Steering systems
Troubleshooting and fixing electrical and hydraulic power steering systems.
Being so fundamental to safety, Rob Marshall examines what can go wrong with the steering system and why Diyers need to be careful but not scared of conducting repairs.
Prior to World War Two, the rudimentary solid front beam axle of early motor vehicles meant that steering and suspension components were kept relatively separate. Especially after the introduction of independent front suspension, as cars became faster and more sophisticated, the steering and suspension became more closely related. Modern motorists should be wary of diagnosing a steering fault, when the suspension, chassis or even tyres could be to blame.
While the steering system of even a modern car possesses relatively few components, its design and specification is immensely complex. Engineers go through a painstaking development process to ensure the optimum balance of kingpin, castor, toe and camber angles to achieve a safe, user-friendly system. Although most of these calculations are of little practical use to the everyday motorist, who wishes simply to maintain the steering in tip-top condition, it is essential to ensure the correct alignment of the front wheels and to adjust the tracking to ensure that the system is working safely and accurately.
A matter of course
It was established early on that the front wheels were better suited for steering duties than the rears. Initial steering systems were purely mechanical, before the advent of power assistance and electronics.
The steering’s gearing had to be balanced with the effort required at the steering wheel, so that the driver could turn the wheel during parking manoeuvres, while not making the car over-sensitive and twitchy at higher speeds.
Many early systems employed a steering gearbox to reduce the gearing accordingly, which worked internally by several methods, such as worm-and-peg and recirculating-ball. The high cost of these and the proliferation of bearings and balljoints – which became worn and introduced excessive free-play, or slop, into the system – saw them being replaced by the simpler rack-and-pinion arrangement, which BMW introduced first to a production vehicle in the 1930s and which Ford of Britain popularised a further three decades later. While you may still encounter steering boxes on relatively modern cars – such as V8 versions of BMW’S E39 range and heavy-duty pickups, such as the Nissan Navara – this feature will focus on the more common and simpler rack-and-pinion arrangement.
Regardless of their design, all steering mechanisms must communicate movement accurately from the steering wheel to the front wheels, as well as impart a degree of feedback, so that the driver can evaluate the loads imposed on the tyres. Undesirable and excessive forces must not be transmitted back, resulting in the steering wheel fighting with, or even injuring, the driver’s hands. Also, a self-centring action is far safer than the
steering winding itself onto full-lock, should the driver release the wheel for any reason. When front-wheel drive became commonplace, hanging the gearbox over the front wheels created further issues, as did more powerful engines, which introduced ‘torque steer’, where the steering wheel tries to wrench itself towards full-lock as more power is applied.
Help at hand
Power assisted steering (PAS) provided not only welcome support for drivers, but also engineers, who could tune the technology to eradicate the consequences of other adjustments that would make the steering either excessively heavy or low geared. Citroën was a particular pioneer for using clever steering geometry to perform some deeply impressive feats on its mass-production models (including the car's stability not being affected by a sudden front tyre deflation, as the famed GS/GSA television/magazine adverts showed us). Even so, the French company's left-field methodology of providing a fully powered steering system to its DS and CX models resulted in the driving experience becoming excessively artificial, a critique that was levelled also at early Americana, where virtually no consideration was given to steering 'feel'. To a certain extent, this shortcoming extended into the 21st Century, as electric power steering (EPS) became more popular.
Citroën aside, the typical 1980s and 1990s hydraulic PAS systems comprise a belt-driven pump, which drove hydraulic fluid via a reservoir into a control gear. This diverted the pressure into the appropriate side of a piston, fitted with the steering rack casting, dependent on the direction of steering wheel movement. These components were refined to balance the need for maximum aid at parking speeds, while reducing assistance as the vehicle’s speed increased.
Despite ensuing PAS refinements, car manufacturers viewed the mechanical pump as an inefficient unit that had a detrimental impact on CO2 emissions. The solution was electro-hydraulic PAS, which replaced the engine belt drive with an Ecu-controlled electric motor to power the pump. Most of the latest hydraulic and electro-hydraulic systems tend to strike a balance between assistance and satisfactory driver feel. Even Citroën caved in and dropped its fully-powered hydraulics in favour of these systems, due to both high production costs and fuel/co2 considerations.
Turning down electric avenue
With ever-tightening emissions legislation, the efficiency savings that were offered, by replacing an enginedriven pump with one driven by an electric motor, were deemed insufficient.
Discarding the entire hydraulic system and mounting an electric motor either on the steering column, or the rack, helped to lower CO2 emissions even further. Not only did the technology save weight and manufacturing costs, it also permitted the steering system to be networked into the car’s Canbus wiring. This means that a number of other driver assistance functions can be provided, such as active steering assist and auto-park. EPS is now a crucial part of autonomous technology, the development of which is continuing at an accelerated rate.
