Bicycle Mechanics - Chain/Gear slips...

when going uphill. As I push the pedal forward it feels as if something gives and slips forward... CLUNK!....like something didn't grab or so.,...
What is it??? I checked the teeth on the transmition looks fine, the chain doesn't look worn out - is it the chain or the tooth on the gear that is wearing out????
Please help...it didn't do it before this last weekend!
Corsaire :(

I sounds as if your chain may have stretched and/or you have worn out your cassette.

I sounds as if your chain may have stretched and/or you have worn out your cassette.

indeed this is a possibility, however it also may be that your deraillieur is not adjusted to perfection, where you may be in a gear however when you apply a high amount of force (mashing) the chain may jump. also did you shift while pedaling hard up the hill? if so you may have caused the slip to happen with the high amount of force on the chain.

how old is the chain and drive train?

If you haven't already, check your chain for wear. If you aren't familiar with the procedure, basically measure from the edge of a rivet to the corresponding rivet across 12 pairs of inner/outer links. (When new, each pair is 1".) If the length is greater than 12 1/16", it's time to replace the chain.

I don't know of a simple go/nogo test for the cassette. So, replace the chain if you need to. Then, check derailleur adjustment per Vegas's suggestion. If it still jumps, replace the cassette.

Funny, mine did that too, and I discovered that my rear derailleur was turned sideways a bit (the lip on it is very small). Re-seating it did the trick. Take off your back tire and check the alignment of your derailleur, and maybe save yourself some cash.

Turned out the transmition was DIRTY. I didn't know heavy grease on the chain and cassette wouldmake the system slip...
Thanks guys for all the help!
Corsaire :)

Turned out the transmition was DIRTY. I didn't know heavy grease on the chain and cassette wouldmake the system slip...

Yes, roller chains are amazing grime-collectors. Do check the length of the chain, however, and replace it when 24 half-links reach 12-1/16", as noted above.

I had the same problem. It was caused by a stiff link in the chain.