Clunk sound and fail massage on reverse
 

Hi, my car is bmw e60 530i 2004 177km, the car drive normally but when I put the transmission on reverse a clunk sound occur and a transmission failsafe activated massage appears, the car moves on reverse but it sticks on the third gear on forward, when I turn it off/on return to work normally, I tried to disconnect the battery without help, gear shift normally on forward and the problem occurs directly when reverse selected, any idea please.

Thanks.

If it's going into failsafe then there has to be a code that's being thrown. Posting the code will help you get better responses. Other than that we can guess at it and say get under the car and check the guibo (flex joint) and your fluid. Other than that then we are just guessing.