How to: - Rebuilding a Borg Warner 4404 | Ford Explorer Forums - Serious Explorations

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How to: Rebuilding a Borg Warner 4404

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Explorer Addict
September 27, 2002
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City, State
Anchorage, Alaska
Year, Model & Trim Level
'97 Explorer XLT AWD 5.0L
I'm still fighting with vibrations in my truck. I've pretty much replaced EVERYTHING that could be the cause. Front and rear axles replaced (for other reasons), which would (most likely) rule out pinion bearings, carrier bearings, and diffs in general.
CV Axles have been replaced numerous times. Wheel bearing/hub assemblies have been replaced more than once (they go bad quick, when you're running 33's on out of round rims). The vibes continue without the front d-shaft, and I even had one custom made, with a double-cardan, to get rid of the POS OEM cv-joint.

So, that brings me to replacing the bearings in my transfer case. If I would apply upward pressure on the rear output, I would hear a clicking. The volume of the "click" would increase with increased pressure.
Also, with my truck having 170k'ish miles, and only 1 fluid change in the t-case (I only changed it once, and I doubt it was changed prior to me purchasing it 5 yrs/80k'ish miles ago), it's certainly not a bad idea to get to this.

Plus, with it being an AWD, there's no shift linkages to worry about.

The parts I purchased:
-TransParts BW4404 Rebuild Kit (bearings and seals); purchased off eBay.
-TransParts TC10-051 Chain (same as Morse TEC HV-051, wrong for my application; I apparently needed HV-070)

Side note on this:
4404 Ford Explorer/ Mountaineer to 97 HV-051 .4346 Pitch x 1-1/4 W x 74 Pitches - RJ
4404 w/5 Liter Ford Explorer/ Mountaineer with 5 Liter Engines HV-070 .4346 Pitch x 1-1/4 W x 74 Pitches - RJ
They are both the same pitch, width, and same number of pitches. Yet they are different by 1 link width. Not to mention the 4404 was only behind Explorer/Mountaineer with 5.oh's :crazy:
My guess is, maybe it changed when they switched from round front output flange to the "cup..." or?


To remove the t-case from the transmission adapter, there are 6- 1/2" head bolts. To break the case apart, you can use either a 10mm socket, or a T40 (although it felt a little loose, but a T45 was too big) torx driver. Oddly, on my case, there is 1 oddball bolt that is a standard hex-head 1/2" bolt.


There are ears on the case, to make prying it open easier.


The rear half of the case. You can see the one bearing, which the front output shaft rides in. And then the huge gear on the right, going to the rear output.


Front half of the case with the gears and chain removed. You can see the bearing for the front output, and there's a replaceable copper "race" (?) where the input shaft goes.


The front of the front-half. You can see the bearing for the front output here, along with the seal for the input shaft.


The input seal removed.


New seal installed.


This clip is holding the front output shaft in the case. It's a PITA to remove, because it's thick, therefore very stiff.


Gears and chain that go into the front half of the case. Note, there are 2 different chains for the BW4404. They have the same exact specs (length, # links, width), yet they are different widths. The chain I happend to get was 9 & 10 links wide. The chain in my case is 10 & 11 links wide.


The large group of gears has this bearing inside of one of the gears.


Here's another bearing. You can also see the viscous coupler (the largest piece). I "cheated" and used a socket to push the shaft out of the bearing.


New bearings and seal installed, gears and chain reinstalled. Luckily, my chain was still good.


Took FOREVER to get the nut off the rear output. I don't think it would have been any easier if I had left it in the truck. I had to use my little propane torch to heat it up and boil(?) the thread locker. Even still, took around 30 minutes between heating and hitting it with my impact wrench at 120psi. Also note, there is a rubber washer/seal that goes underneath the metal washer.


See those little prongs at the bottom of the case? You need to spread those apart, so that you can get the rear output shaft out.
It's a PITA to get the rear output shaft back in. Because again, you need to pry that clip open. (I removed speedo sensor when reinstalling, whether or not it helped, I don't know.


Rear output shaft bearing.


Seal for rear output.


