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New brake balance testing  Rating:  Rating
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 Posted: Wed Aug 7th, 2013 07:40 pm
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Tshirt
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Mana: 
I quite regularly see imbalance reading of +40% on the atl weight rbt i use, most of these are passing on vts now with 20% or so due to lock out figures.

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 Posted: Thu Jul 25th, 2013 11:04 pm
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nesetceri
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Mana: 
From the day one VOSA rule was " you can not measure imbalance by locked wheels figures" however recently with the introduction of ATL roller brake testing equipment ( where the weight on each wheel is measured separately then brake performance calculated by the equipment's computer )there is no problem, say measured weight on N/S wheel is 500 kg, O/S wheel 600 kg because of the weight of the tester, the program will adjust the end result accordingly so correct pass-fail will be printed out. Unfortunately most of our brake rollers do not have weighing facility, so when we put the figures in, it is assumed equal weight imposed on N/S- O/S wheels and also tyre condition etc is the same..This is the problem and I was informed that VOSA is looking into this..so meanwhile if you are certain there is no imbalance, do not fail the vehicle unnecessarily ..

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 Posted: Sun Jul 7th, 2013 12:12 am
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Aylesbury Jock
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Mana: 
DB9 wrote:
According to my last PR report my brake failure rate was 12.5%, and that was before the introduction of this new system, so my memory now serving me correctly I have passed every vehicle test since Monday last week, not one failed, so what happens when VOSA ring and ask;

Why are your brake test entry figures 0%

:D:D

Why would they do that Dave? Do you think they forgot they changed the goalposts?
Favell, I think that is probably the same reason most of us are whining. We get set in our ways and don't like change.

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 Posted: Thu Jul 4th, 2013 01:44 pm
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markharriers
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Mana: 
Hi all :D in all honesty i cant see the problem?? i carry out the test as normal i.e looking for evan application etc ...... front and rear at max efforts before lock up check for fluctuation and all the usual checks then record readings put them on vts and the vts tells you the imbalance readings simples :D:D:D i just thinks its pretty much the same just different wording for rfr really. We could all moan till were blue in the face about agreeing or dissagreeing with the changes but as we all no vosa will allways do as they please :shock: i just cant see the confusion as far as routine on rbt???

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 Posted: Wed Jul 3rd, 2013 12:47 pm
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Favell
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Mana: 
I know what you are saying Jock, but having got used to measuring balance on partial load as well as maximum load, it then seems a step backward to only measure on maximum load.

Our Bradbury brake tester was set up so it wouldn't register imbalance until there was over 40kg of brake effort. Quite often on some tests we would have an excessive imbalance at 50kg, which would then improve with higher brake efforts. Some times we would have several attempts, knowing that the car did a low annual mileage, and just needed a bit of use to free things off. That will no longer be an issue.

Sometimes it's just a case of having to get used to changing my 'MOT head' after doing it the same way for twenty odd years.

Fav

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 Posted: Tue Jul 2nd, 2013 10:02 pm
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Aylesbury Jock
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Mana: 
Favell wrote:
I was aware that the brake imbalance limit was going to be raised to 30% on both axles.

what I hadn't initially clicked onto was that it was to measured at maximum braking effort.

We have already had a situation on a Ford Ka where front brake imbalance partially applied was over 50%, but at measured maximum effort was only 27%.

So it's a pass, but to a much lower standard than previously required!

Fav

But if you think about it, a high imbalance during gentle braking is not as serious as a high imbalance during heavy braking, and I believe this is the reason we only take the readings at maximum effort. The only time it is a problem for me, is if lockout occurs(90% of the time at least), and the figures you enter into the computer do not represent the balance, but are still measured as such.

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 Posted: Mon Jul 1st, 2013 07:14 pm
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DB9
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Mana: 
According to my last PR report my brake failure rate was 12.5%, and that was before the introduction of this new system, so my memory now serving me correctly I have passed every vehicle test since Monday last week, not one failed, so what happens when VOSA ring and ask;

Why are your brake test entry figures 0%

:D:D

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 Posted: Mon Jul 1st, 2013 12:58 pm
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Favell
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Mana: 
I was aware that the brake imbalance limit was going to be raised to 30% on both axles.

what I hadn't initially clicked onto was that it was to measured at maximum braking effort.

We have already had a situation on a Ford Ka where front brake imbalance partially applied was over 50%, but at measured maximum effort was only 27%.

So it's a pass, but to a much lower standard than previously required!

