January 13, 20188 yr I thought MT were 50/50 on front/rear power distribution? assuming equal traction at all wheels yes. But if one wheel slips only a fraction of power (whatever the Viscous center can transfer, not much) goes to the other wheels.
January 13, 20188 yr Ok, I thought it went like this: AWD: Power is supplied to the wheel with the most traction. 4WD (unlocked): power is supplied to the front wheel with the most traction, and the rear wheel with the most traction. 4WD (locked): power is supplied to all 4 wheels. Where am I going wrong? you need to understand differentials. Power goes top the wheels with the least traction. Like water, or electricity, it takes the path of least resistance. IMO, a properly working 4EAT, or a modded one with a lock switch, will perform much more closely to what the old true 4wd cars would do. The hydraulic transfer clutch can lock (as long as plates are not worn) and transfer 50/50 to front/rear. Now the diffs at each end will still send power to the wheel with least traction. On the current full time AWD, how many wheels are putting power to the ground at the same time? 4 of course.......... the operative word being to the ground. If a tires is in little or no contact with the ground, it will get nearly all the power from an MT and half the power from an AT.
January 13, 20188 yr Author Another dumb question. Why would the system be designed to send power to the wheel with the least traction? Seems counter-intuitive. If you have two wheels, and one has traction and the other doesnt, wouldnt you want to send power to the wheel with traction to move the car forward? Sending power to the wheel with no traction seems to defeat the whole purpose.
January 13, 20188 yr Another dumb question. Why would the system be designed to send power to the wheel with the least traction? Seems counter-intuitive. If you have two wheels, and one has traction and the other doesnt, wouldnt you want to send power to the wheel with traction to move the car forward? Sending power to the wheel with no traction seems to defeat the whole purpose. Because that's how differential work. If all roads were dirt, it would not be a problem to run locked center/4wd and locked rear axles (no differential) but since most all roads are paved, it is nessecary to have differential action. More modern subarus, starting around 08 IIRC, use a traction control which uses the brakes to stop spinning wheels which then does send power to the other isde of the diff. But that is the traction system, not the actual AWD. Seriously research differentials and why they exist.
January 13, 20188 yr outbacks from 2001 have VDC models with traction control that do just that. foresters just from 09 get that. and traction control do wonders. land cruiser prado newer models no need lockers almost at all how good they are just with traction control. jeeps traction control pretty good from about '01. land rovers had traction control from old models and its was good enough as well. those 4wd that have only part time 4wd they are not 4wd at city roads at all. they just 2wd or more like 1wd. later 4WD cars got full time 4WD too, that subarus have long time ago, because safety first. full time 4WD just gives you safety on road no matter what. and those old school 4WD with lockers they just good for one thing - going offroad. nothing else. Edited January 13, 20188 yr by scalman
January 15, 20188 yr Ok, I thought it went like this: AWD: Power is supplied to the wheel with the most traction. 4WD (unlocked): power is supplied to the front wheel with the most traction, and the rear wheel with the most traction. 4WD (locked): power is supplied to all 4 wheels. Where am I going wrong? It's not even remotely that simple. And again, not all AWD is the same. Most Subaru 4EATs apply power almost exclusively to the front until it detects the front start to slip, and then power goes to the back, because they don't actually have a center differential. Manual transmissions and VDC cars supply power evenly to both front and rear, but have some sort of LSD to prevent too much speed differentiation. Your description of 4WD locked and unlocked describes both front and rear differentials being locked or unlocked, which is very rare on a factory vehicle, occasionally an off-road package will come with a true rear locker, not just an LSD, and even then there's usually nothing to limit slip in the front. I had our '04 Outback VDC in the deep stuff behind my garage this weekend pulling out my utility trailer which has been parked since late last summer. It did better than any EA Subaru I've ever had, the only time I had any trouble, was breaking through the bank left from the snowblower, towing the snow-laden trailer with one tire completely flat. Even then, a little gentle rocking and it had no trouble.
January 15, 20188 yr Author If I install the switch on the wire from the Duty C selenoid, will it toggle between FWD and AWD, or will it toggle from AWD to locked 4WD, or neither?
