- In the weekly Ask GMBN Tech Show
we quite often get asked a lot of similar questions.
So in this particular video,
we're gonna look at five of those
real common maintenance issues
and how you should tackle them.
(pounding)
(sword slash)
Okay, so let's jump into these questions.
And the most common one that seems to come up
on a weekly basis here at GMBN Tech is,
why do my breaks squeal?
There's a couple of different ways they can work,
but the fundamental results are the same,
and if you're getting squeaking or squealing breaks
it's usually one of a few things.
Now the most common one is
that they're not bedded-in properly.
Now this happens more often than you might think.
So, the telltale sign of that is by looking
at the disc rotor surface itself,
and what I'm looking for here is an equal sheen across it.
Note that I'm not actually gonna touch
the breaking surface itself
because oil in my skin can transmit to that,
which causes contamination,
which is another factor that can make your breaks squeal.
But getting your breaks bedded-in is the single most
important thing in the first place.
And the way you wanna be doing this,
with a fresh disc rotor and a fresh set of disc pads,
is ride 15 miles an hour, something like that,
and you wanna do several sort of firm stops.
And the idea is you're depositing some of the material
from the disc brake pad onto the rotor surface.
But you wanna be doing it in a fairly even way
so it applies it all the way round.
After a while this takes
and you'll find that they mate together really well
and you won't actually get a squeaking brake.
However, there are still a number of things
that can make them squeal
and the next one on the list is contamination.
Now, contamination as I mentioned,
happens usually when you're getting oil,
whether that from the brakes themselves,
or something else on your bike,
or even like I mentioned a minute ago,
the oil from your fingertips.
So if your oil or any type of oil
gets near your disc brake surfaces,
whether it's the rotor themselves or the brake pad,
then actually you're gonna find
that these are gonna squeak
and then the end result is they
just simply will not work adequately
and you've gotta do one of a few things.
The first option is a spendy one,
and that means buy some new disc brake pads
and new disc rotors.
However there is another way around that,
and that is gettin' a complete rejuvenation of your brakes.
And the way to do that
is take those brake pads off the bike,
then you wanna clean these
in somethin' like isopropyl alcohol,
that dries up and leaves no residue.
Then you wanna scrub them down
with a coarse emery paper or glass paper,
then clean them again, scrub them again.
You wanna make sure until there's no sign
of any contaminant in them.
You can use dedicated brake cleaners to do this
because they evaporate as well,
but avoid using anything that could have any trace
of any lubricant or oil in it for obvious reasons.
The same goes for the disc rotor surface.
And once you've done this,
you wanna wait for them to be completely dry,
then start the bedding-in process all over again.
If you're lucky and your brake pads
haven't been too badly contaminated, you can rescue that.
And another cause of brake squeal is vibration,
which transmits into these very fine oscillations,
which basically make your brakes vibrate and squeal.
Now this can happen if your brakes
haven't been bedded-in properly
and you end up with an uneven amount
of material deposited on that brake rotor.
You can actually see this when it's happened,
it's like the visual equivalent
of braking bumps on your disc rotor.
What happens is those disc brake pads vibrate super-finely.
If you think how fast the rotor passes the pads,
it's like incredibly fast operation.
And that will end up in some kind of squeak or squeal,
which can be infuriating.
Now of course, vibrations can also happen in other ways.
It can happen if your caliper bolts are loose,
if the disc rotor bolts are loose,
and course that's incredibly dangerous
so you wanna make sure that all of your bolts
are adequately tight all of the time.
Another thing that can happen is,
the actual disc pads themselves
can vibrate slightly within the caliper.
Now make sure that you've got your retaining clip
and the actual bolt that runs through the back of the pads
is on and is holding your brake pads in place.
Also in some cases, it has been known
for particular bike designs to have
that resonation through the frame
that you just can't get rid of a squeaking brake.
Tends to happen on the back rather than on the front.
As we have seen on a few different bikes,
particularly on a downhill workup scene,
is braking dampers that basically absorb that resonation.
Now on Gee Atherton's bike,
as you can see here on-screen,
he actually has a custom-made braking damper
on his rear brake caliper.
'Course this is a pretty unlikely situation for most people.
Think of someone like Gee doin' average speeds
on a World Cup course when he's hangin' on those brakes.
It's a bit different to you or I doin' regular trail riding.
Now there is one other circumstance
when your brakes can squeal.
Now there are different types of brake pad and,
depending on what you use them for and how you use them,
it is possible to glaze the pads over.
For example, you got sintered and you got resin.
