Auto Union D-Type: Under the skin of Nuvolari's last winner

As Nuvolari’s mount heads for Christies’ saleroom and a probable record price, we investigate the science behind this legendary pinnacle of pre-war racing car engineering

Auto Union D-Type V

C & G's careful restoration of an original D-Type, driven by Nuvolari and Müller, demonstrates the high quality of Auto Union's engineering

Audi

In grand prix racing’s most potent demonstration of yin and yang, the six seasons leading up to WWII were both a golden era for the sport and one malign component of the dark political stain then spreading across Europe. The spectacle of silver German cars crushing foreign competition was not just a public demonstration of Teutonic engineering superiority but a metaphor for what was to come.

Although the Nazis sponsored both Mercedes and Auto Union, and the two teams fought to best one another, they weren’t equally blessed in respect of overall budget and facilities. Depending on your viewpoint, the Mercedes cars were either jewels of engineering or exemplars of how engineering for its own sake can be an indulgence. It was as if the drawing office was always setting stiffer challenges to the machine shop. Auto Union had to cut its cloth, and its metal, more abstemiously but its cars were still handsomely built.

While it is tempting to draw a line direct from the pre-war Auto Unions to the Cooper T51 of 1959 and conclude that it was they who truly began the rear-engine racing revolution, actually the contrasts are clearer than the similarities. The engineering focus of the post-war garagistes like Cooper and Lotus was not on milling metallic art forms but beating the opponent by being cleverer where it mattered: by designing cars that handled and gripped and cleaved the air better.

Auto Union D-Type IV

Parts for car were rescued from behind the Iron Curtain

Audi

Even the D-Type Auto Union, designed to meet the halved 3-litre supercharged engine formula of 1938 and fitted with a De Dion rear suspension to replace Professor Porsche’s dastardly swing axles, was far from espousing such principles. With still copious power and torque, narrow tyres, a high centre of gravity and sit up and beg driving position, it remained a car which few drivers could master. The Cooper was cruder, yes, but smarter.

For insight into the D-Type I talked to Dick Crosthwaite, whose company Crosthwaite and Gardiner has been restoring pre-war German GP cars for decades, and alone is sanctioned by Audi to build Auto Union replicas.

Origins

“It was through Neil Corner that we began working on pre-war German GP cars. He acquired an Auto Union with a broken con-rod and we got the job of restoring the engine. Later Neil acquired a ’39 grand prix Mercedes which we reunited with an engine from the Cunningham Museum.

From the archive

“Out of the blue we then had a telephone call from someone in the States who had two Auto Unions in pieces. That was Paul Karassik, who had been trawling about Russia for 10 years buying anything he could find that was Auto Union. One was clearly a late car, the major components of which were almost complete. And there was a good smattering of parts for the other. We got both up and running as quickly as we could to take them to the Eiffel Classic meeting at the Nürburgring.

“Mercedes was already there when we arrived, with crowds of people watching their car running in the pit garage. So to make an impression, we decided to start both the Auto Unions at once. The Mercedes pit emptied, and you couldn’t get near the Auto Unions the rest of the weekend. One was eventually purchased by Audi and the other one by a private buyer.

“When the cars were finished I suggested to Audi that we make some replicas of the earlier 16-cylinder car. Audi agreed to pay for all the patterns and we got them to borrow the V16 car from the Munich museum so that we could copy parts from it. Audi also acquired the 16-cylinder hillclimb car from Riga, which gave us everything that we needed to build the replicas.”

Driving

Auto Union D-Type

D-Types aren’t thought the easiest to drive by some

Audi

“I think the Auto Unions, including the D-Type, are horrible to drive because you sit far too close to the steering wheel. The cockpit is very cramped and you can’t get any feel for the car as a result. If the seat were further back I think you would have better control. The first time I drove the D-Type at the Nürburgring I spun at the first corner. I didn’t think I was going that fast, and there was no warning. But then I’m not a proper driver and the tyres were probably evil. The Mercedes W154, the D-Type’s contemporary, is a lot better. You haven’t got a lot more room but you sit in a more relaxed position.”

Crankcase

“The 12-cylinder crankcase is basically the 16-cylinder’s but with two cylinders lopped off either end. When we first produced a 16-cylinder crankcase, the foundry had problems with porosity in the main oil gallery, and there was a lot of aggravation with one main bearing – you’d drill to put a stud in it and break into a chasm. The guy at the foundry said it was always going to contract like that when it cooled. Then when we had a really good look at an original, we found there was a lot of welding in exactly the same place, so the factory had obviously had the same problem. We got over it by casting in a steel tube and drilling into that.”

Bearings

“Although Auto Union used full roller-bearing crankshafts and, in one of the later V12s we’ve seen, plain mains with roller big ends, we fitted plain bearings throughout in the first V12 replica we’ve just built because of the use it will be put to.

From the archive

“You have to warm up the roller bearing engine very carefully otherwise the rollers can skid on the crank, that can generate enough heat to bind the cage to the rollers and then the whole lot trips up.

“In an ideal world you’d probably pour hot oil into the engine before starting it. They are so expensive to make, those cranks, that it’s crazy to risk breaking them.

“It probably costs £30,000 to make a roller crank for the D-Type.”

Brakes

“Auto Union braking was supposedly ahead of Mercedes because it used four leading shoes rather than two, so that there were four cylinders on each drum backplate. And the shoes were fairly flimsy, so as the drum moved through heat expansion, the brake shoes could flex and follow it. On the D-Type the shoes are enormous, 2.5in wide. I think they realised that a larger diameter drum just makes for higher rubbing speed and doesn’t always help. There are twin master cylinders on the Auto Unions, one operating the front brakes and the other the back. You can alter the balance, but that wasn’t something the driver could adjust. There is a little rocking bar between the pedal and the master cylinders which was made with different ratios and could be changed in a few minutes.”

Dampers

Auto Union D-Type III

Nuvolari took his final top-tier win at Belgrade ’39 in a D-Type

Audi

“The early Auto Unions used friction dampers all round. The D-Type had hydraulic dampers on the front, whereas the back has both friction and hydraulic dampers. Probably this is because the lever arms were carried over from the V16, so the integral friction dampers were left in place. If so then they probably ran them fairly slack and relied principally on the hydraulic dampers. Or maybe at places like the Nürburgring, with all those jumps, you needed more damping than the hydraulics alone could provide. The friction dampers have shrouds around them, presumably to stop oil blowing on them and ruining the damping effect.”

Carburettors

“One of the carburettors on the Karassik car had a Star of David scratched on it, so we knew it was original. The jets are enormous: with the air filter off you can see spouts of fuel as thick as your finger. The weir-type carburettor that was supposed to have been used on 1939 cars is a mystery. Denis Jenkinson researched and felt it was to do with Bosch, but nobody could find out any more. Pictures have turned up lately, showing it is different from the Solex, so it existed, but how it worked and what advantage it gave we don’t know.”

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