EPS is not perfect. Some versions feel artificial, lacking adequate weight and feel. Additionally, as the car’s speed increases, the ratio changes can be detected by the technically-sensitive driver. Some automotive journalists have even suggested that EPS simply disguises a poorly executed steering system, because electronics can be tuned to dial-in certain characteristics artificially, such as self-centring.
What goes wrong?
The mechanical components of any steering mechanism will wear out eventually. While the column bearings, or bushes, tend to require replacing only in extreme old age, the flexible, or universal, joints between the column and rack can develop play far sooner. Many cars have shields to protect these joints from engine bay heat, but failing to refit the shields after repair work can shorten the life of the joints considerably. Mechanically, the rack can suffer from worn teeth and pinions, as well as play in the inner rods – the majority of these issues will be spotted by an eagle-eyed MOT tester. Unless you are particularly knowledgeable, rack reconditioning is best left to a specialist.
Hydraulic PAS systems suffer leaks from their pipe joints and seals. The rack’s pinion oil seal, as well as those positioned at either end of the casting, can also fail. The gaiters are not intended to retain fluid, so any evidence of liquid seeping out from behind them indicates that a seal is weeping and the rack needs replacing. Look also for accompanying drops in the PAS reservoir level.
Additionally, watch out for any lack of assistance, when the engine is cold. While this can point to a worn pump, it may also be a fault within the control valve assembly that directs fluid into the rack. This is a common fault on Rover 200/400/25/45 models and Ford Kas and Fiestas of the same generation. Full details about how to recondition a worn steering rack appeared in the April 2016 issue of CM.
Both belt-driven and hydraulic pumps fail, with leaks, low pressure and excessive noise being obvious indicators. With mechanically-driven systems, overtightening the drivebelt will strain the pump bearings, raising the leak risk. Running the system empty of fluid, or not attending to blocked filters/strainers inside the reservoir, can also damage the pump.
A useful test is to apply light but constant pressure at the steering wheel with the engine idling. Should increasing the engine speed cause the steering wheel to move, the pump is likely to be worn. Should heavy steering be detected, especially if the pump has become noisy, turn off the engine and open the reservoir to check that the fluid has not
become aerated. The culprit could be air contaminating the system – after entering the pump, it creates thousands of tiny air bubbles. Apart from a faulty front seal in the pump, air can enter through the low-pressure pipes between the reservoir and pump – brittle/cracked hoses and deteriorated end clips tend to be to blame.
Once the cause has been identified, the PAS will need bleeding. While ‘pulsing’ at the steering wheel, when turning the wheel slightly with the car stationary, might be attributed to a problem with the hydraulic circuit, vibration at speed tends not to be a fault of the steering. Instead, an imbalanced tyre, or warped brake disc, should be suspected.
Corrosion can strike not only on the PAS pipes, especially if your car has a cooling pipe fitted ahead of the main radiator, but also the rack. Serious corrosion can result in rebuilders rejecting your original core component as scrap, meaning that you can lose your exchange surcharge deposit, presuming that you buy a reconditioned item. Driving through deep water will exacerbate the problem.
Despite being mechanically simpler, EPS systems suffer from their fair share of issues, affecting both the column and rack. While the causes can be either software- or hardware-related, failure of the electric-hydraulic system and the EPS to provide any assistance, especially after a cold start, can be a sign of a dying battery, or a charging system fault. On the move, any tendency for the power steering to cut out must be investigated immediately – it can cause the steering angle to change suddenly as you negotiate a corner and is a safety issue that can strike hydraulic systems, too. Look also for inconsistent assistance and note that intermittent faults that disappear after stopping and restarting the engine are likely to return and become worse.
Many modern cars with both hydraulic and EPS assistance are equipped with a steering angle sensor. This can be a separate sensor assembly – in many cases, the steering angle sensor consists of several sensors within a single plastic moulding – or integrated with the column stalk assembly. While some types are self-calibrating, many other designs require the task to be performed via the OBD port, when a rack, or EPS component, is replaced. Many technicians recommend that it is also recalibrated after the front wheel alignment is adjusted. Considering that the steering angle is only one parameter that is monitored by electronic stability control system, ensuring its correct calibration is a safety issue. You can check if the sensor is working correctly by using diagnostic software to verify that the steering wheel angle reading changes as the wheel is turned. EPS systems are equipped with a steering torque sensor, which is a common failure item. The sensor can be replaced separately on some cars, while others require a complete new column.
The most common DIY tasks will be either repairing steering racks, or renewing EPS motors that are mounted on the column. We have opted to follow the procedure on a 2001 Fiat Punto, an older vehicle where professional garage labour costs are uneconomical.