Bicycle Mechanics - A silly freewheel/cassette question

Hello,

I have a univega 21 speed mountain bike (I'm pretty new to this so please bear with me). My problem is a rather simple one I'm sure, I've just no idea how to go about fixing it. The sprocket on the back wheel turns freely in either direction. As I understood it, it's supposed to lock when the chain attempts to turn the wheel. Could someone please give me an idea of what I need to do to fix this :(.


Thanks

Hello,

I have a univega 21 speed mountain bike (I'm pretty new to this so please bear with me). My problem is a rather simple one I'm sure, I've just no idea how to go about fixing it. The sprocket on the back wheel turns freely in either direction. As I understood it, it's supposed to lock when the chain attempts to turn the wheel. Could someone please give me an idea of what I need to do to fix this :(.


ThanksI'd suggest a trip to LBS.

Depending on what your bike has, either your freewheel or freehub body is messed up. It's probably going to take some special tools to fix it.

Look carefully at the smallest cog of your rear cluster. If you see a lockring, you have a freehub. If you see a circle of splines or a couple of arc-shaped holes, you have a freewheel. I suspect it's going to be a freewheel which, in your case, is a good thing because it will be easier to fix.

If it is a freewheel, you need to buy a new freewheel and a freewheel remover tool that matches whatever you have on your bike. Lock your tool into the splines with your quick release skewer (leave a little bit of slack), break it loose with a 12" Crescent wrench or equivlent, spin it all of the way off and throw the old one away. Now grease the threads and spin-on your new freewheel. Don't worry about how tight, that will take care of itself as you ride. It's good practice to also replace the chain whenever you replace the rear cogs on your bicycle. You'll need a chain tool to resize the new chain to match your old one before you install it.

If it's a freehub, you'll have a bit more work to do. You need a chain whip to stabalize the cassette, a freehub tool, and a big wrench to remove the lockring. Then you'll need a 16mm cone wrench and another 17mm wrench to remove the bearings and axle from the hub. Finally, you'll need a 10mm allen wrench to remove the freehub body from the hub. Clean and grease everything and put it all back together with your new freehub body and you'll be good to go. You can reuse your old cogs and chain so long as they aren't too badly worn.

Look carefully at the smallest cog of your rear cluster. If you see a lockring, you have a freehub. If you see a circle of splines or a couple of arc-shaped holes, you have a freewheel. I suspect it's going to be a freewheel which, in your case, is a good thing because it will be easier to fix.

Uniglide casettes have a a screw on first cog and no lockring. Hyperglide freewheels use a lockring for securing the cogs,but also use the splined removal tool for removing the whole freewheel.A freewheel might be freed up by dibbling oil thru it,without even removing,assuming it isn't broke.