MOT Workshop 34 – Steering and Suspension

Correct assessment of the condition of steering and suspension components is arguably the most difficult part of the MOT Test, combine that with a very proscriptive process for carrying out the required checks and it can easily be seen how many Testers struggle to make correct decisions or fail to spot potentially dangerous defects. (This article first appeared in MOT Testing Magazine)

By John Parham

It would take much more space than we have here to go into in-depth detail of how to Test every single type of suspension of steering set up, so I will concentrate on the areas where I see most mistakes made either in assessment of condition or method of inspection.

Steering column and wheel

lowerbush optIt is important to ensure that the condition of the lower steering column mounting is checked.

The first area often neglected by Testers is the lower steering column coupling in the driver’s foot well area. Although some cars have shields covering this area, there’s still a requirement to assess the condition of the lower coupling and lower steering column mounting, which requires the Tester to get his or her head down in the footwell, with an inspection lamp to assess the condition. While there, the condition of the pedal box, brake pedal, pedal rubber and the vehicle structure within the prescribed area should also be checked. Note, though, excessive play in the LOWER steering column bush is NOT a failure, only the upper bearing or bush is Testable.

John Parham, MOT specialist

Until a year or so ago, John Parham was a Regional Manager for the RMIF specialising in MOT matters especially disciplinary cases and quality control.

He left school at 16, trained as a vehicle technician in a Rootes Group Dealership, and after qualification worked as a technician in a Jaguar Dealership. He became an MOT tester in 1978. He then moved to a Ford dealership as Service Manager, before managing of a medium sized Independent Garage specialising in MOT Testing, General repairs, breakdown and recovery services.

In 2002 he joined the RMIF. He now runs his own MOT consultancy business The MOT Professional, offering a range of services to MOT Testing Stations. John can be contacted on 01749 342985 or 07858 133415.

John Parham optJohn Parham (above) was an MOT specialist with the RMI for seven years and is now a freelance MOT Consultant.

Remember too, that small amounts of wear or movement are not reasons for rejection and the old maxim of “pass and advise” should applied where there’s doubt that ‘play’ is excessive by the Testers subjective assessment.

Free play at the steering wheel, is however clearly defined. On a standard layout, Testers should expect no more than 75mm free play on non-rack and pinion systems, and no more than 13mm on steering rack layouts. If there are multiple universal joints in the column on a rack system this allowance is extended to a maximum of 48mm at the circumference of a standard 380mm wheel.

Lifts and pits

The process for checking the steering and suspension systems will depend on the layout of the MOT bay and the vehicle type. Testing on a pit with conventional equipment will necessarily be somewhat different to testing on a ramp equipped with wheel play detectors.

Many test stations I visit have ramps with raised grease or turn plates fitted. If the station has this equipment, I think that VOSA’s recommended route creates more problems than it solves. When training new Testers on this type of kit, I always suggest they do the rear suspension checks first. This is because, if the front end is jacked up first, the jack up checks conducted, and then the vehicle is lowered on to the turn plates, the requirements for using the assistant force the Tester to raise and lower the ramp like a fiddler’s elbow, or to risk danger to himself or work colleagues by jacking up the rear end of the vehicle with the front wheels still on the raised turn plates. This procedure is unstable, and can lead to the vehicle running off the plates when the rear end is lowered back down with the handbrake off.

By jacking the rear first, the necessary checks to the rear suspension can be conducted, remember the assistant is not always required during the rear suspension check process. An assistant is only needed if the Tester is unable to have a good view of the components or if he detects play and can’t identify where it comes from.

Once the rear suspension checks have been completed the rear wheels can be lowered back onto the ramp or floor, the handbrake applied, the wheels chocked and the car is then safe to carry out the front end inspection.

Play detectors

For bays fitted with wheel play detectors, it is important to also check the rear suspension while operating the detectors in side to side mode. This check can reveal excessive play in the rear suspension components (BMW upper rear suspension mountings for example), which are difficult to check properly using any other method.

While on the subject of wheel play detectors, I have received starkly conflicting reports from test stations as to their effectiveness. Many Testers tell me that they use the conventional process as they don’t trust the wheel play detectors to show up excessive wear that can be found using an assistant. Yet other Testers who use ATLs or OPTLs swear by them and are confident it’s a better test than before. I have to say this is completely anecdotal as I have not experienced a problem either way. In my experience, if the wheel play detectors are used properly, the results are the same. I have certainly not had a disciplinary case as a result of defects missed using one process and subsequently found using the other.

Jacking the front suspension

One area where I frequently see incorrect testing methods is the front suspension checks while the vehicle is jacked up, mainly because Testers don’t correctly identify the suspension layout before jacking the vehicle up – and end up inspecting joints which are under load, so wear cannot be detected.

The final page in section 2 of the Inspection Manual gives a diagramatical representation of various types of suspension layout. This page has not been amended for many years and it fails to show the front suspension designs used on many modern vehicles, where a suspension strut (NOT a Macpherson Strut) is mounted in a similar position to where a Macpherson strut is mounted at the top, but is then connected directly to the lower suspension arm or wishbone, and employs a non weight bearing upper arm or wishbone to control the top of the hub assembly. This layout is common on Audi, Volkswagen and Honda vehicles, with many more manufacturers adopting similar systems.

The basic rule is that if the suspension load acts directly on the lower suspension component, then the vehicle should be jacked up under that arm, if the load is borne by the upper suspension component or if a Macpherson strut is fitted, then the suspension should be allowed to hang. Failure to follow this rule will almost inevitably lead to excessive wear, especially in the upper arm bushes or ball joint, being missed on the Audi, V/W, Honda type layout, or missed in the lower suspension ball joint or bushes on other types.

