Not bad advice above, but the OP might find it helpful when googling info that the broken part is known as a “jockey wheel”. Also see Sheldon Brown’s site regarding derailleur adjustments. If the mech* went into the spokes, then the stop screw was improperly adjusted. If this was done because the chain didn’t want to shift onto the largest sprocket, then it is likely that the chain tension adjustment(s) were incorrect. When the tension is set correctly, there will be but little chain between the upper jockey wheel and the largest sprocket when in that gear.
When the mech goes into the spokes, it is likely that the mounting point on the rear dropout will be bent. A good bike shop will have special gauges to check this and tools to restore the alignment.
*“mech” is the UK (slang?) term for derailleur. Way easier to spell correctly even if you are a yank like me!
Yeah, since no-one is popping up warning me about getting the right one, I’m guessing this is correct. I think I’m just going to get the TX55. Because it’s in the middle… (I might try swapping the broken gear out first, if it seems easy.)
I’m pretty sure it’s because of the three or four missing teeth on the gear.
So, former bike mechanic chiming in here… Yes, easy to replace a derailleur. Hardest part is breaking the chain (make sure you don’t push the linkage ALL the way out , just enough so you can pull the links apart- go slowly and keep testing to see if you’ve reached the right point).
Some points to remember:
Make sure you stay within the same brand/model of derailleur because different brands can use different chain sizes (eg, the derailleur, chain, and cogset all have to be the same). Not an issue for you as you are sticking with Shimano.
If you managed to get the derailleur into the wheel in the first place, make sure that you inspect the dropout (where the derailleur attaches to the bike) to insure it isn’t bent. If the frame is bent (easy to do) make sure you take it to a bike shop. It isn’t necessarily hard to re-bend it, but you want to make sure you get the alignment right in one shot and not keep tweaking it back and forth, else you’re likely to snap the whole thing off.
As to which to buy, hard to say- the key is to get one that has the same amount of “throw” and chain pick up to it. Throw (the amount of movement from side to side) is easier as the models listed are described as 6-7 gears, same as your bike. Chain pickup is the ability of the derailleur to pivot and keep the chain tension constant. If the distance between the 2 cogs/wheels on the derailleur is two small, you won’t have enough of a pivot arm to pickup the chain slack on a mountain bike. You’ll have to eyeball that one.
Make sure you adjust the set screws (2- one for top end, one for the bottom) on the newly installed derailleur to prevent it from coming off the freewheel/hubset and into the wheel/dropout.
Not really - you don’t have to break open the chain just to put on a new derailleur - just open up the derailleur cage (the metal bars that hold the jockey and pulley wheels) and put the chain in. I’ve done this on the trail, and it’s not as particular as putting a chain back together. Also, it doesn’t require a chain tool.
Heh, glad you said this. Because I was thinking: “why do you need to break the chain? Why not just open up the cage and put the chain in?” but so many people were saying you had to break the chain that I had doubts and wondered if I was overlooking something.
It’s probably faster and easier to break the chain and thread it through if you have the right tool, or a chain with a master link. Opening the cage will be fiddley. Totally doable, but you might spend five minutes doing a job that would normally take one.
I do this from time to time with the front derailleur as the chain routing is much more simple than on the rear.
And also you don’t run the risk of losing bushings, bearing, washers, seals or reinstalling with the the pulley wheels reversed (they are not typically identical).
Also, some cheaper derailleurs have the cage ‘riveted’ on, rather than bolted on.
In my experience, these issues are much easier to deal with than the chain issues, especially for someone who’s not an experienced bike mechanic. Pushing out a chain pin, just enough that you can separate the links while keeping the pin engaged in one side, then pushing the pin back in just enough so that it’s engaged on both sides of the link, is not something I’d recommend for a newbie who just wants to put on a new derailleur (like the OP). Plus, he’s unlikely to have a chain tool already.
I prefer to use SRAM chains with their proprietary PowerLink because you only need a chain tool initially to get the correct length. After that you can break and re-join the chain using the PowerLink without any tools at all.
ISTR from when I replaced the chain on a friends road bike that the 10 speed chains weren’t undo-able like the 9 and 7/8 speed, something to do with the extra stress imposed on a narrower 10 speed chain I think. A great shame. I have undone my 9 speed in the field several times.
The 8 and 9 speed powerlinks are reusable. The 10 speed powerlinks are one time use only. I’ve never tried to remove the 10 speed link, but when I installed it the sound it made was a loud click, which is different than the soft click my 9 speed powerlink makes.
The derailleur assembly came Thursday, but I didn’t get around to working with it until today. I removed the old assembly, but the new assembly is a different design. The shift cable needed to be longer than what the old one was (I’m pretty sure. It needed a significantly longer bare wire, to go around a pulley the old one didn’t have. Maybe I could have cut the sleeve and still had enough wire, but I didn’t try).
So I put the old one back on, but removed the two old gears, and replaced them with the new gears. I didn’t have to take the chain apart, and keeping track of the bits when removing and replacing the gears was easy.
While testing it out, I was able to replicate what my son did. :eek: Going towards the smallest gear on the back wheel, the bottom gear part of the derailleur assembly hit the spokes, and got spun around. I adjusted the stop-screws, stopping the gear arm from getting too close to the spokes, so that this couldn’t occur again.
I also found that the chain had a problem going from the middle front (peddle) gear to the larger front gear. I think the part that moves the gear is a little bent. I moved the chain onto the largest sprocket gear, and told my son to leave it there. The chain on the largest front gear gives the highest gear (hardest to peddle). Adjusting only the back gear seems to give plenty of range. He’ll get a new bike in a year or two, and is kind of hard on them anyway, so this is a good enough solution.
Using just the big chain ring (at the front) and your son getting low ratios by going to the largest rear cog while still on the largest front chainring is a bad idea because the chain is then cutting across at an angle and will wear out fast. I suppose you might not care about this if the bike isn’t going to last long anyway.
Either the stop screw setting the outer limit for the front derailleur cage is in too far, or the cage has been knocked and isn’t where it should be or there isn’t enough cable tension to pull the cage out enough. The first option isn’t likely because the stop screws don’t usually move, assuming it was set right in the first place.
The second option is a possibilty, particularly with a boy who’s hard on his bike (like I was at his age, no criticism intended ;)). The main thing is that the derailleur cage should be parallel to the chain. If it’s been knocked hard it may have slipped a little around so it is not parallel to the chain. Just slacken its holding bolt and rotate it slightly till it is back parallel. It could also have slipped up or down but that is less likely.
You can tell if the cable hasn’t enough tension to do it’s job this way: hold the rear wheel off the ground and get your son to spin the pedals. Set the rear gears so the chain is on about the middle of the cluster. Now try to use the gear changer to shift the chain onto the large chain ring. From what you are saying, it won’t make it. Now reach in and push the derailleur cage out a little with your finger while trying not to whack/pinch/cut off your finger in the chain etc. If the cage will move outward and change up, then the stop isn’t set in the wrong place and all you are lacking is enough cable tension to do to the cage what you just did with your finger. You now just need to take up a bit of slack in the cable. They stretch a little.
Just use the gear shift to put the cage in the inmost position (which will make the cable slack) then undo the cable holding screw, pull a little (half an inch?) through and re-tighten. Wait. Tell your son to stop pedalling first.