M20J gear up limit switch

[PT20J]

The landing gear failed to retract on my 1994 M20J. I removed the belly panel and exercised the up limit switch several times and thereafter it worked again. The switch comprises two components: A micro switch and a plunger. The plunger is spring loaded and I noticed that it was a little sluggish to reset when I removed it so I cleaned it and lubed it with some silicone spray. The problem may have been mechanical or there may have been a problem with the switch, but I replaced the switch anyway.

 

[Wingover]

Is the switch easy to buy? Is it a common part number from an electronic supplier or Mooney?

[PT20J]

32 minutes ago, Wingover said:

Is the switch easy to buy? Is it a common part number from an electronic supplier or Mooney?

It's a readily available Micro Switch DT-2R-A7. TTI, Inc had the best price - $113.47.

[Fly Boomer]

17 minutes ago, PT20J said:

It's a readily available Micro Switch DT-2R-A7. TTI, Inc had the best price - $113.47.

Did you get the number from the IPC, or were there numbers on the switch?

[PT20J]

6 minutes ago, Fly Boomer said:

Did you get the number from the IPC, or were there numbers on the switch?

Both. 

[Ragsf15e]

10 hours ago, PT20J said:

The landing gear failed to retract on my 1994 M20J. I removed the belly panel and exercised the up limit switch several times and thereafter it worked again. The switch comprises two components: A micro switch and a plunger. The plunger is spring loaded and I noticed that it was a little sluggish to reset when I removed it so I cleaned it and lubed it with some silicone spray. The problem may have been mechanical or there may have been a problem with the switch, but I replaced the switch anyway.

 

Funny how the gear won’t go up even when the gear stop tab isn’t pressing on that switch.  In fact, when the gear is down, that switch isn’t doing anything, except apparently preventing the gear from going up?

[PT20J]

22 minutes ago, Ragsf15e said:

Funny how the gear won’t go up even when the gear stop tab isn’t pressing on that switch.  In fact, when the gear is down, that switch isn’t doing anything, except apparently preventing the gear from going up?

The power to the gear motor in the up direction runs through NC contacts in that switch. When the gear reaches the end of it's upward travel, the tab on the retraction rod activates the switch which breaks the circuit and stops the motor. Similarly, if the gear won't lower, it could be a problem with the gear down limit switch.

[Ragsf15e]

13 minutes ago, PT20J said:

The power to the gear motor in the up direction runs through NC contacts in that switch. When the gear reaches the end of it's upward travel, the tab on the retraction rod activates the switch which breaks the circuit and stops the motor. Similarly, if the gear won't lower, it could be a problem with the gear down limit switch.

Yeah I needed to think that through better.  At least it’s easier to get at that one since it’s not compressed by the gear!

Does it easily go right back in the same spot or do you have to put it on jacks and move the gear around to get it positioned right?  If the switch doesn’t activate at the right time, it can get ugly I think, but more-so on the older models.

[PT20J]

13 hours ago, Ragsf15e said:

Does it easily go right back in the same spot or do you have to put it on jacks and move the gear around to get it positioned right?  If the switch doesn’t activate at the right time, it can get ugly I think, but more-so on the older models.

The up limit switch is in a fixed bracket and the adjustment is on the little paddle on the push pull tube, so I didn't have to worry about the adjustment. 

[AZOutlaw]

Hi Skip,

Just to refresh, I've had a gear retraction failure 4 times now and each time it was on very bumpy runways.  Each time, it eventually does come up. 

After we cleaned, lubed, and adjusted the emergency gear lever all seemed good for a few months.  I then found another bumpy runway yesterday and the gear didn't retract.  The override doesn't do anything so I would assume it's not the airspeed sensor.  I would guess that microswitch, mentioned above, could bounce to a closed position, and then release to its open position a little later, allowing the gear to retract.  That make sense to you?

 

Sonny

[PT20J]

31 minutes ago, AZOutlaw said:

Hi Skip,

Just to refresh, I've had a gear retraction failure 4 times now and each time it was on very bumpy runways.  Each time, it eventually does come up. 

After we cleaned, lubed, and adjusted the emergency gear lever all seemed good for a few months.  I then found another bumpy runway yesterday and the gear didn't retract.  The override doesn't do anything so I would assume it's not the airspeed sensor.  I would guess that microswitch, mentioned above, could bounce to a closed position, and then release to its open position a little later, allowing the gear to retract.  That make sense to you?

