Home Focus Feature Understanding Two-Post Hoists

Understanding Two-Post Hoists

by Digital Mayne Media

The average Australian car parc has evolved significantly over the years. We are now seeing long 4WD dual cab work utes, electric vehicles and of course the emerging market of very large American utes.

Many shops still run hoists designed in the ‘80s and ‘90s. Are they safe to lift contemporary vehicles? Let’s take a look at the loads and design parameters of modern two-post lifts and how they may or may not be suitable for safe lifting.

Safe lifting of vehicles should be a safety priority for every manager within the management chain of any workshop lifting vehicles. Safe lifting starts with using the correct hoist for the correct application. Obvious factors include the safe working limit of each hoist, its safe use and ensuring you comply with maintenance requirements. The less obvious consideration is what type of two-post is suitable for the vehicles you intend to lift.

Two post hoists are available in many different configurations. Many manufacturers have different styles of two-post hoists available. To understand what each hoist is suitable for we will need to discuss the different styles of two-post hoist and the terminology behind each hoist.

Uneven pad loading and arm slipping are the primary reasons a vehicle may fall from a hoist. Pad loading is the weight bearing down on the lift pad (the rubber pad which we locate under the vehicle). This is normally designed into the vehicle by the manufacturer.

The spread of weight over these pads needs to be as even as possible – ideally 25 per cent of the vehicles weight on each pad, however the manufacturer of the hoist will have a recommendation of pad loadings displayed as a percentage of vehicle weight such as 60 per cent front pads and 40 per cent rear pads loaded. Many hoists have this on a decal on the side of the hoist. If this is followed and the arm restraint locks are functional it will be extremely difficult to lose a vehicle off of a two-post hoist assuming there are no modifications to the vehicle.

The challenge is achieving that when lifting modified large utes and still staying within the design parameters of the hoist (60/40 weight split). Following manufacturer recommended lift points on the vehicle will ensure correct pad loading (assuming no aftermarket accessories are fitted or the vehicle has no tool tray body on the back). Deviations from standard vehicle conditions are primarily where the risk lies when lifting vehicles. In other words, lifting dual cab utes with loaded canopies and trays.

Due to the popularity of the “clear floor” (baseless) type of hoist we will only discuss this configuration (no obstructions on the floor between the posts – no drive over hump). Assuming there have been no modifications to vehicles we can assess two-post hoists with the following considerations.

ASYMMETRIC POST, ASYMMETRIC ARM TYPE OF TWO-POST HOIST LIFTING A STANDARD VEHICLE
This hoist has rotated posts with a shorter front arm and longer rear arm.

The asymmetric arm combined with an asymmetric post is the most popular style of hoist in the market for good reason. It offers significant advantages for the majority of vehicles. The lifting arms are stowed folded together toward the rear of the vehicle. This allows clear unobstructed access around the front wheel when the vehicle is on the ground (before arms are located under the vehicle or after the arms have been removed). It allows the vehicle to be positioned further back on the hoist. When combined with a rotated post it aids significantly to door opening clearances and access to the vehicle’s interior. This type of hoist generally requires 60 per cent front lift pad loading and 40 per cent rear lift pad loading. Disadvantage – potentially higher post and floor bolt loadings.

SYMMETRICAL POST, ASYMMETRIC ARM TYPE OF TWO-POST HOIST LIFTING A STANDARD VEHICLE
This type of hoist has posts which face each other with a shorter front arm and longer rear arms. It offers similar advantages to the asymmetric arm, asymmetric post hoist. It varies in the way the arms are stowed. The front arms are stowed facing forwards, the rear arms stowed facing rearwards.

This hoist does not have the advantage of unobstructed access to the vehicle. This means a technician must work ‘over the top’ of the stowed arm.

Generally, this type of hoist requires 60 per cent front arm loading and 40 per cent rear arm loading. Similar post and floor bolt loading as an asymmetric post, asymmetric arm hoist.

SYMMETRICAL POST, SYMMETRICAL ARMS
This type of hoist has posts which face each other and equal length arms front and rear. It has a 50 per cent front arm loading with a 50 per cent rear arm loading. The vehicle is considered safe to lift when the weight is in balance between the posts. Its disadvantages are that it does not share the benefits of an unobstructed workspace as the arms are stowed facing front and rear (not folded together). It also does not offer the benefits of having easy access to vehicle interiors. However wider set posts on these types of hoists can increase vehicle interior access as the vehicle can be set further forward between the posts, possibly opening the front doors fully. The obvious cost here is to workshop space. Very little post loading.

In summary, all these hoists are safe if used within their design parameters. Problems start to occur when liftingutes with heavy laden toolbox bodies or canopies as this significantly changes the weight bias on the vehicle. More weight in the back makes the back heavier throwing the vehicle’s centre of gravity rearwards. A vehicle with a rearward weight bias being lifted on a hoist which requires a frontal Asymmetric arms with asymmetric posts Asymmetric arms with symmetric posts Symmetric arms with symmetric posts weight bias is where the problems start.

One solution may be to back the vehicle onto the hoist (this would require confirmation from your hoist supplier). Another solution is to source hoists with arms long enough to allow the vehicle to be positioned far enough forward to bring the centre of gravity more in line with where the hoist was designed to carry its weight (60/40).

Entry level hoists or older designed hoists generally have shorter arms and struggle to achieve the correct weight loading of the hoist. Some hoists offer better arms as an option – this may be worth investigating and or investing in.

If you have any queries, please feel free to reach Don McEvoy at [email protected]

Don McEvoy is a qualified mechanic with more than 25 years’ experience in automotive equipment. He is currently a business partner in the equipment importer, supplier, service company Next Tech Equipment.

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