The backup Brabham behind a 50-year-old record

Change was on the cards in the Brabham world in 1970, though visitors to the launch of the BT33 - not a champagne gala but a here-it-is-mate unveiling in the Byfleet factory - would have been hard-pushed to spot much beyond engineering details and the new car's colours, as blue came in for green alongside the familiar yellow stripe. It was not widely known at the time that Jack Brabham had sold his shares in the company to his business partner and chief designer Ron Tauranac.

And why should it be? Neither man was known for their eagerness to engage in idle banter. As Tauranac 'posed' for pictures in the cockpit of the BT33, his first monocoque Formula 1 car, his expression was not that of a man freshly in charge of his own destiny but one thinking "Do I have to?"

In fact, the BT33 was not exactly new. The first chassis had been occupying a corner of the workshop since the preceding summer. 1969 had been tough on a company which had recently won two F1 world championships and enjoyed the profits of selling high-class machinery in the junior formulae: its dominance in F1 evaporated in 1968 along with the Repco V8 engine's reliability in quad-cam form.

Star driver Jochen Rindt left for Colin Chapman's Lotus while continuing to race in F2 with Roy Winkelmann Racing - which also swapped to Lotus chassis. Brabham's client roster was taking a beating...

Along with that, Jack himself was becoming aware that his finest on-track days were in the rear-view mirror, and that he had perhaps been fortunate to weather this dangerous sport without serious injury. For a man with an aggressive driving style this was remarkable. But he'd missed three races in 1969 after breaking his foot in a shunt during testing at Silverstone.

And Ron and Jack had always been an odd couple, Jack the 60:40 senior partner in the business but unwilling to dig too deeply into his own pockets, Ron simmering with quiet frustration at not always receiving due credit for the cars they produced. This inequality was built into the names of the cars: BT, for Brabham-Tauranac.

From its clandestine roots, Motor Racing Developments (a deliberately anodyne title since Jack was still racing for Cooper in F1 when MRD was incorporated) rapidly built a name for selling tidily engineered and fast racing cars. And if Jack insisted on establishing a separate entity, the Brabham Racing Organisation, so he could have his own name on his F1 cars, Ron was willing to wear it so long as the customer-car business was ticking over.

The BT33 was initially designed as a backstop in case the DFV couldn't be accommodated within the BT26, but when the older car proved super-competitive with the new engine, the BT33 chassis was parked

Tauranac had resisted following the herd towards theoretically lighter monocoque chassis during the 1960s, insisting that a properly engineered spaceframe design could be as light and rigid as any stressed-skin concept. There was a commercial imperative, too: spaceframes were easier and cheaper to repair after a shunt, rendering them more appealing to customers.

PLUS: How pragmatic principles made Tauranac a design legend

But the spaceframe was running out of development runway. It was the experience of designing the BT33's predecessor, the BT26, which provided the final nudge.

"We tried to make a lighter but stronger frame by using alloy sheet panelling instead of tubular triangulations," said Tauranac. "This allowed us to use smaller-gauge, thinner-section tubes for the basic frame, and the whole thing was built in a different way.

"Instead of making the bulkheads first and then joining them together in the jig, we laid down the bottom part of the frame on a flat bed, built the top deck immediately above it, and then put the side members in between.

"It worked OK, but it might have proved cheaper to build a monocoque in the long run..."

When Rindt left for Lotus in 1969, Ford signalled its willingness to furnish two highly prized DFV V8s to Brabham gratis provided a seat could be found for Jacky Ickx, whom it had wooed from Ferrari to join its sportscar programme.

The BT33 was initially designed as a backstop in case the DFV couldn't be accommodated within the BT26, but when the older car proved super-competitive with the new engine, the BT33 chassis was parked. Ickx won twice and finished second in the championship before deciding to return to Ferrari.

New rules for 1970 mandated that every car's fuel tank had to be lined with a rubber bladder to reduce the risk of leaks and spills in an accident, and it was this which tipped the balance in favour of monocoques. The BT33 design was pressed into service but, since the first chassis predated the regulations, its tanks could only accommodate 40 gallons of fuel (not quite enough for most circuits) once bagged. Later examples would be built with a more substantial girth.

Other design features betrayed the BT33's 1969 roots: Tauranac disliked having inboard-mounted coil-over-shock absorbers actuated by rocker arms because the rockers lacked the rigidity of a wishbone setup. But when high-mounted wings were all the rage - until they were banned during the 1969 Monaco GP weekend - it was thought the aerodynamic benefits of rocker-arm suspension outweighed the lack of stiffness.

