HELP: MOT Brake Test Query
05 February 2009, 08:24 AM
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HELP: MOT Brake Test Query
Just had my MY98 Impreza Sport fail its MOT and re-test on brake imbalance.
They tested it with a decelerometer and.........get this.............2wd rollers!!!
Apparently I had a 30% imbalance on the MOT and a 33% imbalance on the re-test (after front brakes were stripped, cleaned, greased and the flexi pipe replaced for the re-test).
They told me I have an active/slip diff which allows to change to 2wd for brake testing? Now I'm new to AWD but I'm pretty sure that's wrong, maybe on newer age cars but not a 10yo Sport? If I'm wrong I am willing to eat humble pie!
From what I've been told from various sources so far, the active/slip diff is rubbish, never test AWD on 2wd rollers, you can't get a % reading from a decelerometer test and contact VOSA about them.
Just looking for as much advice as possible on this before I go daft or start the apologies!
Many thanks in advance.
They tested it with a decelerometer and.........get this.............2wd rollers!!!
Apparently I had a 30% imbalance on the MOT and a 33% imbalance on the re-test (after front brakes were stripped, cleaned, greased and the flexi pipe replaced for the re-test).
They told me I have an active/slip diff which allows to change to 2wd for brake testing? Now I'm new to AWD but I'm pretty sure that's wrong, maybe on newer age cars but not a 10yo Sport? If I'm wrong I am willing to eat humble pie!
From what I've been told from various sources so far, the active/slip diff is rubbish, never test AWD on 2wd rollers, you can't get a % reading from a decelerometer test and contact VOSA about them.
Just looking for as much advice as possible on this before I go daft or start the apologies!
Many thanks in advance.
05 February 2009, 08:31 AM
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Your right you can’t test an Impreza on a 2wd roller (think the sport is the same) without lifting the opposite 2 wheels off the ground.
They were going to do mine on a 2wd roller but I insisted they couldn’t and went elsewhere.
In the end a different place drove the car and used a box on the passenger seat to get a reading (can’t remember what it’s called).
I would report them and let them know they will be paying for any diff damage if any crops up in the near future
They were going to do mine on a 2wd roller but I insisted they couldn’t and went elsewhere.
In the end a different place drove the car and used a box on the passenger seat to get a reading (can’t remember what it’s called).
I would report them and let them know they will be paying for any diff damage if any crops up in the near future
05 February 2009, 09:06 AM
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The lifting up the rear was the way I thought of, but it was never mentioned by them.
That box on the seat is the decelerometer (so I've been told!).
Going to speak to an MOT specialist at VOSA later this morning. Should be an interesting conversation.
That box on the seat is the decelerometer (so I've been told!).
Going to speak to an MOT specialist at VOSA later this morning. Should be an interesting conversation.
05 February 2009, 10:33 AM
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Booked mine in at a garage with awd rollers but they had leccy probs that day and could not test any car, as i needed the test (pass or fail) that day they arranged with another garage to do it. When i got there they only had a single roller and the old boy never even entertained the idea of using the single roller, big old box in the passenger footwell and off we went! I would say you are correct to ask questions.
Let us know what VOSA have to say, could be as you say, interesting!
Let us know what VOSA have to say, could be as you say, interesting!
05 February 2009, 11:38 AM
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Spoken to VOSA this morning who catagorically stated that the brake test should never have been done on the rollers. They want my car at our local Ministry of Transport testing station so they can have a look and do the test correctly (full price MOT!!!). They will however refund the full price if it passes and then I assume they'll be confronting the garage in question.
172sport - I've got my fingers crossed for the same thing - short time, no damage! hopefully.
172sport - I've got my fingers crossed for the same thing - short time, no damage! hopefully.
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05 February 2009, 01:06 PM
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Got a funny feeling they could be in the mire anyway. Co-owners are both ex-subaru garage employees, so very suprised by their testing methods.
Slightly worried if they do find anything else - unrelated - wrong with the car. Could be a costly appeal! Done nothing to it since it was bought in September as a project. I plan do it back up come spring time!
Slightly worried if they do find anything else - unrelated - wrong with the car. Could be a costly appeal! Done nothing to it since it was bought in September as a project. I plan do it back up come spring time!
05 February 2009, 03:48 PM
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05 February 2009, 05:25 PM
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Spoken to VOSA this morning who catagorically stated that the brake test should never have been done on the rollers. They want my car at our local Ministry of Transport testing station so they can have a look and do the test correctly (full price MOT!!!). They will however refund the full price if it passes and then I assume they'll be confronting the garage in question.
172sport - I've got my fingers crossed for the same thing - short time, no damage! hopefully.
172sport - I've got my fingers crossed for the same thing - short time, no damage! hopefully.
It will be fine mate. No different than doing a few handbrake turns of which mine has done plenty...
