front derailer is driving me crazy!

[aa9t8]

my wife and are are riding a norco evolution tandem. at the time we bought it it was middle quality. it is now 3 or 4 years old and even though we are riding it a lot more we only have about 1400 kms on it. right off the bat our lbs mechanic changed the front crank. (my wife works at the lbs by the way) he was trying to shorten the distance that the chain would have to travel closer spacing of the 3 rings. the rear derailer works like a charm has rapid fire shifters one lever up and another to go down. now the front will work like hot dam and then it gets tempermental and may or may not shift properly. i have adjusted lubed adjusted and lubed again. the system always seems to change. and them it works like it is supposed to for a while. now i am thinking that the mechanics best efforts help for a while and my efforts help for a while but it should not have to be adjusted every 3 days? when i look at the bike the chain, that is the back one, is shorter. that is the distance between the front and rear derailers is a lot less than on my mtb. could this be like a wrinkle in the design? please i could use any thoughts on this.

 

[daveornee]

Shorter chain stay means greater chain angle at the extremes. Greater chain angle makes the front rerailer adjustment requirements more precise. You have more cable on a tandem.
Take a close look at the cable, housing pieces, cable ends, cable guide under the rear bottom bracket and how the cable is secured at the derailer.
You should use as high quality cable, housing, and ends as you can afford.
What type of shifter are you using?

 

[aa9t8]

the shifters are schimano rapid fire. ya know one lever for up and one for down. i can not figure out which schimano. the word is printed in a capital A. the componants are i would say medium quality. now it is my understanding that tandem stuff is sturdier. you think i should replace the cable?

 

[boudreaux]

..... right off the bat our lbs mechanic changed the front crank. (my wife works at the lbs by the way) he was trying to shorten the distance that the chain would have to travel closer spacing of the 3 rings. .................... now the front will work like hot dam and then it gets tempermental and may or may not shift properly.

What does this mean in plain english? And what FD are you ussing?

 

[Carrera]

I had heaps of trouble with my front derailier. If it slips or angles wrong, it can be a nightmare. Check your derailier isn't slipping due to grease on the frame and that the allen key is rock hard tight.
Factors for the front derailier are your cable tension, the angle of the derailier and height of the derailier.
Also check it isn't bent or out of shape.

my wife and are are riding a norco evolution tandem. at the time we bought it it was middle quality. it is now 3 or 4 years old and even though we are riding it a lot more we only have about 1400 kms on it. right off the bat our lbs mechanic changed the front crank. (my wife works at the lbs by the way) he was trying to shorten the distance that the chain would have to travel closer spacing of the 3 rings. the rear derailer works like a charm has rapid fire shifters one lever up and another to go down. now the front will work like hot dam and then it gets tempermental and may or may not shift properly. i have adjusted lubed adjusted and lubed again. the system always seems to change. and them it works like it is supposed to for a while. now i am thinking that the mechanics best efforts help for a while and my efforts help for a while but it should not have to be adjusted every 3 days? when i look at the bike the chain, that is the back one, is shorter. that is the distance between the front and rear derailers is a lot less than on my mtb. could this be like a wrinkle in the design? please i could use any thoughts on this.

 

[aa9t8]

it has always been glitchy. and there was a design reason that the mechanic told us about. however i could not remember. now wife tells me the fd retails for 10$. and the mechanic is in a bit of a hissy when he calms down he will explain whatever it is to wifey. she will buy a better derailer and hopefully it will all be good. i keep the bike and chain pretty clean so i do not think it is a build up of grime or grease or lube for that matter. i think it was just designed to bug me!

 

[DannoXYZ]

"he was trying to shorten the distance that the chain would have to travel closer spacing of the 3 rings. "

Uh.. this might be the very problem right here. Make sure your shifter and derailleur is a matched set with the chainring-spacing since the cable-pulls are designed to work with all these components together. If you're trying to squeeze three chainrings into a space on a frame that was designed for only two, you may have a problem. Also the derailleur/shifter-combo has a specific chainring-spacing in mind, you cannot change that. If you do, you need to go to a friction-shifter that lets you make incremental adjustments.

