Mercedes-Benz W125 – 1937 Silver Arrow

2014 Drive-My

Even in top gear, the torrent of power is relentless as the exhaust ricochets off the trees. Driving the fearsome Mercedes-Benz W125 is an honour, but to take it back to the fabled Nordschleife is the ultimate test. Mick Walsh lives his dream – Photography by Tony Baker.

The guardian of the only working Mercedes-Benz W125 in the factory collection is chief mechanic Manfred Oechsle, a distinctive mustachioed character who never seems to take off his Tyrolean hat. Few know more about the 1937 Silver Arrow because he’s dedicated to its preservation and history. Amazingly, though, after years of fettling chassis 6, he has never driven the beast. That fact more than anything underlines the massive privilege of a chance drive in my all-time favourite racing car.

Since childhood, I’ve fantasized about sitting where Richard Seaman commanded this muscular 580bhp single-seater. And nowhere could be more appropriate to try the W125 than the fabled Nordschleife – the challenging 12.9-mile circuit where it was originally tested, and where this sensational supercharged monster raced twice during its single competitive Grand Prix season in the final year of the epic 750kg formula.

Mercedes-Benz W125 - 1937 Silver Arrow

Of the 11 W125s built, just five survive and, of the three owned by Mercedes, chassis 6 is the most original. Chassis 9 is a static exhibit in the Musée National de l’Automobile at Mulhouse, France, and chassis 2 belongs to Bernie Ecclestone but has never been seen working in public. “My dream is to restore the second W125 in the museum to running order,” says Oechsle as he prepares and checks ‘my’ car for warming up.

Just after dawn on a chilly, cloudy April morning, the W125 has been unloaded in a temporary paddock near Meuspath by the Nordschleife’s long straight. The exotic cocktail of fuel is poured into the huge tank inside the W125’s beautifully sculpted tail. It’s not advisable to breathe in fumes from the mixture of 40% methyl alcohol, 32% benzol, 24% ethyl alcohol, and 4% gasoline light. Just imagine the high-octane aroma that privateer Maserati entrant Laszio Hartmann must have inhaled while sitting at the back of the grid behind three rows of C-type Auto Unions and W125s at the Eifelrennen on 13 July 1937.

Mercedes-Benz W125 - 1937 Silver Arrow

Mercedes-Benz W125 - 1937 Silver Arrow

Clockwise: W125 roars up to Kesselchen; two-eared spinner; blown motor sucks mixture from its twin carbs; plate confirms type and engine number.

After the pre-start-up check, Oechsle climbs into the cockpit while his assistant aligns the external starter motor, which sits on a special platform box with a long shaft slotted through the hole in the grille to engage with the nose of the crankshaft. Oechsle gives the OK signal and the starter whirs away. Even in the cold morning air, the mighty straight-eight wakes instantly with a deafening roar that startles birdlife for miles around and alerts residents in the village of Nürburg. The W125’s wild roar is mesmerising, and the devilish blast of massed 1937 titans thundering away from a Grand Prix start must have been incredible. When the oil is warm, Oechsle steps out and retrieves his specially made wooden sparkplug box that’s shaped to fit neatly on the scuttle between the long louvered bonnet and the ’screen. As well as holding the hard plugs that now replace the soft warming-up set, the box contains a few original pre-war items including a unique two-forked tool that releases the W125’s clever flush panel-fasteners. Like every detail of this brutal beauty, the engineering and build quality is stunning.

As the last preparations are made for my run, I learn that rain is due and the north side of the circuit near Adenau could already be wet. Senior engineer Gert Straub looks apprehensive, but I assure him that I have no intention of making the headlines by crashing their prized machine. My refusal to wear a modern lid amuses the team, but I insist on a period cloth flying helmet, as worn by Mercedes aces Caracciola, von Brauchitsch, Lang, Seaman and Kautz at the W125’s ’Ring debut for the Eifelrennen. But at Oechsle’s insistence, I agree to fit earplugs. “It’s important that you are smooth with the throttle, otherwise you’ll oil the plugs,” he advises. “Get into second before you really accelerate, but for the rest of the track you’ll only need third and top. Doubledeclutch and don’t drag the pedal. Don’t pump the accelerator when you come back into the pits: just switch off immediately and let it coast.” Finally, I step over the low side and drop into the well-padded cloth seat. The sparse, spacious cabin suits my short 5ft 7in height, which contrasts with the lofty 6ft 3in Seaman who amazingly also felt comfortable here. As in other GP rivals, the broad wood-rimmed, four-spoke steering wheel is alarmingly close to your chest, but more worryingly there’s a mysterious openended tubular bar sprouting from the lower bulkhead that’s aimed directly at your left shin.

