Gear down - doors stay open, pump running

[Learjetter]

Gang,
‘77 NA G-model, with gear door delete STC.

Interesting occurrence the other night. Took off to keep night current and, per usual, raised gear on 1st pattern. On downwind, lowered gear and after the customary 12 seconds, saw only the pump-running light I installed in 2021, no amber, no green. Looking outside i think the wheels were down and doors open (it was pretty dark). Opted to recycle gear. Same result. This time I pressed the green light and as soon as I did the doors closed and green light came on. Full-stop. Remove seat from my third point-of-contact and go home to read service manual.

The next day:
Jacked aircraft, got same result three times in a row (gear down, doors open, pump running) tapping green light closes doors and turns green light on. Using adequate ground power (24v charger/starter unit) to aid battery. Inspection of green light revealed loose pin. Downlock microswitches all appear normal, good action & rigging, satisfactory click. No obvious leaks anywhere and good reservoir level.

Got a spare green light (thanks M!) and replaced original. Today, Jacked aircraft again and ran gear 9 times over a couple hours with results #4 &#6 same as before with first 3 and the last 4 in a row textbook gear up in 12 seconds and gear down in 10 seconds. I’m suspecting maybe a sticking solenoid or failing pressure switch or leak in the power pack.

Gonna go fly and check it out in the air with 70A of 28.5V power available to the power pack, but wondered if you had any advice before I do so? Insurance is up to date (both mine and the airplane!)

Long term like this winter: (three trips scheduled before cold winter sets in): spend a cold month or two to pull and reseal every hydraulic actuator and replacing every flex line. Also plan to reseal power pack and accumulator and nose strut and shimmy damper. Logbooks don’t indicate anything ever being done except some flex lines when previous owner did the door-delete STC in 2009.

Appreciate any thoughts on the subject!
-LJ

[RandyArizona]

>>>sticking solenoid <<<
When was the last time both of them, (door and gear) were removed, cleaned, and the oring replaced?
Easy cheap stuff first.

[Learjetter]

Thanks Randy!

I’ll do both solenoids first, as logbooks have no record of the solenoids, or the power pack, or the actuating cylinders ever being done. It’s possible the aircraft has vintage 1977 hydraulic fluid in the lines!

Update: removed, clean and replaced packing (MS28775-014) on both solenoids. Jacked aircraft and ran gear 5 times in a row with no issues.
Instructions attached.

[Joes]

Any part numbers for the packing and the instructions would be nice.
Thanks, Joe

[RandyArizona]

337 parts manual, figure 125, item 11:

MS28775-014

One on each solenoid is required.

[Joes]

Randy, thanks you do a good job with the details. Your a lot alike some of the older guys on this site that have now passed. Very detail oriented, keep up the good work with all the others we currently have.
Joe

[RandyArizona]

Thank you sir,
I believe details and facts matter, much more than "my opinion".
Oddly enough, I have been told, that I am rather.. "Rude"? No, "spicy" was the term.
When dealing with aircraft that HAVE to be correct, facts matter.
Have a good day.

[Learjetter]

Welp, after cleaning solenoids and running the gear several times no problem…there is a problem.

No obvious hydraulic leaks. Adequate hydraulic fluid level in reservior. Using additional 24v ground power, not just ships battery.

Gear retraction is normal.

Gear extension is normal, but doesn’t “complete” in the prescribed time of 13-16 seconds. What we’re seeing is normal extension, followed by no green light until after about 20-30 seconds total pump run time. In flight or on jacks, same results.

I’ve read the service manual and examined the wiring diagrams. I’m thinking it could possibly be one of the power pack pressure switches?

[RandyArizona]

If the gear "falls" uneven, it is air in the system which is difficult to get out.
(Just a pain to do., not hard)
How much extra 24 volt ext power?
The gear motor is a heavy draw, so turn off any and all electrics, not attached to the gear.
If the motor is old.. (which is probably, yeah.), the motor may be tired, and need a rebuild.
Do all of the locks "click" closed, and then the pump runs for another 20 seconds??
This system is troublefree- until it isn't.
Good luck.

>>>>>EDIT: I just read that the doors have been deleted from this aircraft.. I've never done one with the deletion mod. Take what I posted above with a grain of salt.<<<<<<<

[Learjetter]

Gear falls fairly evenly and all the locks click solidly. Less than 1-2 seconds between L and R gear locking down. I’ll add one more symptom I just remembered.

After flight Saturday AM, I towed the airplane and put it in the hangar. Several hours later I turned on the master switch to close cowl flaps, and immediately noticed the gear warning horn ON, and no green light.

I stood dumbfounded for 5 seconds then horn quit and green light came on. Pump never turned on.

External power source is either a 24v 20A power supply, or a 24v truck starter unit powered by capacitors. Both work OK to ensure solid 24v with plenty of amps is available to pump. I think.

UPDATE: smoking gun found! Went to airport today and by chance a couple buddies showed up. With all three of us, we jacked her up and ran the gear. Once retracted, I check F and R throttle switches and R throttle switch did NOT set off horn. Then we put the gear down and all gear went down but no green light and HYD pump continued to run. We then tested each gear downlock switch and found L MAIN gear down micro switch (S2088-1) intermittent and then it failed completely showing some 800+ ohms when closed.

Textron has switches in stock ($200 ea). Those little switches are quite fiddly to get out.

Plan is to replace bad switch, check function, and then fly a couple trips. Over the holidays I’m gonna tackle rebuilding every hydraulic cylinder in the system and probably replace hoses (quote from PHT was $1400 for all hoses). Next year, I’ll tackle th power pack itself.

Update 2: installed S2088-1 downlock switch, swung gear a few times, no defects noted.