Bicycle Mechanics - Problem with chainset slipping

This doesnt happen much but when it does it achieves two things,a it annoys me badly and b, it means that my feet come off the pedals, like my testicles alot.
When i put pressure on the pedals ie going up hills every now and then it slips causing the above, what causes this and can i rectify this myself , im hoping it doesnt cost any cash as ive only just bought the bike. The chainset is a 2001/2 XT as are the shifters , freewheel, and deraileurs, didnt expect this from this standard.

This doesnt happen much but when it does it achieves two things,a it annoys me badly and b, it means that my feet come off the pedals, like my testicles alot.
When i put pressure on the pedals ie going up hills every now and then it slips causing the above, what causes this and can i rectify this myself , im hoping it doesnt cost any cash as ive only just bought the bike. The chainset is a 2001/2 XT as are the shifters , freewheel, and deraileurs, didnt expect this from this standard.Could be alot of things. Cheap fix could be a cable tension adjustment. Could be worn chain, cogs or both.Could be bent derailer hanger.Could be tight chainlink. Used bike could be full of issues. You are likely better off having a good LBS check it out,rather than fiddling and buggering something even worse.

....another possiblity is that the hub freebody is slipping internally... but let's hope that's not the case here...

George

....another possiblity is that the hub freebody is slipping internally... but let's hope that's not the case here...

George

I think I'm having this problem... Is there an easy way to tell whether the freehub (or, 9in my case, freewheel) is slipping internally vs one of the other potential causes that have been suggested?

Thanks!

-chris

First, check the length of the chain. If 24 half-links are longer than 12-1/16", replace the chain.

Second, note whether this occurs in all cogs. If so, and if the chain is good, then your freehub ratchet may indeed be the problem.

I think that tommy2pants has it right. Of all the possibilities, I think that a skipping freehub body is the least likely.

BY FAR the most likely is a poorly adjusted derailleur. Try this first:

1. Figure out a way to hang your bike so that the rear wheel is off the ground and you can turn the crank with your hand.
2. Shift into your smallest cog in back.
3. Now move your shifter just one click and turn the crank. If the chain doesn't make a lot of chattering noise and immediately jumps up just one cog, that's good. If it chatters a lot or doesn't shift, turn the barrel adjuster where the cable enters the derailleur 1/2 turn counterclockwise.
4. Repeat "3" for the rest of the gears.
5. Now try to go the other way. If it shifts slowly, of not at all the other way, chances are you have a gunked up derailleur housing.

Hope that fixes it. The other stuff is harder to figure out and costs more to fix.

I think I'm having this problem... Is there an easy way to tell whether the freehub (or, 9in my case, freewheel) is slipping internally vs one of the other potential causes that have been suggested? You might be able to simulate / replicate it by hoisting the bike off its wheels (on a workstand, ideally), holding the rear wheel against spinning, and pushing on the pedal. Or, perhaps have someone hold you up on the bike, tightly squeeze the brakes and try to pedal. If the all the driveline components (crank, chain, cog) move in "unison", but the wheel doesn't move, then yes, the pawls in the freehub/freewheel aren't engaging.

This happened to me several weeks ago when the weather was much colder. A pawl would eventually engage, but there would be a "delay", that is, I'd spin the crank about a half turn before it would kick in. Once engaged, it would stay engaged. But if I coasted, then started pedaling again, I'd get that same phenomenon.

Sometimes you can quick-fix this by shooting spray lube into the freewheel or freehub body. Lay it sideways, and spray between the ring/part that remains stationary and the ring/part that spins as the mechanism "ratchets". They're not that tightly sealed, so some of the lube will probably get in there, and might just free it up. Otherwise, you'll have to disassemble the freewheel/freehub, which isn't brain surgery, but isn't trivial either. Usually it requires a special tool such as a pin spanner.

I wound up replacing the freewheel, and all is well. FWIW, the bike was involved in an auto accident a week ago, and I suspect that the impact did something bad inside the freewheel - might explain why I was having a problem that is apparently normal a few thousand miles from now ;)