The cockpit looks exposed but the round scuttle – topped with just an aeroscreen – effectively protects you from even high-speed draughts down the main straight. The flat, vertical, engine-turned dashboard has just three instruments: a large rev counter in the centre, flanked by smaller oil- and water temperature dials. The lack of an oil-pressure gauge is surprising – Oechsle suggests it was to save weight, but I’m glad of one less distraction. There’s also a small screw-in handle that feeds grease to the water pump. That would have been used on longer events such as the gruelling Grosser Preis von Deutschland, which ran to 22 laps of the ’Ring and 3 hrs 46 mins for winner Caracciola. To the right of the seat is a beautifully made gearlever, with four ratios in a conventional H-gate. First is towards the driver and forward. The action is slick and easy, but the gears are almost redundant with so much torque – 632lb ft at just 3000rpm.

Mercedes-Benz W125 - 1937 Silver Arrow

Lightweight Dural body. Below right: bigger drums than W25, twin leading shoes at front and rear.

Following pre-war GP tradition, the throttle is in the centre – with the brake to the right – but there’s little chance of getting them mixed up with such a responsive accelerator. Briefing over, the starter is again plugged into the striking streamlined nose and Oechsle gives the thumbs up for me to push in and turn the ignition key for the magnetos. With covers over the front, the engine has retained some warmth during the plug change and it roars eagerly into life once more. The hairs on the back of my neck become charged as the strident ‘eight’ resonates through the 749kg racer. The mechanics quickly clear and I am finally waved onto the famous track. In first gear, the throttle response is fierce and, as instructed, I change swiftly up to second gear to ensure smoother control.

Clear of the pitlane, I push down deeper for the first time and the pick-up is staggering. With rear tyres spinning, we spear down the tarmac. You’d need a ’60s dragster or a Can-Am McLaren – both 30 years younger – to match this pre-war legend’s surge. Traction from the de Dion rear end is surprisingly good, but the limitation is always the narrow crossplies fighting the monumental torque. Sitting near the back axle, you feel exactly what’s happening. Jochen Mass, who drives the W125 more than most of the trusted driving team, says that you can spin the wheels at 120mph in top gear even in the dry. The prospect of the next 13 miles – and a wet track ahead – has my heart pounding faster. My right hand trembles as I slot through the gears. Power delivery is smooth and seamless from just 1500rpm to the instructed limit of 5000 – provided you can keep your foot from shaking. Quickly we arrive into the tight bypass link above the modern circuit and here, past the concrete pitwall, the harsh exhaust sounds furious as we accelerate towards the sharp left into Hatzenbach. This section is familiar from playing Forza Motorsport on my son’s Xbox, but nothing prepares you for the physical thrill of following in the tracks of the Mercedes heroes. I was initially amazed by the lightness of the steering, but the action soon loads up as the pace quickens. Seaman and Caracciola never look particularly muscular in old photos, but their upper-body strength must have been immense to cope with three hours around the rolling, bumpy Nordschleife. Thankfully, the surface is smoother today.

Mercedes-Benz W125 - 1937 Silver Arrow

Below: Caracciola en route to victory in German GP; slick four-speed gearbox is largely redundant with 632lb ft peak torque developd at just 3000rpm.

Before unleashing the W125’s fearsome power on the fast run to Flugplatz, I test the drum brakes hard into Hocheichen. Despite the hefty push required on the far right pedal (don’t forget the centre throttle), their feel and stopping power are reassuring, particularly when matched to considerable engine braking as you lift off.

