When do the rear wheels get power

I took the car on some off roading yesterday in what would be very easy make for an AWD system.

The dip pictured below was taken at an angle and the driver side wheel became unweighted. This forced all the power to bleed out through that wheel. I tried the gently apply the brake and press gas method, no luck.

How in this situation would I get power to the rear wheels? My 5EAT is apparently 55% rear biased. Yet with the brake down I was just reving, no power to the rear wheels.

Doesn't this unweighting also simulate ice? So in theory if I get a patch of ice under a front wheel I'm stuck?

Edit//

It seems no one has off road before.. let me fix it here and will edit above.

While off roading, I was required to cross a dip, pictured, the front wheel on the driver side became unweight, and just spun away - bleeding all the power. Due to my slow speed the car just stopped. Flooring it didn't get power rearwards. So I attempted to stop the spinning of the wheel with my brake. This braking style is used in old open diff jeeps. It didn't work. I had to throw the car in reverse, re-weighting the car and proceed at a different angle. The car was acting like a FWD vehicle.

Why didn't I have any power to the rear wheels if my system is to have 55% going rewards?

I cant understand the problem . If only one wheel was unweighted then the other three provide traction , or at least the rear two do . Why apply the brake ?.

Because all power bled out the front lifted wheel and I didn't go anywhere.

http://legacygt.com/forums/showthread.php/explanation-continuous-active-and-vtd-awd-systems-honest-attempt-48112.html

Read this a while back but my experience suggests I got not real power rewards.

It seems no one has off road before.. let me fix it here and will edit above.

While off roading, I was required to cross a dip, pictured, the front wheel on the driver side became unweight, and just spun away - bleeding all the power. Due to my slow speed the car just stopped. Flooring it didn't get power rearwards. So I attempted to stop the spinning of the wheel with my brake. This braking style is used in old open diff jeeps. It didn't work. I had to throw the car in reverse, re-weighting the car and proceed at a different angle. The car was acting like a FWD vehicle.

Why didn't I have any power to the rear wheels if my system is to have 55% going rewards?

According to that link, the TCU is supposed to send power to the rear automatically once front slippage starts.

"A speed differential (front-to-rear) of up to 20% signals the TCU that the vehicle is cornering and torque is distributed to the front wheels to help increase traction during the turn. Anything above 20%, however, indicates to the TCU that wheel slippage is occurring and torque is then distributed to the rear wheels. "

Maybe there is something in your center diff that is slipping and preventing power from getting transferred to the rear?

Maybe. how would one confirm this?

apparently by driving across the dip in different directions until you test every corner?

maybe you need a front lsd?

Well I was looking through the video we shot and it appears my rear wheels are getting power. I am of course joking about being in low.

In the below video I have both a driver side front and a passenger side rear spinning. It would seem I don't have a rear LSD.

Thoughts?

[ame=http://www.youtube.com/watch?v=5FyOt8SUAb4]2005 Subaru Legacy GT Auto Stuck - YouTube[/ame]

apparently by driving across the dip in different directions until you test every corner?

 

maybe you need a front lsd?

I think you're right. Seems I have two open diffs.

The diagonal spin of AWD isn't isolated to Subis only. This is why locking differentials are used in true offroading vehicles.

You have AWD, not 4WD. There's a difference. VDC may have helped with your situation but only to a certain extent.

Have a good read:

http://www.4x4abc.com/4WD101/one-spinning-wheel.html

The diagonal spin of AWD isn't isolated to Subis only. This is why locking differentials are used in true offroading vehicles.

 

You have AWD, not 4WD. There's a difference. VDC may have helped with your situation but only to a certain extent.

 

Have a good read:

http://www.4x4abc.com/4WD101/one-spinning-wheel.html

This is a good read thank you. I was shocked to experience my car becoming a 1 wheel drive car. This recent experience will change my thinking on what's needed for the next car.

Don't think it was a one wheel drive car. Both rear wheels were getting torque, just not enough to move the vehicle. In addition if you had one rear wheel spinning, the rear LSD in most Subarus can transfer something like 12 lbs-ft of torque per 1000RPM. Not sure of the specs on the LSD of manual or transfer specs of the 5-speed auto.

In other words even if the rear axles have enough to move the car, if one is off the ground, the LSD may not be able to transfer enough to move the car.

Hence, as somebody said already, for real off-roading, traditional locking diffs are the only way to go.

As far as cars that would be better, there may not be too many. Electronic diffs that use braking to transfer torque work, but overheat and then completely shut-down in extreme conditions, since they are designed for on-road use only. How long before they overheat is debatable, but there are unless debates about said systems on track days.

Clutch-based electronic diffs (Acura for example) would probably hold up better.

Don't think it was a one wheel drive car. Both rear wheels were getting torque, just not enough to move the vehicle. In addition if you had one rear wheel spinning, the rear LSD in most Subarus can transfer something like 12 lbs-ft of torque per 1000RPM. Not sure of the specs on the LSD of manual or transfer specs of the 5-speed auto.

 

In other words even if the rear axles have enough to move the car, if one is off the ground, the LSD may not be able to transfer enough to move the car.

 

Hence, as somebody said already, for real off-roading, traditional locking diffs are the only way to go.

 

As far as cars that would be better, there may not be too many. Electronic diffs that use braking to transfer torque work, but overheat and then completely shut-down in extreme conditions, since they are designed for on-road use only. How long before they overheat is debatable, but there are unless debates about said systems on track days.

 

Clutch-based electronic diffs (Acura for example) would probably hold up better.

I've had the front wheel open up and send no power to the rear, even at 5K rpm.

We're already buying an MDX so I'll put the SH-AWD system through it's paces to compare.

Yikes, then something definitely wrong with the trans/center diff then. Worth moving on!

It's for the soon to be wife. My father has the RL with SH-AWD. I've had limited snow experience, but deep snow, and it did well.

I am keeping this Legacy + snow tires for a while.

from reading your thread, it appears the root of your problem is "driving slow". Don't you watch Subaru rally vids? No one is going slow and they never get stuck (they roll over and crash, but they don't get stuck).

Next time, more speed.

from reading your thread, it appears the root of your problem is "driving slow". Don't you watch Subaru rally vids? No one is going slow and they never get stuck (they roll over and crash, but they don't get stuck).

 

Next time, more speed.

Ha!

Subaru doesn't have a rally race division anymore and hasn't for years. I bet the tranny's they have are pretty tricked out. LSD mech front/rear and locking center diff. They then sell us all on an 'amazing awd system straight from their rally cars' which is disappointingly not true.

Ha!

 

Subaru doesn't have a rally race division anymore and hasn't for years. I bet the tranny's they have are pretty tricked out. LSD mech front/rear and locking center diff. They then sell us all on an 'amazing awd system straight from their rally cars' which is disappointingly not true.

I had a FWD turbo car that saw alot of off-road action. One lesson I learned early on, when in doubt more throttle.