I wrote earlier here when my '06 F350 didn't want to engage after being revved at a smog-test. Go the truck home, cleaned the connectors and drove back to the inspection again. (Thanks again to all of you, who participated!) Well, I did got it inspected and all, but it's still not running as it should. This time I'm suspecting the transfer case (NP 273 E).

Symptoms: When ever I drive over 40 MPH I will hear a nasty "crunchy" sound under the car. It'll stop immediately when I let of the gas. And will come back again after a while. Noticed that if I drive under 40 MPH, it will not make the sound. As the truck is LWB dually and has 4.10 diffs, it'll actually go trough all the gears and lock the TC even when driving under 40 MPH.

So, the other night I went to friend's garage (where my truck actually fits inside) and unplugged, cleaned thoroughly and put good dielectric grease to all transmission & transfer case electrical connectors. Unfortunately this did not have any effect on the nasty sound. Still got to keep on goin low&slow...

But I did try my 4WD now as the snow is here. The first time I switched on 4x4, it made exactly the same sound for 2 sec. Was driving 5-10 MPH. 4x4 works. Then tried 4LO and it works too. Back to 4HI & 2WD, all great. Next time I switched 4x4 on again, it made the same sound, only shorter.

So, now I'm thinking the sound is from the transfer case synch that makes it! My only trouble is why is it doing it when driving on highway (2WD on) and not touching any switches? And why ONLY when doing over 40 MPH, never under. (Except when switching 2WD->4WD).

Cause? I'm thinking the 4WD-switch or maybe the relays? Maybe either on is resonating exactly at the right (wrong) frequency when driving fast enough and making contact to switch 4x4 on/off quickly?

Has anyone come across anything like this or have any other ideas?

 

It may be time to drop the driveline to clean and grease the slip yoke.

 

Slip yoke?

I'm not saying that it couldn't be, but I don't see how that would cause it. Luckily that's an easy fix, so I guess there's no harm in trying anyways! (It should be lubed up well in any case,.)

I mean the sound was exactly the same when driving 50 mph and it suddenly makes the sound. (Sound stopped when I let off the gas. But came back a minute later when driving on at the same speed.) As it was when I was driving 5-10 mph and switched 4x4 on. (Sound stopped when 4WD engaged.) If it would be the slip yoke being stuck, then I would guess the sound would differ depending on the speed.

 

Probably the 1st thing you did, but worth saying: you change your xfer case fluid and check for metal? What fluid did you put back in?

Don't like the description of that noise it's making...

 

Don't like the noise either.

Didn't drain the transfer yet, as I was suspecting the tranny (until driving home from the garage). It's well below freezing point there so, I'm not keen on lying in the snow. Waiting to get the garage again for that.

What fluid would you suggest? The transfer case is basically just a simple manual tranny, but as it's connected to the automatic and the theoretically COULD be some leakage, I'd probably use same ATF as for the auto-tranny.

 

I made the mistake of putting Mercon V in our Expy. Then along comes our friend Sean and shows pictures of BLOWN UP xfer cases because of using the V. Probably put 7k miles on the fluid and even PM'd Mark K. on whether it was true or not and he said get the V out of there (the Expy is an active xfer case: wet clutch that engages front when rear slips (in Auto mode)).

I went to Wally World and bought a few qts of SuperTech Dex/Merc (original DexIII and Mercon equivalent). What a mess to change and fluid came out ok so that fear is aside. It only took 2 Qts but the pump I used wouldn't pull from the bottom of the bottle so glad I got three.

I'm wondering if it is your chain in the case? You have checked that there is fluid in there, right?

 

Someone said "SEAN"

Anyway I also think it time to drain that transfer case and check for parts.
Just use a fine screen and a funnel and see what you get.

As for fluid because when I did mine the trans was being replaced I just
went with the Ford Transfer Case Fluid. Yes it a bit more money. BUT
it will be the right stuff not the left stuff. Left as in should of been left on
the shelf. I know bad joke.

I attached some service PDFs for you to look at. That way you have an idea
on what the insides of the transfer case looks like and the diagnostics that
you may want to do.

First thing on the list is check the fluid.

Also you can if you have a place to get all 4 wheels off the ground in 4WD and trans in N.
MAKE SURE IT'S SAFE. Or don't do it.
Hand turn the drive lines up as close to the transfer case as you can and feel for any
non-smooth movement.
Then switch to 2DW and hand turn both again.



Sean


6.0L Tech Folder

 

Thank you Yahiko for the docs!

 

Your very welcome.
Let us know how it goes.



Sean


6.0L Tech Folder

 

Just had a look at the xfre docs and wow, this brings back memories! - This seems to be just a scaled up version of a NP used in Jeep TJs. And why shouldn't it, Jeep used NP 231 and this is NP 237 (E). - I rebuilt one with cracked case using a Jeep YJs case with the TJ's original parts inside. Very easy rebuild.

As for oil, I think I used DexIII.in that, but any oil would do. It's for lubrication only, no hydraulics. And there's no clutch discs or anything in it, just the chain, a planet gear and the sychro for the shift on the fly. There's also nothing that really heats up there, at least in normal driving. So, I'd say pretty much any oil will do, and will not damage the xfer. As long as it will not seap out forward into the autobox...

 

It does have an oil pump.
The ford oil may be a bit more but it's cheap insurance when
it comes to a rebuild from the wrong oil.


Sean


6.0L Tech Folder

 

You're absolutely right, totally forgot about the pump... That means the oil should stay liquid even when really cold (like -40). Diff oil is out as that's more like tar in that temp, and mineral oils more like solid.

Good synthetic engine olis and ATFs stay liquid even at those temps.

Also right about using Ford's own stuff. They may actually though about it for a while. - Although it might feel unlikely at times when you're constantly fixing something in your truck...

 

It's starting to unfold...

The sound comes from the xfer case. I'm thinking it's the main bearing that was making the noise. (It's totally worn out.) Although it doesn't matter much exactly where the sound comes from. I have to do full rebuild anyways...

I got to a friend's garage to work in nice dry and warm. After fooling around the electrics for a while I let out the oil in the xfer case. NOT clean! And looking in the hole, there was a piece of metal there... ...so I dropped out the case and called the missus to pick me (and the xfer case) up. The truck's not going anywhere anytime soon...

I opened up the case and something as died inside the case and blocked the oil pickup. That has destroyed the pump and the whole case has heated. Oil pickup tube was melted and shift fork's plastics had disappeared. Pretty much total destruction.

So, now the question is: Where would I find a rebuild kit for the NP 273 F ? (Yes, it's an F, not E as I misread earlier.)

 

Here?:

http://www.ebay.com/itm/Ford-271-273-Transfer-Case-Rebuild-Kit-Bearing-Kit-BK485-BK-485/121505699255?_trksid=p2141725.c100338.m3726&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20150313114020%26meid%3D65c47622ffa74c96bcdf85a505165f9f%26pid%3D100338%26rk%3D5%26rkt%3D28%26sd%3D321553850681
Not sure if it has every part you need...

 

Make sure the kit comes with the pump and pickup. I'd also throw a new chain in it and it should be like new again.