Mechanics Quick Question Thread [Ask Questions Here]

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Mechanics Quick Question Thread [Ask Questions Here]
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Posted: May 11, 2021 at 12:39 Quote
seraph wrote:
I've heard that new crowns can actually reduce premature creaking.

Interesting and encouraging!

Posted: May 11, 2021 at 14:16 Quote
Can I just take one minute to give some advice about looking after your brakes?

Mountainbike brakes make noises. They will always make noises. It doesn't mean they aren't working, and you won't completely eliminate it. If your brakes have suffered a sudden drop in braking power, then you have an issue. However:

Don't set fire to your brakes, pads or rotors
Dont blowtorch your brakes, pads or rotors
Don't put them in the oven
Ever

Boiling anything in water probably doesn't do any harm, but it doesn't really do any good either. It just makes them hot and wet.

You probably don't need to sand them. Sanding can help with glazed pads, although usually it doesn't help much. They will never be as good as new, but sanding does help. However, unless you descended a literal mountain, with your brakes dragging most of the way down, (and I'm talking 5 minute plus descents here, not the 20 second hill on the way home from the corner shop) then your pads probably aren't glazed.

Sanding can help with an overheated rotor. Like if your rotor has actually gone black after an extreme descent.
If your rotor is silver and looks relatively normal, you probably don't need to sand it, except for in very unusual circumstances.

Spraying stupid shit on your bike (mad bike wash detergents, silicone shine, mud repellant, excessive lube and even scented f*cking brake cleaner) will screw up your brake pads. If you have done this, just buy new pads, spray a bit of plain old brake cleaner/ipa/acetone (without any stupid additives, scents or "pad conditioners") on your discs then wipe and hose them off. Fit your new pads. expect them to take a few days to bed in.

If you keep contaminating pads then you probably have a leaky caliper. Get your caliper serviced, stop spraying your bike with scented polish and see if the problem goes away.
(symptoms of contaminated pads being that the wheel literally won't lock up on flat ground with a good hard pull, and makes a loud low pitched honking noise like a goose. Symptoms of contaminated pads DO NOT include "my 2 pot caliper with a bad bleed and 140mm rotor won't stop me when im descending a vertical wall with 40kg of concrete in my backpack")

Sorry for the rant, but I see so many people constantly fettling their brakes, doing all sorts of crazy "hacks" that just make them worse, spraying them with all sorts of different crap, and these peoples brakes never ever work properly. I tried all that shit in the mid/late 90s when discs were just appearing on bikes. I've tried it all. And guess what? Since trying all that stuff and realising it just makes things worse, for the last 20 years all I have ever done to my brakes is:

1) Be absolutely militant about not letting anyone spray anything other than pure IPA on them. And even that only happens extremely rarely, when I have concerns that I might have accidentally got oil on them somehow.
2) Make sure my caliper is nicely centered on my rotor
3) Replace pads when they are 90% worn. Replace rotors when they are bent
4) Bleed my brakes every couple of years
5) Ride my bike

My brakes always work perfectly. Seriously. They do make high pitched squeaky noises. I like this. It means they are working. If they make low pitched honking noises then they are somehow contaminated and I replace the pads. However this hasn't happened more than 4 or 5 times in the last 20 years.

Posted: May 11, 2021 at 14:35 Quote
gabriel-mission9 wrote:
[sensible stuff]

Good advice that needed to be said.

Two minor points:

1. Regions with large mountains and sustained steep grades can overheat pads. Interior British Columbia, for example - some trails there are truly unique. Even so, damage to the surface of the pads usually wears off quickly. Carbonized rubber components, which are part of many friction compounds, can be permanently damaged.

2. Acetone beats isopropanol for cleaning. Most commercial brake cleaners are just acetone with propellant. Some use chlorinated hydrocarbons, which I don't recommend due to toxicity concerns. Apply acetone, blot with a paper product, repeat if desired. If that doesn't clean the pads, I agree that fire and ritualistic incantations probably won't do much better.

Posted: May 11, 2021 at 14:57 Quote
gabriel-mission9 wrote:
Don't set fire to your brakes, pads or rotors

I disagree here. Burning impurities off of your rotor works for me consistently. I do it for customers' bikes and my own.

Posted: May 11, 2021 at 15:09 Quote
Gabriel-mission9
All good points. Some history of these brakes:
Brakes, pads, and rotors are all bought and used since January 2021. I have sprayed break cleaner on the rotors and dried with proper shop towels. This didn't fix squeaking, so I sanded rotors and pads with 240 grit sand paper. Still didn't fix it so I haven't touched them since. Any suggestions?

Posted: May 11, 2021 at 15:12 Quote
diamondback1x9 wrote:
Any suggestions?

Yes.

Posted: May 11, 2021 at 17:14 Quote
How do you avoid getting the bead in the centre channel? I find that without doing that you don't have enough slack to get the other side over. I haven't tried using soapy water, might give that a go and fall back on rim tape and no TLR strip if that doesn't work.

I don't get up to the pumping stage since I can't get the second bead over the rim.

MarkyB916 wrote:
I have the same (Bontrager with TLR strip). I don't get any issues fitting tyres (Schwalbe). The only tip I can give is to avoid pushing the tyre so that the bead drops into the centre channel.

Do you use soapy water ? I've found a bit of this makes tyre fitting a load easier as it allows the beads to pop into the rim, perhaps it would do the same for allowing them to pop out of the centre channel.

Are you also using a boost pump to get the air in. I bought one after many failed attempts to seat the beads using a normal track pump and CO2 cartridges. The first time I used it their was a loud hiss followed by a number of scary popping noises as the bead seated followed by a perfectly fitted tyre.

