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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 05-17-12, 01:36 PM   #1
jaydotosh
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Desperately need help :S

Hello everyone, first time posting here!

I have problem with my bike (~20" MTB) - I hadn't ridden it in around 2 years, stopped after I got injured (broken foot and arm), so I decided to start cycling at from home to college. I have restored the bike about a week ago, which involved me oiling all the moving parts, checking brake cables (mediocre V-brakes), checking tyre pressure etc - all the usual stuff really. I did not thoroughly check the rear derailleurs, although they seemed to function properly (skipped a few gears, but I don't mind that ).

I was on my way from college a couple days ago, and just before I pulled into the sidewalk I switched gears from 4th to 1st; this made the chain slip onto the area between the wheel hub and spokes. I was going pretty fast, so I didn't have much time to react, and unfortunately the back wheel locked up. I knew it was going to be pretty bad. I got off and checked the rear derailleurs - I know they were pretty fudged up so I walked the rest of the way home.

I have finally had the time to check the bike for damage etc, and it seems that the RD is in a position which doesn't look good (I apologise for my lack of mechanical knowledge ).... looked like it was in the fetal position
I can't for the life of me figure out whether the derailleur hanger is bent, or whether the RD itself needs replacing. I have some photos below, and I will upload a video soon.

Thanks in advance!

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Old 05-17-12, 01:50 PM   #2
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It is quite likely the rear derailleur itslef is bent and needs treplacing. THe steel 'claw' type hangers that are used on entry-level and dept. store bikes without built-in hangers are usually much stronger than the derailleur attached to them, and so the derailleur usually bends or breaks before the hanger.

However, a new derialleur with a built-in hanger will likely cost ~$15 - $20 and this will most definiately fix the problem.

THE PROBLEM
THe problem was likely caused by an improperly adjusted derailleur - the 'L' limit screw on the derailleur should prevent you from beingf able to shift into the spokes, but since it din't I would expect its maladjustment was the cause. You didn't say - were your injuries a result of a bike accident? Becuase often derailleurs gent bent slightly in a crash and this can also cause the derailleur to get caught in the spokes, even if the limit screws are set properly.

I suggest you buy a new derailleur with a built in hanger and a new cable and follow the derailleur installation and adjustment instructions on parktool.com
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Old 05-17-12, 02:00 PM   #3
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Thanks for the quick reply, I appreciate it

I was aware of the misalignment issue but I didn't think it was priority. The injuries from 2 years ago were due to parkour.... I've always been a safe cyclist
I live in the UK, and the cheapest replacement (for now) is the same RD in the photo (Shimano TX31), which are for ~12. I was hoping it wouldn't be the RD, so I have uploaded a video.

What are your conclusions based on this video? Any other opinions?


Last edited by jaydotosh; 05-17-12 at 02:29 PM.
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Old 05-17-12, 02:32 PM   #4
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Drop it by your local bike shop.
they see more in person than off web vignettes.
.. and do something about it.
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Old 05-17-12, 02:35 PM   #5
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Hmmm... no quick fixes then

I have college tomorrow, which is why I need a quick fix. All bike shops are closed right now (21:35 GMT) so that's not really an option. Oh well :/
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Old 05-17-12, 03:32 PM   #6
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All is not lost. You just need to put the chain back on the upper derailleur pulley. The minor bend in the derailleur pulley cage and hanger can be bent back, by hand even.

In this photo, the pulley that needs to have the chain wrapped back around it is the non-Red one on the right:




Also it looks like you have very little chain-tension, like the chain is about 4" too long. If you have a triple chainring in front, NEVER ride it around in the smallest chainring up front. Only use the smallest chainring with the two biggest cogs in back on hills. Most of the time, you'll want to be in the middle chainring in front. Then on downhills, use the big chainring with the two smallest cogs in back.

For now, be conscious of which gear you are in back and do not shift up any more than necessary to get into the biggest cog. Change gears one at a time and verify it shifted. If you can find the L limit screw, spin it in a couple of turns to prevent the derailleur from moving past the largest cog into spokes.

