Hello George,

I had a somewhat similar problem. Mine happened only in the gear down
position. No problem with the gear up. Like you, I changed out the dump
valve and the pressure switch...no help. Finally I got some caps and plugs
for the hydraulic lines and fittings. One at a time, I capped off the lines
at the cylinders and pressurized the system at each step. When I capped off
the nosewheel cylinder, the problem stopped. I took the nosewheel cylinder
apart and found a scratch in the cylinder wall at the "down" end. With the
gear up, the scratch had no effect on the operation. With the gear down, the
scratch allowed pressure to bypass the piston, causing the cycling. A new
cylinder was installed and the problem stopped.

In your post you state: "> There are no leaks, the reservoir is full."  My
guess is that what you are saying is that there are no EXTERNAL leaks. You
probably do have an internal leak. It's never fun to break into the
hydraulic system, but put on some old clothes, get a BUNCH of rags, get some
caps and plugs and start trouble shooting. I'll bet you a beer that you'll
isolate one cylinder that stops the problem. Good luck.

PS:  I have a bunch of the caps and plugs. I'd be happy to loan them to you.

Bill Harrelson
5zq@cox.net
N5ZQ  320  800 hours
N6ZQ   IV   0.0001%  (wing jig tables built)