The Ultimate Guide To Bike Rear Mech : Part 1- How To Care and Inspection
All rear derailleur mechanisms (rear meths) need frequent lubrication and occasional ervicing to keep them working sweetly. So give the rear mech a few shots of aerosol lobe every time you lube the chain. Also spend a few minutes cleaning it when dirt starts to build up, or if the gears stop working properly.
You will need to know if the rear mech is indexed or has friction changers. Some older bikes have friction gears but these are now rare. With these, you have to judge how far to move the gear lever each time you want to change gear. Once you have got the hang of them, each change should be crisp and reliable, and makes just one slight clonk.
But most bikes now have indexed gears, with between seven and ten speeds. Tryon can feel and hear a slight click when you move the gear changer, and a tiny answering clonk as the chain jumps onto the chosen sprocket, you have index gears.
Indexed rear meths are usually fitted with a top jockey wheel that moves from side to side a little. This allows the chain cage to run slightly out of line with the sprockets, so the indexing will work even if the adjustment is not quite dead-on.
If your rear mech throws the chain off the sprockets, it needs cleaning and adjusting, as explained on this page. But with indexed gears, you may hear a continuous metallic rattling sound in most of the gears. Maybe you will not be able to get bottom gear, or maybe there is a noise in top gear.
If you just cannot get the gears to work right, bear in mind that Campagnolo and Shimano sprockets are spaced differently, it is possible that someone has fitted a Campag rear meth and a Shimano cassette or the other way round.
If you have to clean the chain due to a build up of dirt, the rear mech will need cleaning as well. Give it a squirt of aerosol lobe or grease solvent and wipe it thoroughly with a cloth. Then lube the main pivots and top pivot bolt.
Pay particular attention to the jockey wheels because they pick up hard-packed dirt from the chain. Soften the dirt with solvent and scrape off with a small screwdriver. Wipe, and then lightly spray lube into the centre of both jockey wheels.
The cable should instantly a transmit cacti movement of the gear lever. To make sure it does work like this, lubricate the inner cable, then operate the gear lever a few times so that the lube works its way right down the outer cable.
The jockey wheels wear out more quickly than any other part. So pull the chain cage forward to free the bottom jockey from the chain, then test for movement by trying to wiggle it. Check also that the jockey wheel turns freely. If it does not, strip and grease.
Pull the chain away from 0 the upper jockey wheel next and do the same check. On most indexed mechs, the top jockey wheel moves sideways a bit, so look for the wobble that indicates wean If the jockey wheel just moves sideways, that is OK.
Hanging down beside the back wheel, rear mechs are often get damaged when a bike falls over or is in a crash. To check for damage, clamp the bike in a workstand or get somebody to hold it upright. Then position yourself behind the back wheel, your eye level with the hub. You should be able to see if the gear looks out of line with the frame. If you suspect it is, check the gear hanger for cracks or chips in the paint - a sure indication that it is bent. It is also worth checking that the chain cage looks straight. If it is, the top and bottom jockey wheels will line up exactly with the sprockets. If the chain cage is out of line, the rear meth may be damaged or just worn out..