Gear warning horn comes on below 22" MP??

[Dcflyn]

My gear warning horn comes on way too soon when I pull the throttle, 20-22" MP. Anyone know the fix?

[kpaul]

I'm interested in this as well, mine comes on at 14.  POH says 12, not as bad at 20-22 though.

[DonMuncy]

The gear warning alert is activated by a switch riding on the throttle cable just behind the panel. It is readily adjustable.

[kmyfm20s]

In my J it was activated by manifold pressure. In my S its activated by a switch on the thottle cable.

[gsxrpilot]

In my C it's on the throttle cable down at the carb. It's very easy to adjust. I've got mine set to come on at 14 inches.

[Bob_Belville]

Mine was much too high as well, about 20" MAP. When we replaced the throttle cable a few weeks ago we mounted the limit switch closer to the panel which fixed the problem, trips @ ~ 14-15" MAP. I wished I'd done it sooner, it was just a matter of loosening the limit switch mount and sliding it so that the throttle cable (rod) has to be moved more to the closed position to trip the switch.

I would not think it would take your A&P 15 minutes to adjust.

 

[Guest]

To make it easier, take a grease pencil and go flying.  Set the throttle to the MAP value which the PoH says for gear warning, mark this position with the grease pencil on the throttle cable.  Now back in the shop you can set the throttle to the mark and adjust the switch.

Clarence

[Hank]

But Which end if the cable is the switch? My C has recently changed from 12" to 14-15" (variable each flight), after having the carb heat cable replaced.,can't find anything inside my throttle quadrant, didn't think to look at the carb end as posted above.

[Bob_Belville]

Hank, Clarence or someone who knows Cs will have to chime in. On my E the switch is mounted on the throttle cable in the cabin, right behind the control panel. 

The pic is of my old and new cable (MacFarland did not mill the slot in the shielding initially and remade it). The limit switch rides in the milled slot and is tripped where it flex cable connects to the rigid rod. I'm not sure why your C would be different though it might be.

[carusoam]

My 65C had the switch ride on the throttle control rod behind the IP.  The throttle control Rod had a divot cut into it. When the throttle was all the way out the switch fell in the machined hole.  That combined with the gear being stowed would sound the gear alert.  It may be adjustable but may take moving the entire cable in and out. The micro switch may have had a small wheel that ran along the rod.

pulling the throttle all the way out while descending would sound the horn.  Better planning and leaving the throttle slightly in gave quieter results.  Not having a JPI also kept the pilot in the dark about over cooling the cylinders by pulling the throttle out during the descent.  The gear warning was also a reminder to leave the throttle in...

fuzzy memories of a PP,

-a-

[gsxrpilot]

As I posted above, my switch is at the carb end of the throttle cable. But another difference is my highly modified C has a vernier throttle. The stock throttle cable might have the switch in the quadrant whereas the vernier doesn't have a place for it, therefore it's at the carb end.

[carusoam]

The twisting knob may cause a challenge with the divot and micro switch routine.

Best regards,

-a-

[Guest]

Traditionally the switch in located on the cable behind the instrument panel. Some are located at the engine end, in either case the adjustment is the same.  Loosen the switch mounting and slid it in the desired direction.  Irratic operation is commonly caused by a worn switch roller.

Clarence 

[Dcflyn]

Thanks to all of you for the helpful comments. I'll be under the panel this weekend figuring it out. Cheers and happy flying.

[AIREMATT]

On January 20, 2016 at 6:39 PM, M20Doc said:

To make it easier, take a grease pencil and go flying.  Set the throttle to the MAP value which the PoH says for gear warning, mark this position with the grease pencil on the throttle cable.  Now back in the shop you can set the throttle to the mark and adjust the switch.

Clarence

+1

Had to do this with my 67C and we flew it and marked the throttle shaft at 12" MP. It is right behind the instrument panel and easy to adjust. I think it took my AP about 10 minutes to adjust it.

[DXB]

Does anyone have a link or a picture for what this switch attached to the slot on the throttle cable housing looks like?  Mine needs adjustment, and I see how it is attached to the cable, but I can't visualize how the thing works (i.e. what actually trips the switch?).   So I'm not sure which direction the thing needs to slide.

