I was there : Testing new suspension on Sherpas

Freight-Rover-Sherpa

In the early 1970s it was thought that there would soon be a breakthrough in the manufacturing process for carbon fibre leading to a big cost reduction. Bristol Aeroplane Plastics were working on ideas for using the new low-cost fibres.

Leighton came up with the idea of manufacturing vehicle leaf springs and so they decided to make some prototypes. As BAP owned a Sherpa van, they designed and built a set of Sherpa springs,

The reason for changing to a composite was to save weight. Every kilogram saved from the weight of a commercial vehicle increases the payload by a kilogram making the vehicle more cost-effective. Alternatively, weight saving improves performance and economy and furthermore composite springs take weight from the unsprung weight of the vehicle which improves the vehicle’s ride and handling. The vehicle ride quality is also improved because the damping effect of the multi-leaf steel spring is removed.

GKN, the technology leader

GKN was, and still is, a major producer of car components especially CV joints. In the 1970s and ’80s they also made a lot of car wheels, chassis members and suspension components (for instance GKN Sankey made Land-Rover and Spitfire chassis, Transit subframes etc.).

So GKN devised the strategy of offering car manufacturers complete suspension assemblies, including wheels, CV joints and drive shafts, differential units, suspensions arms and springs. As we know with 10-15 years hindsight, this never happened, but the composite spring was a central part of this strategy.

GKN did a deal with BAP to productionise the composite spring. One of the most difficult areas was how to attach the rubber bush to the spring. If you imagine the composite material being like a very fine grained wood, then you can see that drilling holes in it and then repeatedly flexing it would lead to splinters and failure. The Engineers at GKN Technology in Wolverhampton came up with a clever way of clamping the bush to the spring without having to drill it.

GKN and Freight Rover join forces

This was in the early 1980s, GKN were in talks with Freight Rover (FR) about the supply of composite leaf springs as FR wanted to launch a revised Sherpa for the 1986 model year. It wanted to add a feature that would give the Sherpa a more high-tech image and gave GKN a letter of intent to order springs starting in mid 1985. On this basis, GKN built a production line in a corner of the Sankey site in Telford.

By mid-1985, all the durability testing had been completed both on test rigs and on vehicles and the vehicle ride and handling had been signed off. GKN found they could get the springs through a thousand miles of Pavé at MIRA but the rest of the vehicle was another matter.

For instance, the battery shook itself to bits so the GKN Engineers rushed down to the nearest Motor Factors for a replacement which was also shaken to bits in a matter of days. As it was superficially brand new, they took it back and got a replacement free of charge.

It wasn’t without issues

Engineering projects seldom proceed without any problems. At the eleventh hour FR found a brake steer problem on composite sprung Sherpas – during an emergency stop a RHD vehicle would veer markedly to the right. It also happened on steel sprung vehicles, but the effect was about five to ten times worse with composites (I know, I did the measurements).

At GKN we worked night and day on a solution, my friend Mike at GKN Technology in Wolverhampton built up a test rig with a complete Sherpa front suspension and steering mounted on a steel frame with hydraulic jacks to simulate the braking loads. Taking a series of measurements over the weekend, he spotted that the front axle bent backwards under simulated heavy braking, this in effect pulled on the steering causing the vehicle to veer off to the right.

The front axle was, and still is, a forging and had not changed since J4 days yet the allowable gross vehicle weight had gone up and up. Once this was demonstrated to FR they agreed to beef up the axle and the problem was eliminated.

Unfulfilled springing project

I also did a project to manufacture some prototype springs for the big Sherpa but this never came to a production order. Neither, unfortunately, did projects for Mercedes-Benz, Iveco or Chrysler, though Chrysler did order production tooling but never actually issued a production order.

The only other production vehicles using GKN Composite springs were the London Taxi Cab and a snow-mobile.

GKN Composites could not survive on such a low production level so GKN pulled the plug in 1991. Interestingly, some of the last development projects we worked on were transverse leaf spring suspensions for Mercedes-Benz, Volvo Car and Nissan and these eventually saw production but with composite springs from other suppliers.

Julian Donald
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5 Comments

  1. I believe some American “Muscle” cars of the same era used composite springs and composite anti-roll bars. The Mustang?

  2. If my memory is correct, the project was kind of reborn for the composite trailing links used on P38A Range Rover, the story I was told at solihull as a new start in chassis design was it was made by GKN as a leaf spring shape then cut into two trailing arms. I did a lot of abuse testing on them, they were incredibly strong

  3. I’m sure I vaguely remember composite leaf-springs being offered as a third-party replacement part for the old “series” Land Rover leaf-springs.

    Seems the idea never caught on and these days everyone uses Parabolics.

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