06/09/2015
The classic Austin Mini, a true icon of British motoring, is renowned for its go-kart-like handling and ingenious engineering. A significant part of this unique driving experience, particularly in models from the mid-1960s and into the 1970s, was its innovative Hydrolastic suspension system. Often referred to as a "wet" suspension, this system replaced the traditional coil springs with a network of interconnected fluid displacers. But for owners of a 1970 Austin Mini Mk II Cooper, a common question arises: should you keep the original Hydrolastic system, or is a conversion to a more modern "dry" suspension advisable? This article delves into the nuances of Hydrolastic, exploring its benefits, potential drawbacks, and the crucial question of preservation versus modification.
What Exactly is Hydrolastic Suspension?
Introduced by Alex Moulton, the Hydrolastic system was a significant advancement in suspension technology for its time. Unlike conventional systems, it used a fluid, primarily a mixture of water and antifreeze, housed within displacer units. These units were interconnected between the front and rear of the vehicle. When the car encountered a bump, the fluid would move between the front and rear units, effectively cushioning the impact and providing a remarkably compliant ride. This interconnectedness also meant that when one wheel hit a bump, the suspension on the opposite side would react, contributing to the Mini's characteristic handling.
The core of the Hydrolastic system consists of displacers, often referred to as "pots." Inside these pots, a diaphragm separates the hydraulic fluid from a rubber spring. This rubber spring, often described as acting in shear, provides the primary springing medium. The hydraulic fluid, being largely incompressible, acts as the damping and also facilitates the fore-and-aft coupling between the axles. It's important to note that the springing medium is fundamentally rubber, not just hydraulic fluid, as some might incorrectly assume.
The Case for Keeping Hydrolastic
For owners of a 1970 Austin Mini Mk II Cooper, retaining the original Hydrolastic suspension is often the preferred route, especially for those who value originality and the authentic driving experience. Here's why:
- Originality and Value: A 1970 Cooper is a desirable classic, and retaining its original "wet" suspension system significantly enhances its originality. This can translate to a higher market value for collectors and enthusiasts who appreciate period-correct specifications. Conversion to dry suspension is often seen as a major loss of originality, diminishing the car's historical integrity.
- Unique Ride Quality: The Hydrolastic system offers a ride quality that is distinct from dry suspension setups. It provides a supple and comfortable ride, particularly at lower speeds, that many find very appealing. The interconnected nature of the system also contributes to a unique handling balance.
- Sympathetic Design: The Hydrolastic system was designed in conjunction with the Mini's structure. While issues can arise, the system was engineered to work harmoniously with the car's chassis.
Potential Issues with Hydrolastic Suspension
Despite its advantages, Hydrolastic systems can develop problems over time, leading to a less than ideal driving experience. The most common complaints revolve around the suspension becoming overly hard:
- Hard Suspension: A particularly concerning issue is when the Hydrolastic suspension becomes excessively hard. As one contributor noted, "When the rubber is hard, as it will be, there is basically no springing." This hardness is often due to the degradation of the rubber components within the displacer units. When the rubber loses its elasticity, it can no longer effectively absorb road shocks.
- Increased Stress on Chassis: A hard suspension places significantly increased stress on the rest of the car's structure. The lack of proper springing means that road impacts are transmitted more directly to the chassis, subframes, and suspension mounting points. This can lead to fatigue fractures in critical areas such as the top arm, subframe, bulkhead, or the welds connecting structural members. Over time, this can result in significant structural damage, potentially leading to component failure.
- Fluid Leaks: Like any hydraulic system, Hydrolastic units can develop leaks. This can be due to perished seals or damage to the hoses that connect the displacer units. A loss of fluid will compromise the system's ability to function correctly, leading to a saggy or uneven ride height.
- Degradation of Components: Over decades, the rubber components within the displacer units and hoses can degrade, harden, and lose their effectiveness. This is a natural process of aging for rubberised materials.
