I thought that it works the opposite way, if a wheel loses grip (or in the air) then the power goes to the other wheels.

I await to be corrected. :)

it only works like that if there is some form of "limited slip" between the spinning wheel and the wheels with "grip" - irrespective of whether you have 2/4/6/8 wheel drive

as I said in an earlier post, in reality the issue is with the amount of "slip" allowed in the drivetrain

open diffs allow 100% slip - that is why you will be able to turn the wheel that is in the air - all power/torque will go to the spinning wheel

There's a first.
Hope the garage didn't try to make a claim off the owner :lol1:

Ok, understood now. :thumb:

This is where it gets really confusing. Which Imprezas have fully open diffs?

Exactly the central point !

Hodgy0_2 has said how to find out what sort of diff a car has.
Anyone can carry out that test.

But would you really want to?

• If it is locked you'd HAVE to find a garage that knows and uses a decelerometer;
• If it isn't you've still spent time and effort testing it.

The guaranteed way to save that effort is just to go to a garage that knows and uses a decelerometer.

One call to an MoT station:

"Hello, MoT's R Us"
"Hi, I've got a Subaru. Do you use a decelerometer to test cars?"

• "Yes we do (if it's 4 or AWD)"
  "Fine - can I book mine in please"
• "Pardon?"
  "Sorry - wrong number".

Why not simply insist on decelerometer for all Impreza?

funnily enough I have spoken to two MOT testers (one who's opinion I value extremely highly)

and they both said they would not put on rollers, not so much for the technical reasons - but simply as people have said for commercial and risk mitigation reasons

VOSA clearly states MOT tester are liable

Ahhh,but what if the test station had a plate brake tester as opposed to a tap meter......