After three kilometres of this awesome circuit, I start to feel more relaxed about this daunting machine. The key is definitely braking early because overconfident entry forces the nose to drift out – a nerve-wracking development on such a narrow track, with so little run-off area. Mass has told me that there’s nothing nasty about the handling and that it’s never caught him out – even in the wet. Reading the corner and feeding in the power smoothly from the apex produces a rewarding drift in the faster open bends such as Aremberg, where I know it’s straight beyond, but it feels a handful through the twisty right-left-right. Every time I accelerate out of a clear bend, the ferocious mid-range punch has me shouting expletives in the cockpit.

Mercedes-Benz W125 - 1937 Silver Arrow

Walsh powers through Döttinger Höhe; radius rods control torque and brake reaction in de Dion rear set-up. Below: neat key to unlatch fasteners.

No pre-war car has ever had this effect. Historic racer Colin Crabbe – who won two VSCC Richard Seaman Trophy events in a W125 at Oulton – said that it felt as balanced as his old Maserati 250F but with twice the power. Little wonder he trounced the quickest ERAs first time out.

After the tricky-handling W25, the stiffened chassis and more compliant independent suspension of the W125 must have been a revelation. No doubt the brilliant direction of Rudolf Uhlenhaut, a gifted young engineer who joined in late ’36, was the key to the team’s turnaround.

The new recruit could really drive, too. Frustrated by the limited technical knowledge and poor feedback from the racers, Uhlenhaut began to evaluate the cars himself. Around the ’Ring – he’d spent years here pushing production cars to the limit – Uhlenhaut discovered that he was almost as quick as the aces, which earned him huge respect. Early testing revealed that the ’36 car suffered from a weak chassis and stiff damping, causing it to jump all over the place. “On one occasion, I lost a rear wheel at top speed on the straight,” Uhlenhaut recalled to Silver Arrows historian Chris Nixon, “and the chassis was so stiff that nothing happened. It was just like driving a motorcycle combination.”

Mercedes-Benz W125 - 1937 Silver Arrow

Clockwise: magnificent side profile of last 750kg titan; Oechsle’s bespoke plug box holds warm-up and race sets; straighteight weighs 250kg, a third of car’s total; oil- and water-temperature gauges either side of rev counter.

Uhlenhaut’s revisions, with softer, longertravel front suspension, a new de Dion rear set-up and an improved gearbox, were the critical developments that made the W125 much less challenging. Hermann Lang’s early success at Tripoli must have shaken up rival Auto Union.

When the W125s arrived at the ’Ring for the first of two major events in ’37, they’d also beaten the rear-engined C-types at the Avusrennen. With Uhlenhaut’s vast testing experience at the venue, it would have been fascinating to have seen him race, but his talents were far more valuable in the design department to risk him in action.

As I blast along the fast run to Kallenhard – and the midway drop to the Adenau bridge – I try to picture two Silver Arrows chasing through this difficult section. A nip-and-tuck battle played out between Caracciola in the new W125 and Auto Union star Rosemeyer in a C-type in the early stages of the Eifelrennen. The two masters chased clear of the rest – and swapped the lead several times each lap – but Caracciola tried too hard and his rear tyres were down to the canvas by lap five. He just managed to limp back to the pits, leaving Rosemeyer to a clear win – much to the frustration of the Mercedes-Benz directors and friends in specially booked seats.

Rosemeyer was to prove the only challenge to Mercedes-Benz during the ’37 season. The Eifelrennen was the debut race for the Saugvergasermotor, which sucked mixture from the carburettors rather than blowing pure air into them (Druckvergasermotor). The new engine was fitted only to the W125 of fresh Swiss recruit Christian Kautz, while the others used the older engine for the last time. Never again would the signature banshee wail of the supercharger exhausting through the flap-valve into the atmosphere be heard in action.

Mercedes-Benz W125 - 1937 Silver Arrow

With miles of the Nordschleife tarmac now spattered with unsightly graffiti – and lined with Armco in place of the original dense thicket – it’s hard to connect with moody images of the ’37 races. But as the course rapidly climbs from the double apex at Bergwerk through the sinister woods and morning mist to the Karussell, the track at last looks more authentic. Here, on the straighter stretches, it’s safe to unleash more grunt, and the torrent of power is relentless even in top gear – particularly when enhanced by the furious exhaust ricocheting through the dense woodland. It’s close to 140mph at 4000rpm, but the chassis feels stable and tracks superbly.

