Can someone explain to me how it is possible that haldex transfers 100% of power to the rear wheels? Isn't 50% maksimum? Does pressing the off road button transfers power to the rear wheels immediately? Or something else must happen befor 4x4 kicks in?

The Haldex works with the ABS and the other onboard gadgets (with three letter acronym's) to transfer the power between the wheels. (i.e. the ABS breaks the ones spinning to transfer the power elsewhere).It works very well.

The off road button doesnt have anything to do with the distribution - its more for changing the way the engine management works, protects the engine by limiting the revs and changes the sensitivity on the ABS to allow lightly more spin (to stop the ABS reducing power to the wheels by breaking them).

Edited 15 November, 201015 yr by RogN

The Yeti is a 4x4 with a Haldex unit in the rear.

The button you are calling the "4x4 button" has nothing to do with where the power is transmitted. It's proper name is the "OFF ROAD BUTTON" and it controls:

Uphill start assist

Downhill assist

ABS off-road

ASR off-road

EDL off-road

If you have a brochure it is explained on page 15.

The Haldex works by sensing "slip" firstly in one of the front wheels, and this transfers drive to the rear axle. If the slippage was so severe that there was no drive at the front then all (100%) could be transferred to the rear. However it reacts so quickly that it can "move" power from one axle to the other quicker than you can think about it. It also acts with the standard ABS.

Hope that helps.

Haldex manufactures site with information can be found here My link

Regards,

TP

Can someone explain to me how it is possible that haldex transfers 100% of power to the rear wheels? Isn't 50% maksimum? Does pressing the off road button transfers power to the rear wheels immediately? Or something else must happen befor 4x4 kicks in?

First you need to understand that the rear axle is driven from a power take-off in the gearbox. This is always rotating at the same speed as the drive to the front axle.

With normal operation of the front axle, the Haldex coupling is open, and the only power transfer to the rear axle is the small amount of friction in the clutch. So, essentially front wheel drive if there is enough friction between the front wheels and the road to transfer all the power there.

If the ECU senses a slip on the front axle, the Haldex closes enough to eliminate it - all the way to complete coupling of the rear axle, so both axles rotate at the same speed. If the front has no friction, all the power goes to the rear axle, except the small amount in the front determined by the friction between the front wheels and the road.

If there is less friction available to one rear wheel, the Haldex limited slip coupling on the rear axle closes, so both rear wheels rotate at the same speed, so the one wheel that has friction to transfer power to the road gets all the power - minus the little that the other wheels can transfer. The Haldex operation is very fast and smooth, so you would normally not notice its operation.

This ia kinda explained in the Haldex website, but to my way of thinking, not very clearly.

The neat trick with the Haldex system is that there is no center differential or transfer case - not needed and no additional drag, except the small amount of power lost in rotating the rear drive shaft and heating up the oil in the Haldex coupling.

But...... Don't forget that the Haldex does not improve traction between the tyre and the road, and does not help braking - or steering, unless you are accelerating.

Edited 16 November, 201015 yr by Agerbundsen

I have read all brochures but still don't understand it...

Correct me if I am wrong...engine and transmission are in the front, front two wheels and transmition shaft (I do not know english term) are driven directly from the transmission (so 50% power to the front two wheels and 50% of power to the shaft which rotates constantly....). When the clutch (which lies at the rear end) is not engaged than all the power goes to the front wheels, when the clutch is fully engaged than 50% of power goes to the front wheels and 50% to the rear. How is it possible that front two wheels do not get any power when they are driven directly from the transmission?

I have read all brochures but still don't understand it...

Correct me if I am wrong...engine and transmission are in the front, front two wheels and transmition shaft (I do not know english term) are driven directly from the transmission (so 50% power to the front two wheels and 50% of power to the shaft which rotates constantly....). When the clutch (which lies at the rear end) is not engaged than all the power goes to the front wheels, when the clutch is fully engaged than 50% of power goes to the front wheels and 50% to the rear. How is it possible that front two wheels do not get any power when they are driven directly from the transmission?

Greg, read the post above. That should explain it. If all 4 wheels are locked together at the same speed, the power goes to that wheel that has friction to transfer it to the road. The other three just follow along...............

Edited 16 November, 201015 yr by Agerbundsen

I have read all brochures but still don't understand it...

