BSA-Triumph conical hubs
aka "comical hubs". But bad brakes are no joke
▲ Two sides of the brake plate from a much derided 8-inch BSA-Triumph conical hub. Some riders are happy with these stoppers. But most are not. We've had mixed results but have learned how to get the very best from them.
Quick links
Top brake tips
1. Chamfer the leading edge of the brake lining material. In other words, put a gentle bevel on it. This helps the brake shoe engage smoothly with the brake drum. Don't breathe the dust. Chamfer the edge in open air, preferably whilst wearing a face mask. Don't make the chamfer coarse or rough. Keep it smooth. Just take the edge of the shoe material.
2. Talk to your brake specialist about the most suitable material for brake shoes. Explain your riding style and habits. Green Ferodo material used to the choice for thousands of motorcyclists. But modern substitutes have long since established themselves.
3. Some riders take a hacksaw and cut two angled slots across the top of each brake shoe to help shift or dispel water. If you try this, you MUSTN'T cut too deeply into the brake shoe material. Think of it in the same way you think of tyre tread. You want grooves, not gouges. Don't sniff the dust.
4. If you allow the brake material to wear down too far, you risk exposing the rivet heads that secure the material/lining to the shoe. Those damaged rivets can score the brake drum (which you don't want), and/or the brake material can break free (and you don't want that either). Check your brakes a couple of times a year at least, and keep an eye on your mileage.
5. Check the cable regularly and look for signs of fraying or other damage, especially around the nipples. Replace a damaged cable immediately. Don't buy cheap eBay cables. Use a cable specialist.
6. Look at your brake levers. Are they right for your bike? In other words, do they appear to have sufficient leverage? Do they "bottom" out against the handlebar grip? If you or someone else has changed those levers from standard, they could help diminish braking power. Talk to owners of similar bikes are compare the levers and braking experience.
7. Check the cable routing. Too many kinks will increase friction in the cable thereby making it harder to apply sufficient force. Teflon lined cables don't need lubricant, but it won't hurt. For other cables, use a light machine oil. Avoid letting the oil travel into the braking mechanism.
8. Don't over-tighten the wheel spokes. On conical hubs such as these, this isn't a common problem. But on a weaker, pressed steel hub, or other lightweight hub, it can distort fairly easily. Nevertheless, wheel spokes can occasionally distort the conical hub brake drum. So go easy.
9. Rivets or bonded brake shoes? Both methods have their fans and supporters. We're traditionalists and we usually opt for rivets. Yes, you can do this yourself. But we'd recommend a specialist every time unless you know exactly what you're doing—in which case you probably won't be reading this.
10. Glazed brake shoes can be gently sanded with emery cloth or similar. But again, put a mask over your nose. Asbestos is no longer generally around, but you might come across some NOS (new old stock) material. It's much better for stopping your bike than much, or most, of the modern stuff. But it can be killer.
11. Some guys have stuck emery cloth on double-side tape to the brake shoes, and then spun the wheel with the shoes inside. This supposedly helps the shoes adjust to the shape of the drum. Sounds right in theory. You might try it if you're on a budget. But wear a mask. Remove minimal material. Take care down there.
12. You can use chalk or engineer's blue on the inside of the brake drum to check where the shoes are making contact and thereby identify problems or dips or high spots. Try it. It might work for you.
13. Before you load up your bike with bling and chrome and paint, sort the brakes out. Get it rolling properly before you get your posing duds on.
14. If you lay-up your bike for a while, try and lay it up dry. Water and condensation will corrode cast iron hubs, and it won't necessarily corrode evenly. You can clean off the rust (wire brush, steel wool, etc), but your brakes could end up "grabby". So make sure the bike is perfectly dry. Ideally, ride it for a few miles and warm up those brake. Also, when it's laid up, spin the wheels occasionally. It makes your bike feel wanted and will help prevent brake seizures.
