BrownhillsBob's #365daysofbiking

On a bike, riding somewhere. Every day, rain or shine.

Posts tagged ‘disc’

#365daysifbiking Brake spring broke

February 5th – I have absolutely no idea at all what’s happened here at all.

It started at the weekend – a rubbing on the front disc brake on my current bike of choice. A light rub, no more that a tickle.

As the days progressed it got worse, and defied my attempts to adjust it away.

In exasperation, I removed the brake pads, which were OK at about 60% remaining.

The leaf spring that keeps them off the disc however, was broken. This was allowing on pad to rub.

An easy, 30 second replacement. But I’ve never had a spring fail like that that hasn’t been worn on the disc as the pad ran down.

This is most peculiar. I shall keep my eye on things in case it’s something significant.

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#365daysofbiking The daily grind:

25th November – A mechanical job that should have been easy was far from it. Replacing brake discs resulted in a struggle with seized fasteners, the failure of a brake calliper and the discovery that the parts I thought I had in the spares box brand new for this eventually were in fact the wrong ones.

The front disc was so badly worn it was starting to warp.

For a job I thought would take 15 minutes and leave me bags of time to get out turned into hours and I was lucky to get time for tea…

Perhaps I shouldn’t leave it so long next time.

#365daysofbiking Spring has sprung:

September 13th – Spotted in a customer’s bike shed, and improvised, clever repair to a brake calliper with a broken return spring.

The return spring – present in some form in nearly every type of brake – forces the brake off once the lever is released.

Since the brake cable pulls the yoke awards the cable end stop to engage the disc brake fitted here, forcing the two apart will duplicate the effect of releasing the brake as performed normally by a return spring. The spring has clearly broken and instead of replacing the whole calliper, the owner has released the cable, threaded on a very stiff spring and re-assembled the cable. The cable retains the spring and the brake operates as normal.

Clever. I’m impressed.

December 13th – The snow, ice and road grit is destroying the brakes on two bikes at the moment. This rear disc is now wearing considerably, and is about 0.3mm thinner than it was new, and the front, 0.7mm. That doesn’t sound much, but once you get to about 1mm worn off, the discs get so thin they buckle and become useless. 

One thing about cycling through the winter: It isn’t cheap!

November 27th – Been a while since I discussed brakes here, but the glazing issue of the rear pads I had – I think I’ve cracked it. And built Frankenbrake as a result.

I, like many utility and commuter cyclists, like to ride a bike that’s essentially a tourer. I like the bars, the variety of positions, and I like that Shimano finally made hydraulic brakes for road and cyclocross bikes with the same bars.

The trouble with tourers for years has been that they’re mongrels. No one groupset (ie. drivetrain with brakes and controls) is wholly suitable. Tourers carry load, don’t mind a heavier bike as it’s sturdy and stable. They like a wide gear range – preferably a triple front ring. And solid wheels with damn good brakes. 

So a good tourer may have utlegra, SLX, XT and 105 series parts all working together.

Brake options have traditionally been anything you want as long as it’s canti, but since road discs and suitable frames appeared – first cable, then hydraulic – our braking options have improved. 

My rear brake – A Shimano R785 lever with a BR785 calliper – has been eating pads. They appear to glaze, loose all friction, and no matter how well cleaned, filed or surface ground, never regain bite. Pads are not cheap. I thought I’d cracked it using Uberbike pads – but the last two sets have gone really quickly.

The last set went a week after fitting, and without the same happening on the front, I decided to solve the issue. I’ve been using a primitive parking brake on trains – I use a rubber loop to keep the back brake on to stop the bike rolling about. It turns out that the brakes aren’t designed for continual operation like that, and the vibration from rocking was weeping fluid out of the piston seals, on to the back of the pad plate, and dropping the odd drip of fluid onto the rotors.

I’ll stop using the band. But that left me with a possibly faulty rear calliper, which has never been quite as snappy as I’d like. And Shimano are transferring to flat mount – a format incompatible with my frame – for their 785 replacements.

I knew the 785 was a variant of the XT mountain bike, 2 piston brake with slight design changes in shape. Reading about, I found people who’d put Shimano 4 piston callipers on XT levers for mountain bike use, so I figured a 4 piston Saint calliper should therefore work with a 785 road lever, as the same oil volume was being moved as the XT model, if you see what I mean. They all use the same hoses and fluid, a light mineral oil.

So I ordered a saint calliper, got the bleed kit out, and got oily. The result is that the Saint calliper works really well, has a much bigger pad friction area, and is nice and firm, yet progressive. It’s a bit more fiddly to set up as the piston stroke isn’t as large, but it’s working well with patience.

To any home mechanic who’s thinking about this, it’s an excellent upgrade – but as with any brake fluid operation, remove pads and keep well away from the disc as you will spill oil everywhere.

Meanwhile, a slow handclap for Halfords. When on the off chance I called in for a bottle of Shimano mineral oil brake fluid, the twit behind the counter said ‘Use Dot 4 – it’s all the same stuff.’ – it so isn’t. Dot 4 is Glycol, not oil, and will swell and perish Shimano seals and cause premature failure. Urrrghh.

Now, let’s see how well these pads last…

September 3rd – It’s been a while since I bored you with disc brake pads, so it’s your lucky day – or maybe not.

I favour a hydraulic disc brake on all my bikes, road or off-road. On road bikes, I think the Shimano 785 based callipers are the bees knees; combined with a decent disc and pads, they control my resplendent girth down the steepest of inclines and without snatching.

