Technical
Albrecht Stachel – My Mind’s Made Up
We Are So Screwed – The Nuts and Bolts of Restoration
A basic key to success in the automobile hobby is an intimate knowledge of how parts are fastened together. One of the best ways to gain that knowledge is to take a car apart. I recommend that this be a parts car, not one you want to restore or improve – after all, you want to be driving that one. Careful disassembly yields buckets of fasteners that can be used for any future project: trim screws are rare and irreplaceable, and unless nuts and bolts are heavily corroded or damaged, they can be cleaned and replated to look new and ready to re-use. My main concern is, of course, the nuts and bolts for the construction of Mercedes-Benz cars built after World War II, and how these have changed over the years.
Form follows function
Methods for fastening and joining parts have been evolving since the first time sinew was used to bind a stick to a rock. Pegs became nails, nails morphed into rivets, screws and bolts. Ancient peoples used screws to transport water and construct pressure presses, but the sheet metal screw, as we recognize it, first appeared in medieval Europe to secure plates on protective armor and replaceable components in firearms.
The virtue of the screw is that, by distributing friction over the length of the thread in what is in essence an inclined plane in miniature, it can join two pieces of relatively thin material. This distribution of friction is ideal for joining and fastening sheet metal parts together – automobile construction has used these methods from the beginning. Industry has developed a plethora of fastener styles and shapes to suit every purpose, with accompanying variety in strength, surface finish and size.
At the beginning, screws were driven with a blade-head screwdriver inserted in a slot on the screw head. Cross-head Phillips screws, with the advantage of self-centering the screwdriver, were introduced in the United States and first used on the 1936 Cadillac, but were not immediately adopted in other countries. I have seen Phillips head screws in models as early as the 1953 300SL Gullwing, but Mercedes continued to assemble the 300 series of sedans, coupes and cabriolets using slotted screws of all descriptions. After all, German armorers had used slotted screws to secure the helmets of grand jousting armor in the 1500s, so slotted screws were certainly still satisfactory to create the top-of-the-line Prunkwagen (magnificent vehicle) in the postwar period.
Through 1962, some W189 300d trim was fastened with wedged and spiral nails. With the introduction of the W110, W111 and W112 fintail cars, Phillips head screws became the norm, but whether due to conservatism or thrift, slotted screws did not disappear.
Methods to drive fasteners changed during the past 50 years, as well. In the old days, one only needed a decent set of slotted and Phillips head screwdrivers to service an entire vehicle’s complement of screws. As power tools became more ubiquitous, however, star-drive, double-hex, and Torx-headed fasteners were introduced, as well as a world of specialty fastener heads (see sidebar), all requiring new tooling. Many of these new driver methods provide the advantage of better tool engagement, which is admittedly useful during removal of stuck or rusted fasteners. Nevertheless, I must admit that a level of nostalgia sets in whenever the Snap-On man comes by with a new set of screwdrivers for the next family of proprietary fasteners.
More alarmingly, traditional fasteners are disappearing from the market. This should concern every reader who owns a Mercedes built before 1992. Fasteners we need for our work on the cars of the 1950s and 1960s are simply no longer available. Chromed round-head slotted trim screws have vanished. German industrial (DIN) specifications are being merged into those of the International Standards Organization (ISO), leaving many DIN fasteners altogether unavailable – even from German manufacturers – as well as from Mercedes-Benz itself.
In fact, all sorts of chrome-plated and other formerly common German fasteners are difficult to come by these days, and they cost like the dickens when found. For example, one may certainly still purchase from Germany a new set of the most needed chromed fasteners for a W186 300 – for more than $1,000. If industry in general is not building equipment requiring these screws, nuts, and bolts, then none of them will be produced; with no demand, supply vanishes and the price of remaining stock skyrockets. I will take this moment to remind you – if you service or disassemble a vehicle, save every fastener.
More with less
In the 1960s, stamped spring steel J- and U-nuts became universal throughout the cars’ sheet metal, replacing cast nuts and bolts in light- and medium-stress-bearing applications. These work rather well, allowing sheet metal screws to align with floating spring steel retaining clips. The technique eases installation, saving time during factory assembly and reducing material costs – nice and efficient. With less metal used in the new fasteners, they were bound to be a money saver compared with the old nuts and bolts. Money saved on manufacturing has historically translated to funds available for research and development: The new S-Class alone cost 10 billion euros to bring to market. Contemporary construction techniques rely evermore on cost-saving measures.
Another evolutionary change in fasteners has been the downsizing of nuts and bolts. DIN standards have changed and sizes consolidated: 19mm hex-head bolts changed to 17mm, 14mm hex heads shrank to 13mm, 11mm dropped to 10mm, and 9mm fasteners essentially vanished. Manufacturers realized they could do more with less. The castellated nut with cotter pin yielded to nylon lock nuts in the mid-1960s. I have also noticed that the lock and spring washers previously used under nuts and bolts are generally eliminated these days. Single-use, stretch-to-yield fasteners are now the norm inside of engines. Remove these fasteners from service and they’re done; new ones will be necessary for reassembly. And, my, oh my, the called-for “torque-to-angle rotation” is a frightening affair. One gets the sense that if one messes up one of these bolts, there will be a world of pain.
Samples of the complex range of fasteners used on classic Mercedes-Benz automobiles.
Better living through chemistry
Assembly efficiency, cost control, and ongoing customer dismay at corrosion often seen at trim mounting points – due in part to vibrating metal fasteners “seeding” rust – has ushered in a large range of proprietary plastic doo-dads to hold all sorts of stuff on our cars. As well as reducing metal-on-metal corrosion points, these one-time-use plastic clips and push-on fasteners are much more easily installed under assembly line conditions than the old nuts, bolts and screws. These plastic clips, snaps, and compression fixtures will present a future hurdle for the automotive-restoration business should any of today’s models retain value for collectors.
Adhesive construction employing fewer welding points and fasteners is also the norm for the future. Fewer metal contact points reduce the possibility of corrosion, making panel bonding ideal. Surface contact between adhesive-joined panels is nearly 100 percent instead of being concentrated at weld points, yielding a stronger bond and nearly eradicating corrosion – capillary moisture draw between the two metal surfaces is eliminated. It is my understanding that Daimler AG is now embracing this new construction method, as well as continuing to reduce the use of steel body panels altogether. These techniques reflect negatively on the possibility for conventional restoration of today’s models, although they are so modular in their construction that many structural components that once would have been welded together from smaller pieces now can simply be swapped.
In the final analysis, today’s automobile-construction strategies certainly allow for more strength and durability. It is clear that the latest generations of Mercedes-Benz vehicles are competently reaching 200,000 to 300,000 miles of service, but fatigue and deterioration will still take their toll. In my opinion, the concept of restoration will be decreasingly relevant for Mercedes automobiles sold since 1992. Mercedes models available through the construction of the W124, W129 and W140 series cars can be refurbished, but not all of those models will be worth the effort. Some models built since then may be worthy of preservation and conservation, but the new construction techniques and design philosophies employed after 1995 will not prove to yield many restorable automobiles. That’s not to say one should not enjoy the current offerings: All Mercedes-Benz cars, right up to the current year, are fantastic – a joy to own and drive. I own a 2004 E500 4Matic wagon and believe it to be a spaceship. I will joyfully drive the wagon until it collapses and then go out and buy another one to park next to my restored 1952 300.