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Keeping it
on the road…For the bulk of us, checking steering and suspension for the MOT has not changed – except for those who can afford a newly approved Automatic Test Lane (ATL) which will make this a much easier examination… and what about electric power steering? We re-visit this whole aspect of the MOT Test, looking at the pitfalls and difficulties faced by Testers…
Testers must also understand how the joint itself works. Is it a ball joint – and if so how is it constructed? If not, how does the combination of suspension movement and steering swivel work? Which way must the assistant push and pull? It is easy to get it wrong, to inspect one type of system as if it were another and mistakenly pass a defective component.
“Worn to excess” and Vehicle specific quirks
Steering and suspension joints are rejected if “worn to excess”, and VOSA’s trainers teach Testers to ask themselves the question “Would you drive with your family in a vehicle with that component fitted?” If the answer is “no”, then the component is considered worn to excess.
For many Testers that goes against the grain, having been taught that a worn suspension joint with clearly identifiable ‘play’ should be changed to avoid failure before the next service. That’s wrong. The MOT is only a minimal safety standard, so unless that joint is really ready to ‘pop-out’, the VOSA creed is “pass and advise”.
Yet that can go against vehicle manufacturer’s safety recommendations. Some insist any play in the suspension joint requires replacement. What happens then?
Hopefully, when Siemens/VOSA have eventually sorted out computerisation, such ‘vehicle specific’ quirks will appear on the ‘Vehicle Specific Information’ spewed off the printer prior to conducting the Test – a useful safeguard.
Training
Training is important here – and a concern. In other countries, Holland for instance, models of different forms of suspension systems are used during training, but VOSA provide scant guidance. VOSA would say “that’s OK because a novice Tester must be experienced before being accepted on their ‘training’ course” -– but what if the Tester has always worked in a specialised dealership and is only familiar with one brand? – on changing jobs and moving to an independent garage Testing all makes and models, problems could arise.
Steering checks and turning plates
This is an old favourite for VOSA’s Vehicle Examiners to catch people out! Make sure you do the ‘lock-to-lock’ check, but also check that the plates turn freely. If you don’t check, the VE will! Even if they are only partially seized, he’ll conclude you don’t use them regularly, or if you do, you are not getting a correct result from the steering examination.
Remember too that the ‘lock-to-lock’ check has to be done both on the turning plates and (for front wheel drive vehicles) when the wheels are off the ground to check drive shafts/couplings.
Loose or corroded
At various stages throughout the Manual Testers are instructed to check for both security and corrosion of steering and suspension components.
This is important. Regular readers may recall an instance we recently reported wherein a corroded suspension component gave way on a motorway and a passenger was killed and it was claimed the Tester should have spotted the corrosion (see ‘Legal Liability’ article, on page 18 – Ed). So really thorough checks for security and unacceptable corrosion are absolutely vital. Remember too, that if there’s extensive surface corrosion which does not warrant a failure – make sure you note it in the advisory notes.
Complex and time consuming
Suspension and steering checks account for a large proportion of the MOT Test – and a thorough check requires a complex and time-consuming examination. And it won’t get any easier. This aspect of vehicle design is under continuous development with traction control improvements, electric power steering and auto-parking systems either here or just over the horizon.
Indeed, one problematical aspect of all this is that the car makers are so far ahead of the MOT Testing authorities that more and more vehicle safety related systems are not being examined or checked in any way during the Test.
Assistants and shaker plates
Currently most Testers rely on muscle power to load the joints whilst they inspect for wear, which has its pitfalls – assistants are not equally strong. The Tester must both look at the joint for wear while checking that the assistant is pushing and pulling hard enough and in the right way so that wear can be detected.
Automatic Testing Lanes (ATLs) use powered shaker plates to load the steering and suspension joints – and the equipment pushes and pulls very hard!
VOSA did a lot of experimentation on this before accepting such equipment in ATLs – their Richard Dixon explains the work they did.
Phase one of their project was carried out at Mercedes dealerships equipped with ATLs. It involved conducting Tests conventionally and then repeating the checks using the ATL to determine whether defects detected conventionally would show up using the ATL equipment and visa versa.
A total of 569 vehicles were Tested, the results indicating that all defects found were detectable using both methods.
