Bicycle Tutor

I am a novice bike mechanic and need some of your expert advice. When I ride under, even minimum, pressure the drive train slips until I am pedaling with no forward momentum. Is there a simple solution to this that I am missing???
glrcoach

Can you see where the drivetrain is slipping? If your derailleurs are set up correctly ( http://bicycletutor.com/part/derailleur/ ) then it could be a stretched chain (see: http://bicycletutor.com/chain-wear/ or http://sheldonbrown.com/chains.html ). Did you change anything?

The pedals turn and the chain moves, as it should, but there is no pull on the back wheel cassette. It's an old (10yrs) Saracen MTB which was working fine until this suddenly started doing this. I've cleaned and dismantled the cassette and it looks okay. I wondered if it was a bottom bracket problem? The chain is good.

Thanks for the quick reply, Joe.
The pedals turn and the chain moves, as it should, but there is no pull on the back wheel cassette. It's an old (10yrs) Saracen MTB which was working fine until this suddenly started doing this. I've cleaned and dismantled the cassette and it looks okay. I wondered if it was a bottom bracket problem? The chain is good.

Sounds like the freehub on the rear wheel may have given out. This is the cylinder that the cassette slides on to. It has the ratchet that allows you to coast, but catches when you pedal. If so, you can try dripping some lube into it as it might just be gummed up.
The other common issue is the chain slipping over the top of the teeth of the cassette, but what you describe doesn't sound like that. Either way, not a bottom bracket issue. That just allow the pedals to rotate.

Thanks Dave. Think I agree with you about the freehub. Can you buy and replace or is a new rear wheel the solution?

That depends on the hub. If you have a Shimano freehub than you can exchange the freehub bodies. Other brands can sometimes be a bit tricky.