Good technical Question

[syncrosimon]

The aim is to get one rear wheel (or both) to spin out, so that you test the front via the VC. That way the vehicle should drag itself along with the front drive only, thus testing the VC.

[lloydy]

that was my original thought. I presumed thats why we had diff locks

[jed the spread]

Take both drive shafts off and you can have a front wheel drive van....

(dont do this by the way I was joking)

I do know someone who has driven a good few miles home after snapping two rear drive shafts and buggering the VC in the process I believe.

jed

[lloydy]

Found this, says jack both wheels off the ground

How to Replicate the VW Test
Using a heavy floor jack with wheels, put a block of wood on the jack and raise the rear of the van using the skid plate. Be careful, you can bend it. The wood block, if long enough, distributes the weight across enough of the skid plate to minimize that risk. Lift both back wheels off the ground 6" or so on a smooth level parking lot, with the jack's wheels parallel to the Syncro's. The rear of the van will be moving on the jack wheels, so you need to make sure there are no obstructions that could catch the jack wheels and cause the van to fall off the jack.

Now, put a 1x1 piece of wood in front of each front tire, 2x4 may work too. You need to block the front wheels like this to be able to test whether the VC is capable of absorbing the spinning of the rear wheels without locking up and causing the front wheels to engage and climb over the wood. If you can get the rear wheels to turn/spin in the air with the clutch fully disengaged, and without the van climbing over the wood blocking the front wheels (can't be too high...1-2"), then the VC is definitely good, or the fluid is not cooked. The van should climb over the blocks as soon as you increase the engine RPMs.

It may take several tries to get the van to do this. The VC is very sensitive, and it will want to engage as you let the clutch out. Some advise using the hand brake to help slow the spin of the rear wheels ... or to start them spinning slowly at first. It is really neat when you get it to work. Suddenly, the VC is working before your eyes in a very graphic way!

Also says putting it in a break test/rolling road and see if you can drive out
Seems the thing they have in common is having both wheels spinning?

[syncrosimon]

Yep, thats all you need to do, just remove drive from the rear, so that it depends on the front. There are many ways of doing it. The brake roller test would be the easiest and safest. One or two rear wheels does not make a difference so long as you dont engage rear diff lock. On my vid I had front diff lock on, just to really see what the VC was doing. The camera would have missed it if the opposite front spun out.

[Essex Nige]

[front wheels chocked with brick]
Cheers, Lloyd

Are you not just meant to use something like an INCH not as high as a brick? and if it raises up the 1" bit of wood thats good?

[syncrosimon]

The front wheel chocks are just to stop the drag in the VC move the vehicle. the brick or block is to give the VC something to do, so you need a bit of power to climb it, to properly simulate a real world situation.

[Essex Nige]

Think i'll give mine a go tomorrow, seeing as im getting the gearbox and front diff sorted might as well see if it works and if its fooked replace it at the same time

[lloydy]

Find it strange that mine wasn't climbing it, maybe it was because it was cold? The front wheel is stiff to turn when it's jacked up, so that kinda proves vc works and hasn't failed open.
Simon was your test done after a drive, or from cold?

[lloydy]

Here's a link to the whole article
http://www.syncro.org/VCTest.html

[syncrosimon]

My test was done cold, it almost locks solid when hot. Will do the test again and see just how much tighter it is when hot.

The tight VC on ice is great, as it does not fishtail very easily.

http://www.youtube.com/watch?v=tewtTLwvL84

[Aidan]

if vehicle is stationary and you only raise one rear wheel it will spin out and because the vehicle isn't moving there is no relative difference between axles thus no action by the front as the vc isn't dumping any power the spinning wheel is dumping it all, these are rwd vehicles with a vc that only transmits power when there is a relative speed difference between axles that causes the plates inside the vc to heat up the silicon and change it's state, lock up the plates and transmit power to the front pinion shaft and thus to the front diff and thence the wheels.
The raising one wheel and manually turning it test is just a quick check, but the fact that you can just rotate the wheel does say that the vc is in some sort of working condition, if it had failed open then it would be easy to turn

with 4 wheels on the ground, in neutral and the vehicle stationery if you take a 13mm spanner to one of the prop bolts you will just be able to turn the prop if the vc is good, again will turn easily if vc failed(failing) and won't be able to turn it if on the tight side

[syncropaddy]

Lifting one rear wheel will let it spin out.

I said that too ....

[lloydy]

if you take a 13mm spanner to one of the prop bolts

i'll report back it 5mins

[lloydy]

Put the spanner on, very, very stiff. So that in conjunction with the front wheel being stiff, looks like the VC works, Which is kinda like it initially felt on the road.[very little wheelspin on ice before it shoots forward].
So i presume the people that the one rear off the ground thing works, have a tight vc, as its engaged?
Thanks for all the info/help