Getting stuck, 'rocking' out, found awesome method.

[CNY_Dave]

Managed to high-center on a packed snowdrift (already thinking 'gee, if the front was a bit blunter, it'd stop instead of riding up and getting stuck', but of course then the approach angle would suck), did some extraction digging under the car, tried 3 methods to rock it out:

 

1) R, ease on the gas, get a few fractions of an inch forwards, starts to spin slowly, stick it into 1 and repeat.

 

2) Same as (1) but give the gas a bit of a stomp.

 

Both left me high and spinning (1 front, 1 rear.Thought the LLBean had LSD in the rear?).

 

Occurred to me to try

 

3) Put it into R, foot on brake, increase gas until its pulling 1500 or 2000 or so. Release brake quickly without letting off the gas. HOLY COW, I shot back a whole foot! Did the same in 1, repeated a few more times, and I was on my way.

 

I'm telling you, using method 1 or 2 the car would not move even one inch. I think with method 3, I might not even have had to shovel!

 

Is this a quirk of the AWD? Maybe this method was the only way to get the limited-slip diff in the rear functioning (assuming I have it)?

 

Any thoughts why this was so much more effective?

 

 

Dave

[SubaruWagon87]

Its probably because the torque was getting sent to the wheels all at once, like if it was a 5-speed. Thats the only thing I can think of...

[Gloyale]

well the wheels probably spun fast with alot of force, right away. And it does take some good fast spin to get the VLSD to heat up and grab. Plus you may have slightly "pre-heated" the VLSD in the rear with you're previous tries.

[idosubaru]

not sure but some limited slip REAR diffs are VLSD (that is probably what yours is if you have one) - viscous type limited slips. the fluid must be heated up due to slippage before they start doing their thing. but with the brakes on i don't think the rear diff should have been turning at all anyway. in the snow, mud, or offroad the clutch type LSD (i have one) are far better. you could have heated the fluid up enough to finally get better traction.

 

the car would stall if the brakes are on....so you must have an automatic.

 

if yours is an automatic it should be able to vary the power split when it detects slipping and give you better traction. that's why i install the Duty C switch so i can control the lock up of the rear transfer clutches (inside the transmission - the rear extension housing). otherwise you have to wait for slipping to start before the TCU says "okay, i see we are slipping, let's do something"...if yo'ure in bad mud or snow you don't want to start rutting and wait even a half a second or one tire rotation for the TCU...that easily makes the difference between rutting and high centering or making it out. at least in the bad stuff, for normal road driving it rarely matters. sometimes it takes a bit for the TCU to give a good power distribution as well, maybe you got better reaction from it with the "launch" verses rocking.

[Gloyale]

 

if yours is an automatic it should be able to vary the power split when it detects slipping and give you better traction. that's why i install the Duty C switch so i can control the lock up of the rear transfer clutches (inside the transmission - the rear extension housing). otherwise you have to wait for slipping to start before the TCU says "okay, i see we are slipping, let's do something"...if yo'ure in bad mud or snow you don't want to start rutting and wait even a half a second or one tire rotation for the TCU...that easily makes the difference between rutting and high centering or making it out. at least in the bad stuff, for normal road driving it rarely matters. sometimes it takes a bit for the TCU to give a good power distribution as well, maybe you got better reaction from it with the "launch" verses rocking.

 

 

I don''t think it was a TCU issue. He said his front and back wheels were spinning. The newer 4EATs have better TCUs. Distributed a fair amount of power right away. I think it is the older 4EATs, in XTs and GL-turbos, that had the problem with slipping a whole lot first. That is why I installed the C solenoid switch in my old GL, but didn't need it in my 93 legacy.

 

My bet is still that givin 'er the onion built up enough force and heat to activate the rear VLSD

[CNY_Dave]

not sure but some limited slip REAR diffs are VLSD (that is probably what yours is if you have one) - viscous type limited slips. the fluid must be heated up due to slippage before they start doing their thing. but with the brakes on i don't think the rear diff should have been turning at all anyway. in the snow, mud, or offroad the clutch type LSD (i have one) are far better.

 

the car would stall if the brakes are on....so you must have an automatic.

 

if yours is an automatic it should be able to vary the power split when it detects slipping and give you better traction. that's why i install the Duty C switch so i can control the lock up of the rear transfer clutches (inside the transmission - the rear extension housing). otherwise you have to wait for slipping to start before the TCU says "okay, i see we are slipping, let's do something"...if yo'ure in bad mud or snow you don't want to start rutting and wait even a half a second or one tire rotation for the TCU...that easily makes the difference between rutting and high centering or making it out. at least in the bad stuff, for normal road driving it rarely matters.

 

 

Yeah, auto (forgot to put that in).

