Cycling UK Forum

What's in a name, eh...? Io is the name of one of Jupiter's larger moons (first spotted by Galileo) as well as in Greek mythology, the name of one of the goddess Hera's priestesses, whom Zeus unfortunately turned into a heifer for some reason. Quite what any this has got to do with a disc brake is anyone's guess, but Io is also the name of one of Tektro's more basic mechanical disc systems, commonly found on workaday fodder such as various Carrera bikes including the Subway disc models for at least a decade. So is this brake an out-of-this-world stopper or -being slightly unpredictable and overweight perhaps- more of a, er, heifer?

I should mention that I have owned used and/or worked on about a dozen sets of these calipers and they have for the most part just worked. Not always brilliantly, admittedly, but I can put problems down to rubbish pads/cables and/or contamination/bent discs in most cases. Finally I have got around to stripping one of these calipers down; below I describe what I found.
First impressions are not enormously favourable; there is a brake arm which lacks any radius for the cable to wrap round, which means the brake MA (mechanical advantage) will vary slightly through the stroke, and the cable may eventually fatigue near the pinch bolt. The brake also looks a bit of an awkward lump by comparison with (say) a BB5 caliper. The caliper body bolts directly to either a post mount or an ISO adaptor, and there is no sign of provision for anything other than slight lateral adjustment; there are no caliper positioning (CPS) washers as found on BB5 and BB7 brakes. The main adjustments are to the cable (eg using the barrel adjuster) and via the fixed pad adjuster (FPA) which uses a 5mm key.

However appearances can be deceptive; the complete caliper (including pads, all bolts and ISO adaptor -large rear 160 type as in the photo- ) weighs 244g, which is only about 12g more than the aforesaid BB5. And when the caliper is stripped down, you can see why there are no CPS washers or similar; they aren't needed. Both the pressure foot (PF) and fixed pad foot (FPF) have an articulated endpiece which bears against the brake pad.

In the case of the PF, this both allows articulation (so that the brake pad always self-aligns to the disc) as well as allows rotation, so that the moving piston can rotate independently of the PF. Both endpieces can articulate about 3 degrees (they are fully offset in the photo); more than enough to allow for any reasonable caliper misalignment and any reasonable angled wear in the brake pads themselves. The articulation is based on a large spherically curved seat, estimated at about 15mm radius. The movement is spring preloaded (in such a way that I couldn't see how to disassemble it easily) so that a substantial pressure is required before the articulation will reset. This means the brake pads are unlikely to move/reset accidentally.

The PF is actuated by the usual arrangement of three balls (in this case 7/32" diameter cf 3/16" in many others) on ramps. Unlike Avid BB calipers, the shaft of the moving piston is a fairly close fit in its bushing. When new this lot is lubed sparingly with a MoS2 paste lubricant; in this well-used brake the lube was still evident. Like BB series calipers the spring provides both return spring torque and axial preload on the balls and ramps. There is a spring preload adjustment grub screw (2mm key) in the caliper body; this adjusts the torsion preload independently of the axial load.

There is another grub screw (2mm key) which can bear against the two flats on the moving piston shaft, where the brake arm mounts to it. This is a (poor) attempt to make up for a fairly sloppy fit between the brake arm and the shaft.

The pads are retained not by springs (as in most other disc calipers) but by magnets set into the foot endpieces. There are two small neodymium magnets set into each one, slightly underflush. When in good condition these provide enough force to retain the pads in position quite well. However they can lose force two main ways; most brake pads create iron dust and this dust can cover the magnets, shunting the field away from where it is needed. This can be overcome by simply cleaning the parts eg when the pads are changed. The other main way the magnets can fail is if they become demagnetised. This will happen if the brake gets above a certain temperature, and the loss of magnetism is permanent rather than temporary. It isn't known what temperature this occurs in these particular magnets, but in Nd magnets it typically varies from ~100C to ~200C depending on the grade of material used.

Now, it seems very likely that on a long descent the brakes will easily get hot enough to cook the magnets, so maybe this is the achilles heel in these calipers. Certainly I have seen other calipers with (less good?) magnets in them which have mysteriously weakened, but not these (yet). This also means that (unlike pretty much every other mechanical disc caliper) I wouldn't recommend that you use sintered pads in these calipers; they conduct the heat many times faster into the pressure foot assembly, and would more easily cook the magnets. So organic/semi metallic pads only, or other pad compounds that don't conduct heat well.

The FPA uses a ~M11x1 thread and is deterred from rotating accidentally by both the magnets and some kind of soft threadlocking on the FPA threads. If the threadlocking fails (as it surely will, in time) the threads can be made draggy again by using a little PTFE tape on them.

To change the pads, it is not normally necessary to split the caliper halves; the caliper body gap is ~4mm at the 'exit' (of the disc as the wheel rotates) and almost 6mm at the 'entry'. This allows pads in and out of the caliper entry once the brake disc is no longer in the caliper gap. It also means that even very worn pads shouldn't eject from the exit gap, but might come out of the entry I suppose if you apply the brake with very worn pads when wheeling the bike backwards. Note that it is possible to wear these pads down more than in many other caliper designs; there are no springs to tangle with the disc when the friction material is half-worn. It isn't a smart idea to deliberately wear pads to the death, (since the remaining friction material may spontaneously part company with the pad backing when it is very thin) but you could wear these pads that far if you wanted.

