The Gears On My Mountain Bike Keep Slipping?

I bought a mountain bike a while back to get into shape in the nicer weathers but whenever I ride it the gears seem to slip randomly. Its a grip shift and even when Im nowhere near the grip the gears slip, as you can guess, it makes for an awkward ride as the pedals jolt when this happens.
At first I thought it could be because Im quite a heavy guy but Im not so sure. I just want to get it sorted as Im sure its not doing the bike any good. Anyone know of any possible causes?

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5 Comments »

MtBikr said:

If the gears and chain are not totally worn out, then the problem is that the derailleur is out of adjustment. What is happening is the chain is moving between two gears, you normally notice this first when you are really pushing hard on the pedals or climbing. Here are two links to help fix it.http://www.parktool.com/repair/readhowto…http://www.sheldonbrown.com/derailer-adj…

# 16 February 2010 at 9:53 pm

Master Tech said:

Several things can be contributing to your problem. A worn out chain, cassette cogs, or chainrings can be the problem. Also, a bent derailleur hanger will cause shifting/slipping problems. Finally, the derailleur might be out of tune.
If this happens only when you are applying hard pressure to the pedals, it’s likely to be a worn chain.
Shift the chain to the smallest rear gear. Shift once. Does the chain shift cleanly to the next gear? If not, your derailleur cable needs to be tightened.
Take a look at the frame piece that the rear derailleur is attached to. Is it perfectly vertical? If not, get it straightened out. This is called the derailleur hanger and MUST be perfectly straight for accurate shifting.
A possibility, but not likely, is that the freehub is beginning to wear out. If it is, you’ll feel the pedals move forward very quickly without feeling any resistance.

# 16 February 2010 at 11:49 pm

newlb4u said:

Dude, your weight is not the issue. The problem is simply that the derailleur is out of alignment.
Depending on where the gear slips, mid range most likely, then all you need do is look for the finger bolt on the derailleur at the back and apply a quarter turn anti clockwise. to tighten the cable, or clockwise to reduce tension.
This is an annoying problem and by rights you should take the bike to the shop and get it sorted, but at some time you will need to do this work yourself, we are, after all men and we are genetically disposed to fix things.
Ideally get yourself a bike support so you can spin the wheels and do the adjustment yourself. They are not expensive and are incredibly use full as is the Haynes book of cycle maintenance.
L

# 17 February 2010 at 6:41 am

Bob A said:

This is a common problem when a bike is new the cables stretch just a little. Look at where the shift cable goes into the rear derailleur. There is a little adjuster with nubs on it. If the bike shifts to a higher gear on it’s own turn the adjuster counterclockwise 1/2 a turn at a time. If it shifts to a lower gear turn it clockwise 1/2 turn.
Watch this video, DO NOT ADJUST ANY SCREWS.http://bicycletutor.com/adjust-rear-dera…

# 17 February 2010 at 9:29 am

Corey W said:

It could be the derailleur, but not as likely, check, and adjust the barrel adjuster as needed, i’ve had a similar problem and just adjusting that fixed it. If you need more explaining,http://bicycletutor.com

# 17 February 2010 at 9:41 am