SNX-L07 hydraulic brake plans tweaks

Discussion for Sonex builders on specific plans page experience. These posts are limited to technical suggestions such as assembly order, challenges, or techniques related to specific plans pages.

SNX-L07 hydraulic brake plans tweaks

Postby kevinh » Sun Feb 04, 2018 5:00 pm

Hi ya'll,

So I'm back building again (I took a couple of months off for back surgery and I feel lots better now). I had seen people in the past with misc complaints about the hydraulic brake plans and I think (at least with the current revision from Sonex) they seem almost perfect. The one remaining problem I think is the hole location for mounting the SNX-L07-07 plates. I've tried to document my solution to this problem here (in hopes it will be useful for others - YMMV - I am not an expert :-) )

Step 1: Errors on SNX-L07 plans (learned from other builders but seems true to me)
  • The clevis pin should be MS20392-3C39 not 49.
  • The cotter pin should be MS24665-132 not 134.
  • One thick (1/16"?) hardware store washer needed as a spacer at the indicated location on detail B to prevent new pads from binding against rotor. As pads wear down that washer can be moved outboard.


Step 2: Proposed procedure to align pants/brakes to vehicle
The existing SNX-L07-07 plate as shipped from sonex includes three pre-punched 3/16" holes around the large axle hole and one large hole to allow passthrough of the brake line fitting. The plans call for using only the bottom 3/16" hole and expanding that hole to 1/4" for the MS20392-3C39 clevis pin to gear mount. That hole might be in the correct position for a trigear sonex, but it is nowhere close for a taildragger. Therefore I recommend the following.

Don't use the existing 3/16" holes or the brake line hole. Instead swap the plates so that you can have adequate edge distance to drill a new 1/4" hole for the clevis pin. Drill this hole in assembly with the landing gear leg and wheel pant. This allows you to trivially set the fore aft position of each pant to be the same (rotating around the gear axle). Once you have the pants where you want them, use a 1/4" centering punch through the axle weldment to mark the location to drill, remove the weldments/SNX-L07-07 plates and then drill a nice 1/4" hole through all three parts on a bench (doing it on the plane would probably be fine also, but removing the parts is pretty quick and easier to get a nice hole on a bench IMO). After drilling the 1/4" hole, screw the brass brake line fitting into the brake and mark where the passthrough hole needs to go in the plate. Then drill that hole to 5/8" diameter with a step drill.

I've included a photo of my SNX-L07-07L plate. Yours will look a little different, because I had already tried to mount my plates per plans when I discovered this problem and worked out this solution.


I think that even for trigear you might want to use this approach, because it lets you easily adjust the wheel pant position for your aircraft. Because the plates provided by Sonex are mostly symmetric in the fore/aft direction you can just flip the plates as needed to allow drilling a new 1/4" clevis pin hole with adequate edge distance from the unused holes.
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Re: SNX-L07 hydraulic brake plans tweaks

Postby MichaelFarley56 » Sun Feb 04, 2018 5:12 pm

Thanks Kevin! My solution was to do almost the exact same thing as you, and it’s worked very well for me. I wasn’t a huge fan of drilling a lot more holes into those backing plates but they seem to be thick enough that they hold together just fine.

I hate to say it, but this is one of the very few items that keeps being brought up to the factory time and time again, and yet it still seems to go unresolved. Given how simple it would be to correct this error, I can’t believe it. I was talking to the Sonex tech support two years ago and supplied pictures, documentation, etc. of this issue and here we are! And as far as I’m aware, the tri gear and taildragger models both use the same main gear leg angles back from vertical so those plates are probably an identical issue for both types.

Regardless, good fix! Thanks for sharing!
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