325iX AWD question

Find that hard to believe. The system has a chain driven transfer case at the back of the gearbox. It's permanent 4wd, nothing fancy.

"John Burns" wrote

Isn't the center differential some sort of limited slip sucker that was troublesome?

FloydR

"The system has a chain driven transfer case at the back of the gearbox. It's permanent 4wd, nothing fancy. "

This is by far, the most ignorant comment Ive heard all year....If you dont know the difference between 4wd and AWD....

That is the difference between 4WD and AWD. It's computer controlled. When you are on a dry, flat, road the computer will drive only the front or the back - usually the back.

Dan

That's an interesting definition. Is this universally accepted?

"Dave Plowman (News)" haute in die Tasten:

IMHO: No. In my personal opinion AWD means that all wheels are driven permanently i.e. yo cannot switch off the drive for one axle. Many

4WD SUVs and All Terrain Vehicles offer the option to switch off one axle. Often they lack a differential gearbox between both axles which means that you have wear and tear when you use the 4WD on other than slippery roads. I know that BMW, VW, Audi and Mercedes use AWD systems. I am not sure with Subaru.

Frank

I have serious issues with your definition of AWD vs 4wd, but I will digress to one point, your concept of awd is that all wheels get power all the time? This being the case it would be similar to running a locker on your front and rear axle that is fully locked at all times? Heres my experience with AWD on BMW and Land Rover (Freelander is AWD) the wheel with the least resistance will get all the power. ie, if you are on stuck in snow, (high centered) you will get one wheel that will spin. NOT all 4, put three wheels up against a large rock, then put one wheel on ice. try to drive out, the only wheel that will turn is the wheel on ice, it will occasionally slow and try to turn the other wheels but there is too much resistance and they will not turn. Here in lies the difference in 4wd and awd. A true 4 wheel drive will give equal power to the front and rear axle, also, a good 4wd will have a lock on the center, rear and front dif which will all "all wheels being driven". This is 4wd. not awd. Comparing the two is like comparing bimmer to a fiat....

Don't the iX models use a transfer case to drive all 4 wheels? It sounds like this car (the one the OP is looking at) might have a bad one. epbrown

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2003 BMW 325i Black/Black 2003 BMW Z4 Black/Black

No, it's definitely not. The AWD in my Ford Exploder is not computer controlled at all. It is full time, meaning that the power is always being applied to the front and rear axles, even when traction is fine.

I would say the definitive difference is that AWD is "Full time" and 4WD is "part time", meaning that the 4WD must be engaged and disengaged manually, while AWD does not. AWD can be either truly "full time" or automatically engaged or proportioned.

I agree.....

Which BMW are you talking about? The E34 AWD has electronically locking center and back differentials and will lock them instantly if the ABS sensors notice wheelspin. The E30 AWD has viscous limited slip differentials with no electronics. The "one wheel spinning in the ditch" effect you mention should not happen with either.

"Corey Shuman" haute in die Tasten:

They get a certain amount of power all the time, yes. But usually they do not get the same amount of power. Otherwise it would be quite different to drive curves on dry roads.

Frank

But surely all permanent 4WD cars have a central differential? Otherwise one axle goes at a different 'speed' to the other when cornering? But this is a different matter from distributing the power.

Dave (News),

I haven't the entire universe yet so I can only say it's not a definition but merely an explanation. The line between the two has changed in the last ten years and is probably more of a marketing tool now than anything else.

My '94 and '98 Jeeps had 4WD. My '02 Acura MDX and '04 BMW X5 had/have AWD. The AWD systems, in this case, use a computer to control the output to each tire. The 4WD systems (Quadra Trac?) were manually configured with a small lever on the floor.

Dan

As I understand it (I have an 89 iX) there is a viscous coupling which transfers power to both front and rear as needed. The "transmission" includes a driveshaft running to the back and CV joints to the front. There are no computer controls on the AWD/4WD in the 89 (my car doesn't even have abs). I've replaced much of the the suspension and CV boots, but the inner workings of the transmission are a mystery (if it ain't broke.....)

Paul

As I understand it (I have an 89 iX) there is a viscous coupling which transfers power to both front and rear as needed. The "transmission" includes a driveshaft running to the back and CV joints to the front. There are no computer controls on the AWD/4WD in the 89 (my car doesn't even have abs). I've replaced much of the the suspension and CV boots, but the inner workings of the transmission are a mystery (if it ain't broke.....)

Paul

The Range Rover was IIRC the first mass produced vehicle with a centre diff, and this dates back well over 30 years. Previously, the Jensen FF (Ferguson Formula) had a centre diff and ABS in the '60s. Mechanical limited slip diffs are even older - but the application of electronics to prevent one wheel taking all the drive in adverse conditions is a more recent invention.

4WD trucks have fixed output 1:1 front/rear from the transfer case. This is why it must be disengaged when running on dry roads.

"Permanent 4WD" is called AWD. And yes, all AWD vehicles have some sort of center "differential" mechanism in the transfer case to allow the front and rear axles to turn at different rates. In many (most?) it is accomplished via a viscous fluid coupling. This allows the proportioning of power to be modified "real-time" as conditions warrant by a computer in the fancier systems using solenoids and valving.

OTOH in my (simple) Ford Exploder it is always the same, 40/60, F/R as I recall. This works fine for what I need it for, but is not ideal for truly slippery conditions (such as off-road). For that, there is no substitute for real 4WD.