Part of the speedo gear, and that small yellow plastic elbow at the bottom, feeds fluid to that bearing that's pressed onto the shaft. There is also a small rubber o-ring that goes somewhere with this speedo gear (I can't remember exactly where it was).


There's another tiny needle bearing on the inside of this. I made the mistake of attempting to remove this bearing; it was not fun, nor pretty. This pretty much requires a blind-hole puller.


Speedo gear and etc removed, although I decided NOT to replace this bearing, as I do not have the proper tools for it.


Clip removed.


Another clip holding the shaft to this "cup" (blurry pic, I know).


That clip removed.

Reinstall parts, silicon the case, bolt back together.

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This little "project" of mine, took a bit longer than planned.
All in all, I spent around 7hrs, but I still have to bolt the t-case back up to the transmission.
I also removed a bearing I shouldn't have; the smallest needle bearing. I knew I shouldn't have tried, but did anyway. That took a long time, as no proper tools for the job, so I "improvised."

I used various sizes of bearing/race/seal drivers. I'm glad I decided to get that set from Harbor Freight.

I did definately find some bad bearings; if I held them in my fingers and spun 'em, I could feel 'em wobble. Hopefully this fixes the vibrations I've had. I'll find out tomorrow.

Addition: I'm going to do my best to post my "how it works"

So as we all know, the 4404 is full time all-wheel drive, with the front driveshaft being driven by a chain, with a viscous coupling between the input shaft and front output shaft.



here are all the parts and pieces that make up the 4404.


this is all the gears assembled, into the front half of the case.


Here, you can see the gear for the front output, chain, rear output, viscous coupling, etc.


This is what it looks like when everything is moved to the rear half of the case. Obviously for show only. But it also shows the input shaft, and being able to see the large rear output "cup"


You can see how the rear output "cup" is attached to 2 separate gears. First, is the casing with the 4 small gears, with 1 at each corner. This piece is splined in the center which the output shaft does go through. And then the viscous coupling also attaches to this.

Now, the viscous coupling and gear that go to the chain, actually just set on another shaft, with a bearing pressed onto the end. So, this means the front output is really, more or less, connected to the rear output, not the input (in a sense).

The input shaft is directly connected to the rear output, with the front output in between.

Now, the only time I could see any slippage in the front output, is if the front output was seized and could not move, but the rear tires did spin. This would cause slippage in the viscous coupling, because the rear output is directly connected to the input. So it will always spin. Therefore, I don't see how driving without a front driveshaft could destroy the coupling. The speed at which the front output spins will always equal the rear output, unless something keeps the front output from spinning.

I got the t-case reinstalled in my truck this morning, filled with fluid, and the rear d-shaft hooked back up.

I just muscled the t-case into place. Weighing in at ~50lbs (give or take), all you really need to do is get it onto the transmissions output shaft which you can use to take some of the weight off, then jiggle it around until it slaps into place. There is also a paper gasket that goes between the t-case and transmission adapter; I slapped it onto the t-case before I wrestled it up.

After filling it up with fluid, but before I hooked the rear d-shaft back up, I started up the truck, and run it in reverse for a min. Shut off truck, put into park, started it up, put it into drive.

I did this, so that the bearings can get lubrication without any real force being applied, which I believe is good practice. I also did this so that if there were any leaks, I would find them before driving around. It's currently appearing to be leak-free. Will it really make any difference? I don't know, but I don't feel like doing this project again any time soon :)

Since it's raining out, and I don't have a garage to work in, I'm just warming up and gettin dry before I take it out for a test spin.

I will report back with my findings.

well the test ride was positive.
Most of the shimmy/vibes I had are gone.
So it was well worth the time it took me to replace all (but 1) of the bearings in my t-case.

Although, when going more than ~10mph, I'm hearing a sqeek/squelch coming from the front output. Not sure why, but doesn't seem to be causing any harm.

It also still appears to be leak-free.

Well, issues have arose since the rebuild.
I made a post earlier, about a strange squeaking.
It's now worse. At lower speeds, it sounds like metal on metal scraping.
At higher speeds, it doesn't seem to be as audible, and becomes more of just a scratching sound.

