When I pedal the rear wheel is not turning
I have a very old bike. It used to work perfectly, but just recently it happened that when I pedal the rear wheel is not turning. Just for notice I pedal in the correct direction, brakes are not stopping the wheel... The chain is properly mounted, the casette or freehub (I don't really know how it is called, that thing on which the chain resides on the back wheel) is spinning while I pedal, but the wheel is not. So I guess the problem is somewhere in the back wheel.
So I thought that something is completely broken, but sometimes the wheel is turning when I pedal. Thus I don't know if it is totally broken or is maybe just clogged, or whatever.
Is there a way to just repair it without buying new things?
Thank you for your time and answers (p.s. sorry for my bad English)
"Just for notice I pedal in the correct direction, brakes are not stopping the wheel..." I'm confused, does this bike have a coaster brake? Are you saying it's not working when you pedal backwards?
It sounds a bit like hub gears where the gear-changing cable has stretched, resulting in the gears slipping in between two speeds and needing adjustment with the lockable bolt thing close to the hub. How varies, but for 3-speed hubs it may be that in 2nd gear the shoulder on the bit going into the hub should be level with part of the hole through which you can see it.
If this is a single-speed bike (no shifting mechanism) then the rear hub is probably seized up and needs to be overhauled or replaced. The hubs are designed to be overhauled by ten-year-olds (at least this ten-year-old did so, many decades ago) using ordinary tools, so they're not particularly complicated if you're mechanically inclined (or have a friend who is).
However, the hub may be so badly rusted that it needs replacing.
If the rear hub is a derailer-type hub with multiple sprockets then likely the "pawls" are broken or stuck as Zenbike suggests. These can sometimes be repaired, but replacement is a better option. Depending on the age of the unit it's either a "freewheel" unit where the pawls are in the sprocket "cluster" or a "freehub" unit where the pawls are in a attachment to the hub itself.
If this is something like an old 3-speed hub (with a thin shift chain entering one end of the axle then it could be just a problem with shifter adjustment, but if not then the bike is probably not worth repairing (unless you can find used parts).
It has 3x7 (or 3x6) shifts. But how come that sometimes it functions just normally. Is it possible that is is just rusty and dirty? If it is, how should I approach this. Open things up, oil everything, use WD?
The freewheel/freehub is likely gummed up. Opening it up is a can of worms, but you might be able to work a little WD40 or (probably better) kerosene into it to free it up.
I'd be uncomfortable with fixing the freehub/freewheel that way if I didn't know what I was doing (which I wouldn't); what if it seized up again while riding? @DanielAHicks, is this even a valid concern or am I being paranoid?
@NeilFein -- But it isn't seized up, the pawls are just stuck. There is a danger that it might fail again in the same fashion, but I think the OP can understand that risk. There's virtually no danger that it could "seize up" and lock the rear wheel or turn it suddenly into a fixie (so long as he *doesn't* disassemble it).