Phase 2 encompassed a wider range of makes and models of vehicles, and included the deliberate introduction of defects to assess whether both methods detected the faults.
Over three months 214 vehicles were checked across a wide cross section of make, model and age and defect type Technical staff were invited to Test vehicles with introduced defects without knowing what the defects were. Richard Dixon noted “They were able to detect the defects using both the conventional and ATL method”.
Altogether the research phases of the project took one year, the risk to road safety being a major consideration.
The successful outcome of this work played a major part in the decision to introduce ATLs into the Testing scheme.
Beating the bumps – Automated Suspension Testing
The Garage Equipment Association’s David Garrat puts us in the picture about the development of equipment to Test shock absorbers.
There are two different types of equipment, and discussions are going on in Europe to decide which is the best.Suspension Testing equipment:
During an MOT, we push down on each wing of the vehicle to check the shock absorbers, whereas in Europe Testers use suspension testing equipment. For example, Belgium introduced the EUSAMA method of testing suspension in 1991. A vehicle is rejected if any wheel has an EUSAMA-value lower than 20%, or if the relative difference between the values of the left and right sides of an axle exceeds 50%. On average, 3 to 5 percent of the vehicles Tested fail.
The French also have ‘MOT’ suspension checks; but they allow each Testing Station to decide which equipment/method to use and only insist on an imbalance test, failing vehicles with a difference across an axle of 30% or more.
There are numerous types of suspension testing equipment available but the main two are the ‘Eusama’ and the ‘Resonance’ or ‘Boge’ methods (see panels below).
The way to go:
DEKRA of Germany and VOSA are currently involved in a joint project appraising suspension testing equipment, which is just as well, because there are pros and cons to each method. Recently the GEA, EGEA and CITA have formed working groups to find an answer to the “which is the best method?” question and hope to provide the answer, or even come up with an alternative solution in the near future.
Shock absorber testing for the MOT?
It is very surprising to many people that some form of automated shock absorber testing is not already a requirement of the MOT Test – especially as both steering and braking are critically affected by the condition of a vehicle’s shock absorbers.
We discussed this with VOSA’s Richard Dixon who said “at VOSA we are keen to instigate automated suspension test equipment into the MOT, but also believe that we should ensure that anything we do harmonises with European standards.” He added “so we are awaiting the outcome of the European research programme before reaching a decision…”
So there we have it; at some stage in the future we can expect the MOT to require automated suspension testing; which method we don’t yet know.
EUSAMA
Eusama stands for the EUropean Shock Absorber Manufacturers Association. Here, the vehicle’s wheels, one axle at a time, are positioned on the test bed. The equipment initially weighs each wheel in its static state, then the plate on which the wheel is positioned vibrates from 0 up to 25-hertz, at a stroke of about 6mm (1/4 inch). During this vibration stage, the equipment constantly monitors the wheel’s dynamic weight; (Effectively measuring how much time the wheel is ‘in the air’ – Ed.) it’s the lowest dynamic weight (the Eusama-value) that’s noted and recorded. This determines the road adherence of each wheel by comparing the difference between the static and the lowest dynamic weight.
A vehicle fails if any wheel has a Eusama-value lower than about 25%, or if the relative difference between the values of the left and right sides of an axle exceeds 50%. However, many equipment manufacturers recommend slightly different values, to best suit their individual equipment.
Resonance Method (Boge):
As with the Eusama system, the vehicle’s wheels, one axle at a time, are positioned on the test platform. Here, however, the platform, which is heavy, is free to move up and down and is connected to an oscillating motor via a strong spring. At the beginning of the test, the motor starts to move the test platform up and down.
Once the platform is oscillating at around 15 Hertz, the motor is switched off and the platform allowed to continue to oscillate but because the motor is no longer driving it, the oscillations decay.
The platform’s weight working against the spring tend to prolong the decaying oscillation, – but the vehicle’s suspension/damping system tries to stop it. The equipment monitors the decaying maximum amplitude and plots a frequency to amplitude graph. If the vehicle’s suspension/dampening systems are OK, the oscillations decay and stop fairly quickly. On the other hand, continued high amplitudes at high frequencies indicate a defective system.
More text and pictures in MOT Testing 47 November 05
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