This is a review that started more than half year ago. We tried to confirm that a strange phenomenon was not accidental, so as not to cause some misunderstanding. When this phenomenon was reproduced, we determined that it was a common problem. In some movies, precise shooters use scales to weigh their bullets for screening, a situation that is the result of poor bullet quality control. If you like this approach, feel free to read this.
In the limited parts evaluation in the past, febi Bilsten is a brand that cannot be bypassed because it is considered one of the top three brands of 140 parts quality (LEMFÖRDER is ahead). Of course, this website has not said too many good things about febi. The reason why it can be in the top three is that there are very few suppliers of 140 parts today, sometimes even the third one cannot be found. Today, we introduce the only option besides genuine part, which has a subtle relationship with genuine part.
The propeller shaft flex disc is a part used to connect the propeller shaft to the gearbox (front) and differential (rear). There are two same on each 140, only supplied as parts kit include bolts and nuts, for the V12 and early V8s, the part number is A1294100115. The part not only apply to 140, but many other models. It is essentially a heavy rubber cake inlaid with a bolt sleeve, which does not seem to have much technological content. As a rubber part, the typical failure is rubber cracking, as the screw sleeve itself will never go wrong. As the cracking becomes more serious, the disc will lose flexibility, causing vibration of the drive shaft and the car body during driving. Replacing this part requires disassembling the rear exhaust pipe and rebalancing the propeller shaft, so it is best to install long-lasting replacement part.
Febi Bilstein is the almost only supplier on the market that provides available flex discs, part number 03412. Of course, there are other manufacturers, but if they have been discontinued or even poorer quality products, they are not worth mentioning, so there is only febi. Genuine parts are still available at a very expensive price, and we use them as a benchmark to test febi. In our experience with febi, we found that sometimes febi does not produce the parts themselves, they usually only produce the boxes of their parts, at least for the 140. This means that febi is more like a sales company, most of the parts they retail are made by other manufacturers, and the parts themselves do not even have febi’s trademark at all. This is why when many genuine parts arrive in a nearly naked state, febi has a fancy red box – that is the only way to declare it’s a febi.
The febi flex disc is produced by SGF. SGF, headquartered in Waldkraiburg in Upper Bavaria, the company was founded in 1946 under the name “Süddeutsche Bremsbelag GmbH”. The range includes flex couplings in cardan shafts and steering columns, vibration absorbers in drivelines, exhaust hangers and dampers, and various rubber-to-metal parts for the mounting of different aggregates. The good news is that genuine parts are also made by SGF. When you compare febi and genuine, the only difference is that the febi copy has the Mercedes star burned off. OK, since this is not retailed by Mercedes, it is reasonable. What a relief, at this point we almost think we got a bargain, just losing a star and we can save 2/3 of the procurement cost. Who needs a $150 rubber star?
Let’s explain the purpose of the flex discs in the restoration process. We assume that all cars’ propeller shaft suffer from deflection and age after 200,000 km, which is a fact, so we send them directly to the shop that repairs them. Common problems reported by the propeller shaft shop include tooth wear and part ageing leading to loss of balance, so every time the teeth are repaired, parts are replaced and rebalanced. Even the propeller shaft that looks good show serious loss of balance in the test bench, so don’t trust your eyes and hands, the gap between the teeth will not be twisted out by hand. It is a time-consuming and expensive job, but it helps a lot to solve the NVH problems in a certain speed range. Compared to a new driveshaft, the total cost is less than 1/3 of it.
Last year we sent Octavius’ propeller shaft to the shop. I thought we had installed all the correct parts and torqued the bolts. Only the teeth needed to be repaired and rebalanced the shaft. Soon the shop called: Why did you install counterfeit parts? This made me laugh and cry. My first reaction was that this was almost insulting, the second reaction was that he was joking. What happened? Before I could say that these are the flex discs that almost the same as the genuine part, he told me that the hole spacing of the bolts were off spec. The dimensions of these adapters were easy for him to find, as anyone can find on Google: 110 mm. One part we sent was 108 mm, and one was 109 mm, he said. The 109 mm would work, but the 108 mm would not work.
