Hitchcocks Forum

I posted this the other day on the tail-end of the Brake Geometry thread, but thought I'd put it up 'in its own right' as maybe a few of you guys might be interested. As a winter project I decided to try to improve my 2000 Classic Twin Leading Shoe front brake, due to almost suicidal performance. So I invested in our host's improved exchange shoes, and also the heavy duty cable which perports to also improve matters. When it came to actually doing the work I found that the 'trunion mod' had already been done on my bike (even though it was new when bought!). I carefully cleaned the drum, and (carefully) ruffed it up a little, balanced the movement as directed in the technical notes, and fitted the HD cable. Since doing the work I've covered around 500 miles and can honestly say that the brake is not a jot better than before - it passes an MOT but i don't know how. Talking to friends in the pub last Friday it was suggested that the best way to improve performance is to have oversize shoes fitted and then have them machined to perfectly fit the drum - shame they didn't tell me that BEFORE I shelled out around 50 squid on parts!!!

Riggers they are right. In addition you should try a longer brake arm if you are using drum brakes. This will significantly increase the mechanical adventage when the lever is pulled. It is a common mod on a Commando and transforms the 2LS front brake. HTH.

hi riggers,i also have the trunion mod,i have asbestos shoes on my indian market bike and the front brake was only adequate ,so i did this ,set bottom brake arm so that it was as far away from cable nipple as i could (on pulling just enough to get nipple in) with cable adjuster fully screwed in then adjust cable adjuster until bottom shoe locks drum then back off until not binding ,then set top arm as far away uphill as poss put link bar in tighten top trunnion nut until top shoe locks drum then back off half a turn then fit 8mmm lock nut ,this procedure has given me a very good front brake locking up on occasions almost not good but working a lot better,i know this will look vague as its hard to fully explain this procedure ,but the trick is to get both shoes in contact with the drum at the same time all the best paul.

Riggers, my setup is as it was from the factory apart from drilling out the top adjuster to assist with easier setup! Now assuming my 2004 braking system is the same as your 2000 setup and you do not have any defective parts I can see no reason why your brake would not work correctly, mine is actually better than that of an early Honda disk brake. Are you confident that the shoe adjusters and cable have been set correctly, if you haven't looked already I'm almost sure this web site has good instructions for correct adjustment, also have you given the shoes a chance to 'bed' in, this can sometimes take a few miles....please keep us posted on the outcome..

Hi Riggers. I've heard of the method of machining the shoes to the drum, but can't really see how this is any different to bedding in shoes conventionally. It is true they would be more likely to perform at nearly 100% efficiency right from the start, but that would not make them perform any better if the linings were of conventional thickness and had bedded in to fit the drum by normal wear from normal application. I have never removed old brake shoes and found any part of them not in contact with the drum, which means that 100% was in contact for them to wear down normally, so as you cannot get more than 100% contact, no machining of them will increase that figure no matter what tricks you do to them. With 2LS brakes there is a very fine line from having them too grabby or having too little braking force. This is because both shoes work on a self servo mechanism....i.e.: the more they grip the harder they force them selves on. So with just a fraction too little friction, the self servo action is reduced dramatically along with the braking force. Whereas with just a little more friction, the braking force snowballs or multiplies and the brake is quite powerful, sometimes even too powerful. I can generally get any brake to work better by stripping the whole unit down and cleaning everything thoroughly. The cam spindles and the cam pressure faces need to be perfectly clean, smooth, polished and greased. Likewise the pressure pads on the ends of the brake shoes should be finely polished along with the pivot ends too. The brake cable should be well oiled. Sometimes cables can be too heavy for their own good and have too much inner friction. The brake surface should not be roughened up as it should be unmarked and very smooth and completely clean, this developes the heat that is required with most linings to operate well. Obviously getting the right friction coefficient on the linings is very important, and one would hope the ones you buy had the best properties but there are friction lining specialists around. I sometimes consider that new brake shoes are often too eased off (chamfered) on the start of the leading edge. This is a very critical area for the self servo action to work correctly. The more you take off this area, the less servo action is produced whereas if you leave too much on, the brake can grab. The trouble is that you are stuck with what you are sold as you can’t put it back unfortunately. Perhaps if you have the time you should strip down the brake again and you will probably find that the shoes still have not fully bedded in, they really can take a lot of time to get that 100% contact. While you are looking, strip them down again and polish and lube the parts I described earlier, assuming you have not done that already. If you have, then it will be down to the other reasons I have mentioned. Another thing that can reduce performance is ovality of the drum; as a drum brake can only work well if the drum is perfectly round and the shoes can apply pressure and get the force multiplied by the self servo action. If the brake drum surface is moving in and out relative to the shoes, the action is spoilt. Longer brake arms can help but too long an arm will create too much movement at the lever. The same effect of increasing leverage can be obtained by using levers that have ¾” pivots rather than 1” pivots. The brake is very similar to a Velo Venom size wise and design wise which is known to be an excellent stopper. So there is potential there.

I have lengthened the levers on my Inter and the Meteor by 40mm but the increase in braking performance was only marginal. Must have worked a bit as I'm still here to talk about it. Probably the reason not many Series 1 Inters left

I find the brakes acceptable on my Classic 350 until they get warmed up; then both front and rear snatch a lot, I've tried cleaning out, chamfering leading edges etc. but to little avail...... any ideas?

Hello P. As you can see from the graph: http://www.nagtroc.org/forums/index.php ... -for-2012/ ..................brake material (I know this is for discs but applies to drum brake linings too) you can see that the friction increases as temperature rises from ambient up to a maximum and then tails of with further increase. Any further chamfering is wasteful of braking power when the brake is cold, but as you have found out, as they warm up the action becomes much more powerful and in your case excessive. It could be that the return springs are very weak or have stretched as this will let the shoes snatch more. Otherwise I reckon the only cure is to try some different linings with a more stable or reduced friction increase V temp.

This graph shows the effect very clearly: http://www.hemmings.com/hcc/stories/201 ... 7848560218

This graph sows why The leading shoes/s takes a time to really bed in and work well:
http://www.hemmings.com/hcc/stories/201 ... 1375....As you can seethe greatest braking force occurs at the pivot end and not at the top cam end. When new the movement outwards will cause the top to contact first which creates the servo action, after the top section of the lining wears down it is only then that the lower section (The most powerful area due to the leverage by the top section) can do its job. This can take some time but will occur naturally. Don't forget that even with the most careful setting up of the 2LS brake's two levers in relation to each other, there is likely to be one shoe contact just a fraction before the other shoe. With further bedding in, everything will contact simultaneously and the most braking power will be obtained from then on.