Cars are complicated machines, and if you're not familiar with how everything works, then fixing them can seem like an impossibility – especially if you can't identify exactly where you're having the problem. If you know that your issue is with the gearbox or transmission, then you've already narrowed it down significantly. Now narrow it even further by checking off this list of common issues and getting in touch with professionals at a place like Stork Gears & Services.
If your gearbox seems to be working fine but sounds very noisy, then this is a clear indicator of an upcoming problem. These can be difficult to diagnose to the untrained ear, so it's best to take it in for repairs at this stage. Do this sooner rather than later; the noise tends to mean that parts which should not touch are grinding together in some way, and this can create wear issues that turn into serious problems very quickly.
If your car won't go into gear, or actually slips out of gear while you're driving, then there's a strong chance it could be related to your fluid levels. Your gears need a good amount of pressure created by this fluid in order to change; if there's not enough fluid in the system, then that's a big problem. You may simply need to top it up, but keep an eye on the level moving forward, as you may have a leak. The fluid could also be old, low quality or burned, in which case it will need to be changed. There could be many other causes too – but this is a common solution.
If you're having trouble pressing or depressing the clutch, or it's impossible to shift gears even when the clutch is fully down, then that's a serious issue and one you're unlikely to be able to tackle yourself. The clutch is composed of a lot of moving parts, any of which could have a problem; it's best to simply hand your car over to the repair shop at this point.
Of course, there are hundreds of different things that can go wrong with your transmission, and it may well be that the answer to your problems is not on this list. In that case, you should take it in to be diagnosed and repaired as soon as possible. If it does turn out that you need another gearbox, then be sure to go for a high-quality one; although it may seem like you're saving money, replacing your gearbox with a cheap part that will wear quickly is a recipe for more expense in the long run. Treat yourself and your car right, and don't let that happen to you. Good luck!