The 'mechanical numpty needs some help please' thread...

The 'mechanical numpty needs some help please' thread...

Author
Discussion

Don1

Original Poster:

15,936 posts

207 months

Monday 21st July 2014
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So, my bike has started throwing a fit in the middle cogs of the sprocket - and generally when going down a gear. It was fine yesterday, but today it's really unhappy. I've checked for obstruction, it's a new sprocket, new chain and I'm out of ideas. Help please! (I think it's Shimano SRAM on a Boardman Team FS).

Benmac

1,465 posts

215 months

Monday 21st July 2014
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Starting with the absolute easiest thing you can do tighten the cable a tiny bit at the barrel adjuster on the rear mech. That'll be by turning it anti clockwise. Just do small increments, maybe a quarter turn at a time.

Have a few goes and that'll hopefully sort it. Cables stretch a small amount over time and can mess up the indexing. If that doesn't sort it you're into setting it up again. I've long found that if it isn't working it's best to just set it up again from scratch. Very easy to do, you'll just need an hex key for the cable clamp (5mm usually), maybe some pliers to hold the cable tight while you tighten it and a screwdriver to adjust the limit screws.

Park do some good guides on all things mechanical and SRAM and Shimano both have their manuals available online.

Here's the Park one for rear derailleurs.
http://www.parktool.com/blog/repair-help/rear-dera...

Some Gump

12,671 posts

185 months

Monday 21st July 2014
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I used youtube for gear setup. Dead easy once you get it.

You say it's chucking a wobbly in the middle - so imo change to big / small, turn the cranks and try to go to an easier gear on the back. If it doesn't change instantly, turn the barrel adjuster anticlockwise 1/4 turn.
If it foes change, keep going up till you get a bother. Again, 1/4 turn at a time. If you get all the way to big/ small and it's changing fine, go to small / big and change down. If it doesn't want to change to a harder gear, do clockwise 1/4 turn.

Nb - you'll always have noisy nastyness on big / small and small / big. However, they should still select fine.

TheLemming

4,319 posts

264 months

Tuesday 22nd July 2014
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Worth checking if you've got something caught in the cassette.

Found mine was playing up at the bottom third of the cassette, till I stripped the cassette off and discovered a bit of tick grass or bramble wrapped around between the cogs - enough to make it sulk in a couple of gears.

Don1

Original Poster:

15,936 posts

207 months

Tuesday 22nd July 2014
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Thanks all - I'll have a play with it over the next few days.

ccr32

1,968 posts

217 months

Tuesday 22nd July 2014
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For rear mech adjustments, the easiest way to remember which way to adjust that I find (and teach others) is to look down on the mech from the top of the bike, and then turn the barrel adjuster a quarter of a turn in the direction that the chain is struggling to go when you are shifting gears.

I.e., if when shifting into a bigger cog, the chain skips and doesn't shift cleanly, turn the barrel adjuster in that direction as you look at it (anti-clockwise). Try again, and repeat if necessary.

And vice versa if struggling to shift down to smaller cogs.

Mech limit screws should be set up beforehand however.

If you are having problems with it shifting cleanly in both directions, check the gear cables - lube your outers (oo-er) and check the ends for obstructions that will make them drag. If they're all rusted and gammy, replace.

Edited by ccr32 on Tuesday 22 July 12:49

richardxjr

7,561 posts

209 months

Tuesday 22nd July 2014
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Just so you know what the tutorials are on about, it's middle sprockets on your cassette, and your rear mech (derraileur) will be either Shimano or SRAM.

When setting your mech up, always get a good view from directly behind, you'll see how it's all supposed to line up and will become clear.

Steve vRS

4,836 posts

240 months

Tuesday 22nd July 2014
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ccr32 said:
For rear mech adjustments, the easiest way to remember which way to adjust that I find (and teach others) is to look down on the mech from the top of the bike, and then turn the barrel adjuster a quarter of a turn in the direction that the chain is struggling to go when you are shifting gears.

I.e., if when shifting into a bigger cog, the chain skips and doesn't shift cleanly, turn the barrel adjuster in that direction as you look at it (anti-clockwise). Try again, and repeat if necessary.

And vice versa if struggling to shift down to smaller cogs.

Mech limit screws should be set up beforehand however.

If you are having problems with it shifting cleanly in both directions, check the gear cables - lube your outers (oo-er) and check the ends for obstructions that will make them drag. If they're all rusted and gammy, replace.

