29/05/2020
The precise control and responsive handling of a BMW are hallmarks of the brand, and for owners of the iconic E60 5 Series, understanding how the front wheels translate driver input into motion is key to appreciating its engineering. Far from a simple mechanical linkage, the E60 employs a sophisticated power-assisted steering system that blends mechanical ingenuity with hydraulic precision, and in many models, advanced electronic intelligence.
Understanding the E60's Steering System: A Deep Dive
At its core, the BMW E60 utilises a system known as power-assisted rack-and-pinion steering. This design is widely adopted due to its direct feel, reliability, and relatively compact nature. But how exactly does it work to direct your vehicle?
The Rack-and-Pinion Foundation
When you rotate the steering wheel, it connects to a shaft that, in turn, spins a small circular gear called the pinion gear. This pinion gear is precisely meshed with a long, flat bar known as the rack, which has teeth cut into one side. As the pinion gear spins, it causes the toothed rack to slide horizontally, either to the left or to the right. The ends of this rack are then connected to tie-rods, which are directly attached to the steering knuckles of the front wheels. Thus, the linear motion of the rack is directly translated into the angular movement of the wheels, allowing your vehicle to turn.
The Hydraulic Heart: Power Steering Assistance
While the mechanical rack-and-pinion system handles the direct translation of movement, the 'power-assisted' part of the equation is where the driver's effort is significantly reduced. A hydraulic pump, driven by the engine's accessory belt, continuously circulates power steering fluid under pressure. This fluid is forced through hoses into pistons located within the steering rack itself. Inside the steering rack, a hydraulic valve intelligently varies the fluid pressure in two separate cylinders. The amount and direction of this pressure variation are directly dependent on how quickly or forcefully the pinion gear is rotated by the steering wheel. By applying hydraulic force in the desired direction, the system effectively multiplies the driver's input, making it much easier to turn the wheels, especially at low speeds or when parking.
The Intelligent Touch: BMW's Active Steering System
Many BMW E60 models were equipped with an optional and highly innovative active steering system, which takes power assistance to another level. This system dynamically varies the force multiplication of the power steering based on the vehicle's speed. At lower speeds, such as during city driving or parking manoeuvres, the steering assist (force multiplication) is at its maximum. This allows for effortless turning and makes the car feel incredibly nimble and easy to manoeuvre in tight spaces.
Conversely, at higher speeds, the steering assist is progressively reduced. This provides the driver with a more direct and 'heavier' steering feel, which is crucial for stability and precision on motorways. Furthermore, at speeds above approximately 75 mph (120 kph), the active steering microprocessor actively reduces driver input into the steering system. This is a crucial safety feature designed to prevent the transmission of unintended, rapid steering movements to the front wheels, which could otherwise destabilise the vehicle at high velocity. This intelligent adaptation ensures optimal steering response and safety across all driving conditions.
Common Maladies of the E60 Power Steering System
Even with BMW's robust engineering, the power steering system, like any complex mechanical and hydraulic assembly, can develop issues over time. Recognising the symptoms early can prevent more significant problems and costly repairs.
The Groaning Pump: Symptoms and Solutions
One of the most common indicators of a failing power steering pump is a distinct groaning noise, often heard when turning the steering wheel from side to side. You might also notice an increased effort required to steer the vehicle, particularly at low speeds. While a pump can certainly leak fluid, a noisy and weak pump is a far more prevalent symptom of impending failure.
The Overlooked Filter: Reservoir Replacement
Inside the power steering fluid reservoir, there's a small, often overlooked, filter. Over time, this filter can become restricted with contaminants and debris from the system. Unlike many other filters, this one is not serviceable separately; if it's clogged, the entire power steering fluid reservoir must be replaced. Interestingly, many instances of a noisy power steering pump have been successfully remedied simply by replacing the reservoir, suggesting that a restricted filter can starve the pump of fluid, leading to cavitation and noise. If your E60's power steering is groaning, starting with a reservoir replacement is often a sensible first step.
Leaks and Loose Connections: Hoses and Clamps
The power steering system relies on a network of hoses to transport fluid under high pressure. Over time, particularly with exposure to heat and vibration, the hose clamps can loosen, and the hoses themselves can degrade, leading to fluid leaks. There are typically two main hoses that connect to the reservoir: one leading to the power steering cooler and the other directly to the pump. These are common culprits for leaks and often warrant replacement alongside the reservoir to ensure system integrity.
DIY Maintenance: Replacing the Power Steering Reservoir (and Beyond)
Addressing power steering issues like a noisy pump or fluid leaks can be a manageable DIY task for the mechanically inclined. The replacement of the power steering reservoir and the subsequent bleeding of the system are common procedures that can restore your E60's steering performance.
Tools and Parts for the Job
For a task like replacing the power steering reservoir, you'll generally need a 10mm socket, a flathead screwdriver, and hose clamp pliers. The essential parts include a new power steering reservoir, potentially new power steering hoses and hose clamps, and, of course, fresh power steering fluid. It's crucial to use the correct type of power steering fluid specified for your BMW E60 to avoid compatibility issues and potential system damage.
The Replacement Process (High-Level)
The procedure typically involves placing an oil drain pan under the left side of the engine to catch any spilled fluid. A helpful tip is to suction out as much fluid as possible from the old reservoir before attempting to remove it, minimising mess. Once the old reservoir and potentially the related hoses are disconnected and removed, the new components can be installed. Following replacement, the power steering system must be properly bled to remove any trapped air, which can cause noise and inconsistent steering feel. This usually involves turning the steering wheel from lock to lock several times with the engine running and the reservoir cap off, topping up fluid as necessary.
Safety First: Essential Workshop Practices
When undertaking any work on your vehicle, safety must be paramount. Always protect your eyes, hands, and body from fluids, dust, and debris. If you are working with any part of the electrical system, ensure the battery is disconnected before you begin. Always use appropriate containers to catch any fluids and dispose of them responsibly. Recycle parts, packaging, and fluids whenever possible. Finally, never attempt a task that you feel is beyond your ability; professional assistance is always an option.
Steering System Troubleshooting Table
Understanding common symptoms and their potential remedies can help you diagnose issues with your BMW E60's power steering system effectively.
| Symptom | Likely Cause | Recommended Action |
|---|---|---|
| Groaning noise (especially when turning) | Failing power steering pump; Restricted reservoir filter; Low fluid level | Check fluid level. Try replacing power steering reservoir. Inspect pump for leaks. Consider pump replacement if noise persists. |
| Increased steering effort | Failing power steering pump; Restricted reservoir filter; Low fluid level | Check fluid level. Try replacing power steering reservoir. Inspect pump for failure. |
| Fluid leaks | Degraded hoses; Loose hose clamps; Leaking pump or steering rack seals | Inspect all hoses and clamps for signs of leakage. Replace affected hoses and clamps. Check pump and rack for seal integrity. |
| Foamy or discoloured fluid | Air in system; Contaminated fluid; Incorrect fluid type | Bleed the system thoroughly. Flush and replace fluid with correct type. Inspect for leaks that might be introducing air. |
Frequently Asked Questions (FAQs)
How do I adjust my BMW E60 steering wheel?
Adjusting the steering wheel in your BMW E60 is straightforward. Locate the small switch or lever on the left side of your steering column, usually underneath the steering wheel itself. Push this switch or lever back (or release it, depending on the design). This will unlock the steering wheel's position. You can then manually move the wheel to your preferred height and angle to achieve an optimal driving position. Once satisfied, push the switch or lever forward (or engage it) to lock the steering wheel securely in place.
Can a wheel steering angle be set to zero in the E60?
Yes, the wheel steering angle can be set to zero in the BMW E60, particularly for vehicles equipped with the active steering system. This is a crucial calibration procedure performed using diagnostic equipment. The 'Commissioning/Adjusting active steering' service function must be run after specific maintenance or repair work, including:
- Axle or wheel alignment.
- Any work performed on the steering column.
- Replacement or programming of the active steering control module (AL).
- Replacement or programming of the steering column switching centre (SZL).
- Replacement or programming of the Dynamic Stability Control (DSC) module.
- Replacement of the steering gear.
The procedure involves several steps, including setting the cumulative steering angle sensor precisely to zero (provided valid sensor values are present), resetting the engine location angle (AL), performing a steering-angle sensor adjustment (if necessary), clearing relevant fault memories (SZL, DSC, AL), calibrating the engine location angle, and potentially clearing the steering angle value for the ARS (Active Roll Stabilisation) system if fitted, and calibrating the total steering angle offset. For an inclined steering wheel without fault entries in the active steering diagnosis, checking the steering-wheel angle (should be 0 +/- 2 degrees) and total steering angle (0 +/- 5 degrees) in the exact centre position is vital. If these values are off, running the commissioning/adjustment with or without steering-angle sensor adjustment, followed by a wheel alignment, is necessary to ensure precise steering and vehicle stability.
What are the signs of a failing power steering pump?
The primary signs of a failing power steering pump in your BMW E60 include a noticeable groaning or whining noise, especially when turning the steering wheel from side to side. Another key symptom is an increase in the effort required to turn the steering wheel, particularly at lower speeds or when parking. While less common than noise or weakness, a leaking pump seal can also indicate a problem.
Why should I replace the power steering reservoir if my pump is noisy?
The power steering reservoir in your E60 contains a non-serviceable filter designed to trap contaminants in the fluid. Over time, this filter can become restricted or clogged, impeding the flow of power steering fluid to the pump. A pump that is starved of fluid will often produce a groaning or whining noise as it struggles to operate efficiently. Replacing the entire reservoir is often recommended as a first step because it introduces a new, clean filter into the system, which can often resolve the noise issue by restoring proper fluid flow to the pump. It's a less invasive and generally more affordable repair than replacing the pump itself.
Conclusion
The BMW E60's steering system is a marvel of engineering, combining robust mechanical principles with sophisticated hydraulic and electronic assistance to deliver that characteristic BMW driving experience. Understanding the intricacies of the power-assisted rack-and-pinion setup, the role of the hydraulic pump, and the advanced capabilities of the active steering system empowers you as an owner. By recognising the signs of common issues related to the power steering pump, reservoir, and hoses, and knowing when to perform maintenance or seek professional calibration, you can ensure your E60 continues to offer the precise, responsive, and enjoyable driving dynamics it was designed for.
If you want to read more articles similar to Mastering the Turn: BMW E60 Front Wheel Dynamics, you can visit the Automotive category.