Apart from your wheels and tyres, your bike's transmission is probably the hardest working part. Almost every terrain change will see a gear shift up or down the ratios. Through everything you and the elements throw at them, your gears do their best to deliver and deserve to be looked after.
There are lots of things you can do to keep them running for longer and make their failure on the trail less likely. In the first part we'll concentrate on the derailleurs and the all important cables that make them move.
The diagram below names the parts and shows a cutaway on the R.
Beneath the plastic sheath of the outer lies a casing made of many strands of steel wire. The structure this creates results in a strong platform for the transfer of the movement of the inner cable which enables gear changing. To help further, the outer is normally lined with a thin layer of plastic to reduce friction.
When cut to the required length, the outer should have a ferrule (or end cap) placed on it before fitting it into the frame stops, derailleurs or shifters. Frame stops are required when there is a break in the outer cable run and they provide a stationary point for the system to push against.
The inner cable is a multi strand wire and acts as direct a connection between the shifter and the derailleur. Stainless steel is usually best for long life and general smoothenss. When buying replacements, look for inner cables which are pre-stretched.
The inners are anchored at the shifters by nipples which are cast directly onto their ends. They are held at the derailleurs using a bolted clamp. Cable replacement will be covered in later pages.
Adjusting the cables in High Normal systems ie SRAM & traditional Shimano models
The first adjustment most riders need to make is taking up the slack that develops in the cables of a new bike. This is an entirely natural thing and not an issue you can really be too hard on the manufacturer for.
The slack occurs as outers settle into the ferrules and the ferrules seat themselves into the cable stops on the frames and barrel adjusters. You will find it happening whenever you replace cables yourself, either when fitting new ones or after popping the ones on the bike out for cleaning.
Shifts from the smallest rear sprocket may be very slow or not happen at all until you push toward the next click of the lever. It may be that the gears skip when shifting or you just can't quite get it onto the largest sprocket for those big climbs.
If any of those symptoms appear it's likely that things need tightening up a little. It is the barrel adjusters that should be used. Set aside thoughts of tinkering with allen keys or screwdrivers until you have used these clever little devices. In the diagram below you can see an enlarged cutaway view of one.
Here's how it works. The barrel 1 is inserted into the spring 2 and the two inserted into the adjuster 3. The grooves in the adjuster marry up to the ridges on the barrel. When the threaded portion on the barrel engages, with the thread in the shifter pod or derailleur 4 a grub screw is created.
The whole assembly, when mounted to the bike should be fully screwed, clockwise, into the body of the shifter ready to increase cable tension as described below.
When the adjuster is turned, the barrel moves in or out according to direction of rotation. The important thing to remember here is that anti-clockwise turns cause the barrel to move out and increase the tension. The spring operates a ratchet by causing the teeth on the adjuster to engage with those on the derailleur or shifter pod body. This action, allied to the grooves and ridges on the adjuster and barrel, maintains the tension.
No tools are required, all you need to do is turn the adjuster with your fingers as seen in the photo on the R. On Shimano models there is also a barrel adjuster on the rear derailleur, which is often more convenient to use. See diagram below. It is also easier to adjust when there is no tension in the system. Do this by down shifting to the lowest gear before clicking back up to the problem zone.
Shimano also supply rear derailleurs which run on a Low Normal bias. In these the mechanism is designed so that the spring settles toward the largest sprocket. One of the advantages of this system is that the cage is less likely to end up in the spokes as can happen when a High Normal derailleur has been over-shifted. The disadvantage is that any additional friction in the system cannot be overcome with increased pressure applied by the thumb. As a result the lowest gear cannot be achieved without attending to the source. Perhaps not so important for racers who would rather make sure they can get to the highest gear but for weaklings like me it's pretty much essential to be able to get to the low ones!.
Adjusting (High Normal)
Unless your bike has taken a knock or has seen a whole load of use then adjusting the cable tension is often all that is required.
As there are very few situations where the system will spontaneously tighten. Lack of tension is the commonest problem and this is easy to sort using the barrel adjuster.
1 Check that the anchor bolt is secure and that cable is not slipping through it.
2 If you are certain that there is no issue with the cable run in terms of kinks increase tension gradually.
3 Check the effect on gear changing by turning the pedals with the rear wheel off the ground.
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In normal situations, it should never take more than a little adjustment to make the difference. If you keep turning and turning the adjuster either you're turning it the wrong way (remember anti-clockwise to tighten?) or something else may be amiss.
