Chain Rub



keydates

New Member
Mar 9, 2004
882
0
0
Here's the story: I brought my bike over from the US to France in a cardboard box (with some padding, of course). Before leaving I had my bike tuned up, so it was running basically like new. Unfortunately, due most likely to being banged up during the flight, the chain now rubs against the front derailleur in almost every gear that I choose (very annoying, of course), and the shifting is a little off.

My question is, for someone with a limited knowledge in bike repair (me), would it be better to try and fix these problems myself, or bring it to a bike shop? If the answer is the former, how exactly would I go about repairing it?
 
Unless the FD or the chainrings got bent, the adjustment for FD consisted of three screw settings. May have some art to it but definitely it's no rocket science. A quick Google would have all the instructions.
 
If rub is the problem, and it only happened after transporting the bike, then my guess would be that either the derailleur got bent or the position of the derailleur on the seat post has slipped.

Two of the screws mentioned by sogood are to set the high and low limit of travel of the derailleur cage. It is unlikely they could be messed up during shipping, and even if they were, it is unlikely that there would be rub on both chainrings. The symptoms of problems with the limit set screws would either be the inability to shift to the smallest or largest ring (but unlikely that both would be affected) or the chain dropping inside the smallest ring or outside the largest ring. Usually once these screws are set, it is best not to fool with them.

The third adjustment is to adjust cable tension. It is possible that chain rub is caused by the tension being out of adjustment. There is a barrel nut where the cable leaves the shifter. You can try turning this barrel nut to see if you can get rid of the chain rub, but in most cases when the tension is off, the chain rub only occurs on either the lowest or the highest gears.

My guess is that if the rub is occurring in all gears, and it was working properly before the bike was shipped, the derailleur is bent or the position of the derailleur on the seatpost has changed. Front derailleurs are a pain when that happens.
 
keydates said:
Here's the story: I brought my bike over from the US to France in a cardboard box (with some padding, of course). Before leaving I had my bike tuned up, so it was running basically like new. Unfortunately, due most likely to being banged up during the flight, the chain now rubs against the front derailleur in almost every gear that I choose (very annoying, of course), and the shifting is a little off.

My question is, for someone with a limited knowledge in bike repair (me), would it be better to try and fix these problems myself, or bring it to a bike shop? If the answer is the former, how exactly would I go about repairing it?
RickF has some good tips. It all starts with the correct alignment and height of the cage. If you have the time and inclination to set things right, suggest you follow the repair procedures on www.parktool.com

Or, seek out the LBS. It's likely a 2 minute job, tops, for a pro mechanic.
 
Let me try and make it simple: The front derailleur isn't designed to hit against the chain. It's designed for the chain to run through it smoothly but the derailleur must shift the chain on and off the big chainring when you use the shifter.
If the chain rubs, here is what you must do.
(1) Mark the height of the derailleur with some tipex, biro or paint as a precaution so you know how high it is.
(2) Change gear to the point the rattling is worst. Find the worst rattling gear - this is usually the smallest gear or first gear while you're on your small chainring.
(3) Dismount and slacken off as much cable tension as you can on the front derailleur. Unscrew the allen key behind the derailleur which will allow you to move it a little up or down and to the side. Now, keep the height the same as it was (using the mark as a guide) but shift the device away from the chain so the chain only just skims the inside as you move the pedals round by hand. Tighten the allen key just tight enough to hold the mechanism in place. Pedal by hand again and test for rubbing. If it still rubs, slacken the nut a touch more, move and retighten. Finally, if all is O.K. tighten the screw fully. The chain should only barely skim the cage in first gear and maybe make a tiny noise in the process. As you change gear there should be no rattle in second or third gear.
(4) Now comes the really hard part. Get on the bike and try to shift to the big chainring but in second gear and be careful as two things may happen. (A) Either the chain won't go on or (B) it may fly right off the ring, so pedal very cautiously and be ready to brake. If the shift fails to happen, then you need to adjust the screws on the derailleur. One screw will bring the derailleur so far inwards and another screw so far outwards. These screws basically make the thing work or you use them to stop the chain totally flying off or maybe flying into the pedals. They make it work but barely affect the rattle.
When I last fitted a brand new Shimano derailleur, I found the screws were fine as they were and the shift worked soon as I mounted the cage on the frame.
If the chain doesn't make it onto the big chainring, adjust a screw till it does.
(5) O.K., so now you have the no rattling on your small ring and you can shift to the big ring but, more often than not, you'll be getting terrible rattling on the big chainring after you shifted (maybe more so in first gear). Usually this can be adjusted by slackening or maybe tightening the cable tension between the shifter and front derailleur. So, slacken the cable. If it's worse, tighten it instead. The rattle should get less, especially as the chain moves its way down the gears.
To simplify things even more: Remember that cable tension alters the position of the derailleur so if the cable is very tight it may actually pull the cage into friction with the chain. So tension is a factor.
Plus, where the chain rattles, you need to move the cage manually away from the chain till it runs through without chatter in the most extreme gears.
Finally, it really does take a bit of practice, cussing and frustration till you get more skilled in the task.
I could do it for you in maybe 35 minutes but I spent hours in the past trying to get rid of chain chatter.


