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I have a problem with my rear derailleur (300EX)

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I have a problem with my rear derailleur (300EX)

Old 08-09-19, 06:23 AM
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Wozza2014
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I have a problem with my rear derailleur (300EX)

Hi.

I took my back wheel off to replace the bearings and clean out of the cup and cone (first time ever doing this). When I put the back wheel back on the derailleur is looking strange. When I shift into the higher gears it scrunches up like in the photo. I have adjusted the b screw to no avail.

I am not too au fait with adjusting derailleurs so I don't want to tamper with it any more until I get some advice from here. After watching some videos on YT I adjusted my derailleur on my hydrid once, which took a lot of trial and error and at the end it did click in my head how to do it but now I have forgotten the knack.

Please see picture and advice best course of action.
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Old 08-09-19, 07:41 AM
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Small sprocket and small chainring combo?

If it is, how does it look small sprocket and large chainring combo or the large sprocket and large chainring combo?
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Old 08-09-19, 07:55 AM
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What I see is the chain touching the cage's tab. cobba's suggestion to check chain length when in the big/big combo is a good one as from this view it looks like the chain is a tad long.

Another possibility is that the B pivot spring is not doing it's job. Without it's counteracting force pulling the parallelogram rearward the cage pivot will wind all the way it can. If this is going on then when in small front and large rear (lowest gear) the upper pulley will contact the cog's underside (pulley knock). It's not hard to pull apart the B pivot but reassembling them with only two hands can be tricky, a bench vice is your friend. Andy
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Old 08-09-19, 08:11 AM
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Is the wheel in the same position in the dropouts as before? If you have it farther forward than it previously was then the chain is effectively longer. Try moving the wheel rearward.
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Old 08-09-19, 08:17 AM
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Hi.

Yes the original photo was taken with small sprocket and small chainring combo. This is a 2nd hand bike that I haven't used a great deal and I have mainly used it with the big chainring and not the small so maybe this issue has always been here but I just never noticed it.

Here are some photos with the big chainring engaged. It rides ok with this chainring. It is just the small chainring that is the issue.

Last edited by Wozza2014; 08-09-19 at 08:21 AM.
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Old 08-09-19, 08:21 AM
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Originally Posted by stanman13 View Post
Is the wheel in the same position in the dropouts as before? If you have it farther forward than it previously was then the chain is effectively longer. Try moving the wheel rearward.
Hi. It is in exactly the same position as before. I could try moving it backwards more to counteract the problem? Do I need to unscrew the springs to be able to push the wheel back into the dropouts more on these frames?

Last edited by Wozza2014; 08-09-19 at 08:26 AM.
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Old 08-09-19, 08:21 AM
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Take 2 links out of your chain. That will fix your immediate problem and it will still be long enough to safely cover the big/big combination.
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Old 08-09-19, 08:31 AM
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Originally Posted by Wozza2014 View Post
Hi. It is in exactly the same position as before. I could try moving it backwards more to counteract the problem? Do I need to unscrew the springs to be able to push the wheel back more on these frames?
I wouldn't necessarily change that yet. I always try to take an investigative approach and look for what could be different from before. Start with simple things and go from there. The complicating factor here is you don't know with any certainty whether this was a problem previously. That's ok. It looks to me like you could either shorten the chain as Retro Grouch suggests or move the wheel position to take up more chain. Looking at the picture of it in the big/big combo I agree that you could shorten the chain a bit.
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Old 08-09-19, 08:33 AM
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How hard is it to shorten the chain? I have never done that before. What tool do I need?

But I'll try pulling the wheel back first and that seems like an easier option for now.
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Old 08-09-19, 08:48 AM
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You would need a chain tool like this:



If you don't have one then moving the wheel back just might be enough. It doesn't look like you need a lot.
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Old 08-09-19, 08:58 AM
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Thanks all.

What are these screws in the dropouts. Do I need to unscrew them slightly to pull the wheel back?
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Old 08-09-19, 01:23 PM
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Originally Posted by Wozza2014 View Post
Thanks all.

What are these screws in the dropouts. Do I need to unscrew them slightly to pull the wheel back?
Was it ever right? I'm thinking from your original post it was. If that's the case, leave the dropout screws alone.
The dropout screws were an aid making it easier to get the wheel straight between the stays. Loosen the QR and pull your hub backward until it bottoms against the QR screws. Now retighten your QR.

If it was right before, my bet is that'll fix everything.
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Old 08-11-19, 08:32 AM
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[QUOTE=Wozza2014;21067431]
.I'm a bit confused by the pics. In one pic, the rear der.cable goes straight thru the cable stop(as it should), while in the other pic it looks like the cable goes into the cable stop, then takes a right angle turn? Am I looking at something the wrong way--the cable stop shouldn't have changed positions, but appears it has! Does the piece with the right angle slide off of the stop? If it does, line it up with the stop, so that the cable runs straight thru instead of making a right angle turn. I've not seen a stop with a piece that slides over it, but there's always a first time!

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Old 08-11-19, 05:30 PM
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Originally Posted by Wozza2014 View Post
.I'm a bit confused by the pics. In one pic, the rear der.cable goes straight thru the cable stop(as it should), while in the other pic it looks like the cable goes into the cable stop, then takes a right angle turn? Am I looking at something the wrong way--the cable stop shouldn't have changed positions, but appears it has! Does the piece with the right angle slide off of the stop? If it does, line it up with the stop, so that the cable runs straight thru instead of making a right angle turn. I've not seen a stop with a piece that slides over it, but there's always a first time!
I think thatís just an optical illusion. They look the same to me though I can see where youíre getting the right angle impression.
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