Make sure that your idle is set properly....when you shift into reverse, your "short" for the override button has already taken place. If your idle is not set properly, you are just "adding" to the short.
I hope this works!!.....also, a srock axle is $250-$280, depending on the vendor. I would also go with a Durablue axle. It is a little more money, but a whole lot more dependable!
My MX 400 Sport