Ever since I got my 1968 PA-30B, there's been a small problem with the gear warning system. The way it should work is...

If the landing gear is up and:
1) One or the other throttle (left or right but not both) is retarded below 12"-14" MP then the amber gear-up light will begin to flash, or if;
2) Both throttles are retarded below 12"-14" MP then an audible warning is heard in addition to the flashing amber gear up light

The way this works is by the physical position of the throttle levers. In the throttle quadrant there are three micro-switches which are pressed as the throttles are retarded. There is an adjustable "arm" on each throttle which has round nylon bushings that press against one or more of three metal "tabs" (or "fingers" as other posts have called them) which then press the respective micro-switch (one switch per tab/finger) as the throttles are pulled back (this can be seen in the attached pics).

The left micro-switch is for the left throttle, the right switch is for the right throttle and the middle switch is activated by either the left or right throttle. The middle switch drives the yellow "gear up" light to flash when it is activated by either the left or right throttle (only if gear is up) and if the outer left and right switches are BOTH activated it means that BOTH throttles have been retarded which triggers the audible alarm (again only if gear is still up). So the logic is: IF the gear is up AND the middle switch is pressed THEN flash the light.... and independently... IF the gear is up AND BOTH the left and right micro-switches are pressed then sound the audible alarm.

The problem I've been having is that the amber gear up light begins to flash at any throttle setting below 20" MP (even 22" sometimes). Not a problem in high power cruise but in descent and general flying around at lower power settings I have a constant flashing light. I don't want to be in the habit of ignoring a flashing amber light or I will end up ignoring it when it counts!

I began to investigate and attached are some pics (comments and annotations in the pics) with my thoughts. First off - just FYI in case it is useful to others later... the cover on my 1968 PA-30B throttle quadrant is just a little different than the cover on 30C/39C pictures I've seen. As you will see from the pic entitled "Quadrant Cover.jpg":

Throttle Quadrant Covers

...the side covers on mine just come off with a gentle pull. From the outside it looks like they are riveted on with solid rivets but in fact the rivets just hold on to one half of a "snap" much like you would find on a pair of jeans. Take a look at this pic and you will see. One has to be careful to pull gently to not crack the plastic but mine came off quite easily. Once off there is ample access to the adjustments. Note: before pulling he cover off one also has to remove the idle cut-off pull button which just has a Phillips screw and also the quadrant friction lock on the right side must be removed by swinging the "lock" tab on it up and then pulling it straight off the spline (all very straight-forward).

Here's the first thing I found... take a look at the pic entitled "Left Arm Loose Screw.jpg":

Left Arm Loose Screw

In addition to the loose screw sitting in the front left seat ....., there was a loose screw on the left throttle. As you can guess and can certainly see from the attached pic, having this screw loose caused a "lag" in the movement of the arm that presses the left and center micro-switch in comparison to the movement of the throttle. When the left throttle was moved forward or backward any "slack" in the slot first had to be taken up as the screw moves through the slot to the other side before the micro-switch arm itself would start moving. I am sure these slots are there for timing adjustment of when the left and right throttles activate the switches which initially I thought was the issue but there's more to it....

On take-off or in high-speed cruise, in spite of the "lag" caused by the loose screw, the arm was actually pressed far enough forward that it no longer pressed the left or center switches. When reducing both throttles for descent, the left switch arm would lag the movement of the left throttle until the screw was at the rear most end of the slot which is also the same position of the screw in the slot on the right throttle. So from that standpoint, left and right throttles would now match (in terms of micro-switch arm position) and in theory press the switches at the same time... so while the screw should not be loose (and I tightened it) I believe it is not the root cause of the problem I'm having (early activation of the center switch causing the gear light to flash at 20-22" MP).

I spent some time moving the throttles as a group and individually, listening to the switches carefully and observing the timing with which they are pressed. Now in theory each throttle arm should depress the center switch and the switch on it's respective side simultaneously but it's not that exact (and I'll explain why in a sec...). First a note... I describe distances in mm or cm below and all those are my eyeball measurements as seen on the face of the throttle quadrant where the arm of the throttle passes through the quadrant.

