TKJava

My wife's bike has a chronic problem of not being able to move from the small ring to the large on the front derailleur. I have viewed video's/posts etc. on front derailleur adjustment in this regard all pointing to for the most part cable tension as opposed to limit screws. The odd thing is I have adjusted the barrel adjuster on rides to get the chain to move and then it does OK for a while. I have taken the bike into the local bike shop and they have adjusted the cable tension and made it so the barrel adjuster still has room to "adjust". The bike works fine for one or 2 rides then it won't go from small to big. I mess with the barrel adjuster and it's fine... for a little while. I cannot understand why would this happen repeatedly over and over. The derailleur height is correct, the limit screws are correctly adjusted. What could possibly be happening here? In all out no holds bar, shotgun approach what things would you try e.g. cable replacement etc. ?

Further information my wife has a 50/34 front chain ring, Shimano Ultegra derailleur (clamp on) and Shimano Ultegra shifters.

Andrew R Stewart 

Will the ft shift work if the cable only is pulled on? Have the casing end caps been checked for their condition? When the ft shifting stops working and if then the cable is pulled will the der move more and the shift be completed? Andy

fietsbob

When, are you demanding the Upshift? are you going down hill,
spinning un weighted pedals?

TKJava

So I have not checked pulling on the cable so I would like to ask a clarifying question. When pulling on the cable do you mean to simply pull the cable and expect to see the chain move or pull the cable and in addition move the shifter at the same time? In either scenario I have not tried this.
I'm also not clear on what is meant by "casing end caps"? Is this referring to the caps that are crimped on to the end of the cable? Thanks.

TKJava

The shifting is being done at a point where there's not a great deal of load on the pedal stroke e.g. flat road not grinding down on the crank. When the shifter is pushed toward the inside (moves the derailleur from small to big) you can see just by looking down at the movement of the cage it's not sufficient to push the chain uphill so to speak, one does not have to pedal to see that it's simply not moving far enough to go up.

DrIsotope

Make sure the crankset hasn't slipped. If the drive-side creeps out even a millimeter or so, the FD can't lift the chain onto the big ring. With any crankset that uses a wave washer, this can happen. If it's a Shimano crank, probably not, unless the little pivot-y guy with the pin wasn't used. Then it could definitely creep.

Easy to check-- whack the crank towards the BB with your hand. Check to see if it will shift.

Andrew R Stewart 

DrI makes a good point, although not common cranks can shift to the outside if the BB is moving within the frame. Hopefully the shop would have noticed this though.

Using only the cable to try shifting a der (ft or rr) serves to remove shifter issues from the system. It's easier to assess a system by breaking it down to fewer components. By checking out the casing end caps one finds out if the casing inner strand(s) have punched through the cap and continue to move slightly further with each shift. Last thing to easily check is the inner cable's condition as it wraps around the shifter's spool. This is a common location to see fraying. Andy

CliffordK

One thing to look for is a bent derailleur cage, or a re-straightened cage. This could especially be true with shifting without pedaling.

I recently damaged the end of my cable housing on one bike. Cut short enough that a sharp turn of the handlebars would pull the housing out of the ferrule, and drop it back in. Eventually causing imprecise front shifting (which Campy has a lot of tolerance for, but one can exceed the capacity of the shifters).

Anyway, check your cable path. Also verify that the shifters aren't moving on the handlebars.

shoota 

Replacing cables and housing is not a shotgun approach and is what I would definitely do right away if for no other reason than to eliminate it as the problem.

Jon T

Is the cable slipping at the anchor point?
Jon

Retro Grouch 

Since you are able to adjust the derailleur so that it works temporarily, it probably isn't the derailleur.

Check your cable housing ends. What you are looking for as a few tiny wires sticking out of the ferrels. If you see that, it's actually because it means that you have found the problem. Replace the cable housing making sure the new housing is cut nice and square and you'll be good to go. What is happening is your cable housing is slowly shortening itself. When that happens you are able to adjust the derailleur so that it works for awhile but the housing shortens itself again and you can't get enough cable tension to make the shift.

Aubergine 

zacster

I would go back to the crank/BB. I have an older FSA SLK crank where the bolt was known to loosen, and one clue as to it being loose is that I can't shift back to the big ring. That's when I stop and pull out my 8mm allen wrench and tighten the crank arm bolt, then all is good again.

TKJava

First thanks for all of the replies, given the fact that the proper operation of the FD occurs at least temporarily then goes out and can be corrected with a tension adjustment and the fact that I don't see evidence of the crank or BB being loose I am inclined to agree with a cable problem. I have a picture below with my own indications of what the "housing" is and what "ferrules" are just to ensure that I understand the terminology correctly. It would seem to me that one would need to replace the entire cable (with housing and ferrules) from the shifter to the FD or can housing and ferrules be changed directly? One thing I should have also mentioned if it matters that the cables are internally routed inside the frame tubes.



Cable housing, ferrule and cable

Retro Grouch 

You have the nomenclature right.

Internally routed cables are a nuisance but not a real problem. The trick is to change the cable and the cable housing one-at-a-time. You use the cable to guide the cable housing through the frame tube and the housing to guide the cable.

Assuming the cable housing is your problem you will probably have to replace your shift cable too unless you have very well trimmed "hairless" cut cable ends. No matter what I do, I'm seldom that lucky.

cny-bikeman

When it shifts OK for a while and then fails a housing fault would be the first thing I would suspect. The reason is that limit screws do not easily change, and the same goes for tension adjusters. If the housing is failing or a ferrule is not properly restraining the housing slack can be created without any change in adjustment, and can keep reoccurring.