Replies to This Discussion

Permalink Reply by Gemma K on August 30, 2010 at 10:17

Might be telling you to suck eggs - but have you checked the derailleur limit screws?

Permalink Reply by Mike Brisco on August 30, 2010 at 11:35

Hi,

I think Gemma is correct - and there follows, some detailed instructions on how to suck an egg, You probably know this, it is a comon adjustment.

FRONT GEARS:

on derallieurs, the range of travel from left to right (ie up and down the gear set), , is set by two small adjustment screws, usually labeled "H" and "L" (High and low gear). These set the position at which the derallieur will stop . It stops the thing going so far to the right or left it throws your chain off the cogs. Alternatively if mis set the chain cant travel far enough, to get on the full range of cogs, on a 7 speed set it might get 1-6 or 2-7 only.

they're easy to adjust. .

Regarding the front derallieur - again the problem sounds like the derallieur limit screws. If it wont go on the largest ring - there should be a pair of screws lableed "H" and "L" . If it wont go onto the large ring, it measn the "H" screw is too far in - that explains both why the chain wont shift, and why the shifter is hard to move.

My usual trick for adjusting these, is to undo the screw in units of either half a turn, or a full turn, then see. If you undo the H screw by a full turn - then try changing - you will see the derallieur moves an extra 2 mm to the right.

Final hint =- to adjust the screws, you dont always need to use the shifter. You can just pull on the cable to see if the derallieur will move.

BACK GEAR
- sounds like a different problem, tension on the gear cable. You say you can get all gears, so the stop screws must be OK.

Where the cable enters the body of the derallieur - there is usually something you can turn to increse/decrease tension on the cable. Or if you prefer, increase/decrease cable length slightly. Often if this is slightly off, the gears dont change smoothly. Worth trhying to adjust this.
Put the gear selector in 4 (middle) ; front selector in 2 (middle) . Raise the bike rear. Turn the pedals. Click the front selector, if correctly adjusted, it should drop smartly into 5 (higher) AND just as smartly up to 3 (lower).

If the thing is off, then the change up may be a lot quicker than the change down. And vice versa.

Usually if you get it right on these cogs, it seems to be OK on the others.

If it is quick to change from 4 to 5 (higher) but slow to change from 4 to 3 (lower) , ie takes 2 revoultions, grumbles, rides on top of the cogs, rattles, then eventually shifts and settles down onto the new gear - increase tension on the cable - screw the adjuster out - this takes up some of teh slack in the cable, increases the tension. .

RE 2 EXIT POINTS

We see a few of these at Bikes for Refugees - I have no idea what they are for either. Maybe someone else knows. They might be, to allow the cable to run properly ,around different handlebar set ups e.g bulky brakes. If gears need adjusting, we usually like Gemma says, find its the derallieur limit screws etc.

Permalink Reply by Gus K on August 30, 2010 at 11:39

Yes.. you are, but that's OK.

I also think the derailleur might be a bit buggered.. a bit.

Getting the back to change I can sort of understand but the front, a simple 1, 2, 3 is weird.

I mucked about with the tensioning as well on/ off etc.

But still "why the 2 cable exits?"

Permalink Reply by Mike Brisco on August 30, 2010 at 12:02

Ok having eliminated those, we progress to some other ways to suck eggs...
-
(a) yes, F derallieur could be worn ,. We had them where the pivots are worn, and they don't move properly. We generally need to replace it. Had this happen on my mountain bike, 2 times in aroudn 10,000 km.
(b) chain is worn - even if the derallieur is OK. The derallieur t pushes the chain but the chain just bends because all the links are worn - no change (has happened on the mountain bike 2-3 times)
(c) final possibility, the cable is too short . The fact that the front shifter is hard to move, suggests that. Front derallieurs, can adjust the tension by the device on the shifter where the cable comes out & the photo shows you have one But that is only fine range adjustment & assumes the cable is the right length in the first place. For larger adjustment, need to go to the derallieur - undo the bolt clamping the cable - and re clamp it 3-4 mm further down ie lengthen the cable. My tip for that, is to use point nose pliers to grab the cable loose end, about 3-4 mm from the bolt. When you undo the bolt, then usually the tension is enough to pull those 3-4 mm through, up to the pliers. The pliers stop it pulling too much through. . You then re-tighten the bolt.

Rear derallieur - worth now, considering wear, on the cogs esp if it is just one gear it wont shift to . Can use as reference, to show what unworn teeth look like a gear you don't use often. Key things seem to be (a) width of the teeth at the top when new is 3-4 mm with wear they get worn down to 1-2 mm ; (b) if you have a good eye for shape, the shape of back edge of each tooth ( where the chain pulls on it) - the chain eats into that surface broadening the U shape that it sits in, making the tooth narrower. Once or twice, had people who always rode in the same gear - and if changes on that gear don't run smoothly.

Anyway -- some more ideas to try. Front derallieurs, when they go wrong, Bikes for Refugees often leaves them as is. We have a box of spares, but it takes ages to get them in the right position, adjusted correctly. Back derralieurs, by contrast, are almost plug and play.

Permalink Reply by Gus K on August 31, 2010 at 22:00

Hi Mike,

Thanks for this. I do think the derailleur might be had it. I did actually undo the clamp and move it a bit not so much to lengthen the cable but to see if it would work better in a different position.

The chain is a new one.

Perhaps I'll roll around and say hi sometime and you can take a look.

Cheers
Angus