Roasty

i've got some problems with front shifting on my bike.

some background. pretty new bike. with rival shifters, rival front de, rival crankset - everything is ok. shifting is quick and no hiccups.

then i bought a new SRAM red 53/39 crankset. at the same time i got these installed at my LBS, I also changed the BB to an Aerozine ceramic BB. at the LBS, i tested shifting on the bike rack and everything seems ok.

got home, rode the bike, and there are issues with shifting from the small to big chainring. it takes ages for the chain to engage the big chainring. occasionally it fails to shift up completely and the chain just dangles in limbo between the inner cage of the front de and the crankset.

took the bike inside and put it on the bike rack, and without tension or load, the chain shifts ok. tried to replicate tension by putting the bike on the trainer and it again fails to engage the big chainring.

i've tried reassembling the front derailleur setup and followed the SRAM manual down to a tee. made sure the derailleur was between 1-3mm from the chainring teeth. checked high and low limits. made sure enough tension on the wire.

my bike has internal wiring; as it exits the region around the bottom bracket, I note that the wire has to hook over the front derailleur spring mechanism when the derailleur is in the small chainring position. this results in a slight (maybe 20deg) bend over the spring before it reaches the wire clasp. I really cant see a way around this.. design flaw? when i shift it to the large chainring, as the derailleur moves outwards, the spring mechanism is no longer in the way, and the wire straightens out. (i'm guessing there is some loss of tension due to the bend..)

possible issues:
- shifter wire slack? (really new components though)
- loss of wire tension due to it bending around the derailleur spring mechanism?
- rival front de not strong enough for the red crankset? i'm just guessing here.. change to force front de?
- problem with the aerozine BB (ie differing width? was told by the LBS there shouldnt be an issue with the BB)

anything i am missing out?

i'd like to try and solve this issue myself so any help will be appreciated (but if i'm reaching wits end or its something i just cant handle, i will just take it back to the LBS..).

motorthings

try pulling the shift cable by hand on the downtube and see if you can get it to shift into the big ring. if you can, it is likely a cable tension issue. it is not unusual for the cables to seat a little bit further into the ferrules right after you install it and ride a bit, and that can introduce just enough cable slack to keep the shift from happening.

mechBgon

Also keep in mind that the shift pins on the big ring should be providing the chain a "toehold." The FD's primary task is to stick the chain onto the shift pin. The FD's secondary task is to prevent the chain from going over the outboard side of the big ring once it does get up there. So after checking that your cable tension is sufficient (the FD's cable tension should be sufficient that the limit screw terminates the outboard swing), next try backing off the outer limit screw about a quarter-turn at a time and do some quick road tests to see if it encourages the upshift, yet does not cause overshifts.

Roasty

the front de wire is routed internally through the frame.. only a short section of wire is visible as it exits the frame to the derailleur.

tried hard to make the wire as taut as possible before clamping to down on the front de; finger tips are aching. short of using a pair of needle nose pliers..

when the front de is in the big chain ring position, I notice that I only get abt a 2mm gap between the chain and out cage of the front de; if I unscrew any further, the screw loses contact with the front de body and ceases to push the cage outwards any farther.

mechBgon

An inline cable-adjusting barrel would be handy here, if you're comfortable redoing the FD cable through the frame in order to add the adjuster.

TrojanHorse

+1 - do you have one?

My shifters exhibited similar behavior to yours and a simple tweak of the barrel adjusters brought it right back up to par.

Another trick would be to adjust the limit screws to loosen the FD (more than you would leave it for normal use) and adjust the cable as tight as you can and then reset the limit screw. That will further tighten the cable if you're having trouble.

MAK

First, if your LBS did the installs on your bike, they should adjust the stuff they worked on for no charge. Id go back to them.

Second, for what it's worth...I just finished a basic maintenance course at my LBS sponsored by Park Tools. The two instructors have over 50 years of wrenching experience between them. When the final session of the course finished, they asked if there were any questions. I asked, "Is there any part of a bike that an ameteur should never attempt to work on and should just bring to a professional." They simultaneously said, "The front derailleur."

I'm sure many on the forum will respond that they fix theirs all the time and that's fine. If you're not really adept at these repairs, you may want to take my mechanic's advice.

Roasty

thanks for all the suggestion guys..

i dont have an inline cable adjustment barrel for the front derailleur will look into getting one.

i'm sure my LBS will get it fixed free of charge. i think i have a nature of wanting to fix things (and dismantle stuff) myself, and wanted to give a try at this before sending into the shop. but this front de is really annoying me. guess i will end up letting the LBS mechanic have a look at it after all.

thanks again all!