15. Brake dust is one of the major everyday brake problems. The dust prevents the shoes from getting a decent bite. To deal with this, remove the backplate and wipe out the dust with a damp (not dripping wet) rag and dry asap. Don't use the family vacuum cleaner unless you're throwing the dust bag away. You don't want to spread that material around the house and murder the kids. Or you might use some duct tape to pick up the dust. Just get it out.
16. When rebuilding brakes, remember to check any bushes or bearings. This kind of stuff is routinely overlooked. So get a little technical, will ya? It's a good habit and might save your life.
17. Don't trust in miracle braking products or sprays or gizmos. Good traditional maintenance is the key. Just be thoughtful and think about what the designer was trying to achieve. Brakes work because sensible mechanics make them work.
18. Remember to use copper grease (Copper Slip or something), and not too much. We know that you're not stupid enough to put grease on the brake shoes or in the brake drum, but we're going to tell you not to, anyway: DON'T USE COPPER GREASE ON THE BRAKE SHOES OR THE INSIDE OF THE BRAKE DRUM. Don't use any grease on the brake shoes or the inside of the drum.
19. Can you fit a later Triumph T140 disc brake set-up to an earlier oil-in-frame Triumph T120 or oil-in-frame BSA A65? The answer is yes, and it's fairly simple. You'll arguably spoil the looks, and you'll lose marks for originality. But if you're planning to do any serious travelling, the disc is the way to go. You'll want the wheel, forks, yokes and everything including the hydraulic master cylinder. You can reduce costs by selling-on your conical hub front end, but you might be wiser to keep it.
20. On the other hand, you can easily convert a disc braked Triumph T140 to earlier Triumph T120 conical hub set-up if you prefer the more "classic" look. We've seen it done a few times, mostly on choppers and cafe racers and suchlike.
| The Problem
It was a few years back, and we had this 650cc Triumph T120. The bike had had a hard life before we got it. But it was almost as cheap as stealing one, and it seemed to have a lot of heart. Some bikes are like that, you know?
Anyway, it was as rusty as Mars. But the engine was pretty free and loose, and the bike could crack-on when you whipped it hard. The gearbox operated by mere thought. The handling was positive. And that T120 just sounded right.
Shame we flogged it.
▲ The BSA-Triumph conical hub brake plate. Simple to understand. Simple to build. Simple to rebuild. But harder to get to work well. However, it's not impossible...
But the brakes had totally lost their grip on reality. We had more than a few near misses on that bike, in between which we fiddled with the mechanism and fooled ourselves that we'd made some kind of improvement. But at the next emergency, fate took up the slack and we understood that it was time to pull over somewhere warm and dry and check the anchors out properly before God checked us out, and then checked us in.
We're talking about conical hubs, of course, frequently referred to as "comical". But the joke is really on the guys and girls who, like us, fail to maintain them properly and fail to understand their strengths and weaknesses.
Fact is, these brakes are simply not the best in the world. Not by a long way. Yes, some guys have got them set up so sharply you could use them to lock up the Bank of England. But if the average guy or girl can't sort 'em in the garage/shed with a few tools and a few curses, then there has to be something more fundamentally wrong with the design. Put another way, a system is only good if it's manageable and works more often than not. And conical hubs are not. Or put that another way, a good system is more or less idiot proof. And this isn't.
But don't panic. If you're running a bike with conical hubs, you can make them perfectly acceptable. In fact, maybe they're already acceptable and you're thrilled with them. But you're never going to make them really GREAT brakes—or maybe someone out there knows better.
Meanwhile, here's what we did...
▲ That's an 18-inch wheel with a typical BSA-Triumph conical hub at the centre. These need to be perfectly round, not oval. That means having them skimmed by a professional. The hole at the back of the drum (at roughly one o'clock) is for getting access to the micram adjusters (see the text for details).
The Solution
The first thing was to get the bike jacked up and supported. There was no centre stand, so we improvised with a jack and some blocks of wood. Then we took the front wheel out of the front fork, removed the tyre and inner tube and just looked at the wheel for about half a hour. Until then, we figured that conical hubs worked like Lego; you stuck the bits one on top of another, and finally you had something that looked right. But clearly it doesn't work like that.
