Last post on Mar 20, 2012 at 9:28 AM
You are in the Ford Expedition
What is this discussion about?
Ford Expedition, SUV
#53 of 60 Re: 4x4 issues please read [azmike2]
Mar 19, 2012 (4:00 pm)
Until proven otherwise put full faith in the indication.
#54 of 60 Re: 4x4 issues please read [alwaysfords2]
Mar 19, 2012 (4:03 pm)
There is NO such thing as a roadgoing vehicle without 2wd. No 4WD of any flavor could be driven on our roadbeds without a 2wd as primary mode.
#55 of 60 Re: 4x4 issues please read [wwest]
Mar 19, 2012 (6:38 pm)
A4WD can be driven on "tractive surfaces". Actually there is at least one year (1999) of Expeditions where there is no 2WD selection. A4WD is your only choice for normal driving. This discussion of course applies to 4x4 models, the Expedition is also offered as a 2WD. You seem to be confused about what A4WD is. It is intended to sense wheel slip in the event the driver doesn't realize the surface is slippery. It normally operates as a 2WD, but automatically engages four wheel drive based on conditions. It does this by monitoring wheel RPMs at all four corners and when a difference is detected it engages 4WD. It keeps it engaged until the sensors say there is no more wheel slip. In other years the selector switch has 2WD, A4WD, 4H and 4Lo. The issue of tires is very relevant to this type of system as it is with AWD. Ask any tire shop. I keep both my 03 and 04 Expeditions in A4WD all the time. One has 165k miles the other has 75k miles, all original mechanicals. I had a 99 Expedition that had 100k on all original mechanicals. I've also had an AWD Explorer as well as a manual locking hub Bronco so I think I'm pretty well versed in the issues.
Mar 19, 2012 (6:35 pm)
Since you are likely to debate what I've suggested, here is the description of it from the owners manual
" A4WD (4X4 AUTO) provides electronic control four-wheel drive with power delivered to all
four wheels, as required, for increased traction. This is appropriate for all on-road driving conditions, such as dry road surfaces, wet pavement, snow or gravel".
You are also wrong to suggest with the front diff locked ABS stops working, but that's another topic.
#57 of 60 Re: 4x4 issues please read [alwaysfords2]
Mar 19, 2012 (8:57 pm)
You said: "..It normally operates as a 2WD..."
That's EXACTLY what I said.
A4WD is a PART-TIME 4WD system that normally operates in RWD (Explorer, ETC) or FWD (idiot vehicles).
Think about it, with the CENTER diff'l locked, Part-Time 4WD, ABS cannot independently control the braking level in the front without impacting the rear, and vice versa. Same goes for TC and VSC. Every system I know of, have read about, that has the ability for actual 4WD (locked center Diff'l) automatically disables the individual wheel or driveline braking unless one driveline can rotate mostly independent from the opposite driveline.
#58 of 60 Re: 4x4 issues please read [wwest]
Mar 20, 2012 (5:20 am)
We are talking by each other. Actually I was talking and you jumped in the middle. I've only been talking about A4WD, you are the one who started in with what could and couldn't be driven on dry pavement, misunderstanding that the discussion was about A4WD.
#59 of 60 Re: 4x4 issues please read [alwaysfords2]
Mar 20, 2012 (9:28 am)
No, you were not the author, "beginner" of the most recent line of questioning on this thread. There are appearances that the questioned vehicles are inadvertently going into, or maybe even unwittingly, being put into 4WD mode on reasonably traction surfaces.
The problem we have "today" is the level of trust that was built up in the past for RWD/4WD and R/awd was well warranted. Now we have a class of new drivers who have not a clue as to the patently unsafe nature of FWD vehicles and now F/awd systems. "It" worked well in the past, so why not today..?
Yes, there are literally MYRIADS of differing AWD system designs out there in the marketplace today, most of them "base" FWD. Base FWD since it is those that can most benefit from the distribution of at least some level of engine torque away from the traction coefficient with which we maintain, sustain directional control.
The only "base" FWD....F/awd system I would recommend would be the SH-AWD. But at the same time we must take note of the inappropriately high driveline component failure rate with the SH-AWD. High failure rate very likely arising from the STELLAR operational nature of the SH-AWD, undue, inappropriate, STRESS level incurred via daily use of torque re-apportioning, up to 80% to the rear in a tight or accelerating turn, even with no threat to loss of traction being present.
Let's also not forget that there are likely a lot more readers of these posts than actual participants, readers who rely on the information posted here.
Yes, these modern day "automatic" AWD systems will often ALWAYS make use, by default, of 4 wheel drive mode at times when Loss of traction, wheelspin/slip, is most likely to result should the roadbed traction coefficient be marginal.
The problem is that means that the clear majority of the time, times when the roadbed traction coefficent is satisfactory, or even well beyond, those systems still put the driveline components under extra stress and heating.
You may note the high level of "awd" driveline stress failures as a result.
Life was much, MUCH easier back in the days when RWD was dominant and extra traction meant having a 4WD mode. It was easy to get owner/drivers to understand why the 4WD mode should only be engaged with specific roadbed conditions.
Now we have automatic "AWD" systems that will switch into 4WD mode, or partially so, the ~90% (99%...??) of the time it is needless, only to prevent todays owner/drivers from being forced to gain a small bit of additional intelligence.
On the other hand the patently unsafe nature of FWD, and/or F/awd, has sorta forced the manufacturer's "hand". As a matter of safety, purely a matter of safety, these MUST always pre-emptively re-apportion engine torque to the rear any time, ANY TIME, there is a high potential for wheelspin/slip to result, otherwise leading DIRECTLY to loss of directional control, or potenially so.
Obviously not an issue with a RWD, R/awd, or even 4WD.
Should those,except the 4WD mode, lose directional control, regardless of road conditions, the fault lies directly with the driver's lack of reacting quickly. Get OFF the gas should that have been the base causative factor, or counter-steer, turn into the skid, should the initial oversteering event be not the fault of the driver. Or BOTH.