And extra friction and crud in the cables may be why your adjustments are changing over time. Cable-housing MUST be cut with the proper slicer tool, you cannot use wire-cutters or else you'll distort the outer-housing and cause it to rub on the inner cable. Make sure the housing-ends fit snuggly on the housing and the hole is concentric with the hole in the housing and that the end that fits onto the frame-lug is snug and gives the cable a straight shot through. Use some teflon dri-slide or some such lubricant on the inner cable. Make sure the pivots on the derailleur is adequately lubed as well.

What are the three chainring-sizes? Make sure you don't have a linear-step like 28-38-48 because the middle-ring will be in the "shadow" of the big ring when the derailleur sweeps. It's better to have the middle-ring poke up a little like with a 28-40-48 combination or a 28-38-46 or 26-38-48.

Also the way most shops train their employees to place the outer-cage of the FD parallel with the outer chainring gives a consistent and easily verifiable adjustment. Albeit, consistently MEDIOCRE performance, but at least it's the 80% solution across the board. That last 20% will require more tweaking than all the previous 80% combined.

There are three adjustments on the FD that makes a difference in performance.

I. FD height above chairings
Put the chain on the middle ring and ove the deraileur in/out so that the outer-cage is inline with the outer-chairning. If you have elliptical chainrings, rotate the crank to the point where the tip of the teeth comes closest to the bottom of the outer-cage. Slide the deraileur up/down on the seat-tube so that the gap between the cage and chairing teeth is between 1-2mm. To large a gap forces the deraileur to move a lot more in order to make the chain move any given amount (think pulling the chain through angles).

II. FD angle rotation and cage-alignment
I've found that having the rear of the FD's cage pulled outwards a little helps balance the sweep-distance vs. clearance considerations. If you put the chain in big-ring front and smallest-cog in rear, making the FD's outer-cage parallel to the CHAIN is best (looking vertically downwards from the top). Then adjust the outer stroke limits so that the outer-cage just barely clears the chain. You get immediate downshifts to the middle ring this way.

Then, the tip of the inner-cage will be aimed inwards, so use some pliers to bend the tip back outwards to that it parallels the chain-rings. Actually having it bent outwards a little more than parallel helps speed up up-shifts from the middle-ring to the big-ring.

Then you need to widen the rear-end of the FD's cage by about 2-3mm to make it wedge-shaped to account for the sweep of the chain across the rear-cluster. Coincidentally, all of these mods I've outline is exactly the kinds of customization that you see in Shimano's front-derailleurs from '92 onwards. There's a two-part step to the outer cage that simulates the wedge and outward-pointing tail while keeping the inner edge of the cage parallel. Then the tip of the inner cage has a little bump that helps push the chain up onto the bigger chainrings.

III. FD sweep-limits and cable-tension
This last step is done once you've made the mechanical alignments. Set the outer limit so that the outer-cage is not in contact with the chain in the big-ring/smallest-cog position, you want just the mininum gap here. If you find that you have to sweep the derailleur far to the outside to get the chain to climb up, the FD may be too high above the chainring, or the tip of the inner cage needs to be bent outwards more.

The inner limit should be set so that you don't dump the chain off the inside. It should be set so that it barely clears the chain when in a small-chainring/largest-cog combination.

Finally, adjust the cable-tension so that the each shifter click centers the derailleur over that chainring between clicks and that you don't get any rubbing on the inside or outside as you sweep across the rear cogs...

 

[boudreaux]

If you're trying to squeeze three chainrings into a space on a frame that was designed for only two, you may have a problem.



What are the three chainring-sizes? Make sure you don't have a linear-step like 28-38-48 because the middle-ring will be in the "shadow" of the big ring when the derailleur sweeps. It's better to have the middle-ring poke up a little like with a 28-40-48 combination or a 28-38-46 or 26-38-48.

BS and nonsense.

 

[aa9t8]

wife is bringing home new derailer
i do not ride with the chain at the extreme angles. and i will just install the new derailer as per the instructions. when the bike was made they changed stuff at the factory. for example the front bb was designed for a 1 piece crank. there is now a piece of billeted aluminum to convert it to a 3 piece bb. i just hope that spending a bit of money will help. oh yeah and thanks for all the input!

