Slipping gears

[MBosh]

I have recently purchased a Giant Defy 4 to get into road cycling. I purchased it used from a guy who said it had only done about 11 miles and it looks new. I did find that I needed to setup the gearing because it was slipping, but after just 50 miles I've found that the gears are slipping again. I have adjusted the gear cable and set up the gearing again, but what do you think is wrong that caused the gears to slip so soon after settings them up?

Do you think this could be the cable stretching or slipping through the bit that tightens the cable to the derailleur? I ask because from what I've read on the internet you shouldn't have to adjust the cable for quite some time after the gears are setup correctly. Any advice would be really appreciated. Thank you!

 

[nickAKA]

As a beginner when it comes to indexing gears my general observation is that most issues I've had arise from overtightening the shifter cable; there's a big temptation to put some unnecessary tension on it. Best place to start if you want to DIY is to watch GCN's how-to's on youtube where they show the method & correct order to adjust things. Short cut - take it to your local bike shop and ask them to do it. The bloke round the corner indexed the wife's bike (a triple) for £15. If you're not confident of getting it right and need to use it, money well spent.

 

[MBosh]

So over tightening the Allen key to much that holds the cable on the derailleur can cause this? Funny you should say this because I did think that tightening it more would stop it from coming lose. So do you just hand tighten it instead of over tightening? Or did you mean over tightening the barrel adjuster causing to much tension on the cable? Thank you!

 

[Ajax Bay]

Read this article and then follow its steps:
https://www.parktool.com/blog/repair-help/rear-derailleur-adjustment
The clamp bolt (allen key) must be tight or the cable will slip, to the detriment of the indexing.
The barrel adjuster is for final tweaks: you need to get it close to right before using it.

 

[Ajax Bay]

it had only done about 11 miles and it looks new

due to worn components (worn chainring, or worn chain and new cassette etc.)

On the basis of quote one I discarded the possibility of quote 2 and am assuming the same as you, @Dogtrousers .

 

[T4tomo]

a bit of cable stretch in a new bike / cable is not unusual..usually takes a few rides and a bit of tweaking the tensioner for all to settle down, hence the free 6-8 wk check a lot of retailers offer.

 

[MBosh]

Yes, the chain chatters at the rear and jumps into different gears. I've set it all up again and will test to see if this happens again. Hopefully, it won't slip anymore, but I'm sure I had it setup right when I did it last week. Everything seemed to work fine for around 50 miles..

 

[Milkfloat]

"I purchased it used from a guy who said it had only done about 11 miles".

Let's wait for the OP to respond with what he means by slipping first.

 

[Ajax Bay]

a bit of cable stretch in a new bike / cable is not unusual.

Stainless steel cables do not 'stretch' other than predictably when a tension is applied (and elastically shorten when tension is reduced or removed). Young's modulus. Making sure the ferrules are snug and the outers are all in the correct stops will eliminate this 'stretch' perception.

 

[Racing roadkill]

If it’s slipping, there’s probably an issue with the chain / cassette. If it’s skipping ( moving up and down the cassette, for seemingly no reason ) it may be the cable / indexing that’s the issue.

 

[nickAKA]

So over tightening the Allen key to much that holds the cable on the derailleur can cause this? Funny you should say this because I did think that tightening it more would stop it from coming lose. So do you just hand tighten it instead of over tightening? Or did you mean over tightening the barrel adjuster causing to much tension on the cable? Thank you!

The latter - tension on the barrel adjuster. Once you've used the alan screw to fix the cable it's just a case of tweaking the tension as mentioned elsewhere in the thread. The temptation is to tighten it like you would a brake cable which isn't the way to do it.