So, Nigella recommends 30 minutes at 200oC.
Question is, does it work, and if so, is it safe?
I used to just give them a good blast with the blow torch 🙂 Just do it in stages and when they stop smoking theres no oil left. The trick is to not overheat them so the friction material falls off the backing !!
The million dollar question is normal oven or fan assisted?
Yes it works, I always just heat them with a blow torch or oxy acetylene until the paint starts look slightly singed. What do you think is unsafe about heating something that's designed to get hot?
Our oven is likely to add oil rather than take it away. Plumbers blowtorch is the thing, a really useful piece of kit to have anyway if you don't already, it'll crisp up your Creme Brulee and do plumbing as well.
They will never be the same again the material is porous and will absorb oil. The pad material is also unlikely to be designed to cope with the heat of the blow torch.
You cant ever sweat all the oil out and the pads will be compromised
Bin them at £12 for 3/4 sets of cheap pads why bother.
I thought it couldn't possibly work. Then I tried it and it did. About twenty minute at 180.
It's worked for me for mildly contaminated pads, but a recent case of pads liberally squirted with hydraulic fluid (don't ask) didn't work, so new pads time.
I'd say give it a try - doesn't take much time and effort, but as above pads are pretty cheap. Do remember to degrease the discs first though !
Muc Off works quite nicely for me, but then I have Hope brakes so contamination is brake fluid based not oil.
You could also try dishwasher.
north country boy - the working temp of a disc brake pad is a few hundred degrees c Much hotter than an oven
I have burnt / baked disc pads a few times. Once it then fell off the backing but a few times it worked
A few times it worked!
steering and brakes are things that need to work properly all the time.
Yup - and you can easily tell if it worked or not. Its standard practise to burn off superficial contamination but then I do not use cheap shit pads. I only use hope sintered
I think your over estimating your brake temp considerably
Stopping
Mass of bike + rider = 100kg
Speed = 10 m/s (36km/h, about 22.4mph)
kinetic energy = 0.5 m v^2 = 5000J
A basic 180mm steel brake rotor weighs about 150g and the specific heat of steel is about 0.5 J/gK (Joules per gram-degree), so converting 5kJ of kinetic energy into heat in the rotor should increase the rotor temperature by 67 degrees (C), assuming none of the energy is absorbed by the brake pad, caliper body or brake fluid (not realistic, but useful to identify an upper bound for the rotor).
Descents
To maintain constant speed on an even slope, the change in gravitational potential energy must equal the heat energy extracted by braking (plus other sources of friction and drag that we're ignoring).
Descending a 1 in 10 slope for a 100m distance gives a height change of 9.95m (not 10m, because the distance is along the hypotenuse).
Gravity on earth is about 9.8 m/s^2.
Energy change = m g h = 100 * 9.8 * 9.95 = 9751J
This would increase the rotor temperature by 130 degrees.
Descending a 1 in 10 slope for a 100m distance gives a height change of 9.95m (not 10m, because the distance is along the hypotenuse).
10m isn't a very big hill.
Sometimes I'm fortunate enough to go places a bit hillier than that.
In fact, come to think of it, even living in Cambridgeshire that's possible. Madingley Mountain is higher than that!
I've had good results getting rid of mineral oil this way. Doesn't take much (10min at 200C). Equally, getting them properly hot on the bike also does the job. I did it a few times when trying to diagnose leaking calipers. Once I eventually got the calipers replaced, one final blast in the oven and they've been perfect since.
Last ones I did , I threw in the oven when it was doing a prophetic cleaning cycle. Think it's about 450 degrees for an hour. Uber pass were fine after, the other lads which I can't remember the name of turned to dust
i have always used the gas hob. Depending on what has contaminated them you can sometimes see a colour in the flame. The problem with replacing pads is that you have to wait for the postman to deliver them.
I sprayed mine with isopropyl alcohol then blowtorched them. They were ok after.
Didn't work so well with Greene King IPA.
I think your over estimating your brake temp considerably
Did you work any of that out or just copy and paste it from here to look scientific?
https://bicycles.stackexchange.com/questions/47326/maximum-brake-temperatures
If you're hard on brakes light brown to bluish discoloration is easily possible which I think from memory indicates around 250-300 degrees C?
The tandem brake discs are blued badly. Regularly get well above boiling point as you can tell when you put water onto them.
Disc brakes are badly misunderstood by many mtbers.
I always tend to think its my disc brakes that don't understand me.
I think your over estimating your brake temp considerably
Stopping
Mass of bike + rider = 100kg
Speed = 10 m/s (36km/h, about 22.4mph)
kinetic energy = 0.5 m v^2 = 5000J
A basic 180mm steel brake rotor weighs about 150g and the specific heat of steel is about 0.5 J/gK (Joules per gram-degree), so converting 5kJ of kinetic energy into heat in the rotor should increase the rotor temperature by 67 degrees (C), assuming none of the energy is absorbed by the brake pad, caliper body or brake fluid (not realistic, but useful to identify an upper bound for the rotor).
Descents
To maintain constant speed on an even slope, the change in gravitational potential energy must equal the heat energy extracted by braking (plus other sources of friction and drag that we’re ignoring).
Descending a 1 in 10 slope for a 100m distance gives a height change of 9.95m (not 10m, because the distance is along the hypotenuse).
Gravity on earth is about 9.8 m/s^2.
Energy change = m g h = 100 * 9.8 * 9.95 = 9751J
This would increase the rotor temperature by 130 degrees.
Just buy new pads, they are not expensive and quite and important part of the bike!
Re: sweating the oil out - obviously you clean them up as much as possible with disc brake cleaner first. The heat then pyrolyses (possibly with some combustion also) the oil that is left. There will still be some "contaminant" left in there, but it will not be friction-reducing oil, it will be carbony stuff. You will need a high temperature to achieve that, I am not sure a hot oven will quite make it, hence the blowtorch.
Descending a 1 in 10 slope for a 100m distance
But our brakes work much harder than that when we need to stop from 30mph at the bottom of a 1:5 in a third of that distance...
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<div class="bbp-reply-content">Just buy new pads, they are not expensive and quite and important part of the bike!
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It's a tricky one - my life depends on these pads and they're contaminated. Shall I attempt a half-arsed bodge in my kitchen that probably won't work, or spend a fiver on some new ones?
I coat my pads and discs in Isopropyl and then use a lighter to burn anything off.
I have recently burned my fingers using a lighter so I have just ordered a camping gas blow torch to use instead, must make sure I am not near any seals when doing this, their fur goes up like a christmas tree!
To be honest, if you usually fit £5 pads I would just buy some new ones.
That sounds snobby, lol, which I don't intend it to sound like! I just mean that some people spend a lot on branded pads so I can see why they try to save them but for a fiver id fit new. 🙂
I don't and won't use cheap brake pads. False economy. Lightly contaminated pads can be cleaned up easily - why throw them away when its easy to save them. The only ones that this failed for for me were cheapo ones - they fell off the backing plate. If the bond is destroyed to the backing plate when heating in a flame then its likely they will do the same when used hard when riding.
Buy cheap - buy twice
Done it on bimble shop bike not on the gnarr bike.
I don’t and won’t use cheap brake pads. False economy. Lightly contaminated pads can be cleaned up easily – why throw them away when its easy to save them.
I'm with you... I've blowtorched Shimano ones no problems from light contamination and mostly they are then more reliable than cheap ones.
@tj
The temperature of an oven is nowhere near to the temperature of a blow torch .
I've got some leaky calipers on the fatbike. If I've not ridden it for a week or more, I need a steep hill and some hard braking to get them to stop squealing and start working well again. No bother where I live, I don't need to brake heading up the hill from my house, and there's plenty of opportunity to get them up to temperature from the top.
I wanted to use it for a ride last week where there isn't a decent downhill until mile 13. Thought I'd try the hot air gun instead. checked disc temp with a spitty finger, and got the pads similarly hot, got a bit of smoking and the bottom-of-a-big-hill burny smell.
Worked a treat.
Some interesting reading on the boiling point of various fluids DOT and mineral. We know that the fluid is insulated from the heat by the piston but the radiant heat must be similar to the surface of the disc / pad.
According to the web site Magura Royal Blood boils at 120 degree C. I would think if the pads were seeing anything close to 200 degrees that would cook the fluid, but it doesn't seem to happen.
http://www.epicbleedsolutions.com/blog/dot-brake-fluid-vs-mineral-oil/
I've soaked in meths and then set fire to them. Seemed to work. Also rubbed them with alcohol. In the absence of Isopropyl, the wifes gin works quite well
Well over 200degrees north country boy. Want to see some nicely blued stainless discs?
We know that the fluid is insulated from the heat by the piston but the radiant heat must be similar to the surface of the disc / pad
You would be surprised how much difference there is between pad temperature and fluid temperature. A lot of race car brake pads work upto 700 degrees C yet the best brake fluids have a wet boiling point of only 270 degrees C.
I have had my fair share of very hot brake discs
1. Don't get shit on your brake pads.
2. Just buy some new ones if you do
I don't think I've ever managed to contaminate brake pads, but I think I'd just replace them.
so what about putting then on the stove. would that be hot enough?
Hi,
Gas hob is doing the trick. Tried it several times whilst having leaky SLX piston. Few minutes of burning over the flame, cool them down, sand with fine sand paper.
Good as new.
Saved my arse whilst I was in Scotland and realized that rotors got black, sticky smears.
Works of course only with metallic or sintered pads. Big no-no for organics, Kevlar and likes.
Cheers!
I.
I clean them up with dish detergent and hot water first, then a quick blast from a blow torch and sandpaper. I always put the damaged pads in the back just in case they fall apart, but hasn't happened yet in probably half a dozen goes over 15 years.
Necro!!
Yes, putting in the oven will bake off some contaminants.
Magura Royal Blood boils at 120 degree C.
Is that at atmospheric or under compression in a closed system?
Is that at atmospheric or under compression in a closed system?
As soon as you release the brakes, the system is open and the pressure drops to atmospheric. The fluid will then boil and force fluid out of the caliper and back into the reservoir. The next time you squeeze the lever, there won't be enough fluid in the system and you won't have any brakes.
If you have a fully closed system, the pressure needed to stop the fluid boiling will cause the brakes to drag.
I would describe a braking system as closed but not a closed loop. If your braking system is open you've got a problem because your fluid is free to leave. That would be bad. Many braking systems don't return to atmospheric when the peadl is not depressed. The MGB for instance maintains around 8psi in a mixed disc/drum system.
When you have the brakes applied, which is when you produce the heat, the fluid is under anything up to around 2000psi. And 120 sounds way low for brake fluid to boil, hence my question.
120 sounds way low for brake fluid to boil
Magura fluid (and Shimano) is mineral oil, which has a much lower boiling point than proper DOT brake fluid. For reasons that I don't understand, people think mineral oil has benefits over proper brake fluid. Overall, I'd much rather have a system with DOT fluid.
DOT brake fluid is mildly nasty stuff if you spill it, it will dissolve paint and is toxic, and it absorbs water if exposed to the atmosphere. When it does absorb water, the water will be distributed throughout the fluid and will reduce the boiling point. However, even DOT fluid with quite a lot of water in it still has a higher boiling point than mineral oil. On top of that, if water gets into a mineral oil system, it will gravitate to the lowest point, which is generally the caliper. The most likely mechanism for it entering the system is working its way through the caliper seals as they flex when you apply the brakes in heavy rain, during water crossings, etc. If this does happen, then the droplet of water in the caliper will boil at 100 degrees Celcius, so it will flash to steam if you are applying the brakes hard and then release them. Mineral oil isn't as harmful to paint as DOT fluid, but it is still toxic, so I don't really see much advantage on that front. On top of that, you can buy DOT fluid at any petrol station, whereas manufacturers of mineral oil systems insist that you must use their special oil (which isn't really special, it's just a hydraulic fluid with a different label on the bottle).
Brake systems are open in the sense that there is a reservoir that is at atmospheric pressure. There is a rubber bladder above this to allow you to turn the bike upside down, but the reservoir itself is not pressurized. When you apply the brake lever, the port to the reservoir is closed and then pressure builds up in the brake system. When you release the lever, the piston in the master cylinder retracts past the port to the reservoir and fluid can transfer between the master cylinder and reservoir. As soon as this port is open, pressure in the system drops to atmospheric. This means that the boiling point is lower once you release the brakes, so water in the system can flash to steam and drive fluid out of the system and back into the reservoir, resulting in brakes that don't work.
Drum brakes require a small amount of residual pressure in the system to prevent the wheel cylinders from leaking. This is not relevant to disk brakes, the seals work in a completely different way. Even then, the small amount of pressure is not enough to make any substantive difference to the boiling point of the fluid. Fluid must be able to return from the wheel cylinder to the master cylinder when you release the brakes or else the brakes would bind, so this residual pressure is massively lower than operating pressure. Systems like this are still open.
Did you work any of that out or just copy and paste it from here to look scientific?
Amazing 😂
Shimano Mineral oil has a higher boiling point than all DOT fluids even before they’ve absorbed any water.
https://www.epicbleedsolutions.com/blog/dot-brake-fluid-vs-mineral-oil/
Sorry, when I said "mineral oil" before, I was referring to the Magura stuff, which has a strangely low boiling point.
One thing about DOT fluid is that the specifications are the minimum requirement, so DOT 5.1 is required to have a dry boiling point of at least 260 degrees Celcius. Good quality DOT fluid will exceed this. As a random example, Castrol SRF is sold as a DOT 4 fluid, but advertised as having a wet boiling point of 270 degrees Celcius and "the ability to withstand temperatures over 300°C". I don't know where the claimed boiling point of Shimano fluid comes from, but the real world benefits are pretty much limited to not melting the paint if you are careless and don't wash it off after you bleed your brakes.
For the record, my bikes have a mix of Hayes El Camino, Hayes HFX, Shimano Deore, and SLX brakes. They all work fine when they are properly bled.
Sorry, when I said “mineral oil” before, I was referring to the Magura stuff, which has a strangely low boiling point.
Hang on. According to the STW "experts" all mineral oil is the same.
I've made a complete mess with brake fluid many times and yes, it only damages paint if you don't wash it off. At least, the paints on which I've spilled it. Also ruins car tyres if you don't wash it off.
I reckon the bladder in most brakes is good enough to seal the system so no water vapour gets in ever. I go many years without bleeding Hope brakes, they still work well.
Depends on if it's a fiber or sintered pad.
Fiber based pad. No. You'll die.
Sintered. Yes, and you'll get more power.
Works of course only with metallic or sintered pads. Big no-no for organics, Kevlar and likes.
Why? They're brake pads, they are designed to get hot. Cooking them for long periods probably isn't a good idea but sticking them in a flame for long enough to get them smoking won't do any harm.