Pete,

If you put 120 PSI directly to the brakes (not through the valve) it should lock the wheels (or close to it) - at least as far as turning them by hand. Does it? I have MM wheels and brakes on my Euro, but I flushed the MM valve and went with the UP-6. The brakes are very positive although I don't think I can actually lock the wheels with the plane on the gear - especially if it has a lot of fuel left on board. Maybe the valve isn't providing the full 120 PSI to the brakes...

Bob