Intermittent delayed gear retraction

[blue eagle]

Dear All,

I have intermittent delayed gear retraction on my M20J (1998). When selecting gear up sometimes it will retract immediately and sometimes it retracts delayed (30s~120s). Pushing the overriding switch (airspeed) does not help. Checked function of speed sensing membrane (connected to pitot static system, this aircraft has no squat switch), all OK. Then changed the Gear switch with no effect, so old switch was OK. Jacked up the plane and did some checks and electrical measurements, gear relays are OK. So we concluded that it must be the gear limit switches.

Because these are very difficult to get, I wondered why. Checked the schematics and the data sheets of the limit switch manufacturers. These switches are very robust and derated tremendously, so it is unlikely that these switches are bad. 

My Questions:

- Is it possible that after 25 years the limit switches drifted?

- What is the procedure for (re-)adjusting? In the Mooney service and maintenance manual on page 32-30-02 a procedure is mentioned to adjust the striker arms on the bellcrank when performing rigging of the landing gear. No mentioning of fine adjustment of the gear limit switches. 

[N231BN]

2 hours ago, blue eagle said:

My Questions:

- Is it possible that after 25 years the limit switches drifted?

Yes, but that is not your problem. Check the relay or the gear motor itself.

Edited April 3, 2023 by N231BN

[ArtVandelay]

So no delay extending the gear? Is the delay consistent?

[blue eagle]

No delay when extending the gear. Also there is almost always no delay retracting at the first take off of the day.

We checked the relay by measuring at the solenoid, when the solenoid gets power the gear retracts immediately. This shows that the relay is functioning.

The solenoid of the relay gets no power when we replicate the problem with the jacked up aircraft . If you wait some time the solenoid does get power and the gear retract immediately.

 

[Ragsf15e]

Lots of lps1 electrical contact cleaner on the limit switches and then “exercise” them to work it in.  This is a relatively common mooney issue and there are a few older threads on it.

[ArtVandelay]

Yeah, it sounds like the gear up limit switch. With the gear up check the resistance between the power supply terminal and the gear up relay terminals, it should be close to zero.

If it’s the airspeed switch you would get a gear warning horn.

[Phil EF]

Ditto on LPS and working the limit switches. 
A recurring issue on the forum and happened to my K also. 
Just one panel to remove. Easy to get to. 

[Mark89114]

I had a same but different problem.....never any issued in the air, but on the Jack's it would stop, sometimes going up, sometimes going down.  Much head scratching and investigative head banging.  Discovered the problem was one of the pins in a connector at pilots sidewall.  There are 3 connectors, buried deep behind CB, second at pilots sidewall and the connection in belly pan.  We looked at the sidewall connector and found a defective pin.  Replaced and no issues since.

[PT20J]

On 4/3/2023 at 11:33 AM, blue eagle said:

No delay when extending the gear. Also there is almost always no delay retracting at the first take off of the day.

We checked the relay by measuring at the solenoid, when the solenoid gets power the gear retracts immediately. This shows that the relay is functioning.

The solenoid of the relay gets no power when we replicate the problem with the jacked up aircraft . If you wait some time the solenoid does get power and the gear retract immediately.

 

If you can replicate it with the plane on jacks, I would get a multimeter and the schematic and trace the problem backwards until you find the problem.

[A64Pilot]

40 minutes ago, PT20J said:

If you can replicate it with the plane on jacks, I would get a multimeter and the schematic and trace the problem backwards until you find the problem.

I think he’s pretty much done that by finding the relay unpowered.

Next step I guess is to validate power goes into the limit switch, but doesn’t come out when the problem exists, or I’d vote just get contact cleaner into the switch.

I like Deoxit myself.

Anyone have a source of supply for the limit switches? Or the manufacturers parts number?

[PT20J]

24 minutes ago, A64Pilot said:

I think he’s pretty much done that by finding the relay unpowered.

Well, I meant to trace back to find out where the problem is that is preventing the power from getting to the relay.

Contact cleaner is just a temporary solution. Quality switches have precious metal plated contacts for low electrical resistance and don't readily oxidize. They are also designed with a wiping action that cleans the contacts. When the plating wears through, the base metal will continue to corrode repeatedly and the part is worn out and should be replaced. 

[A64Pilot]

10 minutes ago, PT20J said:

Well, I meant to trace back to find out where the problem is that is preventing the power from getting to the relay.

Contact cleaner is just a temporary solution. Quality switches have precious metal plated contacts for low electrical resistance and don't readily oxidize. They are also designed with a wiping action that cleans the contacts. When the plating wears through, the base metal will continue to corrode repeatedly and the part is worn out and should be replaced. 

Yes, I know, but contact cleaner is good for fault isolating an intermittent problem.

Do you have a source for the limit switches?

It would seem a good spare to have on hand, I bet they are different too

[flyboy0681]

I had pretty much the identical problem last year, delayed retraction and ultimately, no retraction. This occurred a few weeks before annual and had it investigated at that time. In the end it turned out to be the relay pack. The factory gave a lead time of six months for a new one, but after calling several Mooney service centers nationwide I was able to locate one, ironically, 10 miles from me. 
 

Hopefully your situation is different because the cost will give you a coronary. 

[DEGWS]

Up Limit Switch. Had exactly the same issue!

[ArtVandelay]

Yes, I know, but contact cleaner is good for fault isolating an intermittent problem.
Do you have a source for the limit switches?
It would seem a good spare to have on hand, I bet they are different too

Yes, the down and up limit switches are completely different:



I found replacements on eBay using the part numbers above.

[skyking1]

I have the same problem. We had the plane up on jacks and tapped on the up solenoid which worked. Hope that is the problem. Motor and switch were ok