Mountain bike slipping out of gears

apple tango · Crazy Courier Joined: 03 Apr 2007 Karma :

Bought a mountain bike off gumtree today for £70. Its a bit of a shit heap.

When it's in some of the middle gears on the rear sprocket it seems to slip out of gear from time to time.

What's the cause of this and how can i fix it? The fella i bought it from reckons the chain might be slightly too long or something. He said he's taken a link out of it but it still happens.
____________________
CBR125 -> Bandit GSF600 '99 -> SV650 02

Frost · World Chat Champion Joined: 26 May 2004 Karma :

Skip out in what way? Skip to another gear? Skip to a position between gears? Or the chain just skipping over the sprocket?
Chain length and therefore tension can have something to do with things.

https://t1.gstatic.com/images?q=tbn:ANd9GcRkJf_rOJmFvDVOlD62UXFFgfRlohOYZWYRgvhU558zKW1-KxGq6Q

The position of that will show if the chain is too long.

Howling Terror · Super Spammer Joined: 05 Dec 2008 Karma :

...and maybe worn sprockets.
____________________
Diabolical homemade music Bandcamp and Soundcloud
Singer songwriter, Artist and allround good bloke Listen to Andrew Susan Johnston here
The Harry Turner Project

apple tango · Crazy Courier Joined: 03 Apr 2007 Karma :

Yeah it skips to another gear.

https://img856.imageshack.us/img856/5648/14082011127.jpg

Uploaded with ImageShack.us
____________________
CBR125 -> Bandit GSF600 '99 -> SV650 02

Irezumi aka Reuben · Carrot Top Joined: 28 Sep 2004 Karma :

Go on to the shimano website and download the PDF they do for derraileur(gear) adjustment.

Or take it to your local bike shop.
____________________
Pictorgraphicalfantastical

Frost · World Chat Champion Joined: 26 May 2004 Karma :

Sounds like it's just the adjustment. It might also be a cable catching on something when you turn.

RPM · Nova Slayer Joined: 16 Apr 2011 Karma :

Hi there

On the main part of the derailleur you should find two screws beside each other Thumbs Up

If the gears slip/shift down a gear (towards the wheel) adjust the screw to align the derailleur slightly outwards from the bike.

If it slips/shifts up a gear then adjust the other screw carefully to move it slightly inwards. Be careful not to over adjust, this can cause the chain to be thrown over the top of the largest rear cog (ouch!!)

The screws should be marked with arrows or similar.

If you do this and there is no difference then check the overall chain length. If you remove any more links just make sure that the chain is long enough to fit onto the largest front and rear cogs (sprockets). Yes.... I have previously made this mistake Rolling Eyes

All the best
Mike

apple tango · Crazy Courier Joined: 03 Apr 2007 Karma :

Thanks for the advice Mike.

On two occasions the chain was thrown over the top of the largest cog, so i'll have a fiddle around with these screws.
____________________
CBR125 -> Bandit GSF600 '99 -> SV650 02

Dazbo666 · World Chat Champion Joined: 06 Jun 2004 Karma :

RPM · Nova Slayer Joined: 16 Apr 2011 Karma :

Hi there

@ apple tango

I was also wondering whether the lower part of the derailleur was bent (bike dropped/crashed on the right hand side) if this is the case then you could try to realign it by hand.

Otherwise any adjustment you make to the alignment will have to compensate for this.

All the best
Mike

stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

ITT, a fair bit of inaccuracy and half truths.

There are two screws underneath the derralieur. They are simple stops for top and bottom.

Set the indexing first by putting it on the middle ring on the front and one of the middle rings at the back. Set the position of the indexing using the large adjuster arrowed on Frosts diagram. The jockey wheel on the deralieur should be lined up exactly with the sprocket you're on so twiddle it until it is. When it's set right, turning the wheel using the pedal should have nearly no chain noise.

Once the indexing is set, use the other two screws (which are simply an upper and lower limit screw) to stop it shifting off the top or bottom of the casette while in the relevant gear.

All of that said, it all looks suspiciously clean and shiny. TOO shiny. I'd be very tempted to whip the chain off and check how loose it is. If you can hold it horizontally at waist height and the other end touches the floor, it's fucked. Or simply check how much sideways play there is (should be minimal).

Sprockets take a LOT of wearng out and it would usually be the smallest that goes first. 11 tooth sprockets are notorious for skipping but you don't have one.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

UnknownStuntm... · World Chat Champion Joined: 13 Sep 2007 Karma :

apple tango · Crazy Courier Joined: 03 Apr 2007 Karma :

Cheers Stinkwheel.
____________________
CBR125 -> Bandit GSF600 '99 -> SV650 02

colin1 · Captain Safety Joined: 17 Feb 2005 Karma :

Adjusting the barrel adjuster which is marked with an arrow, will stop it slipping from one gear to the next and back again or being as if its trying to be between two gears.
____________________
colin1 is officially faster than god

JonB · Afraid of Mileage Joined: 03 Jun 2004 Karma :

Agree with stinky. The screws are just stop limits. My first adjustment would be a turn or 2 of the barrel adjuster.
____________________
Be careful whose advice you buy, but, be patient with those who supply it. Advice is a form of nostalgia, dispensing it is a way of fishing the past from the disposal, wiping it off, painting over the ugly parts and recycling it for more than it?s worth.