The sintered pads have particles of metal in them,
they're generally better in wetter conditions,
they cope with that a lot more,
but they'll also cope with high heat.
Resin pads, less so.
On a resin pad, when it heats up massively,
they can glaze over.
So whilst the resin pad is extremely good and powerful,
they can suffer at the hands of becoming glazed over.
And when that happens, it feels like
you're running with polished brake surfaces.
So although the brake will work,
you're not actually gettin' that grabby feel,
and as a result of that, they can get a resonation,
which again transmits into squealing.
If that's the case then you can start
by renovating those brake pads
just like we showed a minute ago,
and the same with your disc rotors.
But if not, then it might be time
for new brake pads for you.
Okay, so the next one on the list
is also braking related and it says,
why does my brake lever pull close to the bar?
Okay, so there's a few things that this can be here.
So on any set of mountain bike disc brake levers,
you'll find there's gonna be at least one adjustment.
That will usually be the reach adjustment.
Now occasionally that can be wound in too far,
which means your brake lever actually
pulls really close to the handlebar
as opposed to coming on straight away.
So you can play with those.
But the real reason your brakes end up
pulling closer to the lever is, actual brake pads wear.
To compensate for that, the pistons push out slightly
and basically, the fluid has to compensate for that.
So you can counter that with that reach adjustment dial,
but it only goes so far.
So you will find that at some point,
you'll max that out and your lever
will start pulling closer to the bar.
This also happens if you have got some air in the system.
So with air in the system, the case is,
you're gonna have to just give your brakes a bleed
because that is the way.
You might just be able to do a level bleed,
which might be the answer for you,
and that's obviously a very quick
and easy way around the problem.
But as for the lever just pulling to the bar
because the pads have worn.
Firstly, if your pads have still got enough life in them
and you're happy to keep using those,
then you can do what's called a mini-bleed,
which is basically just bleeding the lever.
So the idea of overfilling the brake lever is,
you filling up the reservoir here
with as much fluid as you possibly can,
put the cap back on,
and when you go to pull the brake lever,
you'll find, just because you've overfilled the system,
that the brakes actually feel a lot more solid
and therefore your brake lever will not
be pulling all the way to handlebar.
It's quite a simple process to do.
You can do this on SRAM brakes,
you can do it on Shimano brakes,
and Maguras and (mumbles), most other brakes.
And as you can see on-screen,
I'm demonstratin' here with a set of Shimano brakes,
but the principal is very similar using SRAM.
Except with SRAM brakes, you tend to have to use
a syringe in order to get the fluid into the lever.
You can of course, make sure your levers are horizontal
and add brake fluid directly to those.
And of course with SRAM
you need to make sure it's DOT brake fluid.
With Shimanos and Maguras and other brakes,
it tends to be mineral fluids.
So it's essential that you get
the right fluid when you do that.
Okay, next up on that list is,
why is it hard to inflate my tires through a Presta valve?
Okay, so to understand what could be cloggin' it,
we need to identify the type of valve
and make sure you're usin'
the correct pump adapter on those.
There are two types, there's Presta and a Schrader,
which is also known as car valve.
Now this particular one is threaded all the way down,
but it's quite common to find these
with a black rubber stem
and just simply have threads on the top
with a black cap to squeeze in place.
But more commonly, on tubeless tires,
you see the Presta design.
The Presta valve itself has a few components to it.
It has the valve stem, it has the valve nut
which holds it in place,
it has the valve coil which is actually removable,
and then within the coil on the end,
it has the captive nut which tightens,
meaning air can't go in or out,
and loosens, meaning air can go in.
And when you press it or depress it,
then the air can come out.
As you can see when I do this,
you can see it moving on the inside there.
Now this, fundamentally,
is the thing that can create problems.
If you're running a bike tubeless,
then these can get gunked up.
The tubeless sealant can block up the main valve stem
and actually stop this and congeal it,
much like blood does,
which is really how a tubeless sealant works.
It can actually bung this up enough
that you can get pressure through it,
but very, very slowly.
And quite often, when you're pumping,
because there's such resistance
for that air to get through this,
the actual head of the pump
can pop off the valve altogether.
Now the solution is to take these out
from time to time and clean them.
So if you just take the valve core out of the stem
and clean that in some hot water,
and then any rubber bits you can see, you can pull them off.
Alternatively, you can get,
they're quite hard to get but you can get,
these as separate pieces.
And it's always worth, when you have old inner tubes,
taking off the valve cores, keeping them.
And the same goes for Schrader ones.
You can also remove the coils from Schrader valves,
but you don't need to do that as often
as you would with one of these.
