SonexBuilders.net

Greetings,

I pulled the wheels and brakes today, and was surprised to see how much wear there was on the stainless plate they use as a single sided disc. The plate is worn to the point where the bolt heads are starting to wear. I think I read this somewhere before, but assumed it would take a lot of hours to get to that point. I've got just over 100 hrs on the brakes, but maybe only about 175 landings. Our runway is 6500 ft, and I make no effort to stop at the early taxiway, but rather coast to the far taxiway to save wear and tear on the brakes. Hard to believe they're this worn, but I guess there just isn't much surface area to work with.

I'll order new parts (disc plates, bolts, pucks) totalling $183.50, though I may continue using these for a while longer. Does anyone have an unused puck handy? If so, how tall is it? Just wondering how much mine have worn. Mine are currently 0.37"-0.39" tall. The disc looks like it's worn around 0.032".

Rusty

They are most likely designed to wear down below the bolt heads somewhat. Maybe reach out to Sonex and see if they have any minimum thickness advice.

I’m putting my brakes together now. The bolts tighten up flush with the disks, becoming part of the braking surface. The pucks are .625 inch thick.

Waiex 0194 wrote:I’m putting my brakes together now. The bolts tighten up flush with the disks, becoming part of the braking surface. The pucks are .625 inch thick.

Thanks for the quick measurement. I guess mine are 40% gone. I couldn't remember about the height of the bolts, but I would swear the bolt heads were below the disc. I didn't take any pictures of this installation, but on a previous installation years ago, the heads were clearly below. it would really make sense to have the heads flush though.

I'll just place the order and see what the ETA is before making a decision on putting these back for now.

Thanks,
Rusty

I'm still building, so there is no wear on my brakes. The bolt heads are just slightly lower than the face of the disk. maybe a 1/16"

Tony4aro wrote:I'm still building, so there is no wear on my brakes. The bolt heads are just slightly lower than the face of the disk. maybe a 1/16"

That sounds about like what I remember, and what I see in the old picture.
Rusty

My bolt heads are definitely wearing. I had no thoughts of replacing the rotors yet though. They seem to have lots of thickness left.

Has anyone tried to find other puck options for these brakes? I suppose Sonex might cut them inhouse, but I wouldn't be surprised if they're an off the shelf product for something else, like maybe kart racing.

I'm OK with Sonex price for the pucks, but I'd like some option for material. These are only described as "hard", but that's not super helpful. They seem to wear the SS disc pretty fast, so they must indeed be fairly hard. My brake force isn't what I'd like it to be, and I wonder if a softer compound for the puck would help. It would certainly wear faster, but also wouldn't wear the disc as much. Pucks are easy to change, so I wouldn't mind the extra wear.

My usual go-to for material is McMaster-Carr, and if this link works, it will go to a page that shows material with 3 different friction options in 5/8" thickness. https://www.mcmaster.com/products/brake ... ess~0-625/ I wish I knew where the Sonex pucks fit the friction range, then I might try making pucks with the next softer material. I wonder how long an end mill would last cutting brake lining material :-)

Rusty

Rusty,

Good idea!

Maybe some softer puck material could help. As it is now, stopping power is nothing to write home about, and the brakes will not hold the plane during ignition checks much above 3000 rpm, which is too slow for the Rotax. I´m not too concerned about premature wear- the wheels have to come off at least during the annual anyhow.

Kai

Kai wrote:
Maybe some softer puck material could help. As it is now, stopping power is nothing to write home about, and the brakes will not hold the plane during ignition checks much above 3000 rpm, which is too slow for the Rotax.

Kai

Exactly. I can just barely hold the plane at 4000, but it's more effort than it's worth, so I do my runups at 3000 as well.

I'm tempted to order the smallest size of the softest material. I do worry about the fact that the puck has to have enough mechanical strength to resist breaking at the edge of the caliper cylinder. I'll probably send Sonex an email and ask if there are any specs on the material they supply, and if they have an option to get softer compounds.