Don't do handbrake turns in your AWD Subie

There is nothing at all wrong with doing handbrake turns in a Subaru, be it a car with a VLSCD or DCCD. Any damage done to the centre diff when doing handbrake turns is due to poor driving.
 
It's all that, and more. The problem is that people are applying power while they are still applying the handbrake. When you do handbrake turns, you only apply the handbrake to get the car sideways, then you let go and apply power. Depending on the car and how effective the handbrake is, you could just use a short jab or maybe something a bit longer. I have seen a number of people unable to co-ordinate the use of the handbrake in co-ordination with the the throttle. Some people also apply the handbrake before they turn in, which is not the way to do it. The advantage of the DCCD set up is that it uncouples the front to the rear, which helps getting the car to turn in. I recently had a fault in my car where the DCCD did not disconnect, and the car refused almost totally to turn in. It was just a blown diode, but that was enough.
 
Doing handbrake turns on a skid pan or other slippery surface is one thing. Doing one on a hard, un-lubricated surface is another altogether ...

Same as my LC was quite happy in 4WD/HR or 4WD/LR on dirt, but would throw a propeller shaft in double quick time on a dry bitumen surface.
 
That is different. The slippery surface provides slippage for your LC to have wheel differentiation. With the Subaru, the problem is different. You are applying power- lots of it, when the rear wheels are locked and the fronts are free. It is a grossly increased situation of running different sized rims front and rear. The road surface is not relevant in this scenario. The centre diff has an impossible situation to deal with, and eventually dies. While I myself have not done motorkhanas on dry sealed surfaces, I know others who have and their cars have suffered no ill effects to the centre diff a s a result. Why- because they don't simultaneously apply power and the handbrake. I don't do dry motorkhanas because it is even harder on the tyres than a wet one, and the tyre noise becomes a bit much after a while.
 
Gidday Rally

I know that it's a different situation, but it is analogous.

Transfer case wind up in a vehicle that does not have a centre diff, and has open diffs front and rear, causes the weakest part of the drive train to break - usually one of the front universal joints (shorter propeller shaft, therefore more torque per unit length).

When a vehicle has a centre diff, the wind-up forces are again transferred to the weakest part of the drivetrain. This will usually be the centre diff (as the forces are primarily between the front and rear drivetrain components), but may also involve the rear diff, specially if it is a vLSD. Mechanical LSDs are designed to take a lot of these forces. However, they will also disintegrate in grand style if those forces are too great, because they are (usually) still the weakest link in an AWD system.

The drive plates in a vLSD are not designed to be in contact with each other. They should always be separated (and lubricated) by the non-Newtonian fluid in the sealed diff unit. If the force becomes too great, the plates can be forced into physical contact with one another This causes abrasion of the plate surfaces. The particulate matter formed in these encounters causes the non-Newtonian fluid in the diff to stop behaving like a non-Newtonian fluid as it becomes more and more like a Newtonian fluid in composition.

I have seen the difference between the fluid in a rooted vLSD and a brand new one. The difference is stark.

This explains why the rear vLSD can become useless with time and abuse. It also explains why vehicles with a centre vLSD can destroy this component when doing handbrake turns.

I respectfully suggest that most of the people who are doing handbrake turns have neither the skill nor the experience to execute such a manoeuvre in any AWD car, under any conditions. IMHO, you are predicating your comments on the experience of those who do have such skill and experience.

If one tried to do one in my old '68 LC, one would almost certainly be killed in the process ... :(.
 
I have an auto foz, but wired up a switch to lock the center diff then wired two switches in the handbrake (only because i couldn't find a dual pole version of the switch), one to turn off the 4wd lock then the next to "insert" the FWD fuse essentially. So when i pull the e-brake, the center diff is completely open before the shoes are engaging in the drums. Then i just make sure to never apply the throttle when letting the hand brake back down. Did this probably hundreds of times this last winter at the ice track and around town... Even a few times during the summer with no issues yet. The center diff still locks up strong on its own when i'm offroading. Seems to me like a pretty safe way of doing handbrake turns.

This set up actually saved me last winter when i was rallying down a curvy one lane road. I came into a hairpin way too fast (two girls with me in the foz is the explanation for this) and knew i was going to understeer right off into the trees, so i ripped the E just before the apex and gave it enough gas to keep it on the road. As the corner began to straighten, the road went slightly off-camber and the back tires fell off the edge of the road, and we were sliding at full lock towards a tree but with the throttle now wide open, i managed to climb back on the road a few feet before the tree and clean the crap out of my pants.:biggrin:
 
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