Mountain Bike Chain???

Question
Description of problem: I will ride up hill and it feels as if my chain is slipping...I will ride on a flat surface and go to take off by pushing downward on my peddle and the same thing happens...like my chain is not grabbing my "chainrings"???

Answer
John,

There could be a multitude of things going on here.  I will try to list them out so you can diagnose:

1.  If the rear derailleur needs adjustment, the chain may go onto a rear gear initially, but when you apply pressure the derailleur tries to shift the chain off the gear again.  Take a look at the rear derailleur from the back.  When the shifter is in a gear and the chain is on the gear, is the upper pulley (the little wheel on the derailleur that guides the chain onto the gear) perfectly aligned with the gear.  If it is even a millimeter off, that could be causing the chain to try to shift and slip off the gear.  On the derailleur is a barrel adjuster (where the rear cable housing goes into the derailleur).  Twisting the barrel adjuster clockwise adjusts the derailleur to the right and twisting counter-clockwise adjusts the derailleur to the left.

2.  The derailleur is misaligned.  Sometimes a crash or just leaning the bike down onto the derailleur when you put it on the ground can bend the frame where the derailleur attaches.  If adjusting the derailleur doesn't work, this might be the case.  You can tell that it is misaligned if you sight down the chain line and it looks like the derailleur is rotating on a different plane from the chain and gears.  This is not something most people have a tool to fix, so I recommend you take the bike to a bike shop.  Definitely not something to fool around with if you haven't done it before.

3.  If the chain is very old (over 1500 miles) or the gears are worn, sometimes it just won't stay shifted because the chain is too flexible.  If everything else is aligned along the chainline, this may be the case and you will have to replace the chain and the rear gear cluster.

4.  Sometimes chainline problems are caused by the rear wheel not being fully seated into the frame.  Release the quick release and make sure the wheel is all the way up into the dropouts in the frame.

5.  Sometimes when the chain is on the gear and it slips, the cause is the pawls (the ratchets inside the wheel that lock it when you apply power, and then release when you coast).  This is definitely something you don't want to mess with yourself because of all the small parts that can get loose when you open up the freehub.

If you are mechanically inclined, you should be able to fix most things yourself.  However, if you are not, it is probably best to take the bike to you local bike shop for diagnosis.  From my standpoint, it is hard to tell what's going on without seeing the bike shift and observing.

Let me know how it goes.

Graeme