Correct me if I am wrong...engine and transmission are in the front, front two wheels and transmition shaft (I do not know english term) are driven directly from the transmission (so 50% power to the front two wheels and 50% of power to the shaft which rotates constantly....). When the clutch (which lies at the rear end) is not engaged than all the power goes to the front wheels, when the clutch is fully engaged than 50% of power goes to the front wheels and 50% to the rear. How is it possible that front two wheels do not get any power when they are driven directly from the transmission?

Greg,

simple explanation:

Normal use, 99% of drive to front wheels, rear axle just follows along, basically undriven.

Front wheel slips, drive transferred to rear axle and to both rear wheels through differential. Spinning front wheels are "locked" by the ABS, etc system.

One rear wheel slips, rear diff locks and drive split between both wheels equally (acts like a solid axle) ABS acts on spinning wheel.

Technically it would be possible to drive a Yeti with only one wheel actually touching the floor!

First you need to understand that the rear axle is driven from a power take-off in the gearbox. This is always rotating at the same speed as the drive to the front axle.

With normal operation of the front axle, the Haldex coupling is open, and the only power transfer to the rear axle is the small amount of friction in the clutch. So, essentially front wheel drive if there is enough friction between the front wheels and the road to transfer all the power there.

If the ECU senses a slip on the front axle, the Haldex closes enough to eliminate it - all the way to complete coupling of the rear axle, so both axles rotate at the same speed. If the front has no friction, all the power goes to the rear axle, except the small amount in the front determined by the friction between the front wheels and the road.

If there is less friction available to one rear wheel, the Haldex limited slip coupling on the rear axle closes, so both rear wheels rotate at the same speed, so the one wheel that has friction to transfer power to the road gets all the power - minus the little that the other wheels can transfer. The Haldex operation is very fast and smooth, so you would normally not notice its operation.

This ia kinda explained in the Haldex website, but to my way of thinking, not very clearly.

The neat trick with the Haldex system is that there is no center differential or transfer case - not needed and no additional drag, except the small amount of power lost in rotating the rear drive shaft and heating up the oil in the Haldex coupling.

But...... Don't forget that the Haldex does not improve traction between the tyre and the road, and does not help braking - or steering, unless you are accelerating.

Thank you for the answer, you posted it at the same time as I was writting my second post and did not see it…

So we are talking about two different things? % of power going to the axles and % of power going to the ground? In case of slippage both axles get 50% of power, but if only one wheel has traction than (due to EDL and haldex coupling) the only power going to the ground goes thru this wheel (100%)? So if three wheels were off the ground (let say the front two and one rear) than one front would get 50% of power but no power would go to the ground and the rear wheel on the ground would also get 50% of power but would be the only one actually putting the power to the ground (so 100% of power would go to the ground). Now if we change % into HP… let say engine produces 100HP on the wheels at 2000 rpm. In case three wheels are off the ground than 50HP would go to the front wheel spinning and 50HP would go to the rear wheel on the ground…so actually only 50HP would get to the ground >> only 50% of power currently available.

Sorry if my questions don't make sense but I would just like to understand haldex 4x4. Unlike most of you I had a couple of bad experiences with yeti past winter and cannot quite understand them.

First time it happened when I decided to turn a car on the narrow road so I drove the front wheels off the road into deep snow and the rear of the car was on dry tarmac. Now according to theory I should not have any problems going backwards. Not so…front wheel was spinning and the car was stuck. Now I do not know if the rear wheel(s) were spinning or not. If they were than the reason I was stuck is that there was simply not enough weight on the rear axle. If they were not spinning than I am worried because this would mean that not enough power got to the rear axle something very common with some other 4x4 systems on the market (honda crv…) as you can see on youtube.

Second time was even worse…I decided to try out EDL… I drove with left side of the car in deep snow while right side was on tarmac…and although I could hear and feel EDL working not enough power was transferred to the right side to drive the car forward. I had to back the car on the tarmac before going forward…What 's the point of having EDL if it cannot transfer power from one side to another?

One more question…does EDL work on both axles or just one?

