I took apart the diff and gearbox, cas I knew that one washer was installed vice versa(the two sides are not 100% simmetrical, one side being more round than the other) and put some more grease inside, just to be sure.
I was told that the diff was much too loose, so I've tighten it. It really changed the sound of the car, and I could make some wheelies :P ...soooooo nice
Still have some problems. The spur isn't turning straight. It turns a bit like a bike with an 8 in the wheel. How bad is that?
I have also changed the rear springs to some longer ones, from the spare shocks for my monster truck. (I'll try to put pictures with)
Please help me a bit with this spur issue. If needed I will make a video and upload it here.