While the overall shape and mechanical layout were largely carried over from the BT26, a key departure was the pair of Lotus 49-style air ducts at the front end

The first BT33's 'tub' had large box-sections at the front with which to mount the rockers and their paraphernalia, but at launch Tauranac didn't rule out reverting to wishbones.

While the overall shape and mechanical layout were largely carried over from the BT26, a key departure was the pair of Lotus 49-style air ducts at the front end. As with other Brabhams in various formulae, pipes directing water to the front-mounted radiator ran outside the car, at the base of the chassis, to minimise the driver's exposure to their heat.

The jutting chin of the nose aperture was a result of aerodynamic tests carried out with British Aerospace which suggested this reduced lift. As the DFV became virtually ubiquitous across the grid, tyres would become a key performance differentiator and rival designers would embrace the wedge shape, relocating the cooling apparatus further back to put more weight over the rear wheels for greater traction.

Having folded the operation of the F1 cars back into MRD and then sold his share of the company to Tauranac, Brabham was on the cusp of hanging up his helmet. He might have done so at the end of 1969 if Rindt could have been persuaded to return. But - with due reluctance, for he had a fractious relationship with Colin Chapman - Rindt stayed put for 1970, the deal greased by Chapman agreeing to support Rindt's baby steps as an F2 team owner.

The scene was set for Brabham's last rodeo. Helped by Chapman's decision to throw too many innovations at the Lotus 72, Brabham was among the frontrunners - in pace terms - from the off.

At the first round of the season, in South Africa, he claimed what would be his final grand prix win, overhauling polesitter Jackie Stewart's March. Engine failure consigned Rindt to retirement a few laps from the end.

PLUS: Jack Brabham's 10 greatest drives

The Lotus 72 made its GP debut at round two in Jarama but Rindt dropped the car in favour of the team's spare 49C, and again failed to finish. Brabham qualified on pole, and was running second and chasing down Stewart for the lead when his own engine failed. Ickx, who might have been a contender in the new Ferrari 312B, was eliminated in an accident early on in which his car was burned into a pile of twisted metal.

At Monaco Brabham slid out of the lead at the final corner but recovered to second, then neither he nor Rindt saw the chequered flag at Spa. Once the Lotus 72 was shorn of its torsion-beam suspension with rising-rate geometry it proved to be the strongest car in the field in Rindt's hands, and the Austrian embarked on a four-race victory streak mid-season before his tragic accident during qualifying for the Italian GP.

One of those wins came in the British GP at Brands Hatch, in which Brabham held a majestic lead until his car ran out of fuel on the final lap - a consequence of the engine's fuel mix not being adjusted from its richest setting after the V8 had warmed through. Brabham, incorrectly as it turned out, blamed and berated chief mechanic Ron Dennis for the mistake. Dennis took it on the chin and never let on that the true culprit was Nick Goozee, who eventually confessed many years later.

Post-Brands, Brabham lay second to Rindt in the championship; had Jack won there and at Monaco, and not been swindled out of potential victories by mechanical failures in the opening races, he might conceivably have been in the lead.

PLUS: The forgotten F1 car that could have been champion

Brabham was running third in the final round when his engine blew; years later he would express regret at choosing this point to retire from Formula 1, believing he had a few more good seasons in him yet

In the second half of the season nothing went right for him, epitomised by the Austrian GP in which oil disgorged from Francois Cevert's Tyrrell on the opening lap coated Brabham's visor and caused him to run off track. Team-mate Rolf Stommelen, driving chassis three (photographed here) took his highest finish of the year in third.

Rindt's points lead proved insurmountable and he was crowned champion posthumously. Brabham was running third in the final round when his engine blew; years later he would express regret at choosing this point to retire from Formula 1, believing he had a few more good seasons in him yet.

He was probably right.

SPECIFICATION

Chassis Aluminium monocoque
Suspension Rocker arms with inboard coil springs over dampers (f), reversed lower wishbones with radius arms and coil springs over dampers (r)
Engine Ford-Cosworth DFV V8
Engine capacity 2993cc
Power 430bhp @ 10,000rpm
Gearbox Hewland five-speed manual
Tyres Goodyear
Weight 550kg
Notable drivers Jack Brabham, Graham Hill, Rolf Stommelen, Tim Schenken

RACE RECORD

Starts 41
Wins 1
Poles 1
Fastest laps 4
Podiums 5
Constructors' championship points 41