Long term under carriage problem
 

Hi all I would like to explain a problem and after sometime how I over come this
Problem.
My undercarriage would retract up light would come on for moment then off. Rear doors would be partially open.
Would check fluid level and might be bit low, top up and bleed system. All would be well for a while then same thing this went on and off for couple of years. But each time we jacked plane and tested all worked fine.
The problem turned out to be the left rear up switch not adjusted correctly but close enough that if you tested it it would mega as a closed switch.
Only in flight would the switch not close and only occasionally.
Hope this helps anyone with similar problem in the future.

Possible explanation - squirt your uplocks
 

It has been decades, but....

The doors will not close until all the uplock micro switches are all closed (wired in series),
which also turns the UPLOCK light ON.

This makes sure everything cycles in sequence correctly
and prevents doors from closing while gear still in transit (or not all the way up).

As I recall,
that uplock light circuit also allows the system to pressurize to 1200-1500 PSI.
When it hits that pressure limit it pops the gear handle down.
The handle goes down, the system at rest,
and all is well in the land....

In your case
the the gear comes up,
the uplocks close UNDER PRESSURE (but not solidly!!!),
the microswitches are closed (under UP CYCLE pressure)
the uplock light comes on (briefly),
your doors close,
then the light goes off
but the down handle never occurs.

I would bet a nice doughnut against a dollar your uplocks not solidly going 'CLICK'

So under UP-CYCLE pressure they the uplocks in position
CAN AND DO close the microswitches,
but wont keep the switches closed without the UP CYCLE pressure.

So the final pressurization needed to pop the handle never occurs.

-------

ANSWER #1: Check /squirt get to know your uplocks.

ANSWER #2: If the system cannot hit the 1200-1500 PSI to shut off,
it wont lock the system UP correctly.

Yes, a leak or air will do this.
ON THE GROUND, try cycling the gear DOWN CYCLE position.
If system can hold pressure it will pop the gear handle 'up'
from DOWN-CYCLE to the DOWN LOCKED position.
No leaks.

The system is 'self-burping' so a bunch of cycles will burp out the air.

I will accept any decent chocolate-covered doughnut as reward.

EXTRA CREDIT

I have replaced those little beasts with tiny screw in 24 volts LEDs
Nice, cool, will never burn out (again).

D

So, having flown only the "G," what model did the gear handle stop reacting to system sequencing? The "G" is easy, up/down, nothing moving or in-between.

Need to know what model you are dealing with here please

The original Skymaster thru model F had a mechanical gear handle that actuated the system
When Cessna built the G (1973) model it was changed to an electric motor to operate the hydraulic pump, therefore now the gear handle is just a mouse click