BWM- Principals Of Our "Auto" Transfercase.

[97awdx]

For those who want to or have done the BWM. This is taken directly form the Ford Factory Service Manual.

Mechanical Operation

The Borg-Warner 44-11 transfer case is available in the Explorer (A4WD) vehicle. The transfer case transfers power from the transmission to the rear axle, and also to the front axle when electronically activated.

In the Auto mode, torque from the transmission is transferred to the input shaft which, in turn, drives the rear output shaft that drives the rear axle assembly. The electromechanical ball ramp clutch assembly drives the drive sprocket after the 4x4 electronic module activates the clutch coil. The drive sprocket turns the drive chain that rotates the front output shaft and the front driveshaft. In the 4x4 High mode, the operation is the same as in the Auto mode, except that the 4x4 electronic module consistently activates the electromechanical ball ramp clutch assembly.

The high-low shift occurs when the reduction shift fork moves the high-low collar to lock the planetary gear set to the output shaft. Then, torque, transmitted through the sun gear, from the input shaft, turns the front planetary gear set assembly. The front planetary gear set assembly, which is now engaged, provides transfer case speed reduction.

Control-Trac Function

The Control-Trac transfer case uses an electromechanical clutch assembly to control torque to the front wheels. In the Auto mode, while at rest and under cruising conditions, the 4x4 electronic module activates the transfer case clutch at a minimum level. This allows for the slight difference between the front and rear driveshafts which occurs normally when negotiating a corner on dry pavement. Under any of the following conditions, the 4x4 electronic module will increase the torque sent through the clutch to the front wheels in order to prevent or control slip.

Slip is detected (by monitoring the front and rear OSS sensors in the transfer case)
Throttle position (by using the throttle position signal from the PCM)

 

[JCUZ]

So is it OK to do the BWM? From reading that, it would seem to be fine.

I just used mine all week in 2WD mode (4X4 Auto with BWM switch off) driving on sandy beaches and had no issues at all - only flicked the switch to allow 4WD to engage on the really loose stuff.

 

[shadowless127]

So is it OK to do the BWM? From reading that, it would seem to be fine.

I just used mine all week in 2WD mode (4X4 Auto with BWM switch off) driving on sandy beaches and had no issues at all - only flicked the switch to allow 4WD to engage on the really loose stuff.

I think this was meant as more of an educational thread then to deter anyone from doing the BWM. It gives you a better understanding of how the T-Case works. All the BWM does is allow you to control if/when the vehicle send the signal to the clutch coil to engage 4wd.

 

[97awdx]

Just educational, I personally don't think their is any harm in doing a burnout with the BWM. Its a electromagnetic clutch not a viscose coupler in the T-case.

 

[OMEGA4X4]

Sorry if this is a dumb question, but does it state that "some" power is "always" traveling to the front wheels? If so, do you guys the BWM see an increase in overalll MPG?

 

[IZwack]

Just educational, I personally don't think their is any harm in doing a burnout with the BWM. Its a electromagnetic clutch not a viscose coupler in the T-case.

Its not the electromagnet part that gets damage when you do a burnout, its the clutches -- they are always touching each other because there is a tiny spring that exerts a small force against them all the time. When you do a burnout with the BWM, one set of clutch discs are not moving while another set of clutches (sandwhiched in between the non-moving clutches) are moving at X number of thousands of RPM. At that point, since the clutches are still touching due to the spring, the shearing force between the clutch discs overheats the fluid (destroying its lubricating properties) and will destroy the actual friction material thats embeded in the clutch discs.

This is a quick rendering I did a few years back, it shows the tiny spring that pre-loads the clutch discs against each other so that there is always a minimum amount of force against each one of them:

These are two sets of clutches from two transfer cases -- the thing that is destroyed when doing a burnout. Notice that the clutch discs's teeth alternate -- one clutch disc has teeth on the outside edge while the next clutch disc has teeth on the inside edge. The ones with the teeth on the inside edge "spline" into the main shaft of the transfer case while the ones with the teeth on the outside edge spline into an outer "cage" which eventually drives the front driveshaft.

So, to sum up, there is plenty of harm in doing a burnout with the BWM.
Your transfer case may not die in the first 3 burnouts, but eventually, it will. Its already been proven by a few people on the forum.

Just dont do a burnout, its pointless unless you're at the strip. And if you're going to the strip, swap in a manual transfer case, go with a 2wd vehicle, or remove the front drivesaft (just expect the dash to light up as the vehicle detects a non-engaging 4wd)

 

[rhyno]

I certainly dont have 'proof' of why and it may be a coincidence, but my transfer case died on my 97 after about a year of having the BWM. I didnt really do full scale burnouts, but did spin the wheels a bit here and there for fun. Just a FYI.