I have found the source, but not the cause.
The noise is coming from the front output area.
There's a couple things that I can think of that would cause this....
#1 - the cir-clip that holds the front output shaft into the case is scraping on the bearing. Before the rebuild, there was a fair amount of fore and aft movement. After the rebuild, there is barely any movement.

#2 - a bearing is going bad. Already? I guess it's possible... although there's no reason for it to (unless, of course, due to manufacturing, as it appears pretty much impossible for it to be a lack of lubrication that that bearing).

#3 - the most doubtful situation, would be some sort of debris between the "cup" and the case.

For situation #1 - I did 2 things to try and resolve this, to no avail. First, I took my old single u-joint d-shaft flange held it onto the cup with 3 bolts, and took my hammer to it. Attempting to make sure the output shaft is full seated back, and far(ther) away from the bearing. I then also took my slide hammer, did my best to hook it onto same said flange, to attempt to pull the shaft out, to try and get some pressure between the cir-clip and bearing (attempting to re-seat bearing if it came out). No avail. Still sounds terrible.

Situation #2 - well, haven't done anything, as I have no spare vehicle, so no way to work on the junk during the week.

Situation #3 - Sprayed plenty of brake parts cleaner over the case. Took my air hose, at 120psi with air nozzle, and sprayed the hell out of the case (mainly between the cup and case) to try and dislodge any "debris" that may (doubtfully) be there.

Nothing has changed so far. Unfortunately, it looks like I will be pulling my case out again this weekend.... :thumbdwn: :rant: :(

I'm interested too.
After looking through all the pics, and knowing what's what, I don't see what else it could be.

Although the noise definately sounds external, somehow. Just due to the volume, it doesn't sound like any noise is being muffled by the case.

I will delve back into it this weekend, and report back.

It has been long wondered by me exactly how this transfer case works. People say that when one drives without front drive shaft installed, that power is lost to the front output. This makes some sense to me, but I do not quite understand how power is transferred throughout the case. As far as I can tell without opening my case, the link between the input and the rear output is solid. This may not be the case though. How the viscous coupling works and where and what it is connected to is a mystery to me. I tried to study the pictures above, but I couldn't quite put all the parts together in my mind and come up with something that makes sense.

since I'm ripping it apart again this weekend, I'll get some pics that better show how what works ;)

but.. from the pics that I have, I can somewhat explain it.

That very large "cup" gear, that are the last few pictures, is the output shaft. The rear output flange is connected directly to this. As can be seen by pic #3.

This then sits on top of the large set of gears, that is connected to the tailshaft of the transmission.

I do not have a picture of it all together, but... Picture #9 - there's 2 sets of gears, connected by a chain, and then another gear I have lying off to the side. This gear that is off to the side, actually sits on top of the large set of gears. Although, it's actually just a large "casing" with some splines, and 4 small gears; 1 at each corner. This is what the output is connected to. So... the rear output is, essentially, connected directly to the transmission trailshaft.

Picture #11 - you can see 2 gears. The top-most is what the chain hooks to. The large gear (lower-most) is actually the viscous coupling. I'm not 100% sure how these gears are, exactly, connected.

But what basically happens; because the viscous coupling is connected to the front output via a chain, this is where the power is transferred to the front output. Although, to be quite honest, without a front driveline I'm not completely sure you can "destroy" this viscous coupling.

It's going to spin just as fast, regardless of a front driveline... correct? But of course, I'm not 100% sure. I did try to spin the viscous coupling by hand, and I could not.

well this turned out to be more of a combination of ramblings. Wether or not it makes sense is hard to say.
I will do what I can to get better pics of the whole setup this weekend.

I stole these pictures from an ad on ebay for a viscous coupling.



from this same ad, it states:

is this my problem? I don't know. The sounds really appears to be coming from the driver's side of the case; the viscous coupling is on the other side of the case. And how accurate is this, anyway? Hard to say... I'm not sure how it would cause a loud popping, when it's just filled with a viscous fluid :scratch:

But, this picture does give an idea as to how it works.
As you can see, the splined shaft goes all the way through. The fluid is in the outer portion. If you look closely, it looks like the shaft and outer portion are separate pieces. Power is always sent straight through. Slippage happens when the shaft moves, and the outer portion doesn't, or atleast not at the same rate. My best guess.