Brakes exist to convert energy. Kinetic energy, that is. Movement energy. You stick energy in the fuel tank, and you burn it in the engine, and it drives you along. You waste a lot here and there (wind resistance, heat loss, engine component friction, electrical energy, noise energy, and so on). The brakes, meanwhile, are there to convert kinetic (movement) energy into heat energy and get shot of that energy. At its simplest, that's the whole thing.
If you can convert as much kinetic energy as you want or need into heat energy, and then get rid of that heat into the atmosphere, you've got all the braking you'll ever want. Understand that, principle and you're a lot closer to sorting out your brakes.
▲ Looking for a complete conical hub brake? Try this Netherlands-based firm. They seem to be on the ball and have a lot of interesting stuff at competitive prices: www.obsoletebikeparts.com
With this conical set-up, you've got a tapering aluminium housing that carries both the left-side and right-side wheel bearing. The hub tapers simply to cut unsprung weight and save material. On the right side of the housing is the detachable brake plate. Just inboard of that is the right-side bearing. The brake plate carries the brake shoes, the return springs, the micram adjusters and the brake tappets.
The inside of that conical aluminium housing is the brake hub. It carries a cast-iron band. That band is for the brake shoes to press/act upon. Without that band, the brake shoes would have to act upon the aluminium hub, which would soon wear it out. Cast iron, meanwhile, is one of the best/most cost-effective materials you can have for brakes. There are all kinds of technical reasons for this that are beyond the scope of this feature. Just take it for granted that the aluminium hub and the cast iron band are what you want.
However, these two metals expand, and they expand at different rates. That's important to understand too. When that drum is cold, the brakes act upon that drum. The brakes are adjusted (cold) for minimal clearance. We're talking a millimetre or so. Or less. When you grab the brake lever, you're closing that gap. So far, so good.
However, when the brake hub is hot, it expands. The aluminium grows in all directions. The cast iron band grows in all directions too. But whatever else happens, the cast iron band in the hub moves AWAY from the brake shoes. Put differently, the cold brake drum is the RIGHT size.
The brake shoes are designed to press against the inside of that drum, remember. But heat them up and the drum heats up and moves away (outward). Heat the shoes up some more, and the drums move further still. There comes a point when the brake shoes simply can't make sufficient contact with the drums, and that's brake fade.
This is what happens when you ride down a mountain with switchback roads and keep applying the brakes. They fade. Same thing in heavy traffic, or when racing around a track and repeatedly applying the brake. Heat, fade, heat, fade, heat, crunch.
Now check this graphic and see what's moving what.
The two images are of the same component shown from either side. That's the brake plate. It carries the brake shoes and the actuating mechanism. One brake actuating arm on the brake plate operates the top shoe (note that the graphic shows exaggerated travel of the brake shoe. In reality, the movement is very small).
The right hand brake actuating arm (the foremost of the two) operates the lower shoe (once again, the angle of movement is exaggerated in the graphic). Both levers move inwards, and in unison. The mechanism works because the outer brake cable is anchored against the rearmost brake arm (i.e the one on the left; the brake arm nearest the frame). The inner cable is hooked onto the other brake arm (the "front" or foremost one). Therefore, the levers are squeezing towards each other when the brake is applied. And they spring back when you release the brake. The return spring sits between the two levers coiled around the inner cable. This system is a twin leading shoe arrangement. Or 2LS.
Single leading shoe v twin leading shoe
There are two basic types of motorcycle drum brake shoe arrangements on British bikes. Single leading shoe (SLS), and twin leading shoe (2LS).
A LEADING shoe is stronger than a TRAILING shoe, but only when travelling forward. A LEADING shoe means that the shoe is designed to connect with the drum at the OPPOSITE end of the shoe's pivot point. Put another way, a LEADING shoe opens TOWARDS the direction of rotation. Check the image below.