Edited by ccr32 on Tuesday 22 July 12:49
Good advice that!

Steve

Don1

Original Poster:

15,936 posts

207 months

Saturday 26th July 2014
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Thank you very much! All fixed! Except going out for a test ride saw a high speed blow-out... at the furthest point from the house. Joy.

Don1

Original Poster:

15,936 posts

207 months

Wednesday 30th July 2014
quotequote all
FFS. It's not fixed - I just chase the jump up and down the cassette. No happy medium. So, with a new chain, new rear derailer, new cassette sprocket thing, I'm out of ideas. Could the mounting brackets be out of whack?

Also.... four punctures in four rides. New inners across the board - what else should I check? I've done the rims, seen for anything else mechanical. The tyre is looking a bit second hand now, so I'll replace that. Is 'Slime' worth it? I'm not a small lump, so I can imagine the rear wheel takes a battering generally, but I'm not jumping it, pinching rocks or anything else like that....

(At this rate I'm going to give myself an early Xmas present...)

Thanks!

47p2

1,502 posts

160 months

Wednesday 30th July 2014
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Check the rear derailleur jockey wheels are in good condition, if worn replace them as this can often cause the problem you are having

Some Gump

12,671 posts

185 months

Wednesday 30th July 2014
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For the ouncture issue - have they been in the same position? If so, REALLY check the tyre over. I had a small cut in a tyre once and it just kept "eating" through the inner - new tyre in the end. Even the smallest bit of debris sticking through a tyre / misspositioned rim tape etc etc will cause repeated punctures.

Oh, and the deralliur issue - is it always whilst changing in 1 direction, or is it both up and down? If it's only when taking tension off, it could be gunky cable syndrome?

Don1

Original Poster:

15,936 posts

207 months

Wednesday 30th July 2014
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After this ride the rear has cracks in it, so I'm not taking any chances now. Time for a new tyre... Another Mountain King 2.2 I'm thinking....

The changing is up and down, everything has been replaced on the bike within the last year.

Watchman

6,391 posts

244 months

Thursday 31st July 2014
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Get your hanger assessed for trueness. I adjusted my own gears and managed to get either the highest OR the lowest ratios to index but never both. Took the bike to Cult Cycles in Earlswood and the first thing he did was to unscrew my mech, and check the hanger, which was significantly out of true.

Once straigtened, he got them clocking through the whole range with rifle-bolt accuracy. Very satisfying.

Edited by Watchman on Thursday 31st July 12:56

Don1

Original Poster:

15,936 posts

207 months

Thursday 31st July 2014
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Ta.

ndg

560 posts

236 months

Thursday 31st July 2014
quotequote all
Watchman said:
Get your hanger assessed for trueness. I adjusted my own gears and managed to get either the highest OR the lowest ratios to index but never both. Took the bike to Cult Cycles in Earlswood and the first thing he did was to unscrew my mech, and check the hanger, which was significantly out of true.

Once straigtened, he got them clocking through the whole range with rifle-bolt accuracy. Very satisfying.

Edited by Watchman on Thursday 31st July 12:56
Agree with this - if the mech hanger is twisted slightly it is impossible to get it working properly at both ends of the cassette (other than the top and bottom gears which rely on the stops for position). This is the tool to do it, cheaper versions are available:
http://www.parktool.com/product/derailleur-hanger-...

Don1

Original Poster:

15,936 posts

207 months

Friday 1st August 2014
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For the love of God.... looks like both of my disks are now warped as well. ARGH!

TheLemming

4,319 posts

264 months

Monday 4th August 2014
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Don1 said:
For the love of God.... looks like both of my disks are now warped as well. ARGH!
It's really not your week is it?

If it helps I took my summer road bike apart, fitted a new chain, stripped and cleaned the rear derailleur.

Its soooo shiny but also utterly stuffed. Wont index at all. I suspect the rear mech was happy gunked up, but is now very unhappy clean. Also I may have over shortened the chain...

But hey it looks pretty and it wont get dirty again like that.

Professional intervention needed before ridelondon!

Don1

Original Poster:

15,936 posts

207 months

Monday 4th August 2014
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I've waved the white flag and it's at an LBS for some love.

TheLemming

4,319 posts

264 months

Monday 4th August 2014
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Don1 said:
I've waved the white flag and it's at an LBS for some love.
On the bright side it's mostly a new bike by now biggrin