Diagnostics & repairs for the Running Gear category in Car Mechanic Simulator 2015 is probably one of the most difficult and complex parts of the game. This guide covers a very wide variety of the parts, and it overlaps almost every other category. Knowing how to find the faulty parts, what tests may be helpful, and how to find the elusive faults are keys to success.
As with the other parts in Car Mechanic Simulator 2015 it is quite easy to see if the part is defective, assuming you can actually see it. And that is one of the big problems with running gear problems. Many of them are hidden.
With that being said, it is surprising how far a visual inspection can go. Move the camera slowly as you inspect under the car. You can often see a hint of rust poking through even if the part itself is hidden. An example is the wheel hub, which is almost completely hidden. However its bolts and nuts are visible from the back side and may show rust.
Another quick way to find many running gear problems that are otherwise hidden from the eye is to pop off the wheels. With them off you can see wheel hubs, caps, bearings, and various axle components. Don't forget that in the suspension crossmembers you will also find rubber bushings. Each one has 4 of these rubber bushings, and if you look across the top you should be able to see a thin line of rust around them if they are defective. Rubber bushings also hide in leaf springs (easily visible from the side) and in some of the wheel knuckles (usually hidden behind a suspension part).
There are two tests that can really tell you a lot about possible running gear problems, but they can't always get everything. The first test is the Test Drive, while the second test is the Path Test. These two tests can help you find the vast majority of running gear problems quickly enough.