Last Updated on December 13, 2020 by Johannes Kristjansson
There is nothing more annoying than when you are riding your bike up a hill and you are pushing as hard as you can, almost making it up the hill then suddenly crackling you skip gears and lose the momentum and have to stop.
If you have been riding for some time this has probably happened to you.
There are many reasons this may be happening: alignment issues with the derailleur, mech hanger could be bent or there might be friction in the cable.
We are going to go over 5 common shifting problems and how to fix them.
But first, let’s start with the rear derailleur (often referred to as a rear mech).
What is a derailleur
Put simply it is a mechanical device that derails the chain and shifts gear.
The derailleur has two wheels known as guide wheels.
The higher wheel is used to align the chain with the gears.
But the lower wheel is spring-loaded and takes the slack in the chain when you change from a smaller gear to a higher gear.
Now let’s take a look at how we can take care of this shifting problem.
If the derailleur is not aligned correctly it will not shift accurately.
The rear derailleur is attached to the mech hanger and if the hanger is bent the guide wheel will not align correctly with the gears.
You can check that by looking visually at the hangar itself and then you can put the bike in the highest gear.
Now see if the guide wheel and the gear are aligned then you can repeat that with the highest gear.
If the guide wheel is aligned you should get good shifting.
On some bike designs, the mech hanger is designed to break before the derailleur.
Because obviously, it’s cheaper to buy a new hanger instead of a derailleur.
If a Mech hanger is bent you can try to bend it back but be very careful it is very strong and hard to bend and even harder to bend back so it can break.
So if you are riding your bike in the middle of nowhere you are going to be walking back home if it breaks.
The alternative to bending it back, just to buy a new mech hanger and replace it with the old one.
It should not be too expensive as long as you do it yourself.
what you need to do next is to adjust the limit screws.
You have a high and a low limit screw that controls how far the derailleur can travel in either direction.
The first, thing we do is make sure the rear mech is aligned and the limit is set for the highest gear.
You can adjust that with the screw on the left (marked with the letter L).
If the chain is too far to right it will make a noise but if it is too far to the left it will it will go up a gear.
When the chain is too far right then you have to turn the left screw counterclockwise.
Keep turning the screw until the guide wheel is aligned with the lowest gear or the smallest sprocket.
Now you can repeat the same thing just with the highest gear or the largest sprocket.
You can adjust that with the screw on the right (marked with the letter H).
If the alignment is wrong on the highest gear then the chain can hook over the top.
If that happens then a few very undesirable things can happen.
- You could damage the spokes on your wheels
- The chain can get stuck between gear and spokes and snap the chain
- Also if your chain gets stuck back there you derailleur could get ripped off the bike
I don’t know about you but I like my derailleur attached to my bike.
3.Body angle screw
The B-screw is located on the top back of the mech.
It controls the gap between the guide wheel and the lowest gear or the largest sprocket.
If there is too much tension the gap is going to be too large.
Then the downshift will not be good and the mech will be so stretched out it won’t have any spring in it.
If you fully wind the b-screw out the guide wheel could catch the largest sprocket.
You will not get the bike to shift gears smoothly if you have the b-screw fully wound out like that.
Now let’s see what it is like to fully wind the b-screw in and see how the bike behaves.
In this position, the mech is almost locked out which is a very bad position for it to be in.
If you go over a large bump in that stretched position the chain can snap or the rear mech.
The correct B-screw gap is 5-6 mm for most mountain and road bikes.
Before you go running out to the store to buy new cables it is better to check the friction of the cable.
A good way to check that is to undo the pinch bolt on the mech.
Then you can manuali feal the inner cable moving in the outer cabel.
You can do the at the mech end of the cable and the shifter end.
If the cable is easy to move then that is not the problem but if it is stiff then either.
- You can try and clean the cable sometimes that is all you need to do
- Or of course, you can just buy a new one and replace it yourself
Another thing to check is the inner cable routing to the pinch bolt on the mech.
It is very easy to not align it up with all the hols and the guide.
There is a little wheel at the top of the mech that the cable needs to go through.
Then from the wheel, there is a guide and after that a small hole that is easy to miss.
If you do not take this route with the cable it is not going to line up and won’t bull the correct way.
What you should begin with the cable tension is to clamp the inner cable on the rear derailleur.
People commonly get this wrong by pulling the cable through really tight.
But by doing that you are shifting the derailleur slightly, but what you want to do is to pull it taught.
No more than that the shifter will compensate for any other slackness.
What you want to see is one click of the lever corresponding to on gear change.
If you don’t have enough cable tension the chain isn’t gonna hop up in time.
Also if you have too much cable tension the chain will move too far and the bike will skip gears.
Now that you have gone over all of these common problems your bike should be shifting perfectly. So your bike should not skip gears if you follow these tips.
Why does your bike skip gears? check out this video for a more detailed look.