Shimano roller brake BR-IM70R disassembled.
I've had this roller brake for several years. Last time I used it it was racheting but there was no obvious defect. Problem is they are not supposed to be disassembled because Shimano claim they cannot be dismantled or re-assembled. I decided otherwise, so here it is stripped down. :)
It had picked up a lot of bulldust from my time in Queensland which had mixed with the grease to form a rather nasty grinding paste. However there was no obvious wear!
At first I thought the racheting was because the spring clip (round thing next to brake shoes) had come adrift, but I think this happened in disassembly. A more probable reason was because the grease had got claggy with the admixture of bulldust.
(The only components missing from the picture are the grease seal from where the back of the brke butts up against the hub, and the grease port plug for the little hole in the black brake plate.)
It is obviously not designed for use offroad.
The only seal is the one against the hub. There are huge gaps in the mechanism which allows dirt access to the works, and judging by mine lots gets in. Frequent flushing with fresh grease is definitely necessary - something I had not done. The quality of the working parts seems good though.