Must admit I am more concerned now with how they conduct these brake tests.
Surely putting a perm 4 wheeler on a rolling test can not be good.
Having either set of wheels rotating while others are stationary has to be bad.
Can guarantee the tester doesn't put the transfer box into neutral as Dave mentioned and to be honest I would never have thought to tell them to do it.
There are times I wish we had stayed in West OZ. No MOTs. Simpler life.
First you need to get your head around the fact that your car is only 4WD not 'permanent 4wd', if ANY one wheel slips then the vehicle will not move or may come to a standstill except, if the wheel re-establishes traction or if there is a VC or Viscous Coupler fitted, (some have it some don't), if you do have this then there will be an attempt to drive the other propshaft but not with any real force and unlikely to push it out of the roller bay but, continued slip may cause it to overheat and be damaged but not in a few moments. Without one the car will sit there with the engine revving it's backside off and going nowhere. So, your car is ONLY four wheel drive when ALL four wheels have traction, ironic I know but that is how it is.
As a trial slip your car's transfer box into neutral, then select any gear in the gearbox, your car will not move VC or not it is not going anywhere, you have in effect uncoupled the drive from the gearbox, the gearbox drive is there but the TB is in neutral, the same effect as your gearbox in neutral. The testers here are very specific and repeat is the transfer in neutral as they do not know if your vehicle does or does not have a VC or even a LSD in the centre.
Now there are some caveats at work here for example, if you have a limited slip differential that engages when it detects 'excessive' rotational difference of one propshaft for example Honda CR-V, the ecu 'see's the front wheels spinning and yet the rear are stationary, the ECU would attempt to bring in the rear drive and push the vehicle off the rollers but the second caveat here is the rotational speed is way faster than the brake rollers speed so they are not thrown out.
Now go back to your four wheel drive 80, when you turn a corner the outer wheel travels further so the differential allows this to happen so the axle does not bind but, as you go through the corner the front wheels are going to cover more ground that the rear, so the centre differential allows the difference and prevents the drivetrain binding, and of course the rear differential allows the rear wheels to travel separate distances as well. The reason for testers to ensure your car is in neutral as they may or may not know if your car has a VC, the 80 is typical in that early versions did not have one.
In the UK I have never seen a tester take any car out to test with a meter on the floor between his legs for about 35 years, this is not meant to discredit a tester or is methods but, it may be the case he or his station is ensuring that no blame can be levelled at them if the transmission fails two hours after the MOT. I actually had a customer tell me her AC packed up due to her car being thrown out of the rollers, BTW when testing the front brakes your hand brake should be off, it prevents overload of the roller motors.
I hope that helps?
regards
Dave