Last edited by DannoXYZ; 05-18-12 at 01:21 PM.
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Old 05-18-12, 05:07 AM   #7
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Thanks a lot for the input! Finally a decent answer hehe

I'll do what you said as soon as I get home today; the chain tension issue you raised was probably caused by me pedalling gently (with my hand of course) while the bike was upside down. I was doing this just to remove all the grime and dirt that was collected thanks to the lubricant I was using (motor oil).

Again, thanks for your advice and I'll keep the gear changing in mind for the future.

P.S. which component needs to be bent? Is it the metal body of the red pulley?
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Old 05-18-12, 05:30 AM   #8
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If you need to ride the bike. I would suggest to put the chain on the middle front chain ring and the middle back cog. If the chain will run in this position and if you don't do any shifting you should be able to ride the bike until you can get it checked out.

It looks like the chain damaged a couple of rear spokes so you may need to get them replaced and get the wheel trued along with getting the shifting problem repaired.
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Old 05-18-12, 06:05 AM   #9
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First of all welcome! Please look upon my post as advice and not a call out.
I know you didn't ask this but I have to say that motor oil has no use on a bicycle. It's too thick for chains,cables and shifters and it's too thin for cranks and wheel bearings. Leaving excess lubricants on external parts can only introduce dirt into the internal surfaces you're trying to maintain. So clean the parts before and after applying the proper lubricant.
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Old 05-18-12, 09:01 AM   #10
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Originally Posted by jim p View Post
If you need to ride the bike. I would suggest to put the chain on the middle front chain ring and the middle back cog. If the chain will run in this position and if you don't do any shifting you should be able to ride the bike until you can get it checked out.

It looks like the chain damaged a couple of rear spokes so you may need to get them replaced and get the wheel trued along with getting the shifting problem repaired.

Yeah, a few of the spokes are damaged, the rear wheel tends to 'wiggle' and judder on its' axle, though the chain is now repaired. Truing also needs to be done. Good eye btw

Quote:
Originally Posted by jethro56 View Post
First of all welcome! Please look upon my post as advice and not a call out.
I know you didn't ask this but I have to say that motor oil has no use on a bicycle. It's too thick for chains,cables and shifters and it's too thin for cranks and wheel bearings. Leaving excess lubricants on external parts can only introduce dirt into the internal surfaces you're trying to maintain. So clean the parts before and after applying the proper lubricant.
Yeah, I agree. I did clean the chain out and add the oil though.... it was the only thing I had at the time :S


Upon closer inspection, I noticed that certain plastic parts along the RD body are broken. Wow this is getting more and more expensive

Thanks to whoever contributed to this post! Much appreciated

P.S - what is the reason for the rear wheel to wobble on its axle? Missing bearings? Bent axle? How can this be solved? 0.o

Last edited by jaydotosh; 05-18-12 at 09:04 AM.
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Old 05-18-12, 09:24 AM   #11
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Quote:
Originally Posted by jaydotosh View Post
I'll do what you said as soon as I get home today; the chain tension issue you raised was probably caused by me pedalling gently (with my hand of course) while the bike was upside down. I was doing this just to remove all the grime and dirt that was collected thanks to the lubricant I was using (motor oil).
Chain tension is determined by length and in this photo, the derailleur cage is rotated all the way back and not under much tension:

The red pulley should actually be at a 45-degree angle (closer to the ground) relative to the other one. If you're not in the granny-ring up front, then you need to remove 2-4 links from the chain as it's too long and slack.

Quote:
Originally Posted by jaydotosh View Post
P.S. which component needs to be bent? Is it the metal body of the red pulley?
Sorry, typo on my part. It's most likely the derailleur hanger-bracket that's bent. But typically all the parts between the pulley-cage to hanger gets bent. Start with this photo:

Rotate the pulley-cage so that it's vertical, then pull outward to bend back into proper position. The two pulleys should be inline vertically, the lower one is currently bent inwards.
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Old 05-18-12, 09:29 AM   #12
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Originally Posted by jaydotosh View Post
Yeah, a few of the spokes are damaged, the rear wheel tends to 'wiggle' and judder on its' axle, though the chain is now repaired. Truing also needs to be done. Good eye btw

P.S - what is the reason for the rear wheel to wobble on its axle? Missing bearings? Bent axle? How can this be solved? 0.o
The rim is probably a bit bent. You need to have even spoke tension to keep the rim straight. If a spoke is too loose or too tight due to damage or just bad tension, then the rim will either be pulled towards or away from the bad spoke(s).