Thankfully, rain hasn’t reached the circuit as we spear into the bumpy dip of the unmistakable banked hairpin. From here my focus is a smooth line through such legendary turns as the blind right Wippermann, and the fearsome descent of Brünnchen. I savour that glorious surge of power for the final corners. Too quickly the main straight appears and, as I blat into the last mile, I start thinking about Seaman’s tragic battle with Auto Union rival Ernst von Delius.

Seaman made a poor start, but by the seventh lap he had caught and passed von Delius for fifth yet couldn’t shake him off. As they slipstreamed at about 170mph, approaching the Antonius Buche bridge, von Delius pulled out to pass. The airstream deflected the German, who brushed the hedge and, after over-correcting, shot clean across Seaman’s bow. The C-type went through a field and ended up on the road outside the track, while Seaman looked to have sorted the situation before the W125’s nose struck a hidden post.

The resulting spin hurled Seaman out on to the track. At the point where I end my lap to coast in, their dramatic crash unfolded. Von Delius died that night in hospital, but Seaman was lucky to escape with a badly scarred face, heavy bruising and a broken thumb. His Mercedes was wrecked.

As the magnificent W125 cools beside the transporter, I sit quivering in the cockpit. Never has a car exhilarated me so much, and to drive it around the Nordschleife is as good as it gets. One lap here was overwhelming, but I couldn’t imagine how Caracciola felt after averaging 82mph for 22 laps to win the German GP.

Mercedes-Benz W125 - 1937 Silver Arrow

Anatomy of a technical masterclass

Hidden under the W125’s magnificent Dural bodywork, the engineering is a work of art. At its heart is the legendary roller-bearing F-motor, bored out to 94mm from the E-motor’s 86mm to give 5660cc. The dry-sump straight-eight features twin overhead camshafts driven by a rear geartrain with four valves per cylinder. The fabulous one-piece Hirth crankshaft has nine main bearings instead of the W25’s seven. The two-bladed Roots-type blower is mounted vertically at the front of the engine and driven by bevel gears from the crank. Maximum engine speed was still limited to 5800rpm, but output was transformed to 580 or 600bhp on the exotic WW brew. With 27 fewer horses but weighing 250kg less, the W125’s power-to-weight ratio shames even a McLaren F1!

The monster engine sat in a new, stronger tubular ladder chassis. Its front suspension featured unequal-length wishbones with a coil spring interspersed. At the rear was a new de Dion axle with the tube angled around behind the magnesium transaxle and located by a vertical ball that’s fixed on the tube, but was able to move up and down in a track in the back of the axle casing.

Torque and brake reaction on the rear set-up were controlled by radius rods. As revolutionary as the suspension were the hydraulic dampers.




Racing for the other side

British fans had little to celebrate in the pre-war GP years, but that all changed for the ’37 season with the news that Sussex-born Richard Seaman had signed to drive for Mercedes. Better still, they’d also get a chance to see him race the awesome new W125 in the Donington GP.

The season began with testing at Monza, but it seemed cursed. A succession of shunts included hitting a tree at Monza, a tussle with von Delius at the ’Ring and writing off another W125 at Pescara. His highest finish that year was second in the Vanderbilt Cup in America, but the biggest disappointment was being punted off by HP Müller’s Auto Union on lap two at Donington. Seaman’s last W125 drive was a demonstration at Crystal Palace on 9 October, filmed by the BBC.

“He tried to get to the top too quickly, and should have taken things a bit easier,” reckoned Rudolf Uhlenhaut. “He always wanted to be as fast as Lang and Caracciola straight away. If you’re always on the limit, you’re going to have accidents.” Seaman’s loyal mechanic Giulio Ramponi said: “He should have had a season with a less powerful car, such as the Ruesch Alfa 8C-35, before signing for Mercedes.” To prepare for the W125s, Seaman fitted bald tyres to his Lincoln and drove around London on wet nights.

Seaman crashed at the ’Ring after tangling with von Delius

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