Organic pads wear a fair bit quicker than sintered ones, but maybe that is compensated for by being able to wear another 0.5mm off these pads if necessary.

Pads are identical left and right, and if they wear with a slight taper on, can be swapped left for right when half-worn, to even the wear out.

There are two 'tektro' branded M6x1 threaded 10.9 grade capheads which hold the caliper halves together. These have captive washers a bit like the bolts that are fitted to many handlebar stems. They have ~22mm of threaded shank available. I would imagine that slightly longer bolts could be fitted if the female thread is tapped full depth in the LH half of the caliper body. If these bolts are disturbed it isn't a bad idea to use threadlock on them during reassembly.

The barrel adjuster on the caliper body isn't quite long enough to allow for a full pad life, so the cable has to be reset in the pinch bolt or an additional barrel adjsuter (eg on the lever) needs to be used. The standard barrel adjuster also doesn't have any locking mechanism; you can see in the photo that I have added a spring to the dismantled caliper.

Now there is one significant quirk remaining in these brakes: Back in the far mists of time discs were often 165-22 or 165-20 sized, i.e. they were 165mm OD and had a track width of 20 or 22mm. Hope C2 and Giant MPH brakes were made this way; both common MTB stoppers 20+ years ago. BB-series brakes originally used 165mm discs too. However over time things have changed; currently shimano make 160-15 and 160-16.5 discs and these sizes are used by a lot of other brake makers too. So no surprise then to find that Io pads have friction material which is meant to engage with a ~17 mm brake track on a 160mm disc. In fact these brakes are most commonly seen in conjunction with a 160-18.5 disc, which presumably allows for a little leeway in position.

However you can see that the friction material is not centred over the pad backing. Nor is it centred over the pistons, either; in fact the calipers are positioned on their adaptors so that a 165mm disc will fit in them without clashing and if only the friction material were more extensive, they would work with 165-20 or 165-22 discs, which is presumably how they were originally intended to be used. The pad backings that fit these calipers also fit Tektro Gemini, Tektro Novela (pre 2009) and some promax calipers (amongst others). If you go to buy Gemini pads, many of these have a wider, non-offset block of friction material. These can work in Io calipers with 165-22 discs or can be modified (by grinding the friction material away) to work with 160-15 discs (as can Io pads in fact) or 160-17 discs with piston-centred friction material, provided the caliper position is adjusted slightly to suit. Note that full size friction material (22mm x 22mm) on these backings gives the same wear area as many other current brakes (eg 16mm x 28mm) but lower disc temperatures and lower pad/disc wear rates because the track width is greater.


'Io' pads with offset/reduced friction material, suitable for use on 160-18.5mm disc


full-size friction material for use with 165-22 discs

The mechanical advantage of these brakes is about 17.5:1, i.e. the moving piston moves 1mm for every 17.5mm of cable pull, which matches V brake levers fairly well. If you use adjustable levers (eg avid speed dial) you can fine tune the system MA vs the running clearance of the brakes. It also occurs to me that it would be easy enough to file another slot (the other side of the pinch bolt) to make the brake arm a bit shorter, (reducing the caliper MA slightly) in which case these calipers may work well with NSSLR cable pull (i.e. current shimano road STI and some tektro) road levers on a road/touring bike.

The magnetic system in these calipers may in fact withdraw the pads more squarely than in most calipers which have pad springs; these brakes usually rub because the standard discs that come with these brakes are often not particularly straight; with good discs it may be possible to accept a reduced running clearance and use a brake setup with a high overall MA which would be good on a loaded touring bike.

So overall these brakes are better inside than I expected, are (with a little fiddling) compatible with a wide variety of discs and with one or to caveats (such as the possibility of losing strength in the magnets) I think they are nothing like as bad as one might expect.

You've got a response at last, Brucey, five years later! I remember you posting it at the time because I've got Tektro Novela mechanical disc brakes on my Carrera Subway, which I think are more or less the same as the Io brakes - is the Novela a later, slightly tweaked version of the Io? It all looks very similar but I can't find the grub screws you mention.

I know these basic Tektro mechanical disc brakes have a reputation for being pants but I've found that as long as they're properly set up, bedded in and kept adjusted (and people often don't do any of that, that's the problem!), they work just fine, which was evidently your experience too.

The reason I'm posting this, though, is that this afternoon I opened one up for the first time (before I remembered this thread). I found this YouTube video...



...which is a bit basic - he just takes it apart, cleans it and puts it back together but doesn't lube or replace the balls - but it was still helpful.

What I need to clarify is what grease to use for the balls and ramps:

The PF is actuated by the usual arrangement of three balls (in this case 7/32" diameter cf 3/16" in many others) on ramps. Unlike Avid BB calipers, the shaft of the moving piston is a fairly close fit in its bushing. When new this lot is lubed sparingly with a MoS2 paste lubricant; in this well-used brake the lube was still evident.