So we are talking about two different things? % of power going to the axles and % of power going to the ground? In case of slippage both axles get 50% of power, but if only one wheel has traction than (due to EDL and haldex coupling) the only power going to the ground goes thru this wheel (100%)? So if three wheels were off the ground (let say the front two and one rear) than one front would get 50% of power but no power would go to the ground and the rear wheel on the ground would also get 50% of power but would be the only one actually putting the power to the ground (so 100% of power would go to the ground). Now if we change % into HP… let say engine produces 100HP on the wheels at 2000 rpm. In case three wheels are off the ground than 50HP would go to the front wheel spinning and 50HP would go to the rear wheel on the ground…so actually only 50HP would get to the ground >> only 50% of power currently available.

Ignore HP, that has nothing to do with it.

If the car had 3 wheels in the air and 1 on the ground (doesn't matter which wheel) then 100% of the drive would go to that wheel, and all the other wheels would be locked by the ABS. It really is as simple as that!.

First time it happened when I decided to turn a car on the narrow road so I drove the front wheels off the road into deep snow and the rear of the car was on dry tarmac. Now according to theory I should not have any problems going backwards. Not so…front wheel was spinning and the car was stuck. Now I do not know if the rear wheel(s) were spinning or not. If they were than the reason I was stuck is that there was simply not enough weight on the rear axle. If they were not spinning than I am worried because this would mean that not enough power got to the rear axle something very common with some other 4x4 systems on the market (honda crv…) as you can see on youtube.

Second time was even worse…I decided to try out EDL… I drove with left side of the car in deep snow while right side was on tarmac…and although I could hear and feel EDL working not enough power was transferred to the right side to drive the car forward. I had to back the car on the tarmac before going forward…What 's the point of having EDL if it cannot transfer power from one side to another?

One more question…does EDL work on both axles or just one?

I would suspect that you eased off before it all started to work, but when I've had the front in mud the rears have spun a little and then pushed me through. The problem with snow is that it could have built up underneath to hold, especially if you only have the light plastic guard.

Do not confuse the Yeti 4x4 system to that of the Honda system. They are not comparable.

EDL works on the whole car. That sounds like you didn't increase power to take into account the drag from the snow on one side, which can be considerable.

Ignore HP, that has nothing to do with it.

If the car had 3 wheels in the air and 1 on the ground (doesn't matter which wheel) then 100% of the drive would go to that wheel, and all the other wheels would be locked by the ABS. It really is as simple as that!.

I would suspect that you eased off before it all started to work, but when I've had the front in mud the rears have spun a little and then pushed me through. The problem with snow is that it could have built up underneath to hold, especially if you only have the light plastic guard.

Do not confuse the Yeti 4x4 system to that of the Honda system. They are not comparable.

EDL works on the whole car. That sounds like you didn't increase power to take into account the drag from the snow on one side, which can be considerable.

I concur with your comments.

If you had been in a Honda, which as far as I know has an open centre differential, you would be limited in transferring the power to the ground equal to that of the wheel with the least friction = the spinning front.

Ignore HP, that has nothing to do with it.

If the car had 3 wheels in the air and 1 on the ground (doesn't matter which wheel) then 100% of the drive would go to that wheel, and all the other wheels would be locked by the ABS. It really is as simple as that!.

I would suspect that you eased off before it all started to work, but when I've had the front in mud the rears have spun a little and then pushed me through. The problem with snow is that it could have built up underneath to hold, especially if you only have the light plastic guard.

Do not confuse the Yeti 4x4 system to that of the Honda system. They are not comparable.

EDL works on the whole car. That sounds like you didn't increase power to take into account the drag from the snow on one side, which can be considerable.

So accelerating out of a tight corner you have 50-50 ditribution (in best case) and therefor understeering.

I concur with your comments.

If you had been in a Honda, which as far as I know has an open centre differential, you would be limited in transferring the power to the ground equal to that of the wheel with the least friction = the spinning front.

Hi Agerbundsen - I feel this is a very interesting, and pertinent thread - getting to the bottom of how well the Yeti Haldex system will actually perform. Greg570's experience is a bit unsettling though, and it is difficult to argue with the two circumstances quoted - we have to assume they actually happened, and that should not, according to the theory if I read it right, be possible.