Road safety threat

This has road safety significance. Only a few years ago Ford Transits had a weakness in the lower ball joint, causing it to detach completely and the suspension to collapse. This defect was usually detected by jacking up under the lower suspension arm and then levering up under the wheel vigorously. Many Testers failed to detect these defective joints, causing them serious disciplinary problems with VOSA.

Even recently I watched a Tester incorrectly check a Honda Legend’s front suspension. He found no problem with the vehicle, but when we went back over the test and examined the front suspension correctly, we found play in the nearside top ball joint that was both advanced and dangerous. I’m sure he won’t make that same mistake again and I would advise all Testers to be just as vigilant.

Push and Pull – Assistant and Tester

shaking optBoth the Tester (seen here), and the Assistant must vigorously shake the wheel to check for free play in the suspension.

The use of the assistant for pushing and pulling to detect steering/suspension wear has always been a source of confusion. For all non ATL or OPTL equipment, 5 different front suspension checks are required using an assistant. All five checks should be completed by the Tester, and then repeated by the assistant while the Tester is examining the relevant components for wear, here they are…

1. With the vehicle jacked up the Tester grasps the wheel at 9 o’clock and 3 o’clock shaking it to detect free play in the steering components. This check is repeated with the assistant shaking the wheel.

2. The Tester must shake the wheel at 12 o’clock and 6 o’clock checking for wear in the suspension joints/bushes and wheel bearing. This is repeated with the assistant shaking the wheel.

3. Still with the vehicle jacked up, the Tester levers under the road wheel (I recommend a bar at least 24 inches long) levering upwards whilst checking for play in ball joints, top strut mountings and strut itself (between shock absorber rod and housing). This check is repeated with the assistant levering the wheel. .

4. With the vehicle lowered onto unlocked turn plates, the Tester should grasp the wheel at the top and push and pull “vigorously” in and out, checking by ‘feel’ for free play. This is repeated using the assistant to do the pushing and pulling while the Tester examines the components.

5. The Tester should grasp the wheel at 9 o’clock and 3 o’clock again shaking vigorously checking for free play. This must also be repeated with the assistant doing the shaking.

Using the bar under the wheel and vigorously rocking on the turn plates are not required if ‘shaker plates’ are available. The check where the assistant rocks the steering with the front wheels on a solid surface is replaced on an ATL or OPTL by using the wheel play detectors in rotational mode.

Turn plates

The final two checks that I often see missed or incorrectly performed also involve the turn plates. There is a requirement to check for fouling on a full lock, with the vehicle fully lowered onto the turn plates, but don’t bounce against the lock stops! Normally the assistant holds the steering on a full lock while during this check. Although this is easy in a conventional bay, its difficult on an ATL or OPTL.

This is the one check on an ATL that an assistant may be required, as it’s almost impossible to hold the steering on a full lock and carry out an examination at the same time. All I can suggest if you don’t have an assistant available, is to use either the brake pedal applicator, or if you have one, the steering lock device that comes with wheel alignment equipment, to hold the steering on a full lock while you carry out the examination.

Finally, checking the steering for roughness and tight spots, indicating a bent or damaged rack. The vehicle must be lowered onto the turn plates with the Tester in the driver’s seat, turning the steering slowly from lock to lock.

I sometimes find turn plates seized, unloved and unused on MOT ramps and bays. When carrying out an observed test, the Tester often struggles with the equipment, has little grasp of why it is used, or how it is used, this is often due to lack of practice and lack of enforcement by Site Managers and Quality Controllers. Effective use of the turn plates should always form part of the monthly QC check, having an efficient and compliant routine is in the best interest of the business as a whole.

Wear Assessment

This is inevitably subjective when wear limits are not specified.
Section 2.4 of the Inspection manual does give limits for suspension pins as more than:
2mm for a 12mm diameter pin
3mm for a 25mm diameter pin
10% of the pin diameter for pins over 25mm diameter
Deterioration of a rubber bush resulting in excessive movement.
However for ball joints Section 2.2 states:
“f. excessive play in ball joints
Note: Play must not be regarded as excessive unless it is clear that replacement, repair or adjustment of the component is necessary.”

Rubber bushes and bonded mountings

Here the general rule is that they do not fail unless there is excessive movement caused by the failure of the bonding or deterioration of the bush. Upper suspension mountings on a suspension strut are a reason for failure if the bonding has failed, as are rubber or synthetic suspension units (springs), also where the bonding has failed. The Tester must clearly decide which category the mounting or bush falls into before making the relevant decision.

The note in section 2.4 of the manual states:

“Note: Some rubber/synthetic bushes are designed to provide a comparatively high degree of compliance. They are therefore likely to show some movement.”

It’s often not easy to make the correct decisions on all of these items, so take your time, check the manual if necessary and clearly understand the requirements of the standard before committing to a decision one way or the other, and of course use the ‘pass and advise’ maxim if there is doubt as to whether or not a particular defect meets the criteria for failure.

And finally…

Checking a vehicle’s steering and suspension system is both a complex and time consuming part of the MOT Test examination – but it is also a key safety sensitive part of the Test and must be done properly.

It is essentially, therefore that not only must Testers get it right, but that the company’s quality controller fully understand why the checks are being carried out. This will ensure that any systemic errors being made by Testers are picked up and remedied at an early stage. This is about road safety. Should excessive wear in a steering/suspension systems fail to be detected due to using an incorrect inspection procedure, the consequences could be dire indeed!

motw MOT Workshop Magazine


Related posts

Comment on this article