Shimano Roller Brakes

[Malaconotus]

However, if the finger is moving, it probably means that there was a rubber insert to lock it in position and it's missing now.

No doubt you've lost some vibration damping rubber strip.

I missed that part of the problem description. Mick is right, the reaction arm should slot snugly into the fork braze-on (or clamp if there is no braze-on). On my two drum-braked bikes the reaction arm fits snugly into the braze-on itself but I have worked on another bike where a rubber strip inside the braze on ensures no play in the arm. Inner tube and electrical tape should fix it if you have lost this.

It is not, however, the play in the reaction arm which causes the 'loose headset' rocking. That is a design feature of roller brakes.

[Forty45]

Thank you

maybe I'll have to try and make up something to stop it rocking.................

[Nettled Shin]

No doubt you've lost some vibration damping rubber strip.

The datasheet for the HB-IM70 front roller brake, which uses a reaction arm and braze-on, lists a Brake Arm Plug (optional) part number Y-75F 16000. Perhaps it would fit, or you check the datasheet for the actual brake your brother has?

[niggle]

No doubt you've lost some vibration damping rubber strip.

The datasheet for the HB-IM70 front roller brake, which uses a reaction arm and braze-on, lists a Brake Arm Plug (optional) part number Y-75F 16000. Perhaps it would fit

This is Shimano we are talking about, not exactly renowned for making parts that fit more than one thing.

or you check the datasheet for the actual brake your brother has?

If available for a 10 year old brake..... and as for actually getting the part supplied on its own....

I agree that the easy solution is likely to be some packing such as inner tube rubber, possibly glued in place once it has been fettled to fit. My front roller brake uses the ISO disk mount for the reaction arm and it does the same free-play thing at rest, quite noticeably. This also makes checking the headset adjustment a bit more involved, I usually put the bike on a stand and pull/push on the forks to check it.

[Malaconotus]

My front roller brake uses the ISO disk mount for the reaction arm and it does the same free-play thing at rest, quite noticeably. This also makes checking the headset adjustment a bit more involved, I usually put the bike on a stand and pull/push on the forks to check it.

How I do it...

Push front tyre against wall to act as brake. Drop saddle to sit astride bike and stop back end lifting. Check for play without applying front brake.

[jonnyboy]

This is a bit of a resurrection of the thread, but hopefully valid and relevant ...

I was helping a friend of mine with his Shimano Nexus 7 Speed equipped Kona Dr Good, he's new to cycling/bikes and I consider myself somewhat handy with most of the basics. After an injury forced layoff we were prepping the bike for the road, pumped up the tyres, nipped up the front disc brake, re-aligned the rear gears (yellow marks were ~5mm apart) and then we moved on to try and address the rear brakes ... this where I ran into a knowledge shortage.

Fast forward several hours, much googling and reading, and I'm still at a loss as to how to effectively adjust the Nexus (rear) roller brake on his bike.

I read through this thread, and the general opinion (albeit related to front mostly) is that these brakes are a little bit on the limp side, however in my friend's case the lever touches the bar under braking and the bike dribbles to a halt, eventually. We tried adjusting the bolt/barrel to increase tension on the brake, but no real difference was gained.

Is this normal? Can it be adjusted any better?

Thanks in advance,

Jon

[Meshuga]

I have mine set up perfectly, front and rear and I'm more than happy with them after several years use. The way I adjust is - have the barrel adjuster on the lever screwed almost right out, and the barrel near the brake half way out. Next, loosen the cable clamp nut. The next bit may require a friend, push the black bracket that the cable screws onto (the bit that moves when the handle is pulled) towards the front of the bike, whilst pulling the cable tight so it slips through the nut. With everything held in this position, using your third hand (!), tighten the cable clamp bolt.

The brakes should now be too tight, so now screw the barrel adjuster on the handlebars in until they free up totally when you spin the wheel but start to nip on when you just pull the lever. Hope this helps, and if the insides are not greased (need special nexus grease), then the braking will be very harsh and lack modulation.

[Brucey]

Roller brakes need grease, and it has to be a Moly grease to work properly. Shimano sell special grease at considerable expense; it is designed to be squirted in through a hole in the assembly as per the tech specs.

Although there might be fault in the mechanism, it is also quite likely that the cable isn't quite right after a long lay-off. I'd suggest looking at the cable carefully first, and replacing and/or regreasing it.

Apparently despite shimano's warnings it is possible to strip the brake down if you know what you are doing.



