Rear brake binding

[MichaelSydney]

I had something strange happen today.

I went for a fast thrash up a very twisty road. I think it rises about 800 meters in 8 km. Lots of  hairpins and today the summit was above the cloud line.

Last night I did a carburetor rebuild and I was naturally worried when nearing the top the bike seems to lose power. I found a safe spot and coasted to a stop. Except I did not coast.... the bike simply stopped.... rear brake firmly engaged. I could see no obvious problems so simply backed off the adjuster three half turns then all was normal. I later wound two half turns back on before attempting the descent on anther road.

A short while back I had the wheel off and inspected shoes and drum. All seemed in order. What could have happened?

[montmil]

Michael, you may have kicked up some debris as you were drifting the LS through those twisties. Note the five (5) open-to-atmosphere vents on the wheel's port side. Would not be outside the range of probability that a bit o' grit found its way inside and lodged between the leading edge of a brake shoe and the drum.

Just my guess but go ahead and pull the wheel for inspection. You might see a scored line on the drum surface where the odd bit was ground away which restored the usual less than sterling rear brake. Or you may find a pebble!

Just my guess and no more.

[MichaelSydney]

Thank you Montmil, that certainly sounds plausible. I will inspect carefully for any sign of debris in the drum.

[Burt]

Earlier in the year a picked up a spare rear wheel for my K75C which has essentially the same set up as an R series with drum brakes.  I also picked up the FD to match it.  

I noticed that on the outer rim where the wheel hub joins the diff, there was serious pitting all around the mating surface.  As there is a small gap when fitted and the lower mating surface of the FD has pitting, it could be the result of a small stone getting caught.