Tost wheel brake vibration

Hi Folks,

I wondered if anyone else has had a similar problem with a relatively (20 flights) new Tost drum brake.

Up until two flights ago, it operated smoothly and somewhat effectively. Then, on first and second application of the brake during a roll-out there was a loud mechanical click/grinding noise with an accompanying vibration at the same frequency most noticeable on the brake lever. On the last two flights it has done this, and both times on the third pull, the brake has operated smoothly again! Most disconcerting.

A disassembly of the hub brake did not reveal any debris (stone/pad material etc) that could get wedged, nor any visible scoring in a circular manner to suggest some clearance being the problem. Pad wear, what there was of it, was limited to two symmetrical areas towards the moving pivot end of the arcs as expected. The inside surface of the 'drum' was smooth and a seamless press-fit type, so unless it's out-of-round seems OK (but why OK on the third pull?)

So, any ideas? I'll be flying it this weekend to see if removal/reinstall might have affected anything we didn't notice.

If anyone's had a similar experience, preferably with a solution for it, that would be great.

It's not the actual strength of the brake that's the problem, so no 'why not get a disk brake' overkill solutions please.

Thanks in advance,

Chris, You don't say what the weather was like during these tests. If the brake pads were damp when the glider was put away at the end of the day, and in gentle contact with the disc, there could be areas of mild rusting under the pads. The first couple of applications will polish the rust off, but will give an uneven retarding force until the disc is uniformly smooth again. This can happen with cars also, particularly 4WDs after fording creeks and then parking overnight while the pads are still wet. Cheers, John G.

Hi Folks, I wondered if anyone else has had a similar problem with a relatively (20 flights) new Tost drum brake. Up until two flights ago, it operated smoothly and somewhat effectively. Then, on first and second application of the brake during a roll-out there was a loud mechanical click/grinding noise with an accompanying vibration at the same frequency most noticeable on the brake lever. On the last two flights it has done this, and both times on the third pull, the brake has operated smoothly again! Most disconcerting. A disassembly of the hub brake did not reveal any debris (stone/pad material etc) that could get wedged, nor any visible scoring in a circular manner to suggest some clearance being the problem. Pad wear, what there was of it, was limited to two symmetrical areas towards the moving pivot end of the arcs as expected. The inside surface of the 'drum' was smooth and a seamless press-fit type, so unless it's out-of-round seems OK (but why OK on the third pull?) So, any ideas? I'll be flying it this weekend to see if removal/reinstall might have affected anything we didn't notice. If anyone's had a similar experience, preferably with a solution for it, that would be great. It's not the actual strength of the brake that's the problem, so no 'why not get a disk brake' overkill solutions please. Thanks in advance, Chris

Hi John,

Thanks for the input, though I think we can rule that out from this case:

The location is high and dry, <20% humidity most days, ~30-40% at night. The trailer has a 24hour solar fan with battery for overnight. Last rainfall somewhere in March. The glider was used a week before in both cases, and had no sign of any rust in the braking area, or signs of rust-dust else where.

Also, the vibration felt more than un-even braking. There was more feedback to the lever involved.

We're basically landing on a beach in the dirt here that's not particularly well compacted for the first inch. That lead to some grit/sand being considered the most likely suspect.