If the difficulties begin after a crash, there may be more than one thing wrong. In such a case you'll need to
(a) Check derailleur for alignment (seatube band or E-Type mount for front & hanger for rear)
(b) Check derailleur body and links (front and rear)
Signs of any such impacts should be fairly clear and leave the signature of clean metal. Carrying spares might be the only fix if it's bad. If it's none of the above then drivetrain wear might be the cause.
SCOTTISH MOUNTAIN BIKING ADVENTURES
Trail Tips
GEARS
3. Slide the outers along the inners to expose the sections of cable that were contained within the casing. Any trapped dirt will be well seen. Give the cable a wipe with a cloth, a tissue or somebody else's jumper. Sliding the outer back and forth along the inner will remove more dirt. Do this carefully and avoid bending the cable. If bent sharply the ensuing kink will cause a friction problem all of its own. As you do all of this check for fraying or a kink already in the system. .
4. Apply some lube. Get some on the cable itself and allow it to dribble down into the outer if possible. If you don't have any with you suntan lotion or even butter or vegetable spread will do in an emergency. So too will solid soap, or candle grease rubbed directly onto the inner. Remember, carrying a small bottle of lube is easier than carting round a barrow load of household sundries! Reverse the process to reassemble the system.
Having done everything above, re-tension the system and check that it is working. Once you get home change the both cables if it's anything other than a little dirt. If the cables or sheaths have begun to degrade try to avoid the temptation of making them last just that wee bit longer. It's not major cost but if one is duff the other will not be far behind it. To reduce cleaning/service intervals for your cable systems you can either buy a proprietary sealed kit or DIY at a fraction of the cost using the page which will be published here soon.
Have a quick look for any of the causes described above. A prod with a thin stick to loosen any compacted stuff will help and a blast of water squeezed at it from a water bottle can dislodge a fair bit too. If visible dirt has been removed from the derailleurs and there is no damage or loosened bolts the chances are that it may be that a dry/dirty/ corroded or damaged cable is causing the problem. The rear derailleur usually suffers most from this.
Commonly, a section of exposed inner is present near it. This often runs downward into the final portion of outer casing. All the dirt and water that collect on the bare cable are encouraged into the channel through the outer cable by gravity. The movement of the inner cable, on every shift, does the same.
Sorting it! Cleaning an inner cable is not very difficult. In the procedure shown below it is the cable for a front derailleur that is being cleaned but the procedure is the same for both cable runs.
1. Change gear until the chain is under maximum tension and in the largest sprocket or (in the case below) largest front ring.
2. Keeping the rear wheel still and without turning the pedals (some tie the crank to a stay or seatpost just to make sure). Release the tension by clicking the upshift lever in the rear changer, or (in the case below) the downshift lever in the front changer. If necessary, wind the barrel adjusters in by turning them clockwise. The tension is now out of the system. The ferrules (outer cable ends) can now be slid from the frame stops and the cables passed through the slots in their tops...
When there is a reluctance for a High Normal rear derailleur or any front derailleur (R) to move towards the smaller rings this generally means that the return spring is experiencing difficulty in doing its job. The most common cause for this difficulty is a build up of dirt somewhere.
The easiest way to deal with dirt is to clean it off. If the dirt is on the outside and on the derailleurs themselves you may be able to see what is causing the problem. Sometimes it's a build up of fine material that packs itself into recesses and obstructs movement of parts, it may be a piece of grit or twig that has lodged. The front derailleur (R) is very prone as it gets tons of cack dumped onto it from the rear wheel.
Cable stretch and settlement of the system was covered above. The main identifier for this is a reluctance of the gears to change to bigger sprockets/chainrings caused by a reduction in cable tension.
The derailleurs (the gizmos that move the chain) are shifted by cables. The first thing to know about cable systems is that they rely on tension to make them work. The second is that those on a bike need at least two parts to function.
1. The inner : The thin wire which actually causes the business ends to move.
2. The outer : The hose-like part, through which the inner passes.
FRONT DERAILLEUR LIMIT SCREWS
As mentioned above, when you take a new bike out on the trails everything should be adjusted pretty much perfectly. As the bike gets used components will settle. The need for small adjustments should be anticipated and accepted. One thing that needs to be correct from the outset is the position of the derailleur stops or limit screws but these don't really have much of a role to play in anything bar intial instalation. Their mention here is worthwhile just in case anybody feels the burning desire to fiddle about with them or reasons to reassure them of why they shouldn't
WHAT DON'T THEY DO?