[cctsurf]

Here's a pic, notice that there is a thicker area of the cable which pushes the microswitch when the throttle is in, and when pulled back, it can drop in next to the flex cable (as pictured above).

[DXB]

33 minutes ago, cctsurf said:

Here's a pic, notice that there is a thicker area of the cable which pushes the microswitch when the throttle is in, and when pulled back, it can drop in next to the flex cable (as pictured above).

Oh I get it now - didn't realize there were both rigid and flex components of the cable that appear in the slot.  Thank you cctsurf !!

[steingar]

Got the same problem in mine, except mine comes on at 18" instead of 12.  I'll be having my A&P have a lot at it in the near future.

[bradp]

So the adjustment is at the U-brackets holding the assembly frame?  

Mine is at 14 or so.   The switch click also let me know that I've advanced the throttle too far for starting cold.  :-). 

[Vance Harral]

I think there are so many different ways of mounting the microswitch in the various models and years that you just have to look at your particular installation to figure out how it works.  In our '76F with the quadrant throttle, we're lucky: the position of the switch can actually be set with a set screw, which is accessible via a hole in the quadrant.  Literally a few seconds to tweak it.

Someone above mentioned a system where the switch is triggered by actual manifold pressure.  I've never seen one like that and would be interested to know how it works.  As far as I know, (almost) all installation are just based on throttle position.  Note that the exact MAP you get for a given throttle position varies with atmospheric conditions.  The nit-picker in me would argue you set the switch for about "N" inches of MAP, not any specific value.  If you feel like having a bar argument, try bringing up what "N" should be in the context of an airplane that makes landings everywhere from Dutch Harbor in January to Leadville in August.

[cctsurf]

The adjustment is not the u-brackets, the mount has them pinned into the cable you can see the pin holes in the picture Bob posted above.

On 1/19/2016 at 8:36 PM, Bob_Belville said:

The Adjustment is the screws through the microswitch as shown in my picture above:

On 4/28/2016 at 0:09 PM, cctsurf said:

Those screws go through slots in the bracket (you can see part of one of the slots in the picture).  One thing I note, the screws aren't snug in the slots and the microswitch is able to move toward and away from the cable as well as back and forth in their slots.

Another thing worth noting is that the bracket on the bottom had the exact same part number as in the service bulletin m20-174 from 1969 for the 1962 M20C I fly and it came off of a 1982 M20K...  The original cable I'm replacing had the bracket welded to the cable.  There are other ways of actuating the gear horn (from the pitot system, etc), but for the most part, for the old birds (I've checked the parts manuals), this is how it was originally done using the cable.

Edited April 29, 2016 by cctsurf
better wording

[DXB]

1 hour ago, cctsurf said:

The adjustment is not the u-brackets, the mount has them pinned into the cable you can see the pin holes in the picture Bob posted above.

Another very useful piece of info - I'd assumed it was he u brackets!   You just saved me from some serious buffoonery while on my back under my panel.

[Stephen]

Just to add into the library of responses to this, on my 1969 F model, I have a microswitch on the base of the throttle quadrant that rides the bottom base of the throttle handle metal structure. If you pull the Throttle, Prop and Mixture caps and unscrew the plastic covers around the quadrant you can get to it. Looking down through the top, you can see the switch forward of and adjacent to the lower extremity of the throttle arm. I didn't see any adjustment other than to *Gently* tweak  (I used a pair of hemostats) the metal arm that mechanically rides the throttle. The switch doesn't seem to have a slotted mount either on the microswitch body or on the metal plate that it screws in to so that the whole switch position relative to the throttle can be tuned. I jacked up the plane per the service manual, raised the gear ( Master ON, Area CLEAR, Gear Handle Up, then I had to *****gently***  blow into the pitot, ***slowly** raising pressure until the gear airspeed switch activated {around 60 indicated) the gear circuit). Then I adjusted the arm to bring the warning horn activation to approximately the 10" MP throttle position).