Bike chain jerks when i don't pedal or go down hill !?!?

When i start to pedal again it appears the pedals go round a few times before powering the back wheel again.
The bike is quite old and has had little maintenance,
I have turned the bike upside down and pedalled it round, it appears that the springy thing on the back gears is jerking back and forward, creating slack in the chain.

Thanks!

How rusty is your chain? it probably has one or more tight links, due to rust and lack of lubrication. When these tight links pass through the derailleur (also called rear mech) they don't want to bend, so the whole mechanism moves against its spring until the spring tension is enough to pull the awkward link through the mechanism.

If your chain is only slightly rusty, you can improve it a lot with a bit of lubrication. Don't use thick oil, or thin degreaser style oil such as WD-40, use a PTFE or silicone spray, you can get these at a motor factor. use the plastic nozzle tube from the side of the can, turn the bike upside down and turn the pedals with one hand while you spray the chain as it passes over the chainwheel at the front - this will ensure you don't get any overspray on the brake pads or wheel rims.

The freewheel mechanism is also slightly seized, you need to carefully spray a bit of lubricant into the crack (between the moving and non-moving sections of the gear block on the rear wheel).

If you try the above and it doesn't improve, you need to find out what it will cost for a new rear gear block and a new chain. It may cost more than the bike is worth; you could probably buy a better cared for bike second hand for less than the cost of replacement parts.

Finally, don't leave your bike out in the rain!

The "springy thing" on the back gears is called a derailleur, and it's purpose is to move the chain to whichever gear you select, and to take up the slack in the chain.

The reason it's jerking back and forth is because it is out of adjustment, and it's not aligned with the gears on the back wheel.

The reason your pedals continue to go around while coasting is because the little ratcheting mechanism inside of your gears on the rear wheel is either dirty or damaged.

You will need a special tool in order to remove the gears so that they can be cleaned and inpected.

The best thing to do is to take your bike into a shop where it can be tuned up.

to stop it JERKING you could roll the adjuster barrel on the de/railieur but it's a bit tricky and you can b there up and down the sprokets all day, just ride it to your bike shop and they will have it sorted in 5mins, then in a few weeks take it foe a full sevice about 拢35.00 up here and you'll float along , then look after it !

I have had this in the past. The reason for this is either:

It's time to clean the chain (No, really clean it) and give it a damn good lube job.

Dirt build up on your derailleur.

Solution: Clean and oil everything. Loosen up links, if necessary.

Luck

This is a good time to get to know your local bike shop. A service should put things right and cost between 拢30 - 拢40 unless you need parts replaced. Look for bike maintenance classes in your local area, it could save you money.
Happy cycling!

lol your rear springy thing is the rear mech,,,,its supposed to be slack and well looked after,,id say you have a problem with the chain,,maybe new sprockets,,maybe you would be better getting a different bike!!!

Just get a new bike