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New MOT brake imbalance? #

Posted by Sean Savage on June 26, 2013, 3:03 pm
Edited by board administrator June 27, 2013, 8:10 am

How are people finding this new imbalance system?? Are you like us and finding that when carrying out both wheel imbalance check there are no issues but when locking the front brakes individually your os is a lot higher than the ns?? we are getting lots of imbalance fails due to the test procedure when there is no actual fault.
sean

Re: New mot brake imbalance??!!

Posted by aidan birley on June 26, 2013, 7:44 pm, in reply to "New mot brake imbalance??!!"

Sean

VOSA have always used this method of testing imbalance there own truck test, including the 30% limit.

However there automated RBT are programmed to ignore the result (from a fail on imbalance point of view) if the LOWER wheel reading locks.

You don't need to be very bright to work out that measuring imbalance on locked wheels is pointless, but then the same team decided that deliberately disabling SRS lights is acceptable practice !

However in fairness vosa are aware of the problem The special notice issued regarding these changes does point locked wheel could result in incorrect fails,not sure that the advise for overcoming this is totally correct but I am sure you can arrive at a accurate result.

I must admit I thought the intention was to to calculate the imbalance at max braking (i.e. just before lock ) which would be logical.

I guess we are just enforcing yet another questionable EU directive.

Cheers Aidan

Re: New mot brake imbalance??!!

Posted by Alan Lange on June 26, 2013, 9:28 pm, in reply to "Re: New mot brake imbalance??!!"
Alan Lange

I'm glad you've bought this subject up Sean, I thought it was just me! I used to write the imbalance figure in the box provided unless 4x4 but doing away with the box & working it out on the lock figures seems stupid to me. (That's measuring the grip of the tyre surely?) Most modern brake testers will give an accurate imbalance figure & print it out for the customer, I can't use this feature now. Yesterday I had a front imbalance of 12% but vosa's computer made it 27%! I'm sure (hope) vosa will soon get complaints & reinstate the "over-ride" box.

Re: New mot brake imbalance??!!

Posted by Tony Ludford on June 26, 2013, 9:38 pm, in reply to "Re: New mot brake imbalance??!!"
Tony Ludford

Hi Sean, couldn't agree more.

Vosa have recommended running the rollers together (to speed up the testing process?) to get a figure which locks the rollers out at the lowest figure (as Aidan said). This usually gives a good and equal reading.
i.e. rollers lock on n/s/f at 300kg the o/s/f reading is 300~ too.

I can see this could be a problem if you're using older rollers that don't both turn off when run together once one locks out.

The special notice then says (iirc) if the vehicle fails to meet the minimum efficiency then run the rollers individually. (How do you know the efficiency is too low whilst carrying out the test, unless you work it out, have a super duper roller setup or log back onto the Vosa computer to enter the figures)!

Which then negates the time saved from running the rollers together!

VOSA - a**e and elbow as usual?!

Re: New mot brake imbalance??!!

Posted by Alan Lange on June 26, 2013, 10:00 pm, in reply to "Re: New mot brake imbalance??!!"
Alan Lange

Mmm, running the rollers together. Thought we were trying to get the maximum brake figure? Granted we will get a better imbalance figure but you need 50% of the cars weight (though not taking the brakes to the max or three locks but only likely to ever get two) Think failure rate for brakes will sky rocket!

Re: New mot brake imbalance??!!

Posted by Alan Lange on June 27, 2013, 8:23 pm, in reply to "Re: New mot brake imbalance??!!"
Alan Lange

Had a Kia cerato in today, neither rear brakes locked & both made around 200 kgs but I had an imbalance figure of 43%. The fronts both locked with good figures but had an imbalance of 35%. VOSA gave it as a pass so I went in to "brakes"-"brake performance" then "imbalance" & failed it that way. I did try earlier in the day to run both rollers as Tony said but once I get a lock my brake tester just gives me an imbalance figure with no efficiency readings.

Re: New mot brake imbalance??!!

Posted by aidan birley on June 27, 2013, 8:53 pm, in reply to "Re: New mot brake imbalance??!!"
Aidan Birley

Hi

Is it modern computer driven roller that are causing problems.?

My set is 35 years old, works perfectly with new test method and correctly passes or fails on both efficiency and balance.

Cheers Aidan

Re: New mot brake imbalance??!!

Posted by Alan Lange on June 27, 2013, 9:06 pm, in reply to "Re: New mot brake imbalance??!!"
Alan Lange

You could be right Aidan, mine are 2 years old & far too complicated! I'll play with the settings tomorrow.