So why is a leading shoe stronger/better? Because it has a self-servo tendency. In other words, there's an initial "bite" that happens when the shoe and the drum connect. That contact then drags the shoe harder against the drum, thereby increasing frictional contact, and so on.
If the shoe opened AWAY from the direction of rotation, the drum would be trying to CLOSE the shoe rather than OPEN it. In other words, the brake shoe would be DRAGGED along rather than PRISED open.
With the BSA-Triumph conical hub, it's a twin leading shoe arrangement (2LS). Both shoes open TOWARDS the oncoming drum. The rear drum brakes on cars, however, are different. These tend to have one leading shoe, and one trailing shoe. That's because cars need to have brakes that also work in reverse.
To reiterate, a leading shoe is stronger when moving forward. A trailing shoe is weaker going forward. But in reverse, their strengths are also reversed.
Some motorcycles, such as a BSA M20 or a 1959 T120 Bonneville have a single leading shoe (and one trailing shoe). It works, but it could be better. An even better stopper is a four-leading shoe arrangement such as a 4LS Grimeca or similar.
▲ This aluminium conical hub needs to be checked carefully for cracks and other damage. Inspect the wheel bearings too. This is the time to have the hub checked for ovality and, if necessary, skimmed. Brake shoes ideally need to be ground the fit the drum. But you might use off-the-shelf items and get away with a good fit. It happens.
We stripped our conical hub and examined everything. The important thing is to have EVERY part working according to manufacturing tolerances, or better. That's important to understand because manufacturing tolerances aren't always good enough. That means that half a dozen marginal parts can add up to a less than acceptable mechanism. Put another way, one or two components that barely scrape under the bar might not hurt. But the accumulative effect can give you a lousy brake, or a lousy motorcycle.
The best you can do is to consult a factory workshop manual and see if the dimensions are listed. If so, measure them. If they're outside of tolerances, chuck 'em away. Get some new parts, and measure those. Beyond that, try and get your hands on a number of identical parts (at a dealers shop or an autojumble) and compare the sizes. Fudge this and risk bad brakes. As ever, the devil is in the detail.
We checked the rim and the spokes. Decided it would live and saw no other significant problems. Any rim/spoke problems could be dealt with now. We spun the wheel using a couple of axle stands and some make shift clamps and found that the rim had almost no run-out. In other words, it didn't wobble at all. The spokes were tight.
Better still, the drum, amazingly, was mostly okay. Yes, it was a little scored in places (they can pick up stones and grit). But it would clean up well. Actually, we had that checked for ovality and had it skimmed a few thou.
Skimmed? Yes. Machined. By a specialist. The thing is, if the brake drum is oval, nothing else you do will make it better. The drum is the foundation of the braking system. A certain amount of run-out is acceptable. That run-put is different for different bikes. But we ain't going to give you numbers for this because the thinking appears to be constantly changing, largely as a result of new brake shoe materials coming onto the market. But you MUST check the run-out if you want a really good brake. You won't have to do this every week, or every year. But if you're rebuilding a conical hub, or any drum, check for ovality. Talk to an expert.
Next, we refitted the inner tube and the tyre. We used some new rim tape, but the rubber was still good, and we'd spent most of our money anyway.
But the brake shoes needed to be replaced and ground to suit the profile of the drum. This is not strictly essential, but you'd be very well advised to have the same brake specialist deal with this.
Why? Because he'll have the right equipment. He'll have the knowhow and the skill. And he can get a nasty disease from breathing all the brake dust so that you don't have to die young. Well, not from that, anyway.
There are different grades of braking material for different uses; road going and racing, etc. We specified road-going, with a bit of traffic light and roundabout racing, and got what we got.
▲ Extended brake actuating arms. We reused our (standard) arms. But these items are new and offer extra leverage for greater braking muscle. That's the usual "quick fix" that rarely works without proper maintenance. Talk to British Cycle Supply in Nova Scotia. www.britcycle.com
With the hub and brake shoes back from the specialist, everything was checked on a bench and fiddled with. The brake actuating arms were kept. They had been binding in their housings. A lot of muck and grit gets in there, plus a lot of water and road salt. That causes the brake actuating arms to work much less efficiently—and you'd be surprised how these can muck up your stopping power.
