[Gowza]

go through your run up at a slower pace and make sure you focus on that elbow and keeping it straight, it's tough to give much useful feedback without being able to see you bowl but obviously if you're chucking then it means your elbow is flexing and the only way to fix it is by zeroing in and focusing on that elbow and making sure it doesn't move. so as i said earlier my first suggestion would be to do some drills but at a much slower pace than normal then when you've done that quite a few times start to move through the motions a bit quicker until you get used to doing it at full pelt.

repetition is the key, the best way to train your body to not chuck is by practising a legal method as much as possible, the more repetitions you do with the correct action the more your body will remember (muscle memory) and the easier it will get.