Can't change to smallest front sprocket

[Chris S]

I have a 15-speed Raleigh MTB and I normally can't shift to the smallest front sprocket. I've checked the stop screw and it's screwed right out (so is the other one).

I can sometimes change directly from the biggest front sprocket to the smallest if I'm travelling at speed. Does anybody have any ideas please?

 

[CopperCyclist]

As you talk about limiter screws I guess you know how these work, so here's the fix. It's probably just cable stretch/wear.

1. Shift into the smallest front sprocket (yes I know it won't, but shift so that the gears think it is, if that makes sense?
2. Undo the cabling on your front mech that shifts the gears.
3. Try to set the limiter screws to the correct place, but accept you may need to tweak these later. The low one should now be easy as without the cable restricting it, it should have moved into place. If you released it all the way, you may need to adjust it back up to stop the chain falling off.
4. If necessary manually put the chain onto the smallest sprocket, however it should jump on when tuning the pedals, assuming you've adjusted the limiter screws correctly and there are no other issues.
5. Re attach the cable, making sure its tensioned (I.e. no slack in the cable)
6. You may need to fiddle with the high limiter now, but if there are no other problems your ears should be working again.

If my instructions are two confusing, just search for 'adjusting front bike gears' on YouTube!

 

[Chris S]

Thanks - that is how I set up the front gears. The cables are new so it's probably just wear in the other components.

 

[RecordAceFromNew]

I have a 15-speed Raleigh MTB and I normally can't shift to the smallest front sprocket. I've checked the stop screw and it's screwed right out (so is the other one).

I can sometimes change directly from the biggest front sprocket to the smallest if I'm travelling at speed. Does anybody have any ideas please?

If you have difficulty shifting onto the smallest front despite L limit screw coming right out and new cabling, then there are two main possibilities: 1) cable tension too high - have you tried adjusting the front cable tension so that it flops about when on that gear, does the chain still won't go into the small front? or 2) you have a chainline issue, in that the chainset/bb are not matching the front mech, you can likely spot this by looking down vertically and see when the cable is loose whether the front mech is centred or even inboard on the small front ring, if not come back.

 

[Chris S]

2) you have a chainline issue, in that the chainset/bb are not matching the front mech, you can likely spot this by looking down vertically and see when the cable is loose whether the front mech is centred or even inboard on the small front ring, if not come back.

That could be it - thanks.

 

[derrick]

or you may have bent the front deraillier

 

[oldfatfool]

or you may have bent the front deraillier

Or knocked it, if all else fails and if the derallier doesn't appear to be far enough over try repositioning it on the frame.

 

[RecordAceFromNew]

That could be it - thanks.

An easy check that may pinpoint the problem, is that the distance between the centre of the frame to the centre of the middle front ring should be 47.5mm or more for a mtb triple. If it is not then someone likely installed an unsuitable bb/chainset previously.

The other possibility is that the front mech is unsuitable (e.g. one designed for road triple). Knowing its make and model would help.

If the chainline is ok and the front mech is a suitable mtb triple unit, then the problem could be poor front mech setup. This is an excellent guide to sort that.

 

[Chris S]

It turned out to be the front mech not being centred on the small cog, like RecordAceFromNew said. Thanks.