Scary-drum brake & Spoked wheels

[luanaigh]

hello all,
I just wanted to find out if anyone else came across this dangerous problem before.
One evening as i was riding down a steep driveway my back wheel totally locked up.....its an R80GS.
After falling off at low speed i noticed one broken spoke. After further inspection i found the spoke had broken at the nipple threaded into the wheel rim. The nipple had fallen into the drum brake and locked it......
Seriously scary stuff.
Thank god i was only doing 2 or 3 miles an hour.
Has anyone had this problem before???? a serious design flaw?
I had been doing alot of rough riding in woods around europe fully loaded on high tyre pressures so i could understand a broken spoke after lots of this riding.....but with such consequences?
Any thoughts?

[Dean de St Croix]

Question?

The spoke broke at the nipple (this is common for a spoke to brake at either the bend or the beginning of the threads - at the weakest point)

- you said the nipple then fell into the drum? How did it get out of the rim? Did it pull through or crack? it would still be in the rim right?

I have had brakes lock for a number of reasons as even a broken spring inside a drum can lead to a lock up or brake arm movement can spin the brake hub and lock. Scary stuff but still pretty rare.

I suspect the reason for the lock-up was the low speed as any amount of rpm of the wheel would have cracked the hub/brake plate spacing or crushed the nipple end as they are quite soft (so-to-speak). Before tossing you - unless you were in a turn with a slippery surface.

But, you never know.

Seems like a very unlucky coincidence.

Dean

[gsworkshop]

On the GS the spokes on the right is fed through the inside of the hub, so what was most likely meant was that the spoke fell into the drum brake and not the nipple.

[oldbmw]

Originally Posted by gsworkshop

On the GS the spokes on the right is fed through the inside of the hub, so what was most likely meant was that the spoke fell into the drum brake and not the nipple.

Hmm, another bmw 'characteristic'

[luanaigh]

Sorry i should have said,
part of the nipple broke and fell into the hub, the bit of the nipple left in the rim was deformed and broken. the spoke also broke at the just where the threads enter the nipple. (maybe when the spoke broke the force also broke the nipple...)
The part of the nipple left in the rim protrouded into the hub thus damaging the brake shoe as i braked going down the hill, the loose part in the hub seemed to have jammed between the hub wall and the shoes.......thus jamming the wheel.
To be honest this happened a few months ago but this is what happened as i recall. I just wanted to see if anyone else had heard of, or had this happen to them,,,,,,
I can imagine brake internals jamming in the hub also......god those bloody drum brakes.....

[gsworkshop]

I guess it is a Paralever GS with the tubeless rim. These were fitted with a stainless steel spoke and due to the high chrome content in stainless steel it is more brittle and weaker than steel spokes.
When fitting Stainless spokes it is common to use much thicker spokes to compensate for its weaker structure.
On the tubeless rim the nipple is not mounted on the rim but rather on the hub with the head of the spoke being held in the rim sidewall. Sorry for the confusion earlier about what part should end up in the brakes as with the older type tubed wheel it would be impossible for the nipple to find it's way into the hub.
The safe solution for your problem would be to fit normal steel spokes but I am not sure you can find this from BMW and besides they seem to have a serious problem with corrosion on the steel spokes fitted to older bikes at this time.

[luanaigh]

yes gsworkshop your quite right it is the tubless paralever....interesting about the s/s spokes..