 

[aa9t8]

so here we go again
so wifey buys a lx derailer. i follow the instructions and my bike repair manuel. if i put it where the little red tag says when the chain is on the big ring the inside of cage grinds on the second ring. so i have to raise it way too much and i end up with it not wanting to drop onto middle ring. goes up good. so i end up angling the thing so that the back of it is in quite a bit. at least it drops off the big ring most of the time. gonna drive myself over the edge tweaking but i think i am experiencing some improvement. anybody else tried angling derailer? or have any input on said crazyness?

 

[aa9t8]

so i install the lx derailer do many many adjustments. and then do some more adjustments. i try a crank off another bike. and do many more adjustments. now the chain drops down well, but has to be nudjed up. i can not seem to have it both ways. i was not aware that some cranks are innies and some are flat. the one on the bike is an innie and i do not think that a flat crank will help as then the chain will have to travel even further. any ideas?

 

[DannoXYZ]

Did you get the M571 derailleur? What you're facing is very, very typical of these types of conversions. Seen it a hundred times at my shop, in some cases it required cutting off the right chainstay and brazing in a new S-curved one. In addition to trimming the bottom-bracket width down to 68mm to use the properly matched spindle+crank combination. But that may not be necessary in your case, depending upon the measurements we get from our configuration.

First, measure the distance between the smallest chainring to the chainstay.

Second, measure the distance between the center of the seat-tube to the middle chainring and tell me what that is. The lateral spacing between the derailleur and the chainrings is highly critical. What happens when you put a triple onto a bike that was designed for a double is that you may not be able to install the crank in far enough. That's typically due to the chain-stays not being curved for the smallest of chainrings to ride really close to the seat-tube.

So you've got a double-whammy against you. First is a tandem with a wider bottom-bracket. Then using a triple, you're not able to locate the crank in far enough because it'll rub on the chainstays. WIth the crank spaced too far out, the derailleur can't reach up into the big ring properly. That's why you're having these problems:

"if i put it where the little red tag says when the chain is on the big ring the inside of cage grinds on the second ring. so i have to raise it way too much and i end up with it not wanting to drop onto middle ring. goes up good. so i end up angling the thing so that the back of it is in quite a bit."

"now the chain drops down well, but has to be nudjed up. i can not seem to have it both ways."

BTW, the rear of the cage should be angled out, not in. You're making up for having to really crank the FD outwards in order to push the chain up.

If you look from the rear of the bike and sweep the FD across its full-range, you'll see that as it sweeps out, it also sweeps up in an arc. The farther out it moves, the more it moves up and up rather than outwards. There's a limit to how far the derailleur can move laterally and as it sweeps further and further outwards, it just ends up moving vertically with additional cable pull. This is the cause of your lazy shifting into the big-ring.

The third simple measurement is to shift the derailleurs to the smallest chainring and largest cog in the rear. Loosen the inner-limit screw all the way. Looking down from the top, on axis with the plane of the smallest chainring, how is the derailleur cages centered over the smallest chainring?

I've converted many a bikes like what you're doing. The simplest method is to get a braze-on FD tab that reaches out away from the seat-tube more than normal to place the derailleur into the proper operating distances over the chainrings. Due to the wider BB and rear-hub, you need to locate the FD about 5-10mm outwards from it's normal location on a road/MTB bike.

So we're looking for three measurements:

1. gap between smallest chainring and chainstay.
2. distance between center of seat-tube and center of middle-chainring
3. distance between center of smallest chainring and center of derailleur cage with cable fully loosened and limit-screw undone all the way.

If you can take some pictures of measuring #1-3 that would help as well.

 

[aa9t8]

wow
so the 1st mesurment is 10 mm. little ring to chain stay
2nd is 50 mm. from center of seat post to center ring
the 3rd i will have to do after as we are heading out to fort langley for lunch. and it is working as good as it gets for now. and changing anything could go bad. if i am still alive after this ride i will mesure it. thanks so far. and i am not converting this bike i believe norco kinda had some stuff left over and built a tandem out of it. the average tandem does not get riden a lot. so these glitches would not show up. thanks again.

 

[DannoXYZ]

"so the 1st mesurment is 10 mm. little ring to chain stay
2nd is 50 mm. from center of seat post to center ring"

Ok, so we know what the problem is then, the crank sits to far out for the derailleur. You don't need to bother with getting that last measurement. If you look at bikes with triple-cranks, they have S-shaped chainstays because the granny ring is actually placed completely inboard of the crank-arm assembly while maintaining the same seat-tube to big-ring distance as a double. You'll notice that the small chainring actually rides OVER the bottom-bracket, inboard of the outer surface of the bottom-bracket cups. This isn't possible without S-curve chainstays.

