Brake performance testing

Having not been on my course yet I'm rather confused about the way VOSA wants us to do this. I've been using the rollers etc. at work when I can to get experience. I've no idea if I've even been doing that right as we currently don't have a tester yet.

I'm just glad my course is on the 24th after these changes come into place.

Been trying it out every test, just to get the hang of it, alongside a proper brake test of course.

Been a few fails which wouldn't be next week! "brake balance..... 28%? how do I fix that?" "bring it back next week sir, It'll be fine"

However I did a Fiesta which I failed on balance(42%, highest balance reading at about 100kgf) and sills. We're not allowed to weld so it went to a subby to be patched, and I had a spare slot so I delivered it. You couldn't feel that on the road. And at 250kgf, just before lockup, the reading was about 12%. That sort of justified the changes in my mind.

Countdown currently showing 5 Days 38 Minutes. In the General Links box. I can see it using Firefox - can anybody else not see it?

As I understand it

The increased service brake efficiency is applicable to passenger vehicles first used on or after September 01st 2010 with four or more wheels, but does not include quadricyles, and vehicles with more than 8 passenger seats in addition to the drivers are also excluded.

Brake imbalance

The brake imbalance for clasess 3, 4 & 7 vehicles is 30% inline with class 5

30% imbalance applies to all axles (except class 3 and quadricylces, where it is for steered axles only)

Class 3 do not have a two wheels at the front so a brake imbalance omitted is understandable but the criteria must still be applied to the rear axle

Brake imbalance is to be assessed at maximum brake efforts only regardless of whether the wheels lock or not.

VOSA point out that if the brakes lock out at low brake efforts and the NT understands that a higher brake reading should be obtained, then it is permissible to carry out the brake imbalance test selecting one wheel at a time to record the maximum effort and then use the following calculation to establish the brakes imbalance;

Higher reading - lower reading x 100 / higher reading = %

It is also permissible to carry out a decelrmometer brake test if the NT considers the roller brake test results unsatisfactory, where an unjustified fail could be issued.

When roller brake testing each axle we are also asked to hold sustained brake pressure to check for excessive fluctuation at each wheel brake. (I suspose we should be asking here what do VOSA advise the criteria is for excessive fluctuation)?

Grabbing and Judder

This criteria has now been removed from the test, but on class 3 vehicles with a single line braking system the park brake will still require checking for severe grabbing and judder during the application, as well as the maximum 30% imbalance across the rear axle.

Simples really

Brakes tested only once but same full method for both axles @daveg, with the exception of whichever axle has the park brake fitted, that requires an additional test

You must be reading it differently to me David, Method of Inspection paragraph 7 states;

7 / Repeat steps 1 to 6 above for all axles, then record the results of the service and park brake tests via the VTS device.

I may be reading into it more than necessary, but to me the way I am interpreting that information I have already roller tested both axles according to the test methods, then I am told to repeat the test again for all axles?

Now to me I think VOSA have worded this the wrong way round, I would have thought that the method of inspection should have been test the axle, record where lock outs occur, then repeat the test a second time on each axle, thus it is one brake test but two assessments of each axle, what do you think?

Yes David I read what you wrote, but VOSA are now saying repeat steps 1 to 6 for all axles, maybe since the trials they changed the assessment after you did it?

Where do I stand with moi when used in conjunction with a ATL rbt,manual states follow prompts of atl which is not the recommended moi,only if it fails to reach minimum requirements should I run the rbt in manual mode,it seems a total waste of my time to run the rbt in auto mode

Currently axle 1 is tested for maximum effort,then imbalance,then parking brake on whichever axle is relevant,followed by axle 2 for maximum effort & axle 2 imbalance,results are automatically given in percentage,rbt is programmed this way,so i cannot test for imbalance first in either manual or auto mode