The comment that Greg may not have given everything time to happen does not sound feasible, surely. First, I am sure he would have been certain things were not happening as they should, before deciding he needed to take other action. Second, we are told that the Haldex system works virtually instantaneously. We do not have any snow down here at present, but when/if we do, I will be doing some testing to try to replicate these situations, and see what happens. It would be good to know if your, and Llanigraham's comments, are based on how the system has actually worked for you, in similar circumstances, or if they are based on how it should work in theory. Perhaps I am unsettled by that video showing how poorly SOME 4x4 systems actually worked - on the ramp. It is difficult to beat actual experience - I will rely on that over theory every time!

So accelerating out of a tight corner you have 50-50 ditribution (in best case) and therefor understeering.

Not always, no. It would depend on how much grip there was.

For the majority of the time the Yeti is front wheel drive; it only puts drive elsewhere IF IT IS NEEDED. So in that instance if it was dry tarmac it would probably be just front wheel drive, but if it was wet or icy then it could gradually put an increasing amount of drive to the rear, at anything up to 100%.

I think you are trying to be too complicated. The system works very well, and exactly what percentage of drive is where is not measurable, it just happens. It gets you out of the mire (I know, I've done it). Be like the rest of us with 4x4's and don't worry how or why it works, just accept it does.

So accelerating out of a tight corner you have 50-50 ditribution (in best case) and therefor understeering.

No - at least to my understanding, accelerating HARD in a corner - approaching the limits of adhesion:

Rear wheel drive - oversteering (loose!)

Front wheel drive - understeering.( pushing)

Haldex - neutral steering. ( and able to transmit more power to the road.)

Edited 16 November, 201015 yr by Agerbundsen

Be like the rest of us with 4x4's and don't worry how or why it works, just accept it does.

+1

Just to throw my 2 cents in...

Ive specifically tried to out do the haldex in a large snow covered car park a few weeks ago (in Switzerland) and that included front axel in snow, rear on tarmac, vice versa and some more complex things like moving off harder with the drivers side on snow and the passenger side on cleared tarmac. The results were exceptional imo and never showed any signs of traction issues. :yes: imo the generation four haldex is a very capable system and after doing what I did with the car in Germany and Switzerland so succesfully; cant think of any situation in the UK that would cause me to worry!

Iirc I think I found that having the traction control off was better - I played with this when trying to reverse up a snowy incline and Im sure it felt more assured when it was off.

Be like the rest of us with 4x4's and don't worry how or why it works, just accept it does.

The only trouble is, though, forgive me if I misunderstand, Greg570 made the original post because he had a couple of situations where it didn't!

I know that situations where only one wheel has traction are very rare but non the less according to the theory yeti shouldn't stop even in this kind of situations.

Apart from the two mishaps I had I didn't have a chance to really test 4x4 last winter. I plan to do it this year and a report will follow.

One more thing regarding tyres. Stock dunlops are rubbish in the snow. I was unable to make it into my garage and there is hardly any slope in front of it…so if you plan driving in the snow, winter tyres are a must.

The only trouble is, though, forgive me if I misunderstand, Greg570 made the original post because he had a couple of situations where it didn't!

No here's the the original question:

Can someone explain to me how it is possible that haldex transfers 100% of power to the rear wheels? Isn't 50% maksimum? Does pressing the off road button transfers power to the rear wheels immediately? Or something else must happen befor 4x4 kicks in?

Greg570 you might want to look at the video posted in the first post of this thread:

http://briskoda.net/forums/topic/159259-4x4-systems-tested/

That Passat has the same Haldex system as the Yeti and that test neatly shows all the situations described above with various wheels losing traction as well as Agerbundsen's comment re the Honda system.

In PMQ terms, it was the follow up question so you are both correct.

Interesting thread.

Greg570 you might want to look at the video posted in the first post of this thread:

http://briskoda.net/forums/topic/159259-4x4-systems-tested/

That Passat has the same Haldex system as the Yeti

Are you sure about that? I thought that Passat would have been running the inferior generation 2 haldex as I had fitted to my previous 4x4 Octavia???

Are you sure about that? I thought that Passat would have been running the inferior generation 2 haldex as I had fitted to my previous 4x4 Octavia???

Read the my first post in that linked thread! I state exactly that. If the Haldex 2 can do that in the video the Yeti with Haldex 4 can only do much, much more!

Read the my first post in that linked thread! I state exactly that. If the Haldex 2 can do that in the video the Yeti with Haldex 4 can only do much, much more!

Apologies, I only read the info within this thread. Gen 4 is far superior to gen 2 imo.