Or maybe the outer portion does move, and inner shaft doesn't.

As the large "cup" gear going to the rear output, would catch on the outer splines of the outer portion.

Very interesting information. What you describe is kind of what I expected, and was hoping to hear.

I am not sure if you are supposed to be able to turn the viscous coupling by hand or not, probably not though. It probably takes a decent amount of torque to get it to budge. With such a stiff connection, I would find it hard to see the coupling slip if you hit the gas hard. It would match speed with the rear output easily.


i have a 1998 explorer xlt awd and when i put it in 4 wheel high and i turn there is a loud pop noise and the truck jerks know it also happens on the road if i stomp on the gas and if i slam on the brake and the tires lock up it does it to know also it wont go into 4 low do u have any ideas could this be a t case issue or possibly a fronnt end issue?

also i need some step by step instructions on how to start my own forum sorry to intrude on yours

i have a 1998 explorer xlt awd and when i put it in 4 wheel high and i turn there is a loud pop noise and the truck jerks know it also happens on the road if i stomp on the gas and if i slam on the brake and the tires lock up it does it to know also it wont go into 4 low do u have any ideas could this be a t case issue or possibly a fronnt end issue?

also i need some step by step instructions on how to start my own forum sorry to intrude on yours

If you have 4-hi/4-low, then you do not have AWD :)
some of the t-cases do have electronic 4wd, maybe, but not AWD. Different t-cases ;)

But if it's only when in 4wd, sounds like the cv-joint at the t-case on the front drive shaft

FYI, to start your own thread, when you're in a sub-forum you're allowed to make posts in (ie, Explorer & Ranger Transmissions, Transfer Cases, & Differentials), there will be a "New Thread" button on the left-hand side of the screen, just under the sub-forum description.

its awd the button show auto 4high then 4 low i dont have a 2wd setting

it's not really AWD... it's a form of auto-4WD. A true AWD system has no selection for a low range, and both axles are always receiving power.

The automatic-4WD used behind 4.0L Explorers (and some Rangers?) use an electro-magnetic clutch to engage the front output shaft when needed, I believe. There is no power output from the front output shaft, unless slippage is detected in the rear, in which the PCM then sends power(?) to the electro-magnetic clutch, which then engages the front output shaft, allowing power to go to the front tires.

The BW4404 which I have written about here, has no low range. The front output is also driven by a viscous coupling. It is also a fully mechanical transfer case, with the only electronics being the vehicle speed sensor (VSS), which was removed in 1998+ models, due to VSS moving to the rear axle.

The Borg Warner 4404 is also only used behind 5.0L V8 Explorers.
The 4.6L V8 Explorers use a different model of AWD t-case.

its awd the button show auto 4high then 4 low i dont have a 2wd setting

That is auto 4WD, not AWD, vastly different. You have A4WD(auto four wheel drive), AWD means all wheel drive.

Ditto, good thread here, I hope you get it figured out. It looks to me like the planetary gear set in there is what allows the rear shaft to move independently of the trans output. With no front shaft, the viscous coupling can slip and allow the planetary to move in phase with that slippage. That is why on any hill the AWD will allow movement with no front driveshaft. The viscous clutch is what holds the rear shaft to the trans output shaft.

i understand know that explains why when i jacked all 4 tires up there was a slight delay in the front tire movement thanks again great help

Very good Terry, I have the A4WD in my 99 work truck, I wanted AWD because it's much smoother on the street. LOL, now for my V8 I'm changing to the A4WD for performance. Night,

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Today I stopped by school for a couple hours to discuss some things with some friends. I came out to my explorer and the first thing I thought was "I didn't park here!" The explorer was sitting in the middle of the driving lane in the lot, rolled about 15 feet out of it's parking place over a period of two hours. If i stayed at school longer it would have ended up in another parking spot, haha. Good thing I make a habit of parking far out where nobody parks. I knew it could roll, but I guess I just forgot. So remember, no front shaft, use parking brake!