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-   -   Chain hitting front derailleur (https://www.bikeforums.net/bicycle-mechanics/927363-chain-hitting-front-derailleur.html)

chschen 12-24-13 09:26 PM

Chain hitting front derailleur
 
Hi, we are trying to assemble the Mercier Galaxy SC2 (http://www.bikesdirect.com/products/..._al_xi_sc2.htm) and have hit upon a little problem with our front derailleur. We had to adjust the height of the derailleur and also make it parallel to the cassette. But, in the lowest gears and the highest gears, the chain hits the derailleur, despite us adjusting both limiter screws. Adjusting one may fix the problem on one side (e.g. in highest gear), but then it makes the problem worse on the other side (e.g. in lowest gear). Any ideas on how to fix this? Also, I noticed the cable tension is really tight. Does this affect anything? Should we loosen it and readjust everything?

Thanks in advance for your help.

fietsbob 12-24-13 10:06 PM

Not there , cant see, .. maybe your Bike shop nearby can help.

STI FD's scrapes in the cross chain gears , just avoid them ..





Me? I stick to friction shifting, so, scraping sound? I just move the lever ..

FBinNY 12-24-13 10:11 PM

Limit screws don't set the position of the cage. the cable does.

I suggest you watch a few tutorials on adjusting front derailleurs until you have a good sense of the process, then try again.

zandoval 12-24-13 10:14 PM

little more info here is needed - name the derailuer, hitting upper part, lower part, right left, what gears, how big the casset, how many gears on the crank, pics if possible...

chschen 12-24-13 10:33 PM


Originally Posted by zandoval (Post 16357396)
little more info here is needed - name the derailuer, hitting upper part, lower part, right left, what gears, how big the casset, how many gears on the crank, pics if possible...

Derailleur: Shimano FD-2303
It's hitting right and left
Cassette is SUNRACE CSR 12-25T, 8 speed / SUNRACE 8 speed (24 Speed total)
Crank has 3 gears

I will take some pictures soon and post them.

Andrew R Stewart 12-24-13 10:36 PM

There is no linkage between what the limit screws do. One only can effect the outer travel as the other can only change the inner movement. Yes, the cable tension is important. And the front sprockets are usually called chain rings.

So lets get down to basic set up. The first thing i do with Ft ders is to not use the shift lever to move the der during initial set up. I do this by pulling on the cable part way along the down tube. why? Because this separates the "raw' adjustment of the ft der from the lever's built in cable moving function. Set the ft der at the right height off the large ring when the cage is moved so it's outer plate is even with the large ring. The outer cage plate's lower edge is usually about 2-3mm's above the large ring's teeth. Then rotate the der/cage on the frame so it's about parallel to the rings. This is one of the set up aspects that often needs trial and error to get the best position. But this fine tuning starts after the initial set up. Attach the cable to the anchor bolt on the right side of the bolt (The failure to do this correctly will cause all kings of rubbing issues). Then shift into the large cog (easy gear) in back and place the chain on the inner ring. Turn the inner limit screw so the inside or the inner cage plate JUST clears the chain. Shift into the smallest rear cog (high gear) and "shift" (and by this I mean pedal and pull the ft cable by hand to move the ft der outward) onto the large ring. Turn the outer limit screw so the inside of the outer cage plate JUST clears the chain.

Now begins the fine tuning. I still will do the der moving and fine tuning by pulling the bare cable, the coordination with the shift lever waits for now. Shift the rear back into the large cog. Try shifting (pedaling of course) the ft up and down onto and off the middle and small rings. Note how easy the up shift is and how quick the drop down to the small ring is. Shimano ft shifting with STI levers is so abrupt that to prevent overshifting down (and dropping the chain onto the BB shell) you might have to limit the der's inner travel so much that the chain has a slight rub when on both inner cogs (large rear and small ft). Next move to the rear small cog and shift from the ft middle to large and back (yes this means that you'll be holding the cable enough to not shift onto the small ft). What i watch for is how the chain rides up on the large ring's teeth before settling down into them. When i look down from above (my head will often touch the seat) I can see the chain's flexing and side to side movement during the up shift. You want to have a complete up shift with out dropping off to the outside. (Again with STI you sometimes have to accept a BCH of rub when in highest gear to prevent overshift and chain drop). This is the step where ft cage rotation is most sensitive. If you try to slightly change the cage rotation (and parallelness to the rings) then you have to back to the adjustments of the small ring before you can go back to the adjustments of the large ring travel.