Re: New mot brake imbalance??!!

Posted by Dave Hill on June 29, 2013, 8:56 pm, in reply to "Re: New mot brake imbalance??!!"

I am ashamed to say that I only encountered this topic today, as I haven't performed a test personally for a few weeks. Of course I had read the special notices & listened to the views of my testers (honest I have) but it wasn't until I went to enter the brake test figures, that it hit home, just how ridiculous this new routine is.

This subject is particularly poignant to me, because I had a major issue with an employee a couple of years ago. He was failing cars on brake imbalance, by recording their lock out figures in the "imbalance" field on the VTS.

Fortunately he only failed three cars before I noticed the unusual trend & of course I acted upon it. The four year old C Class Mercedes that he failed was a mint car & I knew something was amiss.

I pulled the Mercedes back in & proceeded to do my own brake test. He asked me what I was doing, so I told him that I had to investigate why this pristine car had failed on brake imbalance. My test results concluded a pass & I asked him to justify his test result.

"Errm I entered the lock out figures into the VTS"

I am sure you can imagine the exchange that took place. I tend to be rather overbearing when it comes to matters technical & the guy finished the test he was performing & duly walked out!

So based on the new regulations, he must now think I am a complete Cock! (Join the queue

)

I feel very strongly about this development, particularly because it compromises the professionalism of the many well intentioned & intelligent MOT Nominated Testers out there, who will be forced to manipulate their results, to produce the correct result.

Testers have the opportunity to express any concerns or questions to VOSA via the testing device (the relic of a computer that they lumbered us with

)

I decided to have my say....

(Please excuse the spelling mistakes

)

Re: New mot brake imbalance??!!

Posted by geoff taylor on July 1, 2013, 10:55 am, in reply to "Re: New mot brake imbalance??!!"
Geoff Taylor

this subject is of great interest to me as i am semiretired and help an ex colleague of mine most weeks.up to 3 years ago i was also an mot tester but the workshop is not a testing station and we have been getting back a lot of brake failures but on inspection of brakes can find no faults this post may go someway to explain the reason why.could someone pointout what the different procedure is to when i last tested as i dont have access to latest vosa guide,in the meantime i will try talking to the VTS that carries out testing on our behalf.also have not been able to get a definate answer on airbag light controversy
geoff taylor

Re: New mot brake imbalance??!!

Posted by aidan birley on July 1, 2013, 1:37 pm, in reply to "Re: New mot brake imbalance??!!"
Aidan Birley

Geoff
MOT test manuals are available here

http://www.dft.gov.uk/vosa/publications/manualsandguides/vehicletestingmanualsandguides.htm

Aidan

Re: New mot brake imbalance??!!

Posted by Dave Hill on September 4, 2013, 9:40 pm, in reply to "Re: New mot brake imbalance??!!"

I got a reply to my message (a while back).......

I was prompted to post this today, after I pulled up one of my testers, after he failed a 2007 Fiesta on rear brake imbalance.

The lock out figures demonstrated an extreme difference one side to the other on both the park & service brake. The balance figures just prior to lock out, showed that both rear brake efficiencies were pretty equal.

The tester in question is a mature, well experienced Tech, who is recently joined us, out of a Peugout Dealership. I am sure that in his previous employment role, that he was driven to "up sell" & almost certainly would not have been questioned if he had failed anything that was likely to generate revenue.

My point in posting is that, if this kind of incorrect test result can be applied at a reputable, honest & well intentioned test station, then how many less scrupulous test stations will fall fowl (be it financially motivated or through ignorance of the subject) of this shambolic & flawed test procedure.

Needless to say that the test result was corrected & the tester has been bought up to speed.

Re: New mot brake imbalance reverting back!

Posted by Rob Nicholson on September 24, 2013, 9:30 pm, in reply to "Re: New mot brake imbalance??!!"

Hi,

I had the VOSA man drop in for out testing station inspection (traffic light) check last week he informed me they are reverting back to the 'old' method and a SN will follow shortly

Rob

Re: New mot brake imbalance reverting back!

Posted by Alan Lange on October 15, 2013, 2:53 pm, in reply to "Re: New mot brake imbalance reverting back!"
Alan Lange

Here it is Rob!! https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/249355/mot-special-notice-6-2013.pdf

Re: New mot brake imbalance reverting back!

Posted by Dave Hill on October 18, 2013, 10:30 pm, in reply to "Re: New mot brake imbalance reverting back!"

Haha

Does this now mean that I am not a complete cock after all?

Answers on a post card....

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