Now the other thing of course with these is,
if you're the ham-fisted type,
they're very easy to damage.
Because as you can see, the nut itself,
what it screws onto there is very thin,
and if you bump that,
it's actually never gonna sit in there correctly.
And what that means is, sometimes it's gonna leak air
or you're never gonna be able
to get air into it in the first place.
So make sure that your valves,
and your valve stems, and your valve cores
are all in good working order.
It's well worth getting a valve core removal tool
like this one you can see on the screen now.
You'll never need to get another one
as long as you don't lose it,
and they work really well.
Now of course, the other thing to consider
is the pump itself that you're using.
Now pumps all have a different chuck or a head on them,
but most modern pumps,
you'll find that you won't have to change anything.
They'll actually include Presta and Schrader.
But even then, it's really important
how you put them onto them.
You have to unscrew the captive nut on top of the valve,
and you make sure you push it
fully into the actual head of the pump,
and then you would engage it like so,
and that means that air will come through there.
(air hissing)
And just to demonstrate, if I close that captive nut,
you will see that air will not go through there.
So you're gonna be struggling, gettin' air through that.
And also just to demonstrate, if it's a tiny bit open,
this would simulate if it's got a blockage,
you're gonna see that air will pass through here,
but there'll be a lot of resistance to it.
See, I can actually compress that,
I can hear it comin' out,
but it's actually really strugglin'.
That's the same effect if it's blocked up.
Next question is another air related one.
Why do tubeless wheels leak/lose pressure overnight?
Okay, so there's quite a lot
of different factors in a tubeless wheel.
So the first thing you need to make sure of
is that your tires themselves are tubeless-ready,
which means they're compatible
to be set up tubeless in the first place.
So if you've got a standard tire that's non-tubeless ready,
you'll find that there's an actual
slight open-weave to that tire.
Now you probably won't be able to see this,
but it will be there.
And although it is possible to set them up tubeless,
they will leak quite often as the air just goes through.
It's a permeated fabric basically,
it will come through there.
Tubeless-ready tires basically seal on the inside
of the actual tire carcass
and it's ready to be compatible with a rim
that has also been made ready for tubeless.
So if you start with that and you got a decent tire,
then first things first, it's gonna work.
The second thing is to make sure that
that tire is seated properly on the rim.
Of course in order to do that,
one of the best little tricks to do
is get some warm, soapy water,
spread it all the way around the rim,
all the way around the tire.
And when you pump it up, the actual water
allows it to slide into place and the beads can lock
into those beadlock areas of that rim.
Of course it's absolutely crucial
for that seal to happen all the way around
because that's what, A: keeps the tire on the rim and,
B: what keeps the air in the tire.
Next up is the inside of that rim.
So most rims have holes all the way around the rim
in which the spoke nipple sits.
And then the spoke goes into nipple,
it's basically like a bolt onto a nut,
and tightens up, pulling the wheel tight.
Now obviously air will leak through those big holes,
so you have to seal up those holes.
Now there are certain rim designs out there available
that have a completely sealed rim bed.
And of course, with that design,
you don't need to seal them up
because they're designed to be set up tubeless as they are.
For the rest of 'em, you'll be using something like this,
some sort of tubeless sealing tape,
which does the job of sealing off the rim bed completely
and making it like a tubeless-compatible rim.
But of course, it's absolutely crucial
for the rim to be completely clean and dry
when you apply this in the first place,
and that you've actually covered all those holes
and it's taken grip.
Because if any of that sealant finds its way underneath,
creates moisture, creates bubbles,
then there's somewhere for that air to get in and get out.
And then finally, there's the valve itself.
Now the valve has to be mounted correctly
in the first place, and the valve has to be
the right shape for your particular rim as well.
Now if I just take the little rubber O-ring off,
if you look at this portion of valve,
if you imagine the inside of the rim bed
will be slightly concave.
The idea of this shape is it sits into that.
Now there are a bunch of different valve stems available
that suit different rim profiles.
So it is important when you buy yours,
to factor in if they're actually gonna be
compatible with your rim.
Now it's crucial that your valve stems
fit your rims perfectly.
'Cause if they don't, you're gonna get
some kind of slow puncture
or you might not even get them
inflated correctly in the first place.
Okay and the final one,
which is one that's actually
been comin' up loads at the moment,
especially after Dakotah Norton
and Rachel Atherton both snapped their chains
out the start gate of Fort William is,
why do chains snap?
Okay, so let's take a look at the humble chain here,
just so you can understand the parts of it
and the things that are likely to go wrong.
So look at it in profile.