If the axle bearings are loose, that can also cause wobbling, but spoke problems are the most common cause.
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Old 05-18-12, 09:30 AM   #13
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Originally Posted by jaydotosh View Post
P.S - what is the reason for the rear wheel to wobble on its axle? Missing bearings? Bent axle? How can this be solved? 0.o
This may be due to loose rear-wheel bearings. They may just need to be adjusted.

However, your spokes are severely undertensioned. I can see at least one that has zero tension. The wheel may have previously been damaged into a taco shape and was trued back to look straight with vastly varying tensions. I suggest having a shop adjust the bearings (or learn to do it yourself). Then tighten up all the spokes evenly. If you squeeze two parallel spokes with your hand as hard as you can, they shouldn't bend together any more than 4-5mm. I suspect yours will move 10-20mm.

Here's a good site showing how to adjust hub-bearings: Park Tool - Hub Overhaul & Adjustment
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Old 05-18-12, 09:35 AM   #14
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Quote:
Originally Posted by jethro56 View Post
I know you didn't ask this but I have to say that motor oil has no use on a bicycle. It's too thick for chains,cables and shifters and it's too thin for cranks and wheel bearings. Leaving excess lubricants on external parts can only introduce dirt into the internal surfaces you're trying to maintain. So clean the parts before and after applying the proper lubricant.
How do you define "proper"? There's enough holy-war debates on chain oil here to realize that there's no one "right" lubricant. One of my requirements is longevity of drivetrain and I can get 7000-10000 miles out of a chain before 1/16" stretch.
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Old 05-19-12, 09:44 AM   #15
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Quote:
Originally Posted by DannoXYZ View Post
Chain tension is determined by length and in this photo, the derailleur cage is rotated all the way back and not under much tension:


The red pulley should actually be at a 45-degree angle (closer to the ground) relative to the other one. If you're not in the granny-ring up front, then you need to remove 2-4 links from the chain as it's too long and slack.


Sorry, typo on my part. It's most likely the derailleur hanger-bracket that's bent. But typically all the parts between the pulley-cage to hanger gets bent. Start with this photo:


Rotate the pulley-cage so that it's vertical, then pull outward to bend back into proper position. The two pulleys should be inline vertically, the lower one is currently bent inwards.

Quote:
Originally Posted by Homebrew01 View Post
The rim is probably a bit bent. You need to have even spoke tension to keep the rim straight. If a spoke is too loose or too tight due to damage or just bad tension, then the rim will either be pulled towards or away from the bad spoke(s).


If the axle bearings are loose, that can also cause wobbling, but spoke problems are the most common cause.

Quote:
Originally Posted by DannoXYZ View Post
This may be due to loose rear-wheel bearings. They may just need to be adjusted.


However, your spokes are severely undertensioned. I can see at least one that has zero tension. The wheel may have previously been damaged into a taco shape and was trued back to look straight with vastly varying tensions. I suggest having a shop adjust the bearings (or learn to do it yourself). Then tighten up all the spokes evenly. If you squeeze two parallel spokes with your hand as hard as you can, they shouldn't bend together any more than 4-5mm. I suspect yours will move 10-20mm.


Here's a good site showing how to adjust hub-bearings: Park Tool - Hub Overhaul & Adjustment

Quote:
Originally Posted by DannoXYZ View Post
How do you define "proper"? There's enough holy-war debates on chain oil here to realize that there's no one "right" lubricant. One of my requirements is longevity of drivetrain and I can get 7000-10000 miles out of a chain before 1/16" stretch.

Yeah, that reminds me there was a time (I was a kid then mind you - this bike is ~9 years old) when the front and rear wheels needed to be trued. I went to a backstreet cycle shop, and the guy did it for free. I was later aware of the fact that the moron who "fixed" my bike re-welded the wheel until it was straight. He didn't tru it >:/


Quote:
Originally Posted by DannoXYZ View Post
Chain tension is determined by length and in this photo, the derailleur cage is rotated all the way back and not under much tension:


The red pulley should actually be at a 45-degree angle (closer to the ground) relative to the other one. If you're not in the granny-ring up front, then you need to remove 2-4 links from the chain as it's too long and slack.


