Universal joints can be a weak point on crawlers or other RC off-road vehicles where a lot of torque needs to get to the wheel. The old style CV joints aren't much stronger, and worse they are quite severely limiting in terms of working angle. This can be alleviated by using portal hubs with a reduction or the new planetary hubs, but you may not have those parts or they may not be suitable for your application. If you have this problem, you might have wondered what can be done to strengthen a 3L universal joint. You can wrap bands or string around the connections to strengthen them: This will help to a degree as they won't snap so easily where the one in the first image has, but then you're just looking for the next weak link, and in this case it's the yokes which will spread and spit out the disc never to be seen again. You might like to try the new CV joints without using a planetary hub reduction. They're definitely stronger... ...but they are still a wear part. There are some aluminium universal joints listed on AliExpress. Unfortunately these are pretty janky. They are made of very thin aluminium (they say, but I'm not sure, maybe even cast zinc? ) and the tolerances are appalling. They are very loose on an axle, more so than an old CV joint. Right from new they have about 1/16th turn of free-play in them and in use, the steel pins will wear away at the softer bodies creating more and more play, until at around 1/8th turn of play the yokes can touch each other on each rotation. At that point, they don't have long left to live. Or you can try these better metal joints from Dark Ice Designs. These are not currently listed on the website  but they do have more listed on their eBay store. Pictured here compared with CaDa plastic and Chineseium metal U-joints (Yes I am aware that there are only 2x original Lego pieces in this picture, hopefully even the purest purists among us can get past that): They are basically 4mm steel-bodied RC universal joints chucked up in a lathe, and bored (very cleanly I might add) to 4.8mm. You then use a grub screw to clamp the axle in place, there's no cross-shaped hole here. There is so little free-play in these, it's basically zero. Certainly, they have less slop than a plastic joint has. There are some limitations: They are just the right overall length, but they are thicker, this may affect fitment in some models.  You can't quite get 1L of axle into the joint without it limiting the working angle, which may affect fitment in some models. They should just about take the short end of a 5.5L axle (particularly the newer ones with the slightly shorter stubs) cleanly. You can use them with plastic axles, but the axles will be scrap afterwards because they'll have a grub screw indentation in them. You can also order metal axles from Dark Ice. They list them in odd lengths only but can offer in other lengths against a custom machining fee. Be aware the metal axles have a 1mm rounding added to each end to be gentler to plastic pieces, this again may affect fitment in some models. Even if they're not pure, and even with their fitment considerations... I think this piece solves the problem of broken universal joints once and for all.