MOT brake testing

G-man i think that has answered my question thanks , makes a lot of sense ,

although still concerned that the vcu / drive train components could be damaged if the test isnt carried out correctly

FL1 off for it's MOT about 10.00 am so will ask the question at the station I have booked into about 2 wheel rolling tester as opposed to a 4 wheel rolling tester, and about a tapley meter / decelarometer Arctic.

Had this discussion with joe a few weeks ago - at the test station i go to here in France they have a set of portable rollers that they put under the 2 non-tested wheels - therefore no ird/vcu issues to worry about

Providing one side of the rolling road could be freewheeled there would not be an issue. Have never used a rolling road so don't know if any are designed to work that way. I always used a Tapley meter for MOT testing. But that was many moons ago. Remember doing a 42 seater coach with an apprentice squatting down holding the Tapley mid way along it somersaulting down to the front when i slapped on at 30 MPH. It passed.

I've tested this myself on conventional 2WD rollers. The rollers try to turn but because the front and rear are effectively locked together via the VCU. The car simply rolls off the rollers again. If the HB is applied to stop it rolling forward, the rollers register an overload condition and shut down. I can't see any real damage being caused, unless the IRD or diff are just about to fail anyway.

Passed no advisories i spoke to Mark the mot tester as i take my cars to the same place every year, i was informed that the machine and rolling road takes into account for the AWD if the machine is not up to date then it is supposed to be road tested,