Main Gear Downlock switch didn't work

[Skymaster337B]

While flying today, the main gears came down but the switches did not engage. Landed without incident, but...

What I found was both main gear down switch lever arms slid under the main gear arm -- it should just butt up against it, not go under it. The only thing I did to cause this was put grease around the down lock itself. So I guess it caused the switch arm to slide under the landing gear arm.

Anyone every see anything like this? Now I'm worried about a repeate, but as far as I can tell the switches themselves can not be adjusted.

Any idea?

[Pete Somers]

Yep, i have seen that happen, you should not grease put grease around that area, if you do just use a slight amount.
All the switches are adjustable.

Pete

[Skymaster337B]

So, to adjust the switch, do I just loosen the screw and move it up or down as needed and then secure it? Or is the switch hard mounted to the over center arm, and only that can change the switch's up and down position?

Thanks

[Pete Somers]

You can adjust the switch by undoing the 2 screws and sliding it in/out. But make sure you do at least 3-4 retractions after adjusting just to make sure that the switch works correctly and that the gear is in the down lock.

If the spring levers have been bent and you have striaghten them, i would see about changing them as it will be a weak point.

Cheers
Pete

[Skymaster337B]

I looked for the traditional adjustment slide on the micro switch, but on a 67' the downlock switch is hard mounted to the overlock arm.

So, what has to be done is the glueing of a small shimmy to the lower landing gear arm (the flat side). So the micro switch will not slip under the gear arm again.

Otherwise the locks are all looking good and everything is within tolerance. I guess a 40 year old airplane starts to make it's own tolerances. As it is, the bottom of the landing gear arm seems to have a teflon strip glued to it.

I'll let you know how it all works out, otherwise let me know if you think I'm missing something.

[gfcudahy]

On the later AC the upper screw on the downlock microswitch fits into a small slot on its mounting bracket allowing some adjustment in and out. Probably that way on your AC, but it can not be seen because the switch covers the slot. Both nuts must be loosened with a 3/16" wrench in order to adjust.
George

[Skymaster337B]

On the 67' there is no such adjustment. So I just put a shim under the landing gear arm, and so far so good.

[Skymaster337B]

One more question for about downlocks. Will the downlocks extend after the main gear is down, or will it extend as the main gear is coming down?

The maintenance manual isn't too clear about that. But the schematic suggests there's an orifice that makes the main gear extend down fully first, and then allows pressure into the downlock servos to extend all the way and lock.

The reason why I'm asking is: I can't figure out what the guide wedge attached below the downlock switches are really there for? The wedge is well below the downlock, so if the servos don't extend until the gears are fully extended, then what's the point of the wedge?

[Skymaster337B]

It worked!!!!!!! The shim glued to the bottom of the landing gear works perfect to hold the downlock switch closed.