Repair and Refurbishment Options
The good news for owners who wish to maintain their Hydrolastic system is that repair and refurbishment are indeed possible. Several specialists offer services to bring these systems back to life:
- Displacer Hose Replacement: Companies like MiniMail have developed methods to replace leaking or perished hoses on Hydrolastic units. This is a critical repair that can address many common leaks.
- Reconditioned Units: It's also possible to obtain reconditioned or refurbished used Hydrolastic units. These units are typically pressure-tested, inspected for wear, and may come with new gaiters and hoses. They are often supplied on an exchange basis, meaning you trade in your old units for the refurbished ones.
- Specialist Servicing: Dedicated Hydrolastic (or Hydragas, its successor) services exist that can diagnose and repair issues with these systems. Websites like the one linked for Hydrolastic Service can provide further information on where to find these specialists.
When considering repairs, it's often recommended to keep your old Hydrolastic units even if you opt for a conversion. These can be invaluable to other Hydrolastic Mini owners who need parts for their restorations.
Hydrolastic vs. Dry Suspension: A Comparison
For those contemplating a change, a conversion to dry suspension (typically using rubber cones) is an option. However, it's essential to understand the trade-offs:
| Feature | Hydrolastic Suspension | Dry Suspension (Rubber Cones) |
|---|---|---|
| Originality | High (for period-correct models) | Lower (modification) |
| Ride Comfort | Generally more compliant and supple | Can be harsher, especially on rough surfaces |
| Handling | Unique interconnected feel, can be very engaging | More direct, can feel "sharper" but potentially less refined |
| Complexity | More complex system, potential for fluid leaks | Simpler mechanical design |
| Maintenance | Requires specialist knowledge for repair/refurbishment | Generally easier to maintain, parts widely available |
| Value Impact | Increases value on original cars | Can decrease value on historically significant models |
The amount of rubber used in the Hydrolastic displacer is comparable to that in a dry suspension cone. Both systems rely on rubber to absorb shock, with the Hydrolastic system using the fluid to manage damping and inter-axle coupling. The key difference lies in how this is achieved and the overall system's characteristics.
Frequently Asked Questions
Q1: My Mini's suspension feels very hard. What could be the cause?
A1: A hard Hydrolastic suspension is often due to degraded or hardened rubber components within the displacer units. This prevents the suspension from absorbing road imperfections effectively, leading to a harsh ride and potentially stressing the car's structure.
Q2: Is it true that a hard suspension can damage my Mini?
A2: Yes. If the rubber spring elements are too hard, the suspension effectively ceases to spring. This transmits excessive shock loads directly to the car's chassis, subframes, and suspension mounting points, potentially causing fatigue fractures and structural damage over time.
Q3: Can I convert my Hydrolastic Mini to dry suspension?
A3: Yes, conversion kits are available. However, for a 1970 Cooper, this is generally not recommended if you value originality and the car's potential value. It's a significant modification that alters the car's original character.
Q4: Where can I get my Hydrolastic suspension repaired?
A4: Several specialist Mini parts suppliers and mechanics offer Hydrolastic repair and refurbishment services. Companies like MiniMail are known for their expertise in this area. Searching for "Hydrolastic service" or "Mini wet suspension repair" should provide relevant contacts.
Q5: Are Hydrolastic units repairable?
A5: Yes, many Hydrolastic units can be repaired and refurbished. This often involves replacing perished hoses and seals, and sometimes rebuilding or replacing the internal rubber components. Reconditioned units are also available.
Conclusion
For a 1970 Austin Mini Mk II Cooper, the decision to keep or convert the Hydrolastic suspension is a significant one. While the system can present challenges with age, its contribution to the car's unique character, ride quality, and originality is undeniable. For enthusiasts and collectors, preserving the Hydrolastic system is usually the preferred path, especially since repair and refurbishment options are available. By understanding the potential issues and seeking out specialist help, owners can ensure their classic Mini continues to provide that distinctive, supple ride for years to come, maintaining its historical integrity and intrinsic value.
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