They need to be a free and easy fit, but not sloppy. And they need to be coated in a smear of copper based grease. Better still, take 'm out after a few months of use and grease 'em again. But don't overdo it. Too much grease can melt and get into the hub and get thrown onto the brake shoes. Just use a smear.
The tappets (image immediately below) needed a smear of copper grease. They were checked and double checked for ease of movement. But again, not too loose. You want a nice sliding fit. At the top of the tappets are the micram adjusters (eyes right). These, as their name might imply, allow you to adjust the lift of the brake shoes for that final fit. More on that in a minute.
You can (copper) grease these components too. Just a dab. Later, after you've run up some miles, you can grease 'em again. This is all part of the fun of riding with drum brakes.
With clean hands, we refitted the other components according to the workshop manual. We had a Haynes manual too, which didn't tell us very much new, but helped reinforce what we already understood. Or thought we understood.
After we get the shoes back, we checked the mechanism and ensured that the brake actuating levers were raising the relevant brake shoes. It seemed okay, so we refitted the brake plate to the hub and wiggled it into place. It was tight, so we backed off the micram adjusters and tried again.
This time it slipped in, and we tightened the central nut. That's what holds the backplate to the hub. But—AND THIS IS VERY IMPORTANT— it's the brake torque arm you have to watch. That prevents the back plate from spinning. Leave that torque arm undone, or loose, or fudge it with a weak nut, and it could come free and kill you. Check it. Double check it. Then check it again.
There's a hole in the tapered side of the wheel hub protected by a grommet. You need access to that hole to poke a long screwdriver through and adjust the micrams. That involved keeping one micram backed off and working on the other (you can spin the wheel to get access to both adjusters).
You need to reach a point where the relevant brake shoe is just coming on. It doesn't matter which one you work on first. Just take your pick. Then you need to back that off a little, and you'll probably need to experiment a little until you get a feel for the movement.
Then we rotated the wheel to bring the hole in the tapered side of the wheel hub opposite the other micram adjuster. Then we adjusted that until it just came on, and we backed that off a little.
A little more fiddling gave us the clearance we wanted. You should just hear the brake shoes whisper, but you don't want them chattering or feel them binding. We spun the wheel a few times and tried it over and over again. The wheel kept stopping in more or less the same spot, so we added another balance weight on the opposite side and sorted that out.
▲ Rear conical hub brake diagram. Same principle as the front, but this is a single leading shoe stopper. Has reasonable feel and keeps the nether end in check, but it's not terrific. T120 Triumph Bonnevilles and early T140 Bonnevilles fitted these. Dittos for various BSA twins and triples.
▲ The same maintenance principles apply to this rear brake cam which is suitable for a range of British classics including the Triumph T120, early T140, and X-75 Hurricane, plus the BSA A65, A70 and Rocket 3. But whatever you're running, the important thing is to check the individual brake components for condition and smoothness of operation. Maximum parts efficiency is demanded for maximum braking grip.
Conclusion
Five minutes later, the job was done. Tighten up all nuts. Double check. Check again. Then the bike was road tested. The brake was good. Not perfect, but they never are fresh from the box. They have to bed in a little. The trick with "new" brakes is to use them intelligently and give the shoes and the hub time to cool between "grabs". That above all else.
We've seen painted hubs on some bikes, by the way, and we don't much like those. Paint can help trap the heat in the drum, and we're not convinced that highly polished hubs work best either. We prefer hubs that have been gently bead blasted. A rougher surface helps scrub away the heat.
On reflection, we might have tried to affix a gauze filter on the air scoop to keep the muck and grit out. But it never occurred to us at the time. This job was done a while back, and none of us here at Sump can remember what it cost either. In any case, it's what it costs now that counts, so you'll just have to phone around.
