Back cog not turning rear wheel

[yidorich]

Hi, I'm new to cycling and just bought a 2nd hand road bike, I've tried to do as much to it as I can myself. I've fitted a rear derailer which was taken off so it would be a fixed gear. But now sometimes when pedaling the rear cog goes round but doesn't turn the rear wheel. It's probably really simple but can anyone help?

[TESTUser111]

Do you know if you have a <a href="http://bikeride.com/replace-freewheel/">freewheel</a> or a <a href="http://bikeride.com/replace-cassette-cluster/">cassette</a>? It sounds like the pawls in either your freewheel or <a href="http://bikeride.com/freehub-body/">freehub body</a> are not catching, and may need replacing.

[yidorich]

I don't know! I really need to get more knowledge! How do i tell the difference? Thanks

[TESTUser111]

It's explained a little ways into the <a href="http://bikeride.com/replace-freewheel/">freewheel video</a>, and in the image in the text below the video.

[yidorich]

It's a freewheel! Most of the time it powers the rear wheel but sometimes seams to slip!! Any suggestions? Thanks for the help so far Alex.

[TESTUser111]

What often happens with freewheels is the insides get dirty and the pawls start sticking (which is why they don't catch when you pedal forward). You can either get a good bike shop to flush it out and re-lube it, or get a new one. The flushing option isn't guaranteed to work and a new freewheel is probably less expensive.