMike]

@ 185k, replacement of the xfer case shift motor for P.M. purpose is a good idea. Not difficult, plenty YT vids, I did mine so even an engineer can do it. Mine wore out ~170k, caused sticking in 4Lo & unreliable shifting. There's a wild chance that's it & the flimsy position indicator plates have abraded enough flashed on copper that it might try to "correct" the gear range. Better chance its vacuum shifting front hubs, but that xfer case motor is a definite wear part & when it goes U may be stuck in 4Lo far from service. FWIW