keydates said:
Here's the story: I brought my bike over from the US to France in a cardboard box (with some padding, of course). Before leaving I had my bike tuned up, so it was running basically like new. Unfortunately, due most likely to being banged up during the flight, the chain now rubs against the front derailleur in almost every gear that I choose (very annoying, of course), and the shifting is a little off.

My question is, for someone with a limited knowledge in bike repair (me), would it be better to try and fix these problems myself, or bring it to a bike shop? If the answer is the former, how exactly would I go about repairing it?
 
Sounds to me like his derailleur got pushed out of line by someone squashing the bike or being rough with it. probably the height won't have been altered but the cage may have moved to the side and be all out of line.
I think setting a front derailleur is tricky. Chatter and rattle is a common problem and it drives cyclists crazy. The best mechanics can eliminate the chatter to maybe 3 gears. I can get it down to about 4. Anyone can eliminate the rattle from the small chainring gears but once the shift is used, then it gets hard to have no rattle on both the chainrings.

dhk2 said:
RickF has some good tips. It all starts with the correct alignment and height of the cage. If you have the time and inclination to set things right, suggest you follow the repair procedures on www.parktool.com

Or, seek out the LBS. It's likely a 2 minute job, tops, for a pro mechanic.
 
Carrera said:
Sounds to me like his derailleur got pushed out of line by someone squashing the bike or being rough with it. probably the height won't have been altered but the cage may have moved to the side and be all out of line.
I think setting a front derailleur is tricky. Chatter and rattle is a common problem and it drives cyclists crazy. The best mechanics can eliminate the chatter to maybe 3 gears. I can get it down to about 4. Anyone can eliminate the rattle from the small chainring gears but once the shift is used, then it gets hard to have no rattle on both the chainrings.
Agree the FD was probably knocked around a bit. It has to be set up right, in the right steps, but have not found it hard at all to avoid chain rub on my DA Triple setup.

Using the trim feature on the DA levers, I can avoid rub or rattle in any combination that I care to use. Big ring down to the second-largest cog, or small ring the other way to the second-smallest works just fine once you flick the trim position.
 
Not that I think that it would really change anything, but should add that I have a triple chainring. Maybe it makes thing a little more complicated, though...
 
I agree with DHK2, use the parktool repair website. I used it a couple months ago for my front derailer. After the set up, took it for a ride and only made a couple 1/4 adjustments to fine tune it.

http://www.parktool.com/repair/readhowto.asp?id=75

this is the link for the front derailer. Be sure to make sure nothing is bent or the derailer mount isn't rotated before you start making adjustments. Remember to follow the instructions in order. Some changes do affect others.
 
Adjusting the FD is really easy if you follow the Park tools website.

Essentially, you need to adjust the limit screws first to limit the overall movement of the FD, be sure not to round the heads of the screw. Eg for the larger chainring, the limt screw should be set such that the derailleur moves enuf to shift the chain to the large chainring but not so much as to shift the chain beyond it.

If you have shifting issues, then you have to adjust the tension of the shifter cable. Because the shifting is indexed, and if the cable is not at the right tension, each click of your shifter will not be moving the necessary amount of cable, that is the derailluer is not moving as much as it should be.
Dont be afraid to tinker around, the knowledge you gain will be valuable in adjusting your bike during your long rides!
 
thomas_cho said:
Adjusting the FD is really easy if you follow the Park tools website.

Essentially, you need to adjust the limit screws first to limit the overall movement of the FD, be sure not to round the heads of the screw.
Those instructions assume that the derailleur is positioned correctly and not bent. Positioning the derailleur on the seat post is the tricky part. Once that is accomplished, then the Park Tools website instructions are correct, but if the derailleur is not aligned correctly on the seat post, it is impossible to do the other adjustments.