 

Sonny

Sounds plausible. It’s easy to replace. You could try taking it apart and cleaning the plunger in case it’s just the plunger sticking, but for a little over 100 bucks I figured I would just replace the switch and be done with it.

[AZOutlaw]

Update......We got a new gear up limit switch and the Ovation version is about 7 times more expensive than the M20J version noted above. After removal I tested the 1-2 and 4-5 NC contacts on the old switch.  The 4-5 set didn't ring out, unless I tapped on the switch.   Fairly certain that was the problem.  We're heading back today to jack the plane and swing the gear just to be certain all is in the right place.  We did measure the exact location of the old switch before removal, but seems best to be sure as it could activate and shut down the motor sooner, or later.

Thanks for the help Skip!

 

[N201MKTurbo]

9 hours ago, AZOutlaw said:

Update......We got a new gear up limit switch and the Ovation version is about 7 times more expensive than the M20J version noted above. After removal I tested the 1-2 and 4-5 NC contacts on the old switch.  The 4-5 set didn't ring out, unless I tapped on the switch.   Fairly certain that was the problem.  We're heading back today to jack the plane and swing the gear just to be certain all is in the right place.  We did measure the exact location of the old switch before removal, but seems best to be sure as it could activate and shut down the motor sooner, or later.

Thanks for the help Skip!

 

You need to adjust so the gear just kisses the up bumpers. Maybe a little different depending on how your gear doors are rigged. I would start with the switch adjusted so it stops a bit to soon and creep up on the correct position. The Dukes actuator makes this easier because you can spin the motor coupling with your fingers while under the plane. The newer actuators don't let you do that. Even though you marked the switch position, what you need is the tab position when the switch actuated. Did you measure that? If not, you are starting from scratch. but it isn't that hard.

[FLYFST]

On 6/6/2024 at 4:24 PM, PT20J said:

It's a readily available Micro Switch DT-2R-A7. TTI, Inc had the best price - $113.47.

Hello Skip, when you were researching the gear up limit switch did you by any chance also find an available alternate part number for the gear down limit switch? When I looked the Honeywell 1CH116-6 was no longer available and the alternate part numbers P6-24014 (Otto Controls) and Honeywell 1EN1S were very expensive ($1,152 to $1,768), but not in stock when I searched.

[PT20J]

5 minutes ago, FLYFST said:

Hello Skip, when you were researching the gear up limit switch did you by any chance also find an available alternate part number for the gear down limit switch? When I looked the Honeywell 1CH116-6 was no longer available and the alternate part numbers P6-24014 (Otto Controls) and Honeywell 1EN1S were very expensive ($1,152 to $1,768), but not in stock when I searched.

Sorry, I didn’t look at the other switch.

[PT20J]

I checked with Honeywell. The1CH116-6 is an obsolete part. The 1CH1-6 is available and essentially the same. Both are DPDT switches. The main difference seems to be that on the 1CH116-6, the one circuit must make slightly before the other and the 1CH1-6 does not have this feature. Presumably, this was to make sure the motor shut down before the gear light comes on. But the amount of travel is so small that I cannot imagine it matters especially since the actuator will have a bit of overrun.

1ch1-6_i.1.17.pdf

 

 

[FLYFST]

I checked with Honeywell. The1CH116-6 is an obsolete part. The 1CH1-6 is available and essentially the same. Both are DPDT switches. The main difference seems to be that on the 1CH116-6, the one circuit must make slightly before the other and the 1CH1-6 does not have this feature. Presumably, this was to make sure the motor shut down before the gear light comes on. But the amount of travel is so small that I cannot imagine it matters especially since the actuator will have a bit of overrun.

1ch1-6_i.1.17.pdf
 
 

Thanks for the research Skip!


Sent from my iPhone using Tapatalk

[BadMooneyRising]

I was having the same issue with my 74 F model. This thread saved the day! I went underneath and sprayed the Up Limit switch with contact cleaner, and now the gear works like a charm. Just a temporary solution, but glad I was able to diagnose the problem and get the plane back in the air with the help of this thread. Thanks y'all!