You can see how there can be a lot of back and forth between cage rotation and inner/outer limits. Of course with experience this process goes quickly and without it can be frustrating. Especially if you forget to reestablish the inward movement before continuing the outer movement adjustments. Once you think both "ends" of the ft shifting are equally good then move the chain to a Central rear cog and repeat the ft shifting, but now across all three rings.

In an ideal world you won't shift onto the granny ring unless you are already half way up the rear cogs and likewise won't shift onto the large ring unless you're off the easy rear cogs. But the middle ring should hopefully be able to be used with all the rear cogs.

After all this trial shifting by using the cable only and the fine tuning to get the best shifting performance across the ranges now it's time to get the shift lever in play. To use the shift lever before this point often only confuses and hides issues with the basic der set up and fine tunings. Go back to the start with the rear large cog and small ft ring. Reattach the cable (note proper manor) and while tightening the anchor bolt pull the cable tight (of course the lever should be in it's lowest position). Now shift the lever to the middle position while pedaling and release. The chain should climb up onto the middle ring. If your lever has a middle position trim feature the der will likely have a touch of inner cage plate rub. Trimming the lever BUT still maintaining the middle shift position should eliminate all (or the vast majority) of the rub. Many riders don't understand the trim function or can feel it. THIS IS IMPORTANT TO LEARN HOW TO DO. If there is a lot of chain rub after trimming the lever then the cable needs to be slightly looser. If no rub then tighten the cable till is almost does rub. This tension adjustment can be done with a casing barrel adjuster or with the cable anchor bolt. But keep in mind that allowing the cage to move inward now will also keep the cage from moving outward for the large ring's shift. So next shift the chain into the smallest rear cog and try lever shifting the ft onto the large ring. If the cable is tight enough then the shift will go well and little/no rub will be present. Again there might be a trim feature for the large ring so DO UNDERSTAND TRIM.

If you were able to shift the ft der with only pulling the cable well then you should be able to fine tune the cable tension so that with the lever controlling the der movements the same good shifting can be had. Trying the ft shifting with the chain in the small, middle and large rear cogs again before deciding that you've gotten things ASAP.

All of this presumes that all the components are compatible and of the same brand. Wait, did i say the same brand (like crankset or chain)? Yes I did. Any deviation from the system that Shimano intended can cause a drop off of performance/increased rubbing/slower shifting. The off brands of parts will always claim otherwise, that they design to Shimano's spec. But Shimano will never agree to that.

As i said before there is a lot of back and forth then re base lining before going back to where you had to try something different. As the system wears in cable tension needs to be kept on top of. When tapered square cranks are retorqued on the BB spindle the limits and cable tension needs rechecking. If you shift under power (JAM SHIFTING) and don't know how to soft pedal during shifting that all these adjustments will not matter too much. Andy.

chschen 12-24-13 10:38 PM


Originally Posted by FBinNY (Post 16357388)
Limit screws don't set the position of the cage. the cable does.

I suggest you watch a few tutorials on adjusting front derailleurs until you have a good sense of the process, then try again.

The tutorial I was watching (https://www.youtube.com/watch?v=zLqrhFzW8s0) said that you adjust the limiter screws so that the derailleur is 1 mm from the chain. So it would seem to me that if the derailleur was hitting the chain on the left and right sides, adjusting the limiter screws might help with that. Am I wrong?

Do you have tutorials you recommend?

zandoval 12-24-13 10:47 PM

You bet - The 2303 is a good derailuer for allot of travel - This is good - Take the cable off completely and use thumb pressure to get through all the gears - If it works then follow Stewarts instructions closely...

Enjoy yourself while your doing this - Remember its all fun...

rekmeyata 12-24-13 10:50 PM

Without being there is difficult to assess what's happening. I would have assume the bike should have left the Bikes Direct already adjusted for derailleur height because a pro set alignment block needed to be used to make sure the front gear was set properly for height. Like any front derailleur you need to put the chain in the largest rear gear and the smallest front chain gear before adjusting your low screw and that the clearance is no more than 0.5mm between the chain and the chain guide inner plate of the derailleur, then put the chain in the smallest rear gear and the largest front chain gear and adjust the high screw so that the clearance is no more than 0.5mm between the chain and the chain guide outer plate of the derailleur.