 

I don't think any duty-c magic would have helped on this one, 1 front and 1 rear spun at the same time as all the weight was lifted off the tires... even at my slow pace, the gracefully sloped underside of the nose just lifted the car right up, all 4 wheels.

 

I've done a fair bit of testing on the yard test-track and can tell pretty well when I've got just 1 front (or rear) tire spinning, vs. 1 on the front and 1 on the rear. So far I've had good opportunities with grass, wet grass, and snow. Ice next!

 

I really can't overstate how well this method worked- I mean, tires were spinning uselessly if I gave it beyond just a little throttle, but powerbraking it a bit and then releasing the brakes was like getting a tug from a buddy with a towstrap.

That's why I'm a bit perplexed- the car really had no right moving at all, judging by the lack of traction and lack of weight on the wheels.

 

Dave

[CNY_Dave]

I don''t think it was a TCU issue. He said his front and back wheels were spinning. The newer 4EATs have better TCUs. Distributed a fair amount of power right away. I think it is the older 4EATs, in XTs and GL-turbos, that had the problem with slipping a whole lot first. That is why I installed the C solenoid switch in my old GL, but didn't need it in my 93 legacy.

 

My bet is still that givin 'er the onion built up enough force and heat to activate the rear VLSD

 

Well, I'd expect no heat buildup powerbraking it with no wheels moving- but that doesn't mean the powerbraking didn't affect the LSD action in some other way.

 

I did try spinng the wheels for a bit, just to see if I had a limited-slip rear, and it sure didn't seem like it. On that cars-101 page, it said the beaners in '03 had lim-slip, BTW.

 

Also, neither front wheel slipped while using this method, so whatever was at work affected the front traction as well.

 

 

Dave

[keltik]

Im going to use some physics here to explain it.

 

When you were using your first method, the wheels are being accelerated at a relatively slow rate. Therefore the wheels with the least traction (the ones in the air) would start to spin before the wheels on the ground.

 

When you tried the launch method, the wheels have a good few horsepower spinning them up to speed much quicker. This creates a large difference in the rotational inertias of the wheels.

 

So because of the way your differentials work - whichever wheel needs the least torque to move will spin first. In your first method it was the wheel in the air. With the second method the wheels in the air need more torque to accelerate to speed than the wheels on the ground need to move the car.

 

Therefore the car moves....untill the wheels in the air hit the required speed and no longer have a rotational acceleration inertia.

 

Or you just heated up the rear diff enough to get it working....

[CNY_Dave]

Im going to use some physics here to explain it.

 

When you were using your first method, the wheels are being accelerated at a relatively slow rate. Therefore the wheels with the least traction (the ones in the air) would start to spin before the wheels on the ground.

 

When you tried the launch method, the wheels have a good few horsepower spinning them up to speed much quicker. This creates a large difference in the rotational inertias of the wheels.

 

So because of the way your differentials work - whichever wheel needs the least torque to move will spin first. In your first method it was the wheel in the air. With the second method the wheels in the air need more torque to accelerate to speed than the wheels on the ground need to move the car.

 

Therefore the car moves....untill the wheels in the air hit the required speed and no longer have a rotational acceleration inertia.

 

Or you just heated up the rear diff enough to get it working....

 

 

I could be something like that. I didn't get any spin at all when I released the brakes, but the mechanism you describe would still be valid.

 

What's interesting is I've driven a *lot* of different vehicles in a *lot* of different scenarios and either didn't try this, or tried it and it didn't have much effect. Most of those vehicles were standards, but not all. One was 4WD, some were FWD, some RWD.

 

I've read a fair number of getting-unstuck stories and hints, but I don't recall seeing this method mentioned.

 

 

Dave

[ericem]

Maybe you were on ice and eventually dug through. I think a set of blizzaks would help in these snowy conditions

[Hotshot]

I know I have heard several people here say that lightly holding the brake while hitting the gas causes it to act sort of like an LSD. Maybe thats what happened? I'm sure someone else can explain it much better than I can.

[CNY_Dave]

I know I have heard several people here say that lightly holding the brake while hitting the gas causes it to act sort of like an LSD. Maybe thats what happened? I'm sure someone else can explain it much better than I can.

 

No, I tried that, and have tried it othertimes. Sometimes it does help, usually when slowly creeping over terrain.

 

 

Dave

[awesomedude]

exactly..you have open diffs-even a vlsd is essentially open until working right.

 

This is exactly why people put dual e-brake handles in older subes(one for each wheel).Once one front wheel is spinning hopelessly in the air with the traction wheel doing nothing you can lock the spinning wheel with the corresponding e-brake handle-transfering power to the wheel that was doing nothing while sitting on dry ground.