I have BMW e39 525tds with manual transmission, but i want to change it to automatic transmission. what type of transmissions should i use? or i can use any e39 automatic transmission?  

I'm not a professional but with some research for my  E39 m5 transmission from manual into automatic or semi-automatic.Here's what i found yes,it can be converted from manual to semi-automatic or automatic but with considerations:
a) it would be pretty costly considering that aside from the physical
alterations that have to be made to the pedals, tranny mounts and
probably propeller length, you would also need to get
the proper tranny to handle the power of an M5;
b) you need to install an EGS (tranny module), which your current
wiring system can not accomodate, so you also need to replace
your engine harness or at the very least jury rig additional wires
(and of course, program/code the car anew);
c) after conversion, your M5 will no longer be an original M5 but
some kind of a freaky M5 which most would not buy (if ever you
decide to sell it later on);
d) if you are thinking of converting into an SMG, the prospect
boggles the mind but there is nothing impossible, provided
you can find somebody capable of doing it, and provided
also that you have lots of dough.



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