Fav

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 Posted: Mon Jul 1st, 2013 07:25 am
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volksjim
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Mana: 
one of our testers must be at least 20 stone,,i can tell you his brake imabalance rate is now 99% fail :shock:

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 Posted: Thu Jun 27th, 2013 08:37 pm
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davidw44
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Mana: 
DB9 wrote: My view based on using it since Monday is that the first test and results were an Unfamiliarity issue, I initially felt that a lot of test data had been taken out of the mot test, and when I entered the data into the VTS device I was more than sure that loads of information had been removed from the test, but when I depressed continue and the results screen was displayed I observed the following screen;

Service Brake Roller Brake Test

Brake efficiency = 59% (example figures)

Brake lock = 0%

Result = Passed

Imbalance Roller Brake Test

Brake Imbalance Axle 1 = 05%

Brake Imbalance Axle 2 = 10%

Result = Passed

Park Brake Roller Brake Test

Brake efficiency = 20%

Brake lock = 0%

Result = Passed

Observations from the above data told me that VOSA have simplified the roller brake test, but for some NTs I can see than misunderstanding and misinterpretation of assessements would be present, however once VOSA sort out the software programs to go with the above, the overall consistancy of results from all VTS with computerised rolling roads will be standardised.

Overall I think VOSA have done a good job of this but some training for NTs is now in order.

Thanks for the insight :)

David

Last edited on Thu Jun 27th, 2013 10:21 pm by davidw44

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 Posted: Wed Jun 26th, 2013 10:16 pm
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castrolrob
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Mana: 
i agree with tony,maximum lock is a bit silly with all the possible variables.we are fortunate enough to have 2 sets of rollers,1 of them rated for 4+7,this set typically locks out 50-70kg higher than the class 4 and more evenly,while you can do a decelerometer test in doubtful cases this is gonna add time and grief to it.if you have as many dyslexic/dyxnumeric staff as us then working out the required figures/percentages ahead of entering them on the system is also gonna be a laugh,we will ignore the fact that a 30% imbalance on the rear is probably not gonna be that detectable on a roadtest:shock:

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 Posted: Wed Jun 26th, 2013 05:51 pm
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DB9
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Mana: 
My view based on using it since Monday is that the first test and results were an Unfamiliarity issue, I initially felt that a lot of test data had been taken out of the mot test, and when I entered the data into the VTS device I was more than sure that loads of information had been removed from the test, but when I depressed continue and the results screen was displayed I observed the following screen;

Service Brake Roller Brake Test

Brake efficiency = 59% (example figures)

Brake lock = 0%

Result = Passed

Imbalance Roller Brake Test

Brake Imbalance Axle 1 = 05%

Brake Imbalance Axle 2 = 10%

Result = Passed

Park Brake Roller Brake Test

Brake efficiency = 20%

Brake lock = 0%

Result = Passed

Observations from the above data told me that VOSA have simplified the roller brake test, but for some NTs I can see than misunderstanding and misinterpretation of assessements would be present, however once VOSA sort out the software programs to go with the above, the overall consistancy of results from all VTS with computerised rolling roads will be standardised.

Overall I think VOSA have done a good job of this but some training for NTs is now in order.

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 Posted: Wed Jun 26th, 2013 05:46 pm
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getech.org.uk
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Mana: 
I can comment as a manufacturer. Our new software is now undergoing development. The specification was released to us (in its initial format) on 2nd June but changes were still being made to the flow chart until last week! Allowing for software development time (approx 8 weeks) and then re-authorisation by VOSA/GEA we are probably looking at 12 weeks to introduce fully to the loop to our customers and at a  considerable cost from our side so personally I hope that this change remains in place!

To, hopefully, assist from a testing perspective: we now consider it to be critical to ensure that the vehicle is accurately presented to the centre of the rollers for the test but of course the nearside will always have a tendancy to lock out before the offside as drivers weight assists. Another item that may assist to get the pass often overlooked by NT's is the requirement to build the retardation forces s l o w l y for the most accurate measurement possible.

Hope this helps.

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 Posted: Wed Jun 26th, 2013 05:31 pm
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gluther
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Mana: 
No, it doesn't make a lot of sense at all does it.

Funnily enough VOSA phoned us up today:shock: for our site assessment.

One of the questions was "what was the last special notice about?" Wasn't sure, probably was wrong, but said about the changes to the brake test. Oh, and by the way, were not sure about how it is a better test or if it is even correct.

Person on phone said "don't mention that, the phone has been ringing of the hook here since Monday morning"

So I guess it is causing a bit of confusion to say the least...

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 Posted: Wed Jun 26th, 2013 10:53 am
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Tony Gingell
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Mana: 
So, now the new regs for brake balance testing are active, how are others finding it?

From personal experience, so far I'm not impressed.

Condition of the brake rollers, tyre pressure, tyre tread depth, tyre compound and possibly one tyre being "dry" and the other "wet" will all have a bearing on wheel lock. I honestly can't see these regs staying in place and suspect another coil spring turn around. (Plus I've been told that the software is not in place for ATL brake testers. Is that right?)

And yes I do know we can take the car for a tappley test but that not easy when you are surrounded by speed humps!

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