Had mine tested Friday and it was done on a single set of rollers doing either front or rear...when braking the car was pulling off the rollers, I only thought about it later at home when going through my handbook (drivers side headlight too high and wouldn't adjust!) for fuse id and spotted that there is a seperate fuse setting that should be used for front/rear brake testing...it finally dawned on me then that awd cars have issues with this kind of thing because of the differential gearbox!!
Can anybody throw any light on this for me, should I be taking the car elsewhere and could damage be caused with this test?

thanks for your help...melon

Dont reccommend going back there as being as the majority of 4 wheel drive vehicles these days are "permanent" drive systems, they should either be brake tested on a four wheel roller or tested the "old way" with a decelerometer/road test. YEs, they can cause damage to the centre viscous diff unit if they persist on using these methods.
May be a phone call to their "Vehicle Inspectorate" area office wont go amiss, they may advise them better and may take more notice of such

i think i remember right as i last had a scoob mot'd two yearas ago, they test the brakes not on the rollers on a 4wd but outside the mot station, accelerate, brake, reverse, brake so on
mark

If this was me I'd be having a word with the test centre! Scoobs should not be tested in this way!

Mmmmm, thought as much really just wish I'd thought a bit more at the time, Im well pi55ed off now....I'll certainly speak to the tester but it's a bit late now.
Car seems fine but is it something that will have suffered? or is it someting that 'breaks' if you know what I mean?
I'm back in for the retest on Friday so it'll be interesting to see what they have to say.
Stinks of incompetence though..wonder if garages have insurance cover for this kind as I'm sure this must happen more than you think.
cheers..melon

Had mine tested in this way in January and have coveredd probably 20k miles since (estimate) and no problems..

Likewise I won't be going there again..

He did do it quick on the rollers and back off though but still could have caused damage.. I didn't think about it at the time either.. shouldn't really be up to us to think about it though should it..

JGM

Totally agree with you on that JGM,

My first thought was perhaps I should have mentioned that it was AWD but after speaking with guys at work they pointed out that as a registered centre they should be well aware of this and understand the vehicles that they are going to 'inspect' and test accordingly.
Surely they will have testing protocols for different vehicles to suit various transmissions/emmissions etc...

Again I don't know if the diff can be damaged in any way, is it just like some kind of fluid coupling?

melon

I believe there is a possibility of over heating the viscous coupling (centre diff) I don't think mine was on the rollers long enough.. but who knows..

In theory the diff should do it's job and there be no problem but still adding a lot of unnessary stress to it..

It is there job after all.. they should KNOW!

JGM

I very much doubt the short time and speed of the brake test will have caused any damage to your centre diff, but i agree a single set of rollersis not the way to do this test.

The centre diff isn't really designed to cope with massive differences in rotational speeds (e.g. rears stationary, fronts turning), but you shouldn't have any problems for such short intervals.

If, for example, your car was towed along the motorway with the fronts rolling along and the rears in the air with the handbrake on, then at the very least, I would replace the diff fluid. ;)

As pointed out, it is their job to know (and to ask if they don't), but a little reminder that your car is permanent 4WD and shouldn't be tested on the rollers never hurts.

Cheers guys,
So hopefully no damage done as it was only for a very short period of time, certainly something I will be pointing out in the future though.
I also intend to read up properly and find out what the fuse thingy does, if it can disengage the diff does this mean the car becomes 2wd?

thanks again for the replies...melon

when you go back ask them to let you see the "Mot Inspection manual"

all the pages should be marked with issue date June 2002 in bottom corner

then go to / tell them to look at section 3.7

in the left hand column half way down there is in bold print a sub heading

"vehicles not to be tested on a roller brake tester"

underneath it says

"Certain Vehicles should not be tested on a roller brake tester, e.g. vehicles with

. more than one driven axle permanently engaged

. limited- slip differential

. belt-driven transmission

. brakes for which the servo operates only when the vehicle is
moving

these vehicles should be tested using a properly calibrated and maintained decelerometer or a plate brake testerdesignated as acceptable for the statutory tests"

point out that your scooby is both permament 4wd and has an LSD and see what they have to say.

to be honest i'd expect there to be no problem as the speed of the rollers is very low but its best to be carefull and let them know you are aware of their mistake.

Thanks for that tinvek..

I shall go loaded with that info when I need to get my car MOT'd..

Melon, have you been back for the retest yet?

JGM :)

Tinvek...Very definitive info, it will be quoted thanks!

JGM...Retest on Friday (Subaru to replace headlight under ext.warranty on Thur:D) I will post again and give you their response....red faces and an apology should be in order

Wonder if this is isolated or whether the majority of testers are as ignorant? Bet it happens all the time.

So the conclusion....
Make sure you mention you have AWD and ensure they test correctly or use the fuse setting thingy(I will read up on this and report)

cheers...melon

I have never heard of this fuse you mention and my understanding is that all the AWD system is mechanical so cannot understand how a fuse can effect it.. so interested to hear what conclusion you come too..

JGM :)

I pointed the permanent 4wd to the SVA tester as he was about to brake test my car. He did look rather sheepish.
Did a nice little 20mph test on the braking lane with a very old looking tap-meter