You've got outer links here,
then you've got the inner links,
you've got the rollers,
which are the bits in the very middle there,
and you've got the pins that drive through them.
Now the first thing that can make a chain snap
is if the pin itself that runs through them
has become slightly dislodged from the outer plate.
Now you might not even notice this visually,
but you can have an inspection on your chain.
And you can see from the top if any of those
is likely to be slightly further apart than the others.
If there's daylight between any of those
male and female links or the inner and outer plates,
you're actually gonna see that
that will be where it's gonna break.
Now this is why it's important
to inspect your chain from time to time
and why I always say,
when you're washing and lubricating your bike,
to look at every single link on the way past.
A good way to do that on modern chains
is to look where the master link is
and follow it a complete revolution back to there.
That gives you a reference for looking
at the entire chain all the way around.
Now chains do wear and you do find
that chains stretch out with time.
Now you can get a chain wear tool.
If you're running a chain
that's very stretchy and very old,
it's more likely that the pins can become loose
in those outer plates and then later snap.
So if you're running a chain that is knackered,
chances are, at some point it's gonna snap.
So you have to be very careful of this sort of thing.
Chain maintenance is crucial.
And when you have to rejoin a chain,
if you do break one, make sure you do it in a correct way.
Now it used to be very easy usin' a chain splitting tool
to just rejoin these in the existing pin in there,
but it's actually not the best way to do it these days
because of the way the chains have advanced.
Now with Shimano chains you can use a dedicated
master link which they supply.
Or you can use the Shimano pins.
Now they've dedicate pins for rejoining a chain,
and although this is a SRAM chain I'm holding,
I just wanna show you the process of this.
So you would join the chain back together manually,
then you'd get the pin and push it into place,
into that link, then using a chain tool.
You would drive it through
until this outer part of the pin sits flush,
then leaving this part on the inside,
which we just snap off.
Now the chain will be perfectly joined
and it's not gonna break at that point.
It's very slightly tapered,
which is of course designed
to sit into that outer plate.
There's two other important factors
to take into account with breaking chains.
Now the first one is something
that all cyclists should be good at,
and that's changing gear correctly.
Alright, you shouldn't be stamping on those gears
and changing gear at the same time,
your chain being wrenched sideways across gears.
Especially now with so many gears,
there's quite a lot of stress on that chain.
It's hardly surprising you can actually
pull one apart and those links
can actually split open and snap.
You just have to really consider when you change gear.
Even the best sprinters, they don't change gear
as it's got full-load on there.
You might see them powerin' out the saddle
and changing gear, but fractionally,
just as they change gear,
they'll just release it up on the pedals
just for that split second and then carry on
as the gear has already changed.
And of course you also need to choose your timing.
Don't expect to be able to change gear
goin' up a really, really steep, slow hill
and just change into an easier gear.
You have to do the same thing,
lurch ahead slightly, just so you can back off
on the pedals very slightly as you change gear.
It's really, really important to do that
in order to maintain your drive train,
make sure it continues workin',
of course doesn't stress that chain.
And of course the last one is ensuring that your chain
is the correct length in the first place.
If your chain is, let's just say you snap your chain,
you've had to rejoin it
with a couple of links removed because they were damaged,
make sure you don't use your lowest gear,
or the biggest physical gear,
because that's gonna put additional load onto your chain,
especially if you have a rear suspension bicycle.
At the first opportunity,
you should try and replace those links,
or if you need to, replace the chains,
get it back to the correct length
so you can use all your gears
without additionally stressing everything.
So there we go, there's a few of the common questions
we seem to get here at Ask GMBN Tech.
I will be puttin' some more of those on,
including that common question
about the long fork on a bike.
We're gonna look at all these sort of things
in a future video.
So make sure you get your questions in.
Again, we wanna make sure we emphasize the point,
this video's all about those
common questions we get a lot of.
So hopefully this has answered some of those questions.
If you wanna know a bit more
about some of this stuff in depth,
click down there for Tubeless 101.
So that's a detailed video on everything about tubeless.
The difference in the tires,
how to tape up a rim, how to inflate them,
how to do the dry run like I told you about,
it's the whole lot.
That is the video for you.
And if you wanna know how to join a chain three ways,
click up here.
So that's basically using a master link,
using the Shimano pin,
and using the chain tool,
which of course is a get you home version
of how you should join a chain.
But of course, a chain tool is included
on a lot of multi-tools, so it's very valid.
As always, click on the round globe
to subscribe to the channel.
We've got great content for you
every single week here at GMBN Tech.
And if you found this video helpful, give us a thumbs up!
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