337D : Gear extension took "forever" out of Annual

[AV8ing]

Aviators : First flight following the Annual Inspection, 1965 337D Model, the gear retracted normally but the extension took way too long.
I didn't time it but I'd say it was pretty close to a minute.
No other anomalies noted.
I should add that the left rear main gear door actuator was opened up to repair a small leak, and the hydraulic reservoir was replenished before flight.

Any ideas what may have caused this ?

[Frank Benvin]

Maybe air in the system . After the repair did you cycle the gear several times Open the doors on the ground and start up and close the with gear handle Also after these close hold gear handle down for a few seconds to cycle pump then try and see if you can add more fluid. I did this for the first few flights after we rebuilt actuators and replaced hoses

[hharney]

Originally Posted by AV8ing

Aviators : First flight following the Annual Inspection, 1965 337D Model,

1965 Skymaster is a straight 337, maybe late in the year it could be an A but not a D

[n86121]

The system is supposed to be self-'burping.'

While on the ground, cycle gear handle down.
That pressurizes and cycles everything.

Better to find an issue before takeoff, than after.

It should pop back to neutral down position within around 4 sec when warm out.
In winter maybe 6-8 secs

If it takes much longer, the system may be low, and/or there is probably air in the system.

Top off until it drools out the bottom of the drain under front engine,
Wash rinse repeat.

It can take a while to burp itself happy.

[B2C2]

I have found that for my mechanic, the hydraulic mule that they use for gear swing checks sucks hydraulic fluid out of the system when they shut it down. I always check that they have topped the fluid after they do this, as I had the same experience you did with slow gear action after annual when they first started doing this and check showed low fluid level. You said you topped the fluid, but I would check it again and perhaps drain and fill in case there is air trapped in the system somewhere.

[AV8ing]

FOLLOW UP:

First off, as Herb pointed out, this is a 1968 "D" Model, not '65 .

TRoubleshooting the problem on the ground - performed the hydraulic pump "isolation" test, ie. pumped gear doors open, then started just one engine, and low-and-behold, rear engine hydraulic pump is TU .

Anyone have spare pump the'de like to sell , otherwise who is the "go-to" shop for overhaul these days ?

Thanks!