- Given how exposed the rear derailleur is,
they work really well,
but you've got to look after them.
If your rear mech is poorly adjusted,
a little bit bent or even just old and rattly,
you're not gonna get the shifting that you need.
So, here are the top five shifting problems
that typically occur and how to avoid them happening to you.
(whoosh)
What is a derailleur?
Well, a derailleur simply is a mechanical device
for derailing the chain and putting it in a different gear.
Over the years they've progressed,
and they're a little bit different,
but they still operate on the same principle.
The cage itself has two wheels,
known as jockey wheels or, sometimes, guide wheels.
The upper wheel is there purely just to keep the chain
in line with the cassette and make sure the gears line up.
The lower wheel is part of the sprung cage
and that is there to take up the slack in the chain
that occurs when you're shifting
from a larger gear to a smaller gear.
It's a non-adjustable clutch system, works really well,
and it has a lock on the cage just to get
around that when you're removing the wheel.
On the Shimano system they're got a lever
to turn the clutch on and off,
so you turn the clutch off,
so it makes it easier to manipulate the cage
with less spring tension to remove the rear wheel.
Your rear derailleur, or mech,
will simply not shift accurately
if it is not aligned on the bike.
So, the rear mech itself fixes
to the mech hanger here, okay?
So if that is bent in any sort of way,
you're not gonna get everything lined up.
So, the first two ways to check that,
obviously visually look at the hanger itself.
Then you want to align your bike up in the highest gear,
so that is the smallest sprocket in the back,
and look for the cage, just following
the smallest sprocket down here.
The next point to check is when you're in the lowest gear,
so that's the biggest sprocket at the back.
You want to check that the jockey cage,
that's the guide wheel and the lower sprung wheel,
are following completely in line with that.
So, if the mech itself is bent,
as long as the guide wheel will follow the chain line
you can get good shifting.
On certain bike designs, the mech hanger
has always been designed to break
before the rear derailleur or the rear mech.
These are actually incredibly strong
and very hard to bend or even harder to bend back.
So, if this is bent
and you do need to try and bend it back be very careful.
If your mech hanger is bent, and you need to
sort of persuade it back into shape,
the way to do that really is by using
a proper alignment gauge, like this.
That's quite a specialist and expensive tool to use.
You simply just bend it, and you can align it
with the wheel using this adjustable gauge.
The easiest thing to do actually,
just use a good old-fashioned adjustable spanner.
Adjustable, for obvious reasons,
you can clamp it around the mech hanger itself.
But bear in mind, if you do actually need to do this,
you need to flip your gears so your derailleur is
in the slackest position, so that's your highest gear,
using a five-mil Allen key,
or in some derailleurs now it's a t-25 torx,
remove the actual derailleur from the bike.
Your next adjustment is on the limit screws.
So you get a high and a low limit simply
by just adjusting the parameters of how far
the derailleur can travel in either direction.
So, what we're gonna do first is just make sure
that the whole rear mech is aligned
and limits set on the highest gear,
so that is this furthest one.
If you're too far towards me,
it's just gonna make a bit of noise like this.
(clicking)
See it's not really in the right place,
so it needs to go further in inboard.
If you're too far inboard it's actually
gonna try and shift up a gear.
So I'm just making the adjustment,
turning it counter-clockwise until it looks like
the upper guide wheel is directly below.
So now that the adjustment is made in the highest gear,
so the smallest sprocket,
I'm actually gonna repeat the same thing
but for the lowest gear, so the biggest sprocket.
If you get it wrong on the biggest sprocket here,
and your chain hooks over the top,
a few things can happen.
First, you can damage your spokes on the wheel,
which is never good.
Secondly, the chain can get really badly wedged
down the back there and can snap the chain in doing so.
But a worse one is if it all gets bound up in there
and it rips your rear mech clean off the bike.
The B-tension is on the back here,
and that screws straight on towards the mech hanger.
And what this is for is for setting the height position
of the guide wheel in relation to the biggest sprocket,
so that's your lowest gear.
So, if there's too much tension,
the gap's gonna be really big,
your downshift is gonna suffer at that,
it's not gonna shift very well,
and it's actually gonna stretch the mech out so much,
that it's barely gonna have any spring in it.
With the B-tension fully wound out
I'm just gonna show you the effect this has on the bike.
On this particular bike with it fully wound out
I'm finding that the top guide wheel's
actually catching on the biggest sprocket
as you change into that gear.
'Course, that means your shifting isn't smooth,
it isn't consistent, and it's not ideal.
Now I'm gonna show you the complete opposite.
I'm gonna wind it in too far
so the mech is actually stretched out
and I'm gonna show you the effect that that has.
The mech is almost locked.
That's a really bad position for it to be in.
So, there's two things that are gonna happen.
If you go over a massive bump,
that chain is so stretched there's a really good chance
you're gonna snap the chain or at least the rear mech.
And the other one is, listen to the noise this makes.
You can tell this isn't right.
(clicking)
Rear derailleur should be fairly silent in operation.
Not a sound like that when it's absolutely stressed.
Now, I've got my B-tension correctly adjusted.
I'm just gonna run it through the gears
just to show you how well it shifts.
Instead of just unnecessarily changing your cable,
a good way to check that beforehand would be
to undo the pinch bolt and then you can
manually feel the inner cable moving
within the outer cable itself.
You can do that at both the mech end and the shifter end.
I can feel the cable moving really easily within it.
So, easy to flush out, if I did need
to change the inner cable or even just clean it.
Another thing to check is your actual inner cable routing
to the pinch bolt on the mech.
It's very easy, when you're threading the cable through,
to not line it up with all the holes in the guide.
The cable goes in at the top here,
it goes around a little wheel,
and then follows this little guide through here.
But there's actually a hole
that the cable needs to pass through.
Very easy to not to do that.
And if that happens then it's never gonna line up.
It's never gonna pull the correct amount of cable
that it needs to to shift accurately.
First things first with the cable tension itself
is to actually clamp the inner cable at the rear derailleur.
A lot of people get this wrong by pulling this cable
through really tight.
But by doing that, you're actually
shifting the derailleur slightly
so what you wanna do is just pull it taut.
No more than that.
The barrel adjust of the shifter will compensate
for any other slackness.
Then we'll start working on the gears.
What you're looking for is one click of the lever
corresponding to one gear shifted.
If you don't have enough cable tension
then the gears aren't quite gonna hop up in time,
and if you have too much it's gonna hop up too many gears.
So it's very important to do this just a bit at a time
and work your way up through the gears.
This should shift perfectly now, yep.
It's fully aligned, my limits are done, my B-tension's done,
and the cable tension is perfect.
So hopefully, this video has helped you understand
the top five shifting problems
that you're likely to get with a rear derailleur.
If you want to find out a bit more about
servicing Shimano gears, click up here.
If you wanna see how to
fix a chain three ways, click down here.
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