A bike shop will probably charge about $20 to do it, but if you take it in have them do a basic run through checking everything, it might cost you $40 to do that but worth the piece of mind. I would also contact Bikes Direct about the issue, they may reimburse you or the bike shop for any money you're out especially on the front derailleur issue.

FBinNY 12-24-13 11:04 PM


Originally Posted by chschen (Post 16357433)
The tutorial I was watching (https://www.youtube.com/watch?v=zLqrhFzW8s0) said that you adjust the limiter screws so that the derailleur is 1 mm from the chain. So it would seem to me that if the derailleur was hitting the chain on the left and right sides, adjusting the limiter screws might help with that. Am I wrong?

Do you have tutorials you recommend?

Imagine your derailleur is an elevator, which hangs from cable. For safety there are switches at the top and bottom of the shaft to keep it from hitting the end. These can also be set to stop the elevator to stop in the right place at the top and bottom floors, but it's really the cable that determines the height of the elevator at each floor.

Likewise, the derailleur limits prevent overshifting beyond the chainrings, but the cage position depends on the cable. However on the innermost chainring the cable is slack so the inner limit also sets the cage for low, much as the lower elevator might set the basement stop position.

I hope that helps.

I can't suggest any single tutorial, but I always suggest watching a few. Sometimes something not covered well on one becomes clear on the second. The point is you want to have a sense of the job in your head, rather than simply following steps by rote.

chschen 12-24-13 11:32 PM

Wow, thanks for all that detailed, good information! We're going to give it a try and see what happens! Happy holidays, everyone.

dsbrantjr 12-25-13 10:01 AM

Follow Andrew Stewart's instructions or this one: http://www.parktool.com/blog/repair-...ur-adjustments

When adjusting the low limit be sure not to leave more clearance than necessary; if you do you may find that you are running out of cable pull on the high end.

Merry Christmas!

BLYTZPK 12-25-13 10:59 AM

clean your ear canals out so to ear the rrrrrrrrrrrrrr.....

screws should be set even....parks covers this right ? as if screws have 5 turns total set screws even at 2.5 turns from bottom.

deray gate set to the large ring should almost touch chain and so for the small ring...install a chain preventer on the seat tube.

but the deray's seat tube mounting position determines the gates total effectiveness in passing the chain thru as chain angle to rear cogs varies from 32 teeth to 14 teeth.

the gate/seat post mounting position should clear...when shifted to large ring...to the small rear cog...and from small ring to large cog when shifted.

and remeber...you can hammer and file.

when the system drrrrrrags in transit, loosen the clamp, turn the mount for immediate silence

cny-bikeman 12-25-13 11:32 AM


Originally Posted by BLYTZPK (Post 16358057)
clean your ear canals out so to ear the rrrrrrrrrrrrrr.....

screws should be set even....parks covers this right ? as if screws have 5 turns total set screws even at 2.5 turns from bottom.

deray gate set to the large ring should almost touch chain and so for the small ring...install a chain preventer on the seat tube.

but the deray's seat tube mounting position determines the gates total effectiveness in passing the chain thru as chain angle to rear cogs varies from 32 teeth to 14 teeth.

the gate/seat post mounting position should clear...when shifted to large ring...to the small rear cog...and from small ring to large cog when shifted.

and remeber...you can hammer and file.

when the system drrrrrrags in transit, loosen the clamp, turn the mount for immediate silence

Better to give no instructions at all than ones like the above, which are garbled, inaccurate, and suggest radical procedures (hammer and file) to a novice.

cny-bikeman 12-25-13 11:45 AM

I don't know how you found that video but don't use it. He leaves a lot out, and anyone who talks about "tuning" brakes and "gears" is starting you off behind by using non-standard terms. That's also part of the lack of clarity in your original post. Rather than talking about "lowest/highest gears" you need to tell us the front/rear (chainwheel/rear cog) combo you are in when adjusting and when the problem occurs.

The low limit screw is set ONLY for the innermost front/rear combo, likewise the high limit is for the outer front rear combo. On both large and small chainwheels it is normal for rubbing to occur by the time you shift to the 8th cog away from the one where the adjustment is made - not all combos are necessarily useable.

