Shimano 8 speed casette slips in 7th and 8th gear what could cause it???

Question

My gt avalanche 3.0 the 8 speed cassette slips in 7th and 8th gear all the time what could be causing this to occur

Answer 1

Like the previous poster said, chains wear and elongate over time. They are exactly 1/2 inch per link when new. If it is already slipping, my guess is not only will you need a new chain but you will need a new 8 speed cassette. There is also a chance it is your derailleur adjustment so may as well check that first. However it is more likely the chain and cassette that need replacement.

If you change just the chain and the problem is even worse, then you need a new cassette.

Answer 2

Your chain may be stretched out. It should measure exactly 12 inches for 24 links. If the chain is stretched change it immeadiately - because it will chew away the cogs.

Answer 3

Are the 7th & 8th gears you're speaking of the two highest or two lowest cogs?

If you spend much of your time riding in these two cogs, and you haven't replaced the chain in a long while and/or maintained it, then I agree with the others replying that your worn chain is the reason...AND your cassette may now be worn so much that its replacement is also now due.

If your chain is slipping between the two problem gears (i.e., it "dances" back & forth between the two cogs when either is selected and won't properly stay engaged), perhaps the problem may be at the rear derailleur.  You may need to simply adjust the cable tension and check the limit s***w adjustments while you're at it.

So just spend a few minutes and clean up your chain and cassette.  Measure the chain as others have suggested and inspect the problem cogs for signs of irregular wear.  You should then have your answer.