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what's wrong with my drivetrain!?(11 posts)

what's wrong with my drivetrain!?tobinb
May 25, 2003 7:35 PM
The problem is chain rub, and i swear on a stack of bike mags that i know how to work the barrel adjuster. My bike began life as a 105 triple setup. After a few rides i realized i was never going to use granny gear so i took it off, adjusting the derailler limit screw so the chain wouldnt drop right down. The setup worked ok but the chain still dropped off occasionally. This spring, since i was installing a new drivetrain, i put on 39/53 rings and decided to remove the old bb (118mm i think) and put in a 109mm bottom bracket to finish the conversion to a 2-ring setup. I figured this would give me a straighter chainline and no chain rub. The problem now is when im in my 39, there is chain rub on the lower 1/2 of my cogs, and when im in my 53, there is chain rub on the top 1/2 of my cogs (of course i avoid the big/big combo). There are only 2 cogs in the middle of the cassette that work silently with either chainring. This is driving me insane as i ride on rolling terrain and i have to continually work the front shifter due to the limited range in the back (that doesnt cause a racket).
I was wondering, is the space between chainrings constant between triple and double crank spiders, or are the rings in a triple tighter. This makes me also wonder about the shifter. does one click always move the derailler the same distance weither the unit has 3 or two clicks?
Is the front derailleur that came with my triple setup even compatable with my new chainring combo? I did have to move it up the seat tube a bit for clearance when i went from the 48 to the 53.
Anyway, now im starting to ramble. basically does anyone have ideas to repair my drivetrain; do i need to ditch the remaining parts of my triple to run a dedicated two ring system?
thanks,

d
It's Shimano?Juanmoretime
May 26, 2003 3:27 AM
Sorry couldn't help myself. I'm not sure if 105 STI levers have the ability to trim the front derailluer. I know the Dura Ace and Ultegra STI Levers do. If your next question is what is trimming, those to levers have one or two half clicks that move the front derailluer, to eliminate chain rub but not shift to the next chain ring. I'm not sure if using a triple front and rear derailluer would have any thing to do with it since I don't have any experience with triples on roadbikes.
How well did it work with the 118 bb spindle?Spoke Wrench
May 26, 2003 7:26 AM
It sounds to me like you have tried to make a double chainring crank by taking off the grannie ring and using a bottom bracket for a double. I'm thinking the positioning of the chainrings on a triple crankset might not be the same.
exactly..tobinb
May 26, 2003 9:28 AM
that is exactly what i did, in far less words i should add. I figured that since i didnt have the granny gear on anyway, why not put in the shorter spindle when i replaced the bb. With the 118mm bb, there was an empty space where the chain can fall down into, though it didnt happen very often. To clarify, i do still have the shifter and front derailleur that came with my 105 triple. The shifter does trim a half click, and that certainly helps a bit.
do you think there would there be a difference if i was to put on a dedicated 2-ring crankarm?
The 3x and 2x FDs are not the same…..TFerguson
May 26, 2003 4:13 PM
The two derailleurs do not move the same amount with the same amount of cable pull. When you limited the movement with the stop screw, I believe you also limited the shifter movement that allows you to trim both rings.

TF
So, how's your chain line?Kerry
May 26, 2003 4:29 PM
Things should be set up so that the center of the chainrings is lined up on the center of the rear cogs. If it's not, then you can expect some kind of problems either with the lower end or the upper end. It sounds like (you never say) the chain is rubbing on the FD cage. Any chance the cage is bent? Is the FD cage nearly parallel with the chain rings? Get your chain line right, get your FD lined up properly, and then you can tell what is going on.
A possibility...Lone Gunman
May 26, 2003 4:38 PM
While doing some research on how to swap my Ultegra 42 tooth middle ring for a 39 tooth middle ring on my triple, I discovered why Shimano does not offer the 39 ring as an option on the Ultegra triple. The Ultegra and probably the 105 FD system are designed to handle a 10 tooth difference (53-39=14 teeth, too many teeth for THAT FD) In order for Shimano to offer the 39 middle ring for Ultegra, it would need to offer 2 FDs, which it chose not to do. Alot of people want that 39 ring on a triple and can't get the precise FD shifting offered with dedicated Shimano rings on the Ultegra. You want it, go buy DA triple. You can do 1 of 2 things me thinks; get a new Ultegra or 105 double FD or a DA triple FD which is designed to handle a 30/39/53 ring set up. I can not explain the difference, if you want to read up and noodle on the problem, go to peterwhitecycles.com and look at TA replacement rings section. Myself, I am inclined to go with the triple as an option. I want to be able to ride my bike virtually on any paved road in the US and I like to have that option of bail out low gearing for all that it adds in weight to the bike.
Basic Rulegafino
May 26, 2003 7:11 PM
Hi,

I had a triple drivetrain (Tiagra) b4 on my Giant. To do a perfect conversion to double, u must change the crank, BB & FD. The rest is just tuning. It will work fine..

"FROM MALAYSIA WITH PEACE"

Chao..
Derailleur Hanger Alignmentctheronj
May 26, 2003 7:26 PM
Hi,

My mountain bike had the exact same trouble until I got the derailleur hanger straightened. I took it in to the shop because I wasn't sure if it was bent or not; it ended up being ever-so-slightly out of true, and bending it back was the fix I was looking for.

Not saying this is your problem, but your bike's symptoms sound familiar so it might be worth checking out.
doh! front derailleur??tobinb
May 26, 2003 8:17 PM
OK, different front derailleur. looks like ya hit my head right on the nail with that one. I never realized there was a different unit for the triple. I am going to try out a buddy's ultegra 2-ring unit and see how it works. I should still be ok with my 39/53 rings bolted onto the old triple crank though right?
i guess i will see.. thanks for the good info,
d
re: what's wrong?Chen2
May 28, 2003 10:09 AM
Here's a possibility. Take a look at the stampings on the chain rings. The "53" should face to the right, away from the bike frame. The "39" should face to the left, toward the bike frame. If the 39 is on backwards the spacing is wrong explaining the chain rub.
~Al