I would echo the previous advice that you look and think about what you are doing, observe how things move and interact, rather than following rote instructions. As already mentioned, lots of resources available, most notably at sheldonbrown.com and parktool.com/blog. They will show up near the top of almost any Google search you do for repair procedures. Start though with a search for bicycle parts diagram, so that you can search using the right terms and communicate more clearly when asking questions.

Duane Behrens 12-25-13 02:23 PM

You've gotten plenty of advice here - both kinds - so I won't add a lot more except this: You yourself touched on the importance of initial cable tension, and you were correct. Attempts to "adjust" around an improperly tensioned cable will be frustrating at best. The first time I installed a FD, I actually wore out a cable getting that tension right. But when I DID get it right, the rest of the adjustments became responsive to my touch and tolerant of slight inaccuracies.

Watch the videos - they're helpful - but don't be afraid to start over by re-setting initial cable tension, then going through the steps again. Like me, you may not get it on the first try . . . but you'll get it.

cobba 12-25-13 07:56 PM

1 Attachment(s)
What gear combo is the chain rubbing?

Big front & big rear ?
Small front & small rear ?

8 speed gear combinations that Shimano doesn't recommend using:

http://bikeforums.net/attachment.php...hmentid=356586

migrantwing 12-26-13 05:25 AM


Originally Posted by FBinNY (Post 16357388)
Limit screws don't set the position of the cage. the cable does...

+1

Often overlooked and misunderstood

BLYTZPK 12-26-13 06:52 AM

writing a post or instruction converting words to action is difficult. Instructions here are too dense.

moving the cage on the seat tube both radially, around the tube, and vertically for clearance before or after or during setting screws so the chain 'almost touches' ...

is not dense, just do it.

when you get there at that time or space then you can spin the cranks adjusting the screws so the chain moves onto outside or inside CR.

if you can't read it don't read it

where's the crit for 'screws are not interrelated ?

cny-bikeman 12-26-13 08:19 AM


Originally Posted by BLYTZPK (Post 16359295)
1. if you can't read it don't read it

2. where's the crit for 'screws are not interrelated ?

1. I comment on other members' postings when incorrect information is given, and especially if it may cause rather than cure problems.

2. I don't see those words on any post in this thread, so have no idea what you mean.

BLYTZPK 12-26-13 09:01 AM


Originally Posted by cny-bikeman (Post 16359399)
1. I comment on other members' postings when incorrect information is given, and especially if it may cause rather than cure problems.

2. I don't see those words on any post in this thread, so have no idea what you mean.

rrrrrrrrrrrrrrrrrrrrrrr....:lol:

chschen 12-26-13 11:46 AM

I think we were able to make the adjustments so that the bike works properly. It rubs a little on the extremes--biggest crank ring and smallest sprocket, biggest sprocket and smallest crank ring--but I guess that will happen? My husband tested it out yesterday on some big hills and thought it was fine. Thanks again for all your posts!

cny-bikeman 12-26-13 12:29 PM

It really should not rub in those combos, as they are the very ones that one uses to make the front derailleur adjustments. Please make sure brakes are properly adjusted and that everything is properly tightened.

BLYTZPK 12-26-13 12:40 PM

rrrrrrrrrrrrrr.....


almost there...look at the cage when chin rubs in large CR/small cog and small CR/large cog.

either twist the small CR/large cog screw 1/4 turn..pedal...does the chain fall off ? NO ?

if no then ad lines 8 and 14 thru 9...

If NO then does the noise cease ?

if not or before twisting the screw, look and think about the cage position as it relates to turning the cage with the seat post mount or raising or lowering the mount.

This is important, requires a little special reasoning.

If you can only eliminate 1 rub position then probably go for the small CR/large cog...

when do you use the large CR/small cog ?

move the cage around experimentally with the seat post mountjust to see what goes on there at the large CR...you know...

rrrrrrrrrrrrrrrrerk clang

gsa103 12-26-13 01:01 PM


Originally Posted by chschen (Post 16359755)
I think we were able to make the adjustments so that the bike works properly. It rubs a little on the extremes--biggest crank ring and smallest sprocket, biggest sprocket and smallest crank ring--but I guess that will happen? My husband tested it out yesterday on some big hills and thought it was fine. Thanks again for all your posts!

That would be typical unless the derailuer has a trim adjustment (essentially a half-click).


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