I found that the right throttle will depress the center switch and then with a few millimeters more movement it will also depress the right switch. The left throttle will also depress the center switch around the same time the right throttle presses the center switch (give or take 5mm) but the left throttle will not press on the left micro switch until the throttle is retarded significantly beyond that (2cm perhaps). Thus the right throttle will press the center and right micro-switches at close to the same time but the left throttle will depresses the center switch first and then takes another 2cm of movement before it presses the left micro-switch.

Because of the timing problem described above, I believe someone prior to me picked the lesser of evils and adjusted the switches to make sure the left most switch was depressed no lower than 12"-14" MP which mean that the side-effect is the middle switch (and right switch for that matter) end up getting pressed at the +20"MP level which is what I am seeing.

I believe the root cause of the different "timing" with which the micro-switches are depressed relates to the round plastic / nylon bushings at the ends of the arms wearing at different rates (and perhaps also some general imprecision in the manufacturing / assembly process). Take a look at the picture called "Worn Round Bushings.jpg" to see what I mean:

Worn Round Bushings

Note: In the picture above I am using a flat-head screwdriver to hold up the left most tab / finger so the bushing can be seen... The picture is not perfectly clear but the edge of the bushing that presses against the tab / finger is worn flat. It's not so flat that the metal of the arm contacts the "tab / finger" but it is flattened nevertheless. I also look at small the micro-switch adjustment bolts (which are noted in the 2nd pic). There is a slot for the upper bolt so that the micro-switches can be positioned closer or father from the "throw" of the arms that push against them when the throttles are moved. I started thinking I could use this to change the relative position of all the switches one at a time so that I could compensate for the "slack" caused by the bushing wear. However this adjustment only moves the switches as a group not individually. There is no way for me to move just the left switch further down.

I thought that perhaps I could "rotate" the little round bushing at the ends of the arm so that a fresh unworn side was now facing the switch but unfortunately they seem quite resistant to rotating or moving in position and I don't want to force anything. Another solution might be to use a small "sliver" of metal tape (in layers to control thickness) to "shim" the top of the metal tab that actually presses the plastic red button of the micro-switch thereby allowing me a way to adjust the micro-switches individually. In fact I found a thin sliver of black electrical tape loose inside the quadrant and wonder if someone else tried this approach prior to my ownership. I could also use a sliver of tape to try and "wrap" around the bushing (same sort of concept different placement).

I wondered if anyone has run into this before or has any ideas. Is it possible to get new "arms" or bushings? I noticed a recent post from Pat Keefer looking for these same bushings from someone parting out a '63 Comanche.

Any thoughts appreciated...

- Charles

Text for future search by others: Microswitch Micro-switch micro switch gear warning

Let me say ditto to nearly all you posted.

The reason I asked for that spring fingered-part and bushings is our horn operates similar to yours and I want to fix it. In addition the gear horn always comes on but not consistently at the same MP.

We started by replacing the micro-switches as their condition was slightly wonky and cleaned the entire quadrant and replaced all control cables at the same time.

Then as you'll see in the next flyer or so, we attempted to adjust those same round/flat bushings. Since I'm a female owner the mechanic graciously did not curse aloud but his body language was definitely cussing a blue streak.

What I've noticed is the fingers on the spring are not flat with respect to each other and like yours, our bushings are flat on one side and we have not been able to successfully both adjust and keep them on a rounded side.

I suspect that previous mechanics, rather than trying to adjust the gear horn micro-switches etc, they just bent the finger spring ... or the finger springs just got bent over time but since I've been in the shops when the gear horn MP warning setting was 'adjusted' I'm 90% sure the springs were simply bent ... which is a contributing factor to the gear warning operation today IMHO.

My next step is what you saw ... seeking the semi-holy grail of the finger spring part aka 18418-02 plate and the bushings that go with them.
2 61402-64 bushings
1 27064-00 bushing

before next annual.

