well the box thats in it wasn't able for the power obviously so thats going to keep happening. especially because its a drift only car, and i believe those paddle clutches are a bitch on the box too. try look ino getting an rb25 box is my opinion. do it once and do it right.
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If you are not going for big power (over 330) you can stay with rb20 box-its cheaper solution then rb25.You can buy a good rb20 box for less than 300 euro (best option is to buy a box that was already rebulit).
ur box has broken the end off the lay shaft coman problem fire it over a ditch and get another rb20 box put it in and away you go! no point in putting a 25 box in a stock car save your extra 300euro and buy coilovers for it!! then more power and at a later stage when the 20 box is fucked again then upgrade to a 25 box!! iv got an rb 20 box here if you need one