I've set up mechanical retracts on a few planes now. First off, BillS is right on about the spongy linkage. Make sure the pushrod is secured with a sleeve of some kind (like golden rods). However, travel cannot be set be the radio, as you use a retract servo, which is either on or off, no travel adjustment. A retract servo travels 180 degrees, and is only using power when it moves. When it is at either end of it's travel, the servo is 'off', so as not to constantly pull down your battery. You are using a retract servo, right? If you aren't, then there is no way you will ever get the mechanical retracts to work. Standard servos only work with air retracts.

Hitec sells a nice retract servo.