January 15, 20188 yr If I install the switch on the wire from the Duty C selenoid, will it toggle between FWD and AWD, or will it toggle from AWD to locked 4WD, or neither? Two ways to mdify the control of the 4eat AWD for two different needs. For maximum rear transfer for snow/mud/offroad: You install an interupt switch on the duty c wire you will get : AWD with switch closed, and maximum 4wd "lock" with switch open/interupted You can also run a switch that closes the "FWD" fuse holder circuit. This will toggle you between: AWD with switch "open" FWD with switch "closed" This is useful for running spare tire or mismatched sets of tires front/rear.
January 15, 20188 yr Author When I look at the diagran for the fuse boxes, I dont see a fuse for "FWD". Fuse #14 is marked "Automatic transmission control unit". Is that the one?
January 15, 20188 yr Author When I look at the diagran for the fuse boxes, I dont see a fuse for "FWD". Fuse #14 is marked "Automatic transmission control unit". Is that the one?
January 15, 20188 yr probably not it's the box under the hood on the left side - US drivers. (some older soobs had a small fuse block on/near the right strut tower I think - not sure when they switched) it 'should' presently be empty and a spare fuse of any size can be used in the slot. 'probably' labeled FWD check both places, if you have an owner's manual, look in the spare/emergency tire use section. Edited January 15, 20188 yr by 1 Lucky Texan
January 15, 20188 yr When I look at the diagran for the fuse boxes, I dont see a fuse for "FWD". Fuse #14 is marked "Automatic transmission control unit". Is that the one? No. The purpose is to disable AWD for donut tire use. Read an owners manual about using the donut spare. On your model it will be behind passenger side front strut tower. It's a fuse holder, but really it is just for making contact between the TCU and ground on a signal path to tell the TCU to go into Front Wheel Drive. It is not even actually a fuse circuit. you could jam a paper clip in there to complete the circuit, same difference no fuse action required. What I did on my Forrester was use a section of paired "speaker" wire. Spades on both wires at one end inserted in the FWD fuse holder, and then the other end run into cab to a SPST toggle switch to complete the circuit for Front Wheel drive on demand.
January 15, 20188 yr If I install the switch on the wire from the Duty C selenoid, will it toggle between FWD and AWD, or will it toggle from AWD to locked 4WD, or neither? The way you described it earlier in this post, AWD to "unlocked" 4WD (gauranteeing you have power to the front and rear simultaneously. But you still have open diffs at the front and rear). So in AWD mode it would wait for the front to spin a bit before sending power to the rear, in 4WD it sends it to both simultaneously.
January 15, 20188 yr The way you described it earlier in this post, AWD to "unlocked" 4WD (gauranteeing you have power to the front and rear simultaneously. But you still have open diffs at the front and rear). So in AWD mode it would wait for the front to spin a bit before sending power to the rear, in 4WD it sends it to both simultaneously. A properly working 4EAT should actually send a fair bit of power to the rear at all times. Just not enough to bind if you are tight turning in a parking lot. TCU differences over the years allow a little more or less but should always be something so you aren't peeling out in the snow or gravel. If you are getting any real wheel "spin" before the rear does anything, you're clutch packs are worn thin or the Duty C pressure is low. There is a stop sign at the end of my road. Everyday I start out slightly uphill, turning left, onto a gravel road. It's a bit blind so when you go you gotta go fast to make sure you get across and out of the way if some else comes down the road. With my 98 Forester, I can gun it and get no wheel spin. My wifes 03 H6 OBW, stab it hard and get a tiny bit of slip but really not much.....the engagement is pretty instant. I feel like both of these cars work well enough without needing lock switches. I have driven some older soobs with worn 4eats that require LOTS of initial wheelspin before anything happens. Had a GL-turbo wagon with early 4eat that would not really engage fully at all. Only when I wired in the lock switch (duty C interupt) did it work.
January 16, 20188 yr Author So this should work. If I get a 3 position rotary switch, I can set position #1 to close the FWD circuit, which will give me FWD only. Position #2 I wont connect to anything, so that will open the FWD circuit and give me normal AWD. Position #3 will close the Duty C circuit, which will give me 4WD.