But check those dimensions. Argue. Make sure the components you're using work together BEFORE you put the brake plate back on. Don't scrimp here. A front brake accounts for around 60-70 percent of your stopping power. Or more. If you've got a friendly local partsman, explain what you're doing and take the brake plate into his shop and try and select the range of parts you need and fit it up there and then. That's not so easy to do these days, in which case you'll just have to do whatever you can do. But don't assume the part is the right size or shape just because someone else says it is.
One hundred miles later, the brakes on our T120 settled down nicely. At two hundred miles, they were good, but never great. There was plenty of feel and feedback, mind, and the bloody things just made us ride faster. But they were never bad after that (for the remainder of the time we owned the bike).
Since then, we've had two other bikes with conical hubs (a Triumph and BSA), but our current Triumph Twins are running either discs or full width hubs. But the conical set-up did work for us. And it can probably work for you if you just set it up right.
Think you know better? Good, drop us a line at Sump and we'll include your thoughts/experience.
Conical hub brake links
Adrian Young sells BSA and Triumph spares. Check him on eBay. ades-restorations2012
This firm is well established and is based in Nova Scotia, Canada, and New Jersey, USA. They have a lot of stuff and are very proactive.
SRM are in Wales and have oodles of experience in sorting out general British bike problems. They can also skim drums and sort out brakes.
We don't know too much about this firm. But they're in Biggleswade, Hertfordshire, and have wheel machining/skimming experience. Make your own enquiries.
Sump visitor feedback:
Dear Sump, Knowing your love of the venerable and very useable T140, I thought I would write to tell you the latest news on my own T140/TR7. I got it off a French banker. Yes, that is banker; over in the west of France. Nice man, and an uncommon seller as he openly admitted to not having an ounce of mechanical knowledge in his body. Rare, as most people think nothing of telling you how they have done this and that and how clever they. More often than not one could bet that once purchased and towed home, a full re-build is required. Anyway the banker wanted to offload it as he had realised that this was not going to be his 'second youth’ and on top of that the brakes didn’t work very well!
A year later, Arthur is as always submerged, I brought the bike back to France and gently pottered around while the ’new’ engine fell into place. You can’t really fault a T140 1973 Tiger—aside from the fact that the gearing is a little on the low side. And given the almost empty and very well-maintained roads in France, we tend to thrash it bit over here. Radars are generally pointing at you, so we ignore those and the French motorcycle policeman is an enthusiast and generally understanding of anyone on something ‘oldish'.
So I had a look around the blogs. I had already filed out to put a 21 tooth gearbox sprocket on. It’s an easy job and it nearly gets the revs down enough. Someone told me that they thought it was possible to put a rear 46 tooth sprocket on, others told me it wasn’t as the conical hub gets in the way. Further research led me to Rebel Gears in Crossville TN USA, phone calls were made to Brad Chestnut over there and money sent. This afternoon I put the new one on and went for a quick trip in the cold. The results are perfect, so anyone with a conical hub and a yearning for less revs, pointless to do it for higher top speed, should not, in my opinion, hesitate. www.rebelgears.com
|
Our parts looked to be mostly scrap. The cable was fairly new, but was looking a bit ugly. The operating brake arms were shot. The brake shoes were worn and glazed. The micram adjusters were dead (we'll come to those). The brake cam tappets were badly worn too (we'll come to them in a moment, as well). There were no obvious cracks on the drum. The wheel bearings felt fine (actually they had been changed about six months earlier). The brake springs (see inset, right) were changed as a matter of course, and the new ones felt much better.
These conical hubs have brake arms that squeeze together. Each arm operates a small brake tappet. That converts rotary movement into up-and-down movement. And it's that movement that directly raises the brake shoe.
It gets a big fiddly hooking the springs over the shoes. But they will go in the same way they came out. If we did that job today, we'd use a digital camera at every step and record it all. But this happened when we were still using film cameras, so we had to rely on memory.
With the wheel refitted, we put the new cable on, and we smeared some more copper grease on pretty much anything that moved. Except the tyre. Then we shifted to the opposite side of the bike.
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