Changes to Brake Performance Procedure and Standards (Special Notice 03-13)

vosa logoThe following changes to the brake performance test were introduced today (23 June 2013)

  • Increased minimum service brake efficiency for some passenger vehicles
  • Amendments to the service brake imbalance requirements
  • Checks for excessive fluctuation
  • Removal of the RfRs for severe grabbing or judder on RBT/PBT service brake test
  • A simplified RBT test procedure
  • New checks on secondary brake
  • Amendments to the brake result screens

These changes are a little complicated so it is important that NTs read and ensure they understand the information below, as well as the amended Inspection Manual pages in Sections 3.7, 3.8 and 3.10 which will all ‘go live’ at the same time.

Service Brake Efficiency

For “M1” vehicles first used on or after 1 September 2010 the minimum service brake efficiency is

increased to 58%. “M1” in the MOT scheme means passenger vehicles with 4 or more wheels (except quadricycles) and not more than 8 passenger seats in addition to the driver’s seat,

Regard dual purpose vehicles as passenger vehicles, unless the presenter provides evidence that it was type approved as a goods vehicle, i.e. the vehicle category is shown as “N1” on the registration document (V5C).

For quadricycles, the NT will follow the normal process, although the question “Is the vehicle a trike or quad within scope of Section 9 of the Inspection Manual: [No/Yes]” will be changed to “Is the vehicle a three-wheeler or quadricycle: [No/Yes]”.

Imbalance – Service Brake

The requirements and method of inspection will change as follows:

Maximum imbalance for Classes 3, 4 & 7 is 30% (in line with the Class 5 requirement)

It is checked across all axles (but not Class 3 and quadricycles, where it is for steered axle only)

Imbalance is measured at maximum brake effort only, regardless of wheel lock.

It is expected that when carrying out imbalance checks us ing a roller brake tester, some aspects such as premature lockup can occur which could lead to an unjustified failure. If the NT considers this is the case, the check should be repeated running each roller individually (unless this was originally how the test was conducted). Alternatively, the service brake test can be repeated using a decelerometer.

Fluctuation

During the check for rate of increase on the service brake, there is now a requirement to hold the brake at a steady pressure to check for excessive fluctuation of brake effort on all wheels.

Grabbing/Judder

With the introduction of the fluctuation check above, the reasons for rejection relating to grab and judder on the service brake have been removed.

Simplified RBT Test Procedure

A simplified service brake test procedure has been introduced for manual roller brake testers. The new procedure is detailed in section 3.7 of the Inspection Manual.

Those with an ATL RBT should continue to follow the RBT prompts but be aware that the service brake effort will be used by the VTS Device to calculate imbalance. Therefore, any imbalance calculations made by the RBT must be ignored.

Bind, rate of increase/reduction as well as excessive fluctuation must be manually assessed on all axles when the rollers automatically restart. We will advise of any requirement for an ATL software upgrade sometime in the future.

 

Secondary Brake Requirements

On vehicles with a single line braking system the parking brake also provides the secondary brake

function (which is why it has a minimum efficiency requirement of 25% rather than 16% for split/dual systems). This type of secondary/parking brake will also need to be checked for severe ‘grabbing’ during application as well as maximum imbalance across the axle of 30% at maximum efforts. As MOT Computerisation will not automatically calculate secondary brake imbalance, the NT must calculate this using the formula in Section 3.8 and where required enter any RfRs manually.

Brake Results Screens

When entering the brake test results for a Class 4 vehicle first used on or after 1 September 2010, a new ‘passenger/goods’ vehicle drop-down box will appear on the initial brake results entry screen. This box will default to ‘passenger’ as these make up the majority of tests for most VTS. When the vehicle tested is a goods vehicle, including car derived vans, the NT must change the selection to ‘Goods’. The ‘imbalance’ sections of the brake data entry screens will be removed as imbalance will be calculated using the ‘user entered’ maximum brake efforts only.

For some vehicles, imbalance defects must be manually entered. In these cases a prompt will appear on screen instructing NTs

that the “Brake imbalance defects should be accessed via Apply RfRs screen”.

Source: http://www.dft.gov.uk/vosa/repository/SN%2003%202013.pdf

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2 Replies to “Changes to Brake Performance Procedure and Standards (Special Notice 03-13)”

  1. I have noticed since the beginning of the week and the change to the “simplified” method of brake testing , the possibility of an incorrect failure particularly in the case of the handbrake, where the vehicle lifts out of the rollers at a relatively low brake force without locking of wheels, thus apparently a failure on low efficiency, it’s essential that chocks should be used to recheck in cases like this. Also under the traditional method of inspection I’d regularly have locking on all 4 wheels, now vehicles that were previously doing this are apparently only just a pass.

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