They don't have any effect, whatsoever, on how much cable moves when the shifter's trigger is used.
WHAT DO THEY DO?
They limit how far the derailleur can move in relation to the largest and smallest sprockets on the rear cassette.
ADJUSTING THE LIMIT SCREWS : LOW
The low gear has been chosen first as a mistake here can easily cause hundreds of pounds worth of damage. If allowed to travel too far the chain can jump inboard of the cassette, chew up the spokes and get damaged itself. The derailleur cage can also end up in the spokes. If this happens it will be trashed along with the spokes, the hanger and the chain. If you're really clever the whole lot can be dragged round into the seatstays and your frame will need to be binned.
Object of Adjusting Low Gear Limit Screw
To line up guide pulley jockey wheel with largest sprocket and ensure accurate shifting.
To stop the rear derailleur 'over-shifting' into the rear wheel.
Before adjusting
Remove chain (to ensure free movement)
Remove tension from cable
Clean system thoroughly
Make sure gear hanger is straight and properly seated.
Make sure cassette lockring is secured
Make sure derailleur hanger bolt is fully tightened
Make sure wheel quick release is firmly closed
To Adjust
Push parallelogram, toward centre line of bike and in a downward and forward direction, as far as it will go, making sure it does not contact the cassette.
If centre of pulley jockey is in line with centre of largest sprocket your work is done.
(a) If centre of pulley wheelgoes past largest sprocket : Keep pressure applied and turn L screw clockwise to pull system away from the centre line of the bike until the two line up.
(b) If centre of pulley wheeldoesn't reach largest sprocket : Keep pressure applied and turn L screw anti-clockise andcontinue to push the system toward centre line of the bike until the two line up.
ADJUSTING THE LIMIT SCREWS : HIGH
If the high gear limit is set wrongly and the chain jumps off next to the frame damage to the area round the dropout may result. Chips and nicks in this high stress area can concentrate forces that accelerate fatigue and can result in premature frame failure. Here, it has to be stressed that none of the issues of kit failure should be looked at in purely financial terms. They can leave you stranded, miles from anywhere, with a bike to push and make the walk home more interesting.
Object of Adjusting High Gear Limit Screw
To line up guide pulley jockey wheel with smallest sprocket and ensure accurate shifting.
To stop the rear derailleur 'over-shifting' into the frame.
Before adjusting
Remove chain (to ensure free movement)
Remove tension from cable and/or cable (as above)
Clean system thoroughly (as above)
Make sure gear hanger is straight and properly seated.
Make sure cassette lockring is secured
Make sure derailleur hanger bolt is fully tightened
Make sure wheel quick release is firmly closed
To Adjust
Allow parallelogram to move out from centre line of bike.
If centre of pulley jockey is in line with centre of smallest sprocket no further djustment is necessary.
(a) If centre of pulley jockey goes past smallest sprocket : Keep pressure applied and turn H screw clockwise to push system into the centre line of the bike until the two line up.
(b) If centre of jockey pulley doesn't reach smallest sprocket : Keep pressure applied and turn H screw anti-clockise to pull the system away from centre line of the bike until the two line up.
WHEN SHOULD I ADJUST THEM?
On the trail it may be necessary to give the limit stops a tickle if you've replaced a bent gear hanger but that's about it. For that reason, to know how to deal with them is a valid trailside skill. It's also a get out of jail card for anyone with a setup that has been moved.
HOW DO I KNOW WHICH ONE IS WHICH?
Most makes have a wee letter painted, embossed or moulded somewhere near each screw to tell you which is which. This is another of the many cruel jokes kit manufacturers play on customers. Have you ever tried to read those tiny wee letters when they're covered in coo cack or the wind is blowing hailstones up your nostrils?
Far better just to remember which is which. I'm not great at mnemonics or mind maps so I'll leave it to you to work out how to remember which is which from the dizzying choice of two.
NB Everything above applies to a High Normal derailleur where the spring causes it to settle to the small sprocket. Shimano also do a Low Normal type where the springs make it settle to the large sprocket. In that case the instructions should be reversed.
The info. above applies to a rear derailleur. The principles are exactly the same for the front derailleur.
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