Bicycle Mechanics - Have I exceeded my derailleur?

I built this old Pinarello with a Campy RD (older Athena) and a 7-speed freewheel that is 12-28. Friction shifters. 53-39 crankset.

Neither one of the limit screws are useful, screwed all the way in they still don't touch. If I'm not careful, I could push the RD and the chain into the spokes. I can shift through all gears but am worried about hitting the spokes.

Is the freewheel too big? Should I drop to a 25 or 26 big cog?

Another thought is the chain may be too long; I didn't do any measuring other than to eyeball it.

http://gallery.mac.com/bbattle/100320/100_4376/web.jpg?ver=13147061150001

http://gallery.mac.com/bbattle/100320/100_4377/web.jpg?ver=13147061160001

Well, one step at a time with all the issues you mention (limit screws, chain length, etc). The limit screws don't have anything to do with chain length, for example, two separate issues. As for the limit screws, in the photos they don't appear to be screwed all the way in, not even close. Are they? Limit screws will usually screw in below flush with the derailleur's body.

Another thought is the chain may be too long; I didn't do any measuring other than to eyeball it.

I don't really know what you mean by that. One thing's for sure, the chain should be long enough to shift to the big/big combination without damaging anything. If it's too short for that shift, it likely will damage something, and badly. I doubt you're beyond the derailleur's capacity in any way, I just think you need to correctly size the chain.

The largest cog on the freewheel has nothing to do with the limit screws not touching. Maybe they're too short? Replaced at one point perhaps?

I've never used Campy but on most RDs if you turn the limit screws in you can lock the chain into one or maybe two cogs. I find it very surprising they're not having any effect in either direction. Something is messed up.

As well biked says, your limits are probably fine, but the right way to confirm is to remove or slacken the cable and see the RD's range of motion. With the cable off or slack, set the outer limit so the RD trims correctly in high gear, (it's best to adjust with the RD pushed in a bit so it's not leaning on and binding the screw). Now shift to low by pushing the RD in with your hand, or by pulling the cable away from the down tube and adjust the inner limit until it can't shift to low. next back it off only so far that the shift is possible, and reliable, and no more than a hair more.

Now that the limits are set you can attach the cable and test and adjust the shifting throughout the range.

Chain length is a different issue. It needs to be long enough to loop the big/big without pulling the RD cage beyond it's range, and short enough for the RD to take up all the slack on the small/small combination. Anything that meets both conditions is OK.

Neither one of the limit screws are useful, screwed all the way in they still don't touch.

one of the limit screws won't touch until you start changing gears. the other one should definitely touch though


if the screws are too short, get longer screws

check sheldon's site for how to get the proper chain length

When setting the low limit screw the chain must be on the smallest chain ring in the front and the largest cog in the rear. When setting the high limit screw the chain must be on the largest chain ring in the front and the smallest cog in the back.

While your buying stuff, you may want to purchase a pair of threaded chain-adjuster screws for the drop outs. It can negatively affect shifting to have the wheel axle too far back. Note that you have existing dropout marks about 1cm forward where the wheel was clamped. You may want to keep clamping the wheel axle there.

Next, check the RD hanger for alignment, then tilt the RD body down a few degrees by screwing in the B-screw on the back a little so the top RD pulley just clears the bottom of the big cog when shifted to lowest gear.

Now check the RD limit on the inside cog. I've installed a number of SunRace FWs and they all push the cogs out too close to the outboard axle lock nut, providing just 1 - 2mm of clearance between dropout face and the smallest cog. This means the default limit settings on most RDs will never reach the highest gear (smallest cog) and will shift into the spokes in the lowest gear (largest cog inside). But with the RD hanger aligned, you should be able to set the limit screws without issues.

On older 126 mm axle spacing hubs, I've sometimes had to add two 1mm washers to each side and increased axle width for clearance from the right dropout face. This allows the RD H-limit to work.

If the RD hanger is aligned but the cage still looks like it's going to hit the spokes when in the big cog (lowest gear), I wiggle the RD while mounted in the RD hanger and look for cage alignment. If the cage looks bent and there are signs of previous damage, I may disassemble the RD and adjust the RD cage/arm by taking it apart carefully and straightening the main arm. If there is slop in the RD hanger fixing bolt/bushing which is also sometimes the B-screw mounting plate, and this slop will cause the RD to tilt inward a few degrees when mounted, I've been known on rare occasions to flex the RD hanger outward by 2 - 3 degrees to compensate.

I've yet to see an RD with missing or replaced limit screws that wasn't destroyed in an accident. But your picture shows almost an RD in mint condition. That would indicated other issues in RD/hanger alignment and FW clearance being issues as opposed to RD limit screws.

Thanks for the tips; I'll check for hanger alignment and see if the RD is straight. Everything looked okay before assembly but it only takes a degree or two to cause real problms.

I set the limit screws before I replace the chain , when I have to do both.

Set the screw so as to stop , when the roller lines up directly under the cog.


short cage , suggests a 12 tooth difference between chainrings is about right.
13 to 28 t freewheel probably fine, your chain length can influence capacity feel.

and placing the wheel in the front of the dropout may be better
than putting the wheel all the way back, as you have done.