However there may not be much point since spare parts are not available, you are meant to change the brake unit in one piece.

cheers

[niggle]

On my Carrera Subway 8 there are three possible points of adjustment, the barrel nut at the brake actuating lever can be loosened and moved along the cable, there is a cable adjuster at the brake end of the cable and also the usual adjuster at the handlebar lever. I back the brake end cable adjuster most of the way out, as that is the easiest one to use to loosen off the cable if you need to disengage it if required for wheel removal at the roadside. I then adjust at the barrel nut to get it to the point where the lever is about 1cm from the bar grip when pulled to the max, then finally adjust by road testing and using the brake lever adjuster. There seems to be a slight servo effect when braking on the move, which firms it up relative to the feel when stationary. Roller brakes only seem to need adjustment at quite high mileage intervals once they have bedded in.

The issue with the front roller brakes is a power modulator device built in to the dedicated front hub. Roller brakes are not mega powerful, but the back roller brake should be powerful enough to lock the back wheel with a firm pull when adjusted right, as it does not have the power modulator.

Greasing is only necessary when the brake starts to sound dry (like a worn out disc brake). If not greased it will start to grab and lock too easily, often with a loud shriek. Lack of grease certainly does not reduce stopping power, quite the opposite really. For a bike equipped with two roller brakes it has taken me three winters to use up the tube of Shimano grease which I bought for about £20, in which time a rim brake would have cost at least as much in pads, needed much more attention and have cause a fair degree of expensive rim wear, so I really rate these brakes, which do not seem to be about to wear out in any obvious way either, though I wish the front one did not have the blasted power modulator. For commuting purposes I think they could only be beaten, possibly, by Sturmey Archer drum brakes.

I note that the Kona came equipped with the disc front and roller rear brake combination (neat idea IMO), so the brake pull on the two levers should be different and appropriate for the different brake types, i.e. there is different cable pull needed for disc or v-brakes compared with drum/roller or caliper brakes. The levers could be identical in appearance and have an adjustable pull as found on some Shimano brand levers, worth just checking this point I suppose if the back brake has always been weak.

[jonnyboy]

Thanks for the tips, I'll have another go next week.

Jon

[Brucey]

re the brake levers; if they have two cable mount positions inside the lever, use the one closest to the pivot for a roller brake.

If they are single mount levers, the cable mount should be ~25-27mm from the pivot for a roller brake.

Levers with the cable mount ~35mm from the pivot are for 'V' brakes only and generally won't generate enough force for a roller brake.

cheers

[niggle]

re the brake levers; if they have two cable mount positions inside the lever, use the one closest to the pivot for a roller brake.

If they are single mount levers, the cable mount should be ~25-27mm from the pivot for a roller brake.

Levers with the cable mount ~35mm from the pivot are for 'V' brakes only and generally won't generate enough force for a roller brake.

cheers

Diagrams pinched from Shimano tech doc:

[Nettled Shin]

Roller brakes need grease, and it has to be a Moly grease to work properly.

This is what I suspect it is, but do you know this for sure? It is hard to tell apart from graphite grease.

[Brucey]

re the grease; good point; I read that somewhere but goodness knows where....it was described as being 'a moly grease, a little thicker than CV joint grease'. But they may not have known for certain either; I don't wish to be passing on duff information. If in doubt use the Shimano stuff.

I know that people have tried other stuff (sometimes in desperation in which case anything is probably better than nothing) and there are likely to be two issues;

1) friction; has to prevent excessive wear whilst allowing enough friction for braking.

2) heat tolerance; has not to fail by burning or coming out of the hub.

In either case a grease that is rated for CV joint use should work well in this application too; the ball contacts in CV joints are truly horrible (possibility of sliding under great pressure) and they can get rather hot too.

I guess if the grease is wrong there are only two outcomes;

a) the brakes don't work as well as they should
b) they wear out faster than they should

I've never heard of anyone wearing these things out altogether, but then most people would just buy a new unit I suppose. If the grease made the brake work less well, I guess you could flush it out with solvent and reinstate the shimano grease.

edit; does anyone have any experience of the 'wrong' grease radically altering coaster brake performance? After all the roller brake is similar to a coaster brake except in dimensions and actuation; its still a 'lubricated metal on metal' brake.

[edit- found mention of it being a moly grease here;
http://forums.bicycletutor.com/thread-1642.html but that isn't where I saw it first; could all be misinformation....]

cheers

[niggle]

The official stuff is not drastically expensive (eg. compared to the hub dipping oil kit), £12.70 with postage from SJS for the 100g tube, which does last a fair while: http://www.sjscycles.co.uk/shimano-nexu ... rc=froogle