Resolving the mystery of the cog

Sifting through some nutsy-boltsy happy snaps recently I came across something I had long forgotten. I’d taken the shot of a 1994 McLaren-Peugeot, one of the largely unloved MP4/9 cars campaigned by Martin Brundle and Mika Häkkinen. Martin finished second in one at Monaco – where the Finn had qualified second-fastest. Mika also finished third at Imola and had a couple of fourth places, so the cars were perhaps not quite as poor as many might recall.

Formula 1 engineering is so often beautiful – sculptured intricacy always conceived, designed and crafted against the clock. but on the right side of the MP4/9’s transverse gearbox was an attachment I didn’t recall, and could not understand. Mounted there, out in the breeze, heat and quite likely flying grit and spray, was what a Devonian special-building pal of mine would have called “a girt big cog”. this mystifying mechanism bugged the hell out of me, so at the british racing mechanic club’s Brooklands bash I showed the photo to McLaren veteran Neil Trundle, who instantly put me out of my misery. “Ah”, he said, “no mystery, Doug – that’s the reverse gear!”

The smaller gear the photo shows is also the layshaft nut which was torqued-up with a specially made pin socket engaging the gear teeth. The layshaft also had a coarse spline machined within this end to engage a long external starter probe which had to be inserted from behind, under the car’s tail. the probe had a small 90-degree drive at its tip which engaged with the layshaft splines – so it had to be inserted from the rear and then jiggled left to mate up. “Quite a delicate operation,” neil recalls. “The reason for the compact 90-degree drive was because of the car’s stepped floor, which also eventually killed off the transverse ’box or we might still be using them today.”

The larger external gear wheel visible was on the end of the transverse gearbox’s mainshaft with its driven gears and final-drive pinion, which drove straight-cut to the final drive and diff. These two outer wheels didn’t engage each other, a small third gear obviously being needed between them to achieve change of direction for reverse. This was a small external gear mounted in a hydraulic actuator which slid it into engagement when required.

“The whole mechanism relied on a patient driver to gently ease in the clutch to back out of a slip road (which mika managed to do) or it would destroy the gears. It’s the same now with all formula 1 car reverses – ask Jenson.” Eell, well – we never cease to learn.

Doug Nye