I'd to look up 'MoS2 paste lubricant' - is this what I'd use? The balls and the ramps were pretty dry. And just out of interest, why that type of lube?

Thanks.

MoS2 paste typically contains about 50% MoS2 whereas moly grease typically contains far less, about 1% or so. The paste will carry on lubricating without melting, even at elevated temperatures. Honda call out the paste in the assembly of some items. Sometimes you can get away with something else, but sometimes you can't. Be suspicious of any grease which claims to be good for car wheel bearings, because it cannot have a high proportion of MoS2 in it, since it causes the balls to skid at high speeds, which quickly becomes destructive. It is just possible to have a grease which has enough solid lubricants for use in CV joints etc, but not so much that it causes skidding. Most of the Moly greases you can buy fall into this category, because they are cheaper to make and they are 'safe' too; if it looks like grease, sooner or later someone will stick it in a car wheel bearing.

Thanks, Brucey. So it's paste I'm looking for, not grease. That tin in the link might not be the right stuff, then. Don't suppose it matters, it's just a tiny amount - you said 'sparingly' in your first post. I'll maybe just give it a smear of Parks grease - I don't run these brakes hot, the bike is just used for transport and gets a quiet life - no mountain descents!

It's just that I came across this post from another forum that came up randomly in an internet search - I found it before you even posted this thread and I've been a bit concerned since, which is why I eventually got around to opening the brakes up, but it's never happened to me and the bike must have done at least 10,000 miles (I've just replaced the pads a few times):

The caliper uses 3 ball bearings that run on 3 ramps. When you press the lever the ramps move, and the bbs push outward against the shallow part of the ramps. For some reason, which I suspect has to do with too high tolerances in the manufacturing process, the bbs will sometimes 'jump' into the next ramp and land in the deep part of it. This results in a 'click' and total loss of braking power. It seems to happen when the bbs have worn a little and it doesn't happen in every caliper. My front Novela never had this issue and it's the one that gets used the most often and the hardest. I replaced the 3 bbs with new ones and put some new grease in. The issue was solved. About 8 months later it happened again with the new owner of the bike. I changed the bbs for a second time and the brake is stopping once more. I don't know how long it will last.

More reassuringly someone else came up with this in response:

I have serviced those brakes a bunch of times and it usually ends up being a "step up bearing" issue - one of the bearings becomes worn, out of round, so no matter how much force you apply they won't hold. You can easily fix it by taking the caliper apart and replacing the bearings, The standard bearings are cheap ss/g100 bearings, so when you replace them use chrome stainless steel, with at least a grade 25, and then those calipers will last forever.

So once I've double checked what size I need I'll get a pack of grade 25 bearings (IIRC they're 3/16" - I've got one of these Park Tool rulers that let you measure spoke length and bb size - I checked one but forgot to write it down!).

I think maybe the 'issue', which would be serious if it happened, might be because the rider isn't keeping the brakes adjusted and the actuation lever is having to move far further than intended, causing excessive wear on the bearings.. That's my theory anyway, you can tell me if you think it's right or not.

What a great read - thanks. Makes you realise how much knowledge, skill & effort goes into modern artifacts. Also the big difference between a brake like this and a relatively simple design like one of Tektro’s own cantilever designs, say.

what you want is for the entire depth of the ramps to be used up either never or once there is no life left in the pads. If you see wear marks which indicate that the balls have run nearly all the way up the ramps, you know that you are perhaps using a worn disc, worn pads, or perhaps the caliper isn't very well made. All mechanical 'road' calipers have short, steep ramps and (especially if the design was originally for a MTB brake) the arm can appear to just stop, seemingly only half-way through it's travel. Or, (especially if there are no pads and no disc) it might just go 'click' as the balls run off the ends of the ramps.

Either way, it is as well to find out what limits there might be to your brakes before your life depends on it.

Brucey wrote: ↑11 Apr 2024, 5:45pm Either way, it is as well to find out what limits there might be to your brakes before your life depends on it.

That's why I opened them up and dug out your thread!

My life's been depending on them for a while, mind you - I found the forum posts I quoted from years ago, when I was learning to set the brakes up and I've been wary since. I've heard a wee 'click' every now and then when I apply the brakes, even from when the bike was new, but there's never been an issue. It doesn't sound as if it's happened to you either, even though you said you used these brakes extensively yourself, or I guess you'd have mentioned it. When I inspected them yesterday, I took a magnifying glass to inspect the ramps and balls and there's no wear I can see, although the ramps/balls were dry.

Even when I keep everything perfectly adjusted, the braking is never as good when the pads are more than half worn than when they're new, although I think that might apply to most brakes. Tektro advise compressionless cables in the tech doc and the Subway didn't come with them, just spiral wound, so I might as well fit some with new cables as well as the new pads and see how good I can get the braking to work. It's not bad as it is, though.

My other Subway with the same brakes took me round 'The Wee Mad Road' (I only found out it was called that after I'd ridden it!) from Lochinver around the Assynt Peninsula to Kylesku Bridge, the bridge in the avatar. The descents around there are as mad as the climbs and the corners and I survived.

have you identified what will happen if you try to use more travel than normal?