05 February 2009, 07:33 PM
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iv always had my 4wd/awd done on 2 rollers and never had a problem thats what the center diff is for drove land rovers for many years on the road and off road competeing with only 2 diff failers in five year its only the same
the problem arise if you have a locked center diff but then any road driving will kill this
the problem arise if you have a locked center diff but then any road driving will kill this
05 February 2009, 07:37 PM
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Thanks for all your guidence on this. The local VOSA station as much as said pay your MOT with us but we're unlikely to side with you.
So, it's off for MOT tomorrow somewhere else. Fingers crossed this time!
So, it's off for MOT tomorrow somewhere else. Fingers crossed this time!
05 February 2009, 07:58 PM
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it will be fine the roller rotates quite slowly compared to what the diff has to cope with at speed going around corners and roundabouts, i wonder how many people have pulled their handbrake on in the snowy weather and buggered their diff my guess is none.
05 February 2009, 09:45 PM
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When the MOT examiner enters your car details on the computer at the start of the test it should advise him not to test on 2wd rollers and use the decelerometer instead.
That said my first Scoob was tested on the rollers several times under the old system with no problems.
That said my first Scoob was tested on the rollers several times under the old system with no problems.
22 September 2009, 09:26 PM
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Just dragging this back to life again..
What I can't understand is this, if your awd scoob is running a viscous diff then surely the low speed differential involved in doing a single roller brake test isn't going to be an issue..? After all the plates in a viscous diff do not have any mechanical connection, ie viscous. It's only the friction caused by the plates moving at different speeds that create a 'coupling' or torque transfer. At low speed the effects/drag would be minimal. By contrast towing, on a 2 wheel dolly for instance, involves MUCH higher speeds for far longer periods, therefore a viscous diff would overheat in no time..!
It's a limited slip diff, not a fixed/locked diff and as such allows for some speed differential between axles.
Now a mechanical (STI) diff is a different matter.
VOSA, rather than differentiate between all the various AWD/4WD systems on the just cover themselves by stating the brake test be done in car with a deceleration meter.
All IMHO of course, but I do think this needs to be cleared up for future reference.
BTW, I'd rather take my chances on a single roller brake test than allow some tester out for a spin at the wheel..Lol..!
What I can't understand is this, if your awd scoob is running a viscous diff then surely the low speed differential involved in doing a single roller brake test isn't going to be an issue..? After all the plates in a viscous diff do not have any mechanical connection, ie viscous. It's only the friction caused by the plates moving at different speeds that create a 'coupling' or torque transfer. At low speed the effects/drag would be minimal. By contrast towing, on a 2 wheel dolly for instance, involves MUCH higher speeds for far longer periods, therefore a viscous diff would overheat in no time..!
It's a limited slip diff, not a fixed/locked diff and as such allows for some speed differential between axles.
Now a mechanical (STI) diff is a different matter.
VOSA, rather than differentiate between all the various AWD/4WD systems on the just cover themselves by stating the brake test be done in car with a deceleration meter.
All IMHO of course, but I do think this needs to be cleared up for future reference.
BTW, I'd rather take my chances on a single roller brake test than allow some tester out for a spin at the wheel..Lol..!
06 October 2009, 08:24 PM
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Just dragging this back to life again..
What I can't understand is this, if your awd scoob is running a viscous diff then surely the low speed differential involved in doing a single roller brake test isn't going to be an issue..? After all the plates in a viscous diff do not have any mechanical connection, ie viscous. It's only the friction caused by the plates moving at different speeds that create a 'coupling' or torque transfer. At low speed the effects/drag would be minimal. By contrast towing, on a 2 wheel dolly for instance, involves MUCH higher speeds for far longer periods, therefore a viscous diff would overheat in no time..!
It's a limited slip diff, not a fixed/locked diff and as such allows for some speed differential between axles.
Now a mechanical (STI) diff is a different matter.
VOSA, rather than differentiate between all the various AWD/4WD systems on the just cover themselves by stating the brake test be done in car with a deceleration meter.
All IMHO of course, but I do think this needs to be cleared up for future reference.
BTW, I'd rather take my chances on a single roller brake test than allow some tester out for a spin at the wheel..Lol..!
What I can't understand is this, if your awd scoob is running a viscous diff then surely the low speed differential involved in doing a single roller brake test isn't going to be an issue..? After all the plates in a viscous diff do not have any mechanical connection, ie viscous. It's only the friction caused by the plates moving at different speeds that create a 'coupling' or torque transfer. At low speed the effects/drag would be minimal. By contrast towing, on a 2 wheel dolly for instance, involves MUCH higher speeds for far longer periods, therefore a viscous diff would overheat in no time..!
It's a limited slip diff, not a fixed/locked diff and as such allows for some speed differential between axles.
Now a mechanical (STI) diff is a different matter.
VOSA, rather than differentiate between all the various AWD/4WD systems on the just cover themselves by stating the brake test be done in car with a deceleration meter.
All IMHO of course, but I do think this needs to be cleared up for future reference.
BTW, I'd rather take my chances on a single roller brake test than allow some tester out for a spin at the wheel..Lol..!
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