 

[shadowless127]

Disconnecting front drifeshaft to do a burnout in a 4wd or AWD vehicle FTW.

 

[guitarfrk741]

does anybody know if the signal to activate the electromagnetic clutch Is just a 12 v current ? Basically say I didn't have a 4x4 transfercase by it's self ..would a 12 v current to the brown wire "activate" the case?

 

[IZwack]

Yes but I think its actually a pulse width signal -- not constant.

 

[guitarfrk741]

[Well if it's not a problem does someone think they could put a volt meter up to the brown wire and then engage 4high .. The reason I ask is I'm in the planning stage of converting my mounty to a true 4x4

 

[IZwack]

[Well if it's not a problem does someone think they could put a volt meter up to the brown wire and then engage 4high .. The reason I ask is I'm in the planning stage of converting my mounty to a true 4x4

Go with a manual transfer case instead of the electric ones -- they are more dependable and are actually a "true" 4wd system. With the manual transfer case, you can do all the burnouts you could ever want. The only difficult part is removing the center console, removing at least one seat (just makes it easier), and pulling the carpet back in order to install the shifter.

 

[guitarfrk741]

Go with a manual transfer case instead of the electric ones -- they are more dependable and are actually a "true" 4wd system. Plenty of members on the forum that have gone this route. With the manual transfer case, you can do all the burnouts you could ever want. The only difficult part is removing the center console, removing at least one seat (just makes it easier), pulling the carpet back, in order to install the shifter. But this has been covered in the writeups.

i didnt think there was a manual tcase swap for a 3rd gen?

my plan was to bolt on the front end stuff..(cv shafts driveshafts front diff etc) swap my output shaft on my tranny and throw in the auto4wd tcase..and since my mounty doesnt have the 4wd computer or control box i was just gonna rig up a manual way to select b/t low high and neutral gears and then put a switched 12v line to the brown wire..

then when i activated the switch the shafts would lock together and it would be in the mode my manual selector was in

 

[IZwack]

i didnt think there was a manual tcase swap for a 3rd gen?

Wow I think you're right, I spent 20 mins looking for a manual transfer case..

 

[guitarfrk741]

yep thats why im trying to figure out what signal i need to activate the electromagnetic clutch

 

[BobWiersema]

So is it OK to do the BWM? From reading that, it would seem to be fine.

I just used mine all week in 2WD mode (4X4 Auto with BWM switch off) driving on sandy beaches and had no issues at all - only flicked the switch to allow 4WD to engage on the really loose stuff.

I HATE YOU. IT'S -6F outside today.

 

[JCUZ]

I HATE YOU. IT'S -6F outside today.

At least you're not in Dakota! I hear it was -36 there!

We are currently on holiday in Sunny Queensland (Australia), with temps up around 30 degrees celcius (no idea in fahrenheit, but hot). It was actually hotter in my home town at 37 degrees C, but there are no beaches.

Anyway, good to know that using (not abusing) the truck in 2WD should be OK. I did have to use 4WD Low at one stage, and I now know that to avoid it smelling, not to use too much power in Low range.

Here's one teaser pic of the type of terrain we were running in/on, using mostly 2WD, but flicking to 4WD as required:

 

[97awdx]

From that picture I guess you would burn out the clutches, thanks for the photo.

 

[Detainabull]

I know this is hashing up an old thread but to better understand how this works, 12V goes to the coil making the balls move on the ramp. So then #24 in the drawing presses against the clutches?? Nothing in #26 moves, correct?

 

[Mr. Truckles]

IZwack described it really well.

What the PCM does is also easy to understand.
In auto mode the pcm compares the front and rear wheel speeds using the sensors. If the rear is faster than the front at any time, it increases clutch pressure until both speeds match. If it cannot get them to match, it will put the system into 4x4 high. Ideally, there should never be any slipping in the clutch.

If you do a burnout with the BWM there is a lot of slipping due to the pre-load on the clutch pack. The friction surfaces of the clutches can be burned and particles from the clutches will mix into the fluid which lubricates all of the bearings etc. I pulled apart my case with a Ford transmission specialist and this is the conclusion that we came to.

Currently I only use the BWM on the road during normal driving because of my rear mechanical locker. When cornering with a locker, the speed of the rear wheel being driven will always be faster than the slower of the two front wheels, which confuses the PCM. The PCM will attempt to apply the clutch to compensate when it doesn't need to which causes binding. In this case, the BWM does less harm to the case than allowing it to bind, but neither are really good