Lower Rear gear door not closing completely

[ET57C]

On a recent flight in my 1979 P337H the gear took a long time to retract. Low fluid was the problem and has solved the issue. Since then I have noticed the lower rear gear doors do not fully close. There is a 1/4" gap on both outboard sides. Previously if the plane sat for a few weeks these same doors would sag down open but as soon as the master switched on they would close tight. That same thing happens now but they are not fully closed. I can push the doors closed easily, the 1/4". When I pump them open to inspect, they are rigid with no slop or give. My mechanic has adjusted the rods but that did not make a difference. The issue is not to an adjustment but seems to be hydraulic. Reading the service manual it describes every possible gear problem but this one. There is mention of solving some problems with bleeding the system. I would think when the gear pump reservoir was low, it was caveating, while trying to get gear up and possibly allowed air in. I could not find anything in the service manual about bleeding the system. Has anyone had this issue?

[Kim Geyer]

I would check the accumulator

[ET57C]

Could you be more specific.

[Learjetter]

It’s possible the pump cavitation put air in the system and some is trapped in the door actuator. Assuming no leaks anywhere and everything else working normally, read everything in the service manual about the gear system. After you’ve identified the locations of all the parts, and know the gear up/down process, consider talking this over with your A&P:

Remove floor coverings and pilot side floor plates & tunnel plates. Service the accumulator with 500psi nitrogen. Open the doors with hand pump, ensure reservoir is full, then jack the aircraft. Put the gear up and see how doors close. If still unsatisfactory:

Controversial part #1: Crack open the door actuator hyd hoses one at a time until fluid runs out while raising and lowering door. Tighten hoses. The idea is to get any trapped air out of the system at the actuator.

Then manually move each gear leg and door up and down almost to the locks multiple times,and keep adding fluid to reservoir as needed. Slightly overfull reservoir is better than slightly low. Then run the gear system with the handpump.

Controversial part #2: It is possible to pump gear both down and up. Pull 30A HYD CB and put gear handle up with battery ON and use handpump to pump gear up and close doors. Put gear handle down and turn off battery and pump gear doors open and gear down.

After a couple of those, hook up external power and reset the CB and run the gear up/down with the power pack several times while keeping reservior full. To fully bleed the system just takes lots of cycles. Cycling the gear and doors manually and with the handpump varies the local pressures and speeds of hyd fluid and may shake loose stubborn bubbles. The air will leave the system via the hyd overflow by the nose gear.

[ET57C]

Thanks for that detail. I will take your advise to my A&P. and will report back.