What he meant by not working was that the 108 mm one would not fit into the existing flange of the test bench unless he made me a separate one with 108 mm spacing. This would cost more, but more importantly I still didn’t believe it, so I said: let’s stop, send me the parts back, I need to check it out. Before this I installed the discs to the shaft myself and torqued it, it fit, but it was a little tight, I tightened each nuts step by step to 60 nm. It was not a smooth fit, but I didn’t think about the spacing. And how much difference would 2 mm make to 110 mm? I don’t know if the temperature has affected it.
I immediately measured these brand new febi flexible adapters once I got them back, I even started to distrust the caliper, so I tried different ones. I soon learned that 108 mm is not close to 110 mm, no matter how different the calipers are, dude was right. The center hole distance can be calculated by measuring the distance between the two hole edges and subtracting the diameter of the screw hole, which is 12 mm, as they were designed and gauged by us. The genuine disc is 122 – 12 = 110 mm, which is exactly in line with the specifications. The febi is 121 or 120 – 12 = 109 or 108 mm. In the meantime I got a few used and new genuine discs, and they were all 110 mm, even though the well used ones had cracked like cookies.
Since the febi had been purchased for a while and could not be returned, I reordered 2 more. This put our propeller shaft project on hold for a while… This time I checked them as soon as I received them, and they were still 109 mm! Well, I returned the new febi pair and sent a pair of expensive genuine discs from stock to the repair shop. As for the febi, it had to lie back in the warehouse. Have a look at the difference before and after. Instead of balancing to 5 to 6 grams with parts that were out of spec, we can now get to under 2 grams, which is beyond most automotive factory accuracy.
However this incident was not forgotten by me, but it was not motivated enough to take the time to turn it into an article, until recently we dealt with febi flex disc again.
We were doing a propeller shaft refinement for another V12 again, this car had obvious vibrations between 80 km/h and 120 km/h, and all chassis parts except the propeller shaft were new. This car had traveled more than 300,000 km, and the shaft can’t be good. The reason it was left until last was because the owner didn’t believe in the function of the drive shaft. People always believe that replacing the bushings and ball joints will get a new car, but they ignore the things that are spinning at high speed next to them. After replacing the hanger and bridge bearing, it was sent to the repair shop for inspection. The flexible discs are genuine, and it had been installed for about 10 years but had not cracked. We sent it to the shop for inspection and waited for their suggestions.
After receiving the propeller shaft, the shop reported several problems. The first, tooth was actually not bad, compared to the 8 teeth out of 21 that Ocatvius got repaired, which was not fatal. The second was that the bolt sleeve of one disc was a little loose, and it was recommended to replace. So what? We ordered another febi from our supplier, send them directly to the shop. It’s rejected again! The hole spacing this time is only 119 – 12 = 107 mm !
It was a tactic to get our febi supplier and the repair shop to fight directly, so that the supplier would not question that I was joking with them, and the repair shop would not question that I deliberately gave them parts that were not in spec. The febi supplier never believed that there were febi that were not in spec before, and now they learned. I firmly believed that there was a febi with 109 mm or 110 mm hole spacing somewhere, so we let them keep looking. Well, they finally found us a 109 mm disc, but we really didn’t find any 110 mm. And every genuine disc is 110 mm. So far we have febi discs from 107 mm to 109 mm, different febi, diffrent dimensioin…
So SGF is like selling perfect discs to Mercedes and non-spec ones to febi. Maybe they can’t effectively control production accuracy and can only do it through screening, just like H&K got their G3 SG/1 barrels… Of course, the slight dimensional impact is subtle, few people will measure or even rebalance the shaft, so there will be no chaos. You can even imagine some PR language: put a smaller disc on for a while, it may become larger. Even if we rebalance the shaft, we are not automotive engineering experts, so we can’t say that febi is completely unusable. At least you have a chance to get a part close to the spec… New search found that SWAG is also supplying the same part. They use the same tactics as febi and rebrand the SGF part with their own packaging. We have ordered one to see what it is like.
Please note that all parts are brand new and purchased in recent times (2023 and 2024), they represent the current status of these manufacturers only and do not imply anything about the past or distant future.