Since my Y belt tensioner worked out so good I decided to make a belt tensioner for the X axis. It works the same as the Y belt tensioner and has a similar design. I've tested it and it works perfectly.
There's also a X motor mount to go with this
X motor mount: http://www.thingiverse.com/thing:1730523
Y belt tensioner: http://www.thingiverse.com/thing:1704100
Y motor mount: http://www.thingiverse.com/thing:1704123
What you need
Use everything from the old bracket. The extra you need is:
10x M4 T-nut
1x M4x40 screw
1x M4 Nut
1x M4 washer (optional)
How to install
Mount and install the same way the old bracket is installed. The pulleys are installed into the mechanism without the lock washer and the nut. Use only the screw and the lock nut.
M4x40 goes through the mechanism and the backplate.
M4 Nut is pressed into the turnwheel.