So the best we can do with what you have now to get a 18mm shorter bottom-bracket spindle to move that crank in so that the smallest chain-ring is just 1mm away from the chainstay. Depending upon the rotation of the eccentric bottom-bracket adaptor, you may have clearance issues with the bottom-bracket as well. So pick a spindle-length that brings the granny ring as close as possible to the part that has minimum clearance. The FD will then work MUCH, MUCH better because that sweep from the middle-ring to the big ring will move the cage laterally, rather than moving it up, which doesn't push the chain very far sideways.

Also watch for the clearance between the inside of teh crank-arm end vs. the chain-stay as well. The narrower Q-distance (spacing between outer-surfaces of crank-arms) actually helps relieve knee-pain in a lot of cases.

While moving the crank inwards is still not the most optimum solution, but it will work tonnes better than what you have now. The best solution is of course, a frame designed for triples with a braze-on derailleur tab that moves the deraillleur mounting 10mm out further from where it is now. This then keeps the crank more centered over the wider 145mm rear-hub spacing.

 

[John M]

wow
so the 1st mesurment is 10 mm. little ring to chain stay
2nd is 50 mm. from center of seat post to center ring
the 3rd i will have to do after as we are heading out to fort langley for lunch. and it is working as good as it gets for now. and changing anything could go bad. if i am still alive after this ride i will mesure it. thanks so far. and i am not converting this bike i believe norco kinda had some stuff left over and built a tandem out of it. the average tandem does not get riden a lot. so these glitches would not show up. thanks again.

The suggestion to get a shorter BB may help some. If your bike uses a clamp-on FD, an alternative approach that might work to get the FD closer to the chainrings is to use a FD designed for a larger diameter seat tube with a shim underneath it to make it fit the smaller seat tube. This would bring the FD outwards and would not change the chainline between the crank and the rear cogs like a shorter BB would. Not an elegant solution, but it might help.

 

[aa9t8]

and we were thinking!
first we did our first 100 kms today!!!!!!!!
there will be a memorial service for my legs and winky.
what if we just got a new crank with only 2 rings?
what all else has to be changed then?

 

[DannoXYZ]

what if we just got a new crank with only 2 rings?
what all else has to be changed then?

Let's think about this. Imagine taking the crank you have now, and removing the 3rd inner granny ring. What do you have? A crank with 2-rings. Does that change anything in the relationship and spacing between the derailleur and the big-ring that you're causing so much trouble with now?

You'll still need shorter bottom-bracket spindle to move the crank closer to the seat-tube to work within the range of motion of that derailleur. It's the location of the chainring's that causing us trouble and we want to move them inwards. Regardless if the crank's got 2 or 3 chainrings, the big-ring's distance away from that derailleur's still gonna be too far away.

John's got a good idea there. Get a FD with 1-3/8" clamp. We can actually make an eccentric spacer, like the adaptor you have on the BB to use a road-bike bottom-bracket. The eccentric off-center hole is off to once side so that when the derailleur clamps down, the entire extra space within the clamp is pushed to one side to move the derailleur outwards as far as possible. This will move the derailleur out about 10mm, perfect! You can preserve your chain-line centering over the rear-cluster and have proper FD performance.

So the solution to your problem is pretty easy:

1. move crank inwards or
2. move derailleur mounting outwards.

Simple, just choose one.

 

[aa9t8]

okay okay
you have been very helpful. now just to clarify the way my brain sees things. now firstly that is a new derailer and buying another one to mickey mouse just does not appeal to me. but i will use it as a last resort.
now what troubles me is the granny ring on the bike is already concave how is "shortening the bb going to bring the rings in any closer". and the crank is already just clearing the chain stay by about 4 or 5 mm. riddle me this? it is quite possible that i have missunderstude something and what may seem obvious to you i could be missing completely. thanks again

 

[aa9t8]

what i am meaning is that the crank is only a 2 or 3 mm from the bb how is shortening the bb crank thingy going to bring it any closer?

 

[aa9t8]

what i am meaning is that the crank is only a 2 or 3 mm from the bb how is shortening the bb crank thingy going to bring it any closer?