Sorry, typo on my part. It's most likely the derailleur hanger-bracket that's bent. But typically all the parts between the pulley-cage to hanger gets bent. Start with this photo:


Rotate the pulley-cage so that it's vertical, then pull outward to bend back into proper position. The two pulleys should be inline vertically, the lower one is currently bent inwards.

Quote:
Originally Posted by Homebrew01 View Post
The rim is probably a bit bent. You need to have even spoke tension to keep the rim straight. If a spoke is too loose or too tight due to damage or just bad tension, then the rim will either be pulled towards or away from the bad spoke(s).


If the axle bearings are loose, that can also cause wobbling, but spoke problems are the most common cause.

Quote:
Originally Posted by DannoXYZ View Post
This may be due to loose rear-wheel bearings. They may just need to be adjusted.


However, your spokes are severely undertensioned. I can see at least one that has zero tension. The wheel may have previously been damaged into a taco shape and was trued back to look straight with vastly varying tensions. I suggest having a shop adjust the bearings (or learn to do it yourself). Then tighten up all the spokes evenly. If you squeeze two parallel spokes with your hand as hard as you can, they shouldn't bend together any more than 4-5mm. I suspect yours will move 10-20mm.


Here's a good site showing how to adjust hub-bearings: Park Tool - Hub Overhaul & Adjustment

Quote:
Originally Posted by DannoXYZ View Post
How do you define "proper"? There's enough holy-war debates on chain oil here to realize that there's no one "right" lubricant. One of my requirements is longevity of drivetrain and I can get 7000-10000 miles out of a chain before 1/16" stretch.



Just got back from Halfords (automotive/bike/camping shop which also deals with repairs) and on the way I realised that it was probably one of the bearings. Oh, and I forgot to mention that the rear mech is completely FUBAR - it's cracked and broken in a few places which is why it isn't a quick fix


Total cost of parts + labour of fixing the bike (incl. rear mech, bearings etc) comes to roughly 50.


Quote:
Originally Posted by DannoXYZ View Post
Chain tension is determined by length and in this photo, the derailleur cage is rotated all the way back and not under much tension:


The red pulley should actually be at a 45-degree angle (closer to the ground) relative to the other one. If you're not in the granny-ring up front, then you need to remove 2-4 links from the chain as it's too long and slack.


Sorry, typo on my part. It's most likely the derailleur hanger-bracket that's bent. But typically all the parts between the pulley-cage to hanger gets bent. Start with this photo:


Rotate the pulley-cage so that it's vertical, then pull outward to bend back into proper position. The two pulleys should be inline vertically, the lower one is currently bent inwards.

Quote:
Originally Posted by Homebrew01 View Post
The rim is probably a bit bent. You need to have even spoke tension to keep the rim straight. If a spoke is too loose or too tight due to damage or just bad tension, then the rim will either be pulled towards or away from the bad spoke(s).


If the axle bearings are loose, that can also cause wobbling, but spoke problems are the most common cause.

Quote:
Originally Posted by DannoXYZ View Post
This may be due to loose rear-wheel bearings. They may just need to be adjusted.


However, your spokes are severely undertensioned. I can see at least one that has zero tension. The wheel may have previously been damaged into a taco shape and was trued back to look straight with vastly varying tensions. I suggest having a shop adjust the bearings (or learn to do it yourself). Then tighten up all the spokes evenly. If you squeeze two parallel spokes with your hand as hard as you can, they shouldn't bend together any more than 4-5mm. I suspect yours will move 10-20mm.


Here's a good site showing how to adjust hub-bearings: Park Tool - Hub Overhaul & Adjustment

Quote:
Originally Posted by DannoXYZ View Post
How do you define "proper"? There's enough holy-war debates on chain oil here to realize that there's no one "right" lubricant. One of my requirements is longevity of drivetrain and I can get 7000-10000 miles out of a chain before 1/16" stretch.

See above.


The oil I used is chain lube.


Cheers
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