Please post if you have success with a different path.

It sounds like the problem we are trying to solve is the same or at least very similar. However, in my case the finger spring thing does not really appear to be bent per-se though as you may see from my earlier pics the fingers don't spring back to the exact same position. At any rate my finger spring does not have an specific bends in it that indicate someone has "adjusted" it that way before. I did think about bending the fingers to try and and get the switches into adjustment but decided my "shimming" idea is probably a better approach in that it can be more finely controlled (adding or removing layers of thickness). Also for the bending to work one would have to bend in such a way as to have the round bushing push the finger into the switch before the bushing was actually under the switch. I think this could be done but over time, with use it might start to bend back and come back out of adjustment. If that did happen it would be adjusting itself such that the warning would go off at lower and lower throttle settings and perhaps eventually not at all.

Here are some diagrams to illustrate my thoughts...

First here is a diagram with the parts labeled - I add the labels because my sketch is not the best...

If a bend were put in the finger to take up the slack I think the arm would have to be set to push the finger into the bushing before the bushing was actually under the switch itself...

This diagram is intended to show what I mean by "shimming" the top of the finger.. by metal tape I am talking about the metallic tape used in duct work. My brother uses it on his race car to secure tape weights to the wheels. I think in aviation terms it is often called "200 mph tape". I think black vinyl tape could also be used but my though on the metallic is that it would have less "give" and stretch over time and would retain it's thickness better than vinyl...

So with the shim idea the tape "shim" takes up the slack and pushes the button earlier than it otherwise would. So the goal is to find the first finger to be pressed and then shim the other fingers to that they end up getting pressed at the same time. Here is a diagram showing the shim pressing the button...

I think I am going to experiment with the shim idea. As long as I can get the buttons all being pressed simultaneously then I can adjust the micro-switches and arm through adjustments to get the MP setting correct. One comment on that... since the switches are pressed by the relative position of the throttle I don't think the MP setting will ever be exactly the same. MP changes for a given throttle position with atmospheric pressure (slightly) and with altitude (more significantly) so for me I'd be happy to just have them working in the 12-14" MP range near Sea Level.

Regarding your bent finger tab thing... I would think it would be easy to get a machine shop to produce a new one. It's just a flat piece of metal with slots cut in it to create the "fingers". If you need a new finger tab thing I'd consider taking it out and giving it to a machinist to reproduce. My brother knows of a fellow here in the DC area that runs a shop out of his backyard.. he's retired but makes a hobby of reproducing one-off things to solve problems like this. Apparently the USAF has enlisted his help in making new gears for machinery that they can no longer get parts for. He fabricated parts for my brother's race car as well. After I try my shim idea I may see if he could help produce new bushings or perhaps a new finger arm if I need it. Anyway just some thoughts...

Pat - question for you... how difficult was it to take the whole throttle quadrant apart?

- Charles

Clifton Aero does the work on the Twin. The concern wasn't taking it apart - it was getting it back together that was the concern. The parts manual actually had the best diagram of how to do that. Double click for large view and back arrow to return to post.

The attached is why I think the fingers have been bent at the base. Also notice the worn areas.

I figured you had a good A&P / IA working on your plane. So far I have taken the side covers off and done basic investigation the internals myself but sine my PA-30 sits in the same hangar with my 135 Op I plan to have my DoM who is an IA / A&P work with me to put it back together. I am quite comfortable doing it myself (it isn't that complicated) but I want to keep it legal and frankly... as Mark Twain said; "It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so." I've done a lot of work on cars over the years (frame up restorations, engine rebuilds etc...) but I expect that means I know just enough to be dangerous on an airplane

- Charles

- Charles

Thanks,

- Charles

Agree and may do this at a future annual. However the down time is of concern to me. I do have an operating gear warning horn today. I'd like it to be more perfect but the downtime cost of that last small improvement has questionable value and no safety improvement to me. We've already done a lot in this area. So this is still on the list but not at the top. Does that make sense?

Gary

- Charles