Custom-made plastic bearings for Trabant wheel suspension

These are hard times for 30,000 "Trabis" in Germany. Spare parts for the GDR cult car are under threat of becoming extinct. Fortunately there is Frank Hofmann - a Trabi enthusiast from Zwickau, who has replicated wear-resistant parts. His latest coup: A pivot bearing bushing for the steering, made of high-performance plastic from the Cologne-based company igus and thus considerably more robust than the original.

An SUV with 400 HP, wide, high and dominant, weighing two tons. For many people such a heavyweight is a status symbol. But not for Frank Hofmann. The heart of the trained radio and television mechanic from Zwickau beats for another vehicle. It is small, modest and only 26 HP strong. We are talking about the Trabi - built by VWB Automobilwerk Zwickau from 1958 to 1990: the symbol of German reunification.

As a small boy, Hofmann fell in love with the GDR cult car, a Trabi 500, which belonged to his grandfather's neighbour. "For me, there was no finer car. I had particularly taken a liking to the rear end," Hofmann enthuses. "It was clear that one day I would be the proud owner myself. As a young adult, in 2000, an attempt was made to restore a defective Trabi. "I looked through spare parts catalogues for weeks. Terribly frustrating, because many parts simply no longer exist," Hofmann recalls. But crises are also known to be opportunities. "Suddenly I had the idea of becoming self-employed, with my own online shop for spare parts. “ Said and done! The shop Trabantenwelt.de went online in 2006.

Steering knuckle of a Trabant with pressed-in iglidur J plain bearings

The wear-resistant and maintenance-free iglidur J plain bearings are pressed into the steering knuckles.

Problem

It is very difficult to find spare parts for the Trabi. The required plain bearings also have a special geometry, which makes the procurement of newly manufactured spare parts costly. The bearings must also guarantee smooth running, be wear-resistant and withstand the loads in the steering knuckle.

Solution

With plain bearings made of the material iglidur J Trabant lovers have found a maintenance-free and lubrication-free solution that also offers an excellent coefficient of friction. With a special part, manufactured by injection moulding, it is possible to produce the plain bearings cost-effectively. This allows them to be matched precisely to the application.

"Many manufacturers offer production only from a few hundred thousand units upwards. I was therefore pleased that igus was able to produce much smaller batches economically as well".

Frank Hofmann, CEO of trabantwelt.de

30,000 Trabi owners are eagerly awaiting spare parts in Germany alone

Hofmann struck the mark. Trabi enthusiasts can be found all over the world - 30,000 vehicles are registered in Germany alone. And all owners sing the bitter song of spare parts supply. "I started out with three boxes in the cellar," says Hofmann. Today, 13 years later, Trabantwelt.de is market leader in Germany. "The spare parts fill three warehouses - from individual screws for trim strips, to hinges for boot lids, to entire chassis and tuning engines with 35 HP." Twelve employees take care of the shipping of the now 1,800 parts and ensure supplies.

The spare parts supply has its pitfalls. Example steering. Pivot bearing bushings for the steering knuckles and the pivoting wheel bearings are in short supply. "After the Wall came down, there was a warehouse in Werdau that was being cleared. We carried off the original bushings in shovels and had peace and quiet," says Hofmann. But then the shock in the warehouse when the blue box with the bushings was empty. What next? Imported goods made of simple plastic were out of the question, the quality is too poor, the service life too short. "We therefore wanted to have the components manufactured in-house. " And so Hofmann searched the Internet for a partner to manufacture the pivot bearing bushings.

Left GDR originals made of textile waste pressed with resin, right bushes from igus made of wear-resistant iglidur material

Cross racing as baptism of fire for plastic pivot bearing bushes

Hofmann found what he was looking for at igus - a Cologne-based company that has been specialising in the development of high-performance plastics for decades and manufactures batches and special bearings using injection moulding and 3D printers. "Many manufacturers offer production only from a few hundred thousand units upwards. I was accordingly pleased that igus was also able to produce much smaller batches economically ," says Hofmann.

And thus began the collaboration. One original bushing was sent by mail to Cologne. A construction drawing followed. A lathe produced a prototype. Hofmann wanted to test the prototype before high-volume production. The eight-hour stubble field race in Pausa, Saxony, was a perfect opportunity. The racing Trabants dash for hours over uneven terrain - a test of strength for the steering. A friendly racing team was able to convince Hofmann of an A-B comparison. In one vehicle the original GDR bushings were used, in the other, the bushings made of iglidur high-performance plastic. Which variant would prevail? After the cross race Hofmann lay down under the cars, eager to see how the bushings fared. The result was surprising. The GDR bushing took a beating, whereas the competitor from Cologne in contrast looked somewhat fresh. "That was a phenomenal baptism of fire," Hofmann rejoices. "For us it was clear from that moment on: The products are worth their weight in gold as spare parts. " And thus the high-volume production began.

The injection moulding process was used, in which molten plastic is injected through a nozzle into a closed tool and is allowed to harden. The injection-moulded plain bearings are even more robust than the machined versions. "With this quality, we almost shoot ourselves in the leg as dealers," Hofmann laughs. "The plain bearings are so robust that they last incredibly long. A customer who buys the bearings will not need another one so quickly. “

Steering knuckle of a Trabant with wheel suspension and pressed-in iglidur J plain bearings

Steering knuckle of a Trabant with wheel suspension: Pivot bearing bushings made of iglidur J high-performance plastic (beige) are pressed into the component.

High-performance plastic makes steering smoother

But what makes the difference in quality? The original bushings consist of textile waste pressed with resin. In contrast, the counterparts from Cologne are made of iglidur J, a high-performance plastic that igus developed in the laboratory. "The material has a density of 1.49 g/cm3 and a compressive strength of 35 MPa - this corresponds roughly to the pressure of two small cars resting on one index finger," explains Kevin Buettner, technical sales consultant at igus. The material is so robust and wear-resistant that it has become a popular alternative to metallic plain bearings in industry.

"The high-performance plastic is a mixture of a base polymer, fibres and fillers as well as solid lubricants," says Büttner. "The base polymer is crucial for the wear resistance. Fibres and filling materials also reinforce the bearing to absorb high forces and edge loads " Another advantage to the original bushings: The GDR product is hygroscopic. It absorbs water via its porous surface and swells up like a sponge. "Many Trabi owners therefore have to struggle with heavy steering," explains Hofmann. "A problem that the plain bearings made of high-performance plastic have solved. " The moisture absorption of bearings made of the polymer iglidur J is about 0.3% in normal climate. "The steering therefore remains permanently smoother. “

Visit to Trabantwelt.de in Zwickau: CEO Frank Hofmann (right) and Kevin Buettner, technical sales consultant at igus (left).

Users do not need to lubricate the bearings - they enable dry operation with the lowest coefficients of friction. Solid lubricants, microscopic particles, dissolve automatically, lubricate the bearings and reduce friction. There is another reason for Hofmann to recommend customers to lubricate the bearings anyway. Lubrication protects the steering shaft from corrosion.

Fast delivery directly from stock with no minimum order quantity

Hofmann no longer has to worry about the availability of the pivot bearing bushings. If the stock runs out, the CEO reorders the bushings from igus. The injection mould is stored and is available at all times. And the buyers are also enthusiastic about the products. "So far we have only received positive feedback," says Hofmann happily. And that is how it should be. "Tinkering with the Trabi is a hobby, a passion that should not lead to frustration. It's supposed to be fun!"

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Individually manufactured components from iglidur materials

iglidur J plain bearings

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