Adohrn

I have completely rebuilt this bike so that the only thing left of the original drive train is the rear wheel and cassette. I’am now having trouble shifting onto the largest rear cog which is 24 tooth. I can manually shift to the largest rear cog by pulling on the cable (takes a fair bit of pulling to do this) and have set the L limit screw doing this. When trying to use the shifters in friction mode I cant get there no matter how tight I make the cable. The cable has been tightened up to a point that it can no longer shift down to the 11 and 12 tooth cogs but still nothing. Tried completely loosening the L limit screw as well as playing with the B limit to make sure excessive chain wrap wasn’t causing the problem. Now left with a lot of ideas, but no clear starting point. Here are some of them.

1. Bar end cables run under the tape creating to much friction and interfering with shifting
2. Either bent derailer cage or frame
3. Chain line
4. Spacing and dishing of back wheel

Hopefully someone can help.

Matching set of 105 front and rear derailers and cranks

Shifters 105 Bar End 8 set in Friction mode, Cables run under the handlebar tape, Handlebars are ergonomic which creates a little extra friction as the cables have a few more bends.

Cassette 7 cogs 11-24

Campy bottom bracket with 105 cranks. The Campy axel is 3-4mm longer than original, but still the net affect is that each side is a least several mm closer to bottom bracket. It is an Italian bottom bracket so my selection was limited.

The rear was definitely a replacement when I got it. The Frame is an Olmo Corisca. Late 80’s steel with a 126mm spacing.

Sorry about the pics. Trying to reduce the images to less than 100k has resulted in more of a line drawing than anything else.

Adohrn

Ok checked chainline and found that it is 3mm closer to bottom bracket than it should be. After reading up found that most chainline problems had to do with front chainrings and not shifting in back or falling off of derailleur wheels. So I don't think its chainline.

Read up on shifting problems and don't think it is Cable issues either. Running the cables under the tape if it were the problem should have created to much friction. If this were the case it shouldn't shift properly in most gears. Shifting multiple cogs at a time or rear derailleur spring not having enough pull to get to 11 tooth cogs ect.. So don't think its that.

Checked dish and its fine.

Derailleur does not appear to be bent. Not an expert opinion so take a look yourself.

Is it possible that this derailleur does not have enough throw? I don't know how old it is, but just by looking I would think it was more than modern enough to handle a 7 sp cassette.

Should I take it to the shop and have them see if the hanger for the derailleur is bent?

Would appreciate any help.

joejack951

I'd suggest starting from the beginning with your derailler install. Remove the cable then set the high and low limit screws by eyeballing them to get in the ballpark. Manually move the derailler to set the low limit screw. Now move your shifter all the way in the direction that releases the cable. Now, attach the cable to the derailler. Try shifting through the gears again and see how it goes.

Panthers007

As above - but shift it slowly on a stand. You want the RD to align directly under the large cog of your cassette - no further inward. Ditto for the small cog.

Adohrn

Will do. I worked it over for several hours already, but maybe approaching it fresh might do the trick.