Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

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GT_II
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Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by GT_II » Sun Nov 07, 2021 3:15 am

Just a quick heads up that I have reason to believe DVSA have uploaded the wrong test weight figure for at least some versions of the Mk2 Scirocco onto the MOT system, which massively suppresses the brake efficiency calculation. This apparently only applies to test centres that use a manual roller brake tester, as more modern automated roller brake testers calculate the brake efficiency using the actual weight of the car at the time of the test, not the theoretical test weight figure recorded by DVSA.

The last two years my GT II has only just scraped through, which I found surprising, as this had never been an issue on previous tests. After a lot of probing with the MOT garage and then DVSA, DVSA confirmed that they had used a brake test weight of 1230 kg. This didn't sound right to me as the maximum permissible gross weight of the car on the VIN plate is only 60 kg more at 1290 kg.

Up to very recently, DVSA didn't supply brake test weight figures so MOT testers were expected to enter their own figure from a published source, such as an MOT data wall chart. I managed to get hold of an out of print Autodata MOT brake test data chart published in 2010 for vehicles on the road before the year 2000 on ebay. This shows a test weight figure for the Mk2 Scirocco of 1040 kg, much closer to what I would expect for the weight of the car plus fuel plus driver. The figure for the Mk1 Scirocco is even lighter at 970 kg. The figure for the Passat/Santana GL5 is listed 1230 kg, so I wonder if the admin assistant's (or quite likely IT contractor's) eye slipped down a few lines as they were manually entering the data from the wall chart onto the MOT database.

This makes a massive difference to the brake efficiency calculation. Using the Autodata figure, the brake efficiency on my Scirocco would increase from the stated 51% (pass mark 50%) up to 61%. I think this is a good figure for a non-ABS car with rear brake pressure limiters, even comfortably over the 58% pass mark for cars registered from 2010.

DVSA customer service suggested I email them and ask the MOT policy team to review this discrepancy. I will update the thread when I hear back, hopefully within a few weeks.


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
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essextom
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Re: Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by essextom » Mon Nov 08, 2021 8:33 am

good spot. hopefully helps some people out.


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Re: Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by RussGLAuto » Tue Nov 09, 2021 7:38 am

Could that be something to do with Gladys failing back in 2018?

Rear Brakes imbalanced across an axle Axle 2 (1.2.1 (b) (i))


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Re: Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by essextom » Tue Nov 09, 2021 8:32 am

RussGLAuto wrote:
Tue Nov 09, 2021 7:38 am
Could that be something to do with Gladys failing back in 2018?

Rear Brakes imbalanced across an axle Axle 2 (1.2.1 (b) (i))
imbalance is a separate issue to lack of brake effort.


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Re: Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by big_wig_074 » Mon Nov 15, 2021 9:47 pm

Put my Scirocco on a weigh bridge once, 980kg apparently



GT_II
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Re: Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by GT_II » Fri Nov 19, 2021 12:47 pm

Good news, at least for my car. Email from MOT department at DVSA:

"I have checked our records and the weight of 1230 was associated to the vehicle in 2016. I have arranged for the brake test weight in our database to be amended to 1040."

"I should also point out that over the years and improvements in technology, some MOT test stations have Automated brake testers, these testers measure the actual weight at the time of test and it is this weight used for the performance calculation and not the default theoretical weight."

I have asked whether this error was just for my car or all Scirocco Mk2s - I'll update when I hear back.


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Re: Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by mr.brown » Mon Nov 22, 2021 10:31 am

Excellent work!



GT_II
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Re: Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by GT_II » Mon Nov 22, 2021 3:04 pm

GT_II wrote:
Fri Nov 19, 2021 12:47 pm
I have asked whether this error was just for my car or all Scirocco Mk2s - I'll update when I hear back.
It seems the error only affected my car: Their response "It is likely to be a one off, entered by a tester in 2016". Slightly non-committal, but suggesting the MOT system hasn't been pre-loaded with a standard test weight figure for the Mk2 Scirocco, but that the figure entered by the MOT tester on the first MOT test is carried forward to the following year's test, unless amended.

2016 was the first year my car was MOT'd after being off road for 10 years, so this would have been the first time a test weight was entered onto the MOT system, just before I bought the car.

Although the correct weight figure now gives a comfortable pass, performance has still fallen off since 2016. I renewed the brake fluid and front brake hoses 3 years ago, so now plan to dismantle, clean and lubricate the drum brakes, renew the rear brake hoses and pipes and renew the brake fluid again. Are there any other common issues that affecting brake performance that I should check?


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
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2015 Skoda Yeti SE Outdoor 1.2 TSI DSG 105PS 35k
2013 Fiat 500 Pop 1.2 69PS 40k
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Re: Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by mark1gls » Wed Nov 24, 2021 11:43 pm

The auto adjuster on the rear drums does not always work very well so you can help it out by pulling down on the adjustment wedge, you can see it through a wheel bolt hole.

If you Jack up the rear of the car both sides and have the wheels removed you can check the rear brakes are adjusted.

I use the bar from my trolly Jack to hold the brake pedal on by wedging it between the brake pedal and the seat, if you use the metal part of the seat near the nut to stop the seat sliding out then move the seat forward to get the bar to press the pedal down. You don’t want the brake pedal all the way down and fully adjust the wedges or the rear brakes will stay on…

Once adjusted make sure the drums don’t bind on the shoes, if it goes wrong push the adjusting wedge up then press the pedal hard several times to bring the wedge back down, hold the brake pedal on the pull the wedges down.

Once I’m happy with how they are set I do try and set the pedal so the rear brakes are just on then check both sides have the same amount of friction when turning the drums, I put the wheels on for this part.

A link to show how to adjust the rear the brakes manually.

https://vwgolfmk1.org.uk/forum/index.ph ... adjustment


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GT_II
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Re: Wrong MOT Brake Efficiency Calculation for Mk2 Scirocco

Post by GT_II » Thu Nov 25, 2021 1:06 am

mark1gls wrote:
Wed Nov 24, 2021 11:43 pm
The auto adjuster on the rear drums does not always work very well so you can help it out by pulling down on the adjustment wedge, you can see it through a wheel bolt hole.
Good tip, I released and "reseated" mine a few years back, after I stupidly left the handbrake on through the winter. I'll check they are free and adequately lubed up when I dismantle and clean the shoes.


1992 VW Scirocco GT II 1.8 90PS Brilliant Black 30k
2011 VW Caddy Van C20 Startline 1.6 TDI 102PS 65k
2015 Skoda Yeti SE Outdoor 1.2 TSI DSG 105PS 35k
2013 Fiat 500 Pop 1.2 69PS 40k
2009 VW Fox 1.2 54PS 60k
2009 Smart Fortwo Passion 1.0 mhd 71PS 25k