New guy here. I am doing the shake down inspection on
  my new 360 and can not get the main gear to lock when
  I open the dump valve. The nose works fine and the
  left worked OK until I put new seals in the cylinder.
  Everything swings very smoothly if I disconnect the
  hyd lines. It seems to me that the overcenter springs
  have no strength. I can easily move them and they seem
  shorter than the ones that I see in some of your
  pics.The hydraulic system works fine under power.
  Everything comes and goes as it should in the
  barn.Thanks.

Jim,

 

Welcome to the hi-speed herd.

 

1.  With the dump valve open, crack the nose gear overcenter link and push on the nose gear - you should have at least a 25 pound push to start that gear aft.  If not, get a new gas spring.

 

2.  The over center main gear springs were never meant to apply any more force than that necessary to keep the over center link locked.  It should take no more than 2-3 pounds pushing outward on the gravity decended main gear to get it to lock.  BTW, any "unlocked" gear should not light the locked light.  Make sure nothing is binding and the moving parts are lubricated.  Look for binding in the entire main over center link, especially at the end that is attached to the spar - this end is like a rod end and can rotate fore and aft somewhat - it can bind a bit as can the fwd and aft pivots (spherical bearings also).  Look to make sure the actuator rods are not bent.  Look to make sure the main gear pivot bar (between the fwd and aft spar) is not bent.

 

3.  Make the in flight check.  Slow to 87 KIAS, pump and relay breakers pulled, gear sw to down, open the dump valve.  Doors should snap open, nose gear should come down and lock smartly, mains should drop more slowly and the plane should be skidded (slipped) to easily lock any main not already locked.  If there are any problems (nose not locking, sticky main, etc.), fix them.