1955 Mk IX (T36/T37)

Introduced for 1955, the Mk IX represented the last real evolution of the Cooper 500. The car made its debut on Boxing Day '54 at Brands Hatch and helped Les Leston to clinch the title. For '55, the works cars were driven by Jim Russell and Ivor Bueb, winning 15 out of 28 races, and earning Jim the Formula 3 Championship with Ivor second by a point. Ivor also won the Irish Championship in '55 and ran his Mk IX under the banner of Ecurie Demi-Litre through 1956 and '57.

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The works Mk IX of Ivor Bueb, photo courtesy David Woodhouse.

The principle developments from the Mk VIII, were:

An overall lowering of the car. This was achieved by means of flattening the springs to lower the ride height, lowering of the scuttle and seat hoop chassis tubes and and by flattening the fuel tank (still above the drivers legs).

The introduction of a single, centrally mounted disk brake at the rear, replacing the pair of drums on each wheel. This reduced overall and un-sprung weight but caused mixed reactions from the drivers as, while the disk brakes are undoubtedly more effective, the mixture caused the front and rear brakes to "come in" at different rates.

Roll stiffness was introduced at the rear using a centrally mounted curled leaf spring as had been the practice at the front for the Mk VIII.. The leaf spring mounting rollers were moved further apart to 15 1/2 inches at the front and 12 inches at the rear to increase overall roll stiffness.

Detail of the final drive assembly showing the new single disk brake and fuel pump.

Cooper Mk9 Rear Brake Detail.jpg (61436 bytes)

The rear uprights were now made from magnesium alloy to reduce weight and the Armstrong dampers were re-sited to allow more vertical alignment (following Beart practice). The 18 gauge aluminium body was retained however Cooper did experiment with glass fibre mouldings. GRP was then in its infancy and early attempts were unsuccessful however later cars did appear with glass fibre bodies.

Overall the Mk IX was lighter, lower and slimmer than the Mk VIII. Wheelbase was 7ft 3in, front track 3ft 9in, rear track 3ft 7in. The height was only 2ft 7in to the top of the screen and body was only 1ft 11 1/2 inches wide. Officially the production cars weighed 530lbs dry with a Norton engine although works cars featured lighter chassis tubes. Ivor Bueb's car was reduced to under 500lbs to compensate for his 15 stone frame. The price was £620 without engine or £718 with a JAP 500 fitted. Two versions were offered for 500cc (T36) and 1,000cc (T37).

The business end of a Mk IX showing the Norton engine and megaphone exhaust. The roll spring can just be seen on top of the main suspension spring.

Engine view of Cooper Mk9 Norton may 55.jpg (49796 bytes)

Cutaway drawing by Theo Page.

Revised upright and hub as brake drum removed.

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Cockpit showing revised scuttle tube.

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Les Leston tries the Mk IX for size on Boxing Day '54 at Brands Hatch.

Ivor Bueb leads Les Leston (Beart Cooper) at Goodwood, Easter 1955

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Jim Russell in committed style.

Jim Russell in Cooper Mk9.jpg (347721 bytes)

By 1955, Cooper domination of Formula 3 was almost total with only Don Parker's Kieft offering any really consistent challenge. In line with Charlie Cooper's views on not changing something that was working so well, all subsequent Cooper 500 cars were almost identical to the Mk IX although new Mk numbers were issued each year.

David Woodhouse in the Ivor Bueb Mk IX, leads the Mk VIII of Gordon Russell and the Mk IX of John Turner at Goodwood in 2008

Charles McCabe's Mk IX at Monterey in 2006. Photo by Llew Kinst

You don't need a wind tunnel to see the bullet shape of the Mk IX