I disagree, and my local Ford dealer disagrees.

 

It doesn't make any sense to send power to the diff in 2wd. With all the crap they have to save MPGs why would that add that drag?

 

In reading about the Borg Warner TOD torque converter, the minimum pulse duty cycle going to the electromagnetic clutch is 4%. This means the torque going to the front diff never goes to ZERO, and it's always driven.

 

What we know from simple physics is if the center differential shaft turns, then the half shafts turn as well. If the half-shafts don't turn, then the transfer case is not transferring any torque to the diff, which should be the case, but I don't know for sure. Only a camera on a healthy truck would shed light if the shafts are turning at all or not (now I'm curious. Ha ha). If 4% of power is transferred, then shafts should be turning slowly, but turning some all the time (any truth to that? ). When 4A is engaged, the IWEs are engaged, meaning the wheels are turning the half-shafts, which in turn turns the differential and middle shaft to the transfer case. But even though all the shafts are turning, there's no power sent to the front wheels in 4A unless the clutches transfer power when the rear wheels slip. It's basically like if you had the clutch pedal depressed on a manual car while coasting in neutral: wheels and shafts turning, but no power transmitted. In 4H, power is transferred continuously to both differentials (and shafts).

 

you would seem to be correct except as someone stated 2 posts ago, the front gets a minimum of 4% power in 4a. So everything is turning at speed but the vast majority of the power goes to the rear wheels. When slip is detected it goes to the front wheels somehow in a fraction of a second.

 

4% is the minimum pulse duty cycle in 2H, or 4A mode. As previously stated, the IWEs are engauged in 4A mode.The maximum pulse duty cycle in 4H, or 4L is 98%

 

Yeah I was referring to elptxjc. He stated that “no power” is transferred when there is always some power. Anyhow so you’re saying it’s a minimum of 2% and not a minimum of 4% as I incorrectly ascertained from a previous post?

 

It shouldn't. It's designed to be run most of the time and IIRC the bearings are the same or similar to the ones in the rear. If they are bad from new - or they didn't get good lube or ? There have been a number of issues with front diffs - not tonnes but more than a few. Some are bad bearings and some have too tight a gear mesh.

So might be a touch of semantics saying driven. BUT - yes if you put the thing up in the air with tires unloaded - and in 2WD and you have the 4A option system - then it does provide a little bit of torque thought the line at all times. Why - so nothing is bound if you go in 4A at any moment and the system wants to push say 30% forward. So there is always some movement.

Driven however - no there's not enough torque there move anything but the tires. It's that whole where do you define the limit of the system sort of thing. The other model I do believe where you have to point it as 4H or 4L - from 2WD standard - might not do this. I'm not 100% sure. The idea here is it keeps the parts moving with some torque there - and the fluid moving etc.


Thus it's never slammed in from a dead 0. I don't think this caused your noise - but you have a bad bearing. Premature failure happens.

 

I stated 4% in post #23.

 

From DJFLLMN's post (#15) it looks like the The Borg-Warner 4469 (NON 4A) torque converter has the same electromagnetic clutch.