January 16, 20188 yr So this should work. If I get a 3 position rotary switch, I can set position #1 to close the FWD circuit, which will give me FWD only. Position #2 I wont connect to anything, so that will open the FWD circuit and give me normal AWD. Position #3 will close the Duty C circuit, which will give me 4WD. Yes if wired correctly, that’s what you’ll get.
January 16, 20188 yr Author It seems so simple, I cant understand why Subaru just didnt add a selector to their cars. FWD, AWD, 4WD. Just like the big boys.
January 16, 20188 yr Author When going into the different modes, can this be done on the fly, or does the vehicle need to be standing still? Does some amount of wheel rotation need to occur in order for any of the modes to function?
January 16, 20188 yr When going into the different modes, can this be done on the fly, or does the vehicle need to be standing still? Does some amount of wheel rotation need to occur in order for any of the modes to function? Nope, just flick away. It seems so simple, I cant understand why Subaru just didnt add a selector to their cars. FWD, AWD, 4WD. Just like the big boys. I agree personally. But - do you expect people to think about a button when they already have the weight of texting, holding a Starbucks Organically Sustainably produced Mocha Latte in their hand while they're listening to their GPS directions too? That's just too much to ask. Subaru was way ahead of the curve in 1996! For real - the masses aren't versed, interested, or care about actual mechanical principles, they want it distilled - in the same way many of us want information in others areas simplified and distilled when we really haven't put in the work, research, experiences to understand it. in general - most people want information and options distilled for them. We might not be like that with Subaru's but we probably are in other areas. In any event there has been and will be a huge upside for touchless 4WD.
January 16, 20188 yr A properly working 4EAT should actually send a fair bit of power to the rear at all times. Just not enough to bind if you are tight turning in a parking lot. TCU differences over the years allow a little more or less but should always be something so you aren't peeling out in the snow or gravel. If you are getting any real wheel "spin" before the rear does anything, you're clutch packs are worn thin or the Duty C pressure is low. There is a stop sign at the end of my road. Everyday I start out slightly uphill, turning left, onto a gravel road. It's a bit blind so when you go you gotta go fast to make sure you get across and out of the way if some else comes down the road. With my 98 Forester, I can gun it and get no wheel spin. My wifes 03 H6 OBW, stab it hard and get a tiny bit of slip but really not much.....the engagement is pretty instant. I feel like both of these cars work well enough without needing lock switches. I have driven some older soobs with worn 4eats that require LOTS of initial wheelspin before anything happens. Had a GL-turbo wagon with early 4eat that would not really engage fully at all. Only when I wired in the lock switch (duty C interupt) did it work. Yep, I'm exaggerating the delay, but it's still pretty noticeable IMHO.
January 16, 20188 yr So this should work. If I get a 3 position rotary switch, I can set position #1 to close the FWD circuit, which will give me FWD only. Position #2 I wont connect to anything, so that will open the FWD circuit and give me normal AWD. Position #3 will close the Duty C circuit, which will give me 4WD. Theoretically that's possible, but I think it'll take some creativity in finding a switch that functions that way. It would need to have one circuit closed in #1 & #2, but open in #3, and the other circuit closed in #1 and open in #2 & #3. Might be easier to use a more traditional DPDT 3-way to control an SPDT relay to reverse the polarity of the Duty C circuit.
January 16, 20188 yr It seems so simple, I cant understand why Subaru just didnt add a selector to their cars. FWD, AWD, 4WD. Just like the big boys. While I agree. Look at all the domestic pick up trucks with 4x4. Most if not all of them now a days have "auto" so you as a driver don't even have to switch it to 4x4.it will do it for you. Subaru just did Awd as a default because no body is going to end up changing that switch except for the.1%
January 16, 20188 yr It seems so simple, I cant understand why Subaru just didnt add a selector to their cars. FWD, AWD, 4WD. Just like the big boys. I can say on snow and ice it wouldn't help if the AWD is working properly. Hardcore offroaders say they see some benefit, I haven't gone that far offroad myself.
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