The only issue I have – and I’ve covered this before – is the mystery of what exactly happens to rear pads in particular when they overheat. Sometimes, despite the best care, pads will develop a sheen, lose the nice grip and squeal horridly. I’ve been trialling aftermarket alternatives all summer to see if other manufacturer’s inserts are better.

I tried Kool Stop, an expensive brand. They were nothing special, and glazed out. Clarks performance was tepid, but lasted well. My best results have been with Uberbike sintered and semi-metallic. These are an interesting design – 785 road pads normally have a backplate with cooling heatsink fins. Uberbike have separated the two, so you can re-use the cooling fins on a slightly thinner pad, which are only £6 a set instead of the £20 for a set from Shimano. And they work a dream.I had one set glaze out near the end of life, but other than that, great.

I thought the front set had taken the same dive while winding down from the Roaches the day before, becoming squeaky and losing friction, so swapped them in the workshop the next day, to find the pads had worn to the spring, and that was the wail.

I really do recommend Uberbike pads.

February 23rd – Back to brakes. This has really caught my attention, sorry.

Following the brake trouble I’ve talked about where pads suddenly lose effectiveness in my hydraulic disc brakes, I’ve decided to try alternatives to the stock Shimano pads. 

I wasn’t expecting them to be any good – I was wrong.

I’ve tried the Kool-Stop first. This company makes a very highly regarded road brake block, and I was interested to see how that translated. After initial disappointment, I’m actually quite impressed.

These resin pads are described as having a ‘rotor saving compound’, which usually means they’re soft and not too effective. My fears seemed to be confirmed on the first two or three days of use, when stopping power was poor and the brakes noisy. 

I then rode in the rain. This appeared to bed the pads in and they’re now every bit as good as manufacturer originals in use. They aren’t quite as snatchy, which is good, to be honest, but they do bite when demanded.

The question is, how long will they last? We shall see. But my initial feeling is that although they took an age to bed in, they’re great pads.

January 25th – It perhaps hasn’t become apparent yet to most folk, but to cyclists and those bound to the outdoors, this has been quite a grim winter. 

We’ve had far more frosts this year than last, and consequently, there’s been a lot more salt on the roads. The damp but not terribly rainy conditions have led to a corrosive, goopy, sticky road grime that coats the bike and is taking a steady toll, particularly on the wheels and brakes. 

Investigating a rub tonight, I noticed the corrosion on the disc pads, and the badly grooved disc. Aluminium parts are developing a familiar white bloom. There is surface rust on the exposed bare steel surfaces of pedals and bottom bracket.

When the weather clears, all this will need attending to. 

September 20th – Spotted in a customer’s cycle shed, two bikes side by side that illustrate something that annoys me.

Shimano, the Japanese industrial giant that revolutionised cycling are not what many people imagine them to be. They are essentially production engineering experts, probably more than they are bicycle technology or fishing equipment manufacturers.

Shimano make loads and loads of great, well thought out products that I love. their work to refine the derailleur gear system in the 80s and 90s, their clipless pedal systems and electronic gear technology have changed cycling for the better immensely. But something more than these innovations has had a massive influence.

Shimano sell innovative kit to bike manufacturers. That means they also sell and produce the tooling to manufacture bikes en masse. Shimano often market products to manufacturers because they’re cheaper or easier to assemble on a production line, but sometimes of little discernible end-user benefit.

Shimano pioneered the external bottom bracket, a frankly piss-poor idea that is hated by lots of cyclists for it’s increased wear and susceptibility to corrosion. Shimano invented it to make assembly of bikes from one side far easier. It shifted to producers in large numbers and is now, sadly, ubiquitous.

Similarly, for years, bicycle disk brakes – which I love as a technology – had their rotors attached to the wheel hubs by six M5 screws, like the bike in the top picture. This ‘6 bolt’ design has been a standard for more than a decade, and works well. You can feel if there’s a securing issue without the loose disc being dangerous, and the rotors are light and easy to replace with standard workshop tools – usually an Allen or Torx driver.

Shimano recognised that a big cost in disc brake adoption to mainstream bikes was assembly of the disc onto the wheel – six screws require either a complex, mutispindle head or an operator repeating the same action 12 times per product. So they invented Centerlock(sic).

The lower picture shows a bike with a Centerlock rotor.

Centerlock uses a splined male dog on the hub, and a special brake disc with a mating female recess. The rotor slides onto the splines, and is held in place by the same type, thread and tooled ring that holds the gear cassette on a rear wheel, thus requiring one tool to fit the cassette and two brake rotors, a huge cost saving in production.

Centerlock rotors are heavier, and you need a special tool to fit or remove them. If the ring comes loose, there’s nothing else to hold it.They limit consumer choice of aftermarket replacements.

There’s a whole industry sprung up around centre lock to 6 bolt adaptors.

This change in technology was introduced purely for the benefit of bike manufactures, arguably to the detriment of consumers and to me, is inferior.

Rant over.

August 1st – A mechanical mystery. Three month old Shimano hydraulic brake pads, which suddenly lost grip and appeared to be glazed or contaminated. The pads are the sintered metal type and are genuine manufacturer parts.

Sometimes, long periods of braking can ‘glaze’ pads. causing them to become highly polished and shiny, meaning they don’t work well. The common treatment for this is to file the surface of the pad and pop them back in. 

These I have degreased, cleaned, filed and even surface ground, but whatever I do they quickly glaze again. New pads of the same type were just fine.

Anyone got any idea what’s going on here? I’m wondering if overheating has caused the pad material to harden…