Tuesday, December 23, 2008
Q&A: Pulley puzzle, waterlogged carbon frame
Q: I recently disassembled my rear derailleur’s bottom cage (Shimano Dura Ace). Got confident and no reason other than looking for a challenge and something to use my tools on. I removed the bottom cage, both pulleys and cleaned the entire system. Well worth the effort. I believe I have reassembled everything correctly, as I followed the spec. diagram provided on the Shimano website and instructions from your bike repair book. However, I now get a bit of vibration from my system when on the first and second smallest cogs (11T & 12T). I can’t figure out what is causing this.
Look forward to your response.
A: Nice to hear from you, Fred. The rear derailleur cage and pulleys aren't overly complicated but there are some things that can go "wrong" during disassembly and cleaning and reinstallation, if you're not careful. First, it's a great maintenance job to do. A lot of people wait until the pulley bushings/bearings are dry and they hear the chirp, chirp sound that drives you crazy. Doing it routinely is much wiser and ensures your pedaling is silky smooth and efficient. It's even possible for pulleys to "freeze" and create a lot of additional pedaling resistance and you don't want that. Also, while you can spray or drip lube on the pulleys, even if you're careful and lay the bike on its side and get the lube to enter the sides of the pulleys where they turn on the bushings, it's difficult to get the lube to fully penetrate the pulleys and thoroughly lube them (though that technique is better than letting them dry out). Ideally, you'll disassemble and relube at least yearly.
Since you followed a diagram, you probably didn't make this mistake, but I sometimes see the cage put on upside down. The closed/loop end of the cage should be on the bottom. Another easy mistake is to put the top pulley on the bottom and the bottom on the top. The top pulley has sideways play to assist in aligning the chain during shifting, so that needs to be on top. You can wiggle the pulleys to tell the difference. Another issue is assembling the pulleys incorrectly. Usually there's just the pulley, a ceramic bushing that presses into the center and 2 dust caps. All should be cleaned, lightly lubed and reassembled. You should then hold the pulley by the dustcaps with your thumb and forefinger holding it the way it will be held in the derailleur cage and then spin the pulley to make sure that it spins nice and smooth with little resistance. If not, take it apart, clean it some more, lube it and try again.
Once the pulleys are cleaned and lubed, reinstall them. And, here there is an option, too. They can go on in two directions, the way they were, or flipped the other way. Ideally you'll put them back the way they were as you have worn them in in this direction so they're sort of "adjusted" now to this rotation of the chain.
So, if the cage is not upside down, the most likely thing is that the pulleys might be reversed, top on the bottom. If that's not it, it might be that the pulleys are flipped over and now rotating in a different direction, or maybe only one pulley is. The easy way to try to find the issue is to check each thing and then try the next. So, I would check the cage, then check that the top pulley is on top. Then I would try flipping the bottom pulley and see if that solves the problem. If there's no change, I'd put it back the way it was and flip the other pulley, and hopefully that will do the trick.
All of this assumes that the issue really is the pulleys or cage because if you maybe cleaned the chain, too, that could be the issue. Or, if the pulleys are worn out, cleaning them reduces their size slