22/04/2015
When embarking on vehicle maintenance, especially tasks that require lifting the car off the ground, understanding the correct and safest placement of axle stands is paramount. While many might instinctively opt for what appears to be the most robust part of the chassis, such as the subframe, a closer look at engineering principles and practical experience reveals that alternative jacking points can offer superior stability and safety. This article delves into the common practice of using subframes for support and explores why other points, like wishbone mounts, are often recommended by seasoned mechanics, offering a comprehensive guide to secure vehicle lifting.
Understanding the Importance of Secure Support
The primary function of axle stands is to bear the weight of a vehicle when it is elevated, preventing accidental drops that can lead to severe injury or death. Unlike a jack, which is designed for lifting and should ideally never be the sole means of support, axle stands provide a stable, static resting point. Therefore, the choice of where to place them is not merely a matter of convenience but a critical safety consideration. A poorly placed stand can shift, collapse, or fail to engage properly with the vehicle's structure, turning a routine repair into a dangerous situation.
The Subframe: A Tempting but Potentially Risky Option
The subframe, also known as a cradle or chassis, is a substantial structural component that often supports the engine, suspension, and drivetrain. Its inherent strength can make it seem like an ideal jacking point. However, placing axle stands directly under a subframe, particularly on its lower edges or lips, comes with significant caveats.
Critical Consideration: The subframe is often designed with specific load-bearing points for its intended functions, but these might not always be perfectly suited for the concentrated pressure exerted by the flat or curved head of an axle stand. If the stand's head doesn't have a secure mating surface with the subframe, there's a risk of slippage. The lip of a subframe, while appearing strong, can be rounded or angled in a way that doesn't provide a stable, flat surface for the axle stand. This can lead to the stand 'walking' out from under the load as vibrations or minor movements occur.
Furthermore, the shape of the subframe can vary significantly between vehicle models. Some subframes might have a more suitable profile for axle stands than others. However, without detailed knowledge of a specific vehicle's subframe design, relying on it as a primary jacking point can be a gamble. The potential for the stand to not sit flush, or for the subframe itself to deform under concentrated load, makes this a point of caution.
The Wishbone Mount: A More Engineered Solution
An alternative, and often preferred, jacking point is the suspension wishbone mounting point. The wishbone (or control arm) is a suspension component that connects the chassis to the wheel hub. Its mounting points to the chassis are specifically engineered to handle significant forces, including the dynamic loads of the road and the static weight of the vehicle.
Why it Works:
- Designed Load Bearing: The points where the wishbone attaches to the chassis are designed to bear substantial weight and rotational forces. These are typically robust bracketry or pivot points.
- Favourable Geometry: Many wishbone mounting points, particularly where the pivot bolt passes through, offer a curved or semi-circular surface. The heads of many common axle stands are also designed with a similar curvature, allowing for a snug and secure fit. This interlocking geometry significantly reduces the risk of slippage.
- Stability: Placing stands closer to the centreline of the vehicle, often facilitated by using wishbone mounts, can improve overall stability. If one stand were to fail, the vehicle would tilt rather than fall completely, potentially giving the operator a chance to react.
Practical Application: Placing the Stands
When using the wishbone mounting point, the process typically involves:
- Locating the correct jacking point on the car's sill or chassis, as specified in the owner's manual.
- Using a hydraulic jack to lift the vehicle at this designated point.
- Identifying the wishbone mounting point on the suspension assembly. This is often a stout bracket where the wishbone pivots.
- Adjusting the height of the axle stand and carefully positioning its head under the wishbone pivot point. Ensure the stand's saddle conforms to the shape of the mounting point.
- Slowly lowering the jack until the vehicle's weight is fully supported by the axle stand.
- Repeat for the other side of the vehicle.
Safety Tip: It is often advisable to leave the jack lightly in place under the jacking point, even after placing the axle stands. This provides an additional layer of security, acting as a backup should the axle stand fail unexpectedly.
Comparative Analysis: Subframe vs. Wishbone Mounts
To summarise the key differences and considerations:
| Feature | Subframe Jacking Point | Wishbone Mount Jacking Point |
|---|---|---|
| Structural Integrity | Generally strong, but not always designed for concentrated stand pressure. Risk of deformation or slippage. | Engineered to handle significant dynamic and static loads. Often provides a more secure seating surface for stands. |
| Stand Fitment | Can be hit or miss. Lips and edges may not mate well with stand heads. | Often features curved surfaces that complement the shape of axle stand heads, reducing slippage risk. |
| Vehicle Stability | Can be stable if placed correctly, but placement might be further out, potentially leading to a greater tipping arc. | Often allows for placement closer to the vehicle's centreline, potentially improving stability and reducing the severity of a fall if a stand fails. |
| Accessibility | May be more exposed, making them easier to access but also more vulnerable to accidental impact or theft if left unattended. | Can be more recessed, offering some protection and potentially being less obtrusive. |
Frequently Asked Questions
Q1: Can I always use the wishbone mount?
A1: While often a good choice, always consult your vehicle's owner's manual or a reliable repair guide. Some suspension designs might have specific reinforced points on the subframe or elsewhere that are intended for support.
Q2: What if my axle stands don't seem to fit the wishbone mount well?
A2: If the fit is poor, do not force it. Re-evaluate the subframe for a suitable, flat, and stable jacking point, or consider using a different type of support, such as a block of wood (ensuring it's strong hardwood and placed correctly) between the stand and the subframe, though this adds complexity and potential for error. Prioritise a secure fit above all else.
Q3: Is it safe to lift the entire car on just two axle stands?
A3: Yes, it is standard practice to lift one end of the car (either front or rear) and support it on two axle stands. For full access underneath, you would typically lift both front and rear, supporting each end with two stands, for a total of four. Ensure all stands are rated for the vehicle's weight.
Q4: Should I use the suspension spring perch as a jacking point?
A4: Generally, no. The spring perch is part of the suspension and not designed to be a static support point. Using it can damage the suspension components or lead to instability.
Conclusion: Prioritising Safety and Stability
While the subframe might appear to be the most logical place to put axle stands due to its substantial size, the reality of vehicle engineering often favours other points. The wishbone mounting point, being specifically designed to handle significant loads and often offering a superior mating surface for axle stands, presents a more secure and stable option for many vehicles. By understanding the structural nuances and choosing the appropriate jacking points, you can significantly enhance the safety of your DIY repairs. Always remember to use the correct equipment, follow manufacturer guidelines, and never compromise on safety when working under a vehicle. The correct placement of your axle stands is not just good practice; it's a life-saving measure.
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