In-line 8, MFI, power taken from a center gear on the crank between cylinders 4 and 5, no valve springs (desmo), 310 HP, 1900 lbs in 1955 - magnesium tubular chassis, 72 gal of fuel, 9 gal. of oil. Driver had the tranny between his legs. Sadly, it killed a lot of fans at Le Mans
"A hydraulic pump driven from the back of the transmission provided power for the second electrifying innovation of Le Mans: the air brake.
The 300SLR's air brake worked on a completely different principle than the rooftop brake that had appeared so dramatically and briefly in practice at Le Mans in 1952. It also kept on working reliably in spite of the tremendous forces it was asked to withstand.
The air brake's surface was formed as a second skin over the full width of the body just behind the seats. When it was down, a body-surface moulding along its front edge prevented air from getting under it and flipping it up prematurely. Made like an airplane wing with interlocking ribs and stringers skinned with light-alloy sheet, the brake was hinged at its rear edge to the inner frame structure of the car. It had a single small plexiglas window in it at first; a second was added at the request of the Le Mans scrutineers.
Two operating rods reached up out of the deck to connections on the air brake surface. The one on the left came from a shock absorber whose only chore was to damp the violent impact of the brake's opening at high speed. The right-hand rod came from the hydraulic cylinder that made it work. It was powered by engine oil, drawn from the main reservoir and brought to a pressure of 220 p.s.i. by a special pump at the back of the gearbox. From the pump the oil went to a control valve on the instrument panel, moved by a protruding lever, and then to the operating cylinder.
When the brake was folded down, pressure was automatically maintained on the piston to hold it in the `down' position. When the driver flicked the control lever up it prompted the cylinder to elevate the brake. After the car had been slowed and the corner taken, the cylinder was signalled to pull the panel down again either by a further movement of the control lever or by an interlock with the gear-lever gate, depending on the way the car was set up.
The brake panel, which included the headrest on its upper surface, had an effective area of 7½ square feet. Drivers found it to be very powerful, slowing the car at a rate of 0.31 g. at 175 mph, diminishing to 0.27 g. at 150 mph.
John Fitch first tried it at Hockenheim, where a full 24-hour Le Mans dress rehearsal was scheduled with the only complete spare 300SLR during the week before the race. The test was cancelled when the car was written off by a factory test driver, but Fitch had already noted that "an unexpected bonus from the new device was the stabilising effect it had on the car through fast bends.
"Since the centre of its air resistance was behind the centre of gravity of the whole car," Fitch concluded, "it felt as though the rear of the Mercedes was held into the curves against its normal tendency to drift out as if restrained by some invisible but delicately handled cable. Although there was a good deal of wind buffeting when the flap was up, the total result was most satisfactory." Like the men who designed the brake, Fitch was aware that it offered special advantages when the road surface was slippery, since its retardation was unaffected by road conditions.
Stirling Moss interpreted its effect differently when he first tried the air brake at Le Mans, saying that "this device increased rear-tyre adhesion due to aerodynamic download. I first discovered this download effect as the flap was on its way down after I had used it to slow into the tricky White House bends. With it still lowering and loading up the rear wheels I found I could apply the power earlier and harder than normal. I wrote in my diary, `The airbrake was fantastic!'."
Rudolf Uhlenhaut further elaborated on the advantages of the `wind brake' as quoted by Briton Rob Walker: "He said that if you were to take a course like the Swedish Grand Prix, where there was one corner which started as a very fast one, then suddenly tightened up on you; if you braked hard in the middle of the corner where it tightened up, it would naturally tend to send the car out of control, but if you used your wind brake in the same position it would tend to give you more control and hold the tail down, rather than making it difficult; in fact it generally helped the cornering ability of the car."
The Swedish G.P. at Kristianstad, the next event after Le Mans on the Stuttgart schedule, was the only other race in which the air brake was used. "