Hope that might be of some help.

Simosis wrote:
Does anyone have tips on changing tyres on a bontrager rim with the TLR rim strip? I have not managed to successfully get both beads on (have to pay a mechanic to do it). The strip only has a very narrow channel in the middle which seems to be as wide as one bead. I get the first side on fine, then I can't get the bead out of the channel to get the other side in.

Considering removing the strip and just taping the rim as I would on another wheel, but apparently this rim strip has benefits so it would be great if I could figure out how to mount new tyres myself.

Posted: May 11, 2021 at 17:18 Quote
seraph wrote:
gabriel-mission9 wrote:
Don't set fire to your brakes, pads or rotors

I disagree here. Burning impurities off of your rotor works for me consistently. I do it for customers' bikes and my own.

Agree with this comment burning rotors is extremely effective

Posted: May 11, 2021 at 19:21 Quote
Simosis wrote:
How do you avoid getting the bead in the centre channel? I find that without doing that you don't have enough slack to get the other side over. I haven't tried using soapy water, might give that a go and fall back on rim tape and no TLR strip if that doesn't work.

I don't get up to the pumping stage since I can't get the second bead over the rim.

MarkyB916 wrote:
I have the same (Bontrager with TLR strip). I don't get any issues fitting tyres (Schwalbe). The only tip I can give is to avoid pushing the tyre so that the bead drops into the centre channel.

Do you use soapy water ? I've found a bit of this makes tyre fitting a load easier as it allows the beads to pop into the rim, perhaps it would do the same for allowing them to pop out of the centre channel.

Are you also using a boost pump to get the air in. I bought one after many failed attempts to seat the beads using a normal track pump and CO2 cartridges. The first time I used it their was a loud hiss followed by a number of scary popping noises as the bead seated followed by a perfectly fitted tyre.

Hope that might be of some help.

Simosis wrote:
Does anyone have tips on changing tyres on a bontrager rim with the TLR rim strip? I have not managed to successfully get both beads on (have to pay a mechanic to do it). The strip only has a very narrow channel in the middle which seems to be as wide as one bead. I get the first side on fine, then I can't get the bead out of the channel to get the other side in.

Considering removing the strip and just taping the rim as I would on another wheel, but apparently this rim strip has benefits so it would be great if I could figure out how to mount new tyres myself.
Look towards the bottom of this article

https://nsmb.com/articles/bontrager-line-elite-carbon-wheels/

Posted: May 12, 2021 at 3:15 Quote
diamondback1x9 wrote:
Gabriel-mission9
All good points. Some history of these brakes:
Brakes, pads, and rotors are all bought and used since January 2021. I have sprayed break cleaner on the rotors and dried with proper shop towels. This didn't fix squeaking, so I sanded rotors and pads with 240 grit sand paper. Still didn't fix it so I haven't touched them since. Any suggestions?
I agree with the previous mentioned points. If the brake power is normal, than the squeaking is not a problem, but just a 'feature' of the type of pads.

In my experience also inconsistent feature: humidity, rain, cold it can all influence if it decides to squeak on that particular day. Anyway those things have more influence than trying to something about it yourself.

Posted: May 12, 2021 at 4:06 Quote
seraph wrote:
gabriel-mission9 wrote:
Don't set fire to your brakes, pads or rotors

I disagree here. Burning impurities off of your rotor works for me consistently. I do it for customers' bikes and my own.

Same here. 3 mins on the bbq is better than replacing the pads for me.

Posted: May 12, 2021 at 9:06 Quote
I have fought with brakes a lot, and 8/10 times, new pads are the answer.

I have also had trouble getting metal pads to bed to a rotor that had previously been using resin pads.

I am also flabbergasted with how long it takes to bed in sintered pads on used rotors. Maybe I suck at it, but the video descriptions that imply just a half to a dozen quick stops and they'll be good is not my experience. Water trick, dozens upon dozens of quick stops with appropriate cooling. Always seems like a battle.

Brakes that work 100% when wet, but are shiiiiiit when they dry... sign of contamination or not bedded in yet properly?

Posted: May 12, 2021 at 9:28 Quote
ShawMac,

It's also possible the used rotor has a slightly concave braking surface and the pads are flat. Pads with higher metal content may be stiff enough that there's little contact between the surfaces until the pads wear into a matching concave profile.

Posted: May 12, 2021 at 9:35 Quote
R-M-R wrote:
ShawMac,

It's also possible the used rotor has a slightly concave braking surface and the pads are flat. Pads with higher metal content may be stiff enough that there's little contact between the surfaces until the pads wear into a matching concave profile.

Yeah for sure. I usually look for that; it's easy to see the contact points on the pad. I actually managed to improve that once with a bit of emery cloth to shape the pad once. One needs to take extreme measures when replacement 203 rotors are as rare as unicorns

The latest ones I was fighting with have evidence of good contact across the pad. It's a bike I am selling so I am giving up tossing in resin pads as I think they'll bed in quicker.

Posted: May 12, 2021 at 10:14 Quote
bishopsmike wrote:
seraph wrote:
gabriel-mission9 wrote:
Don't set fire to your brakes, pads or rotors

I disagree here. Burning impurities off of your rotor works for me consistently. I do it for customers' bikes and my own.

Same here. 3 mins on the bbq is better than replacing the pads for me.

I agree with everything gab says except fire. I have had good luck with spraying pads and rotors with IPA and lighting them up until the IPA is burnt off. Sometimes though the contamination is too deep and it doesn't help. Best advice IMO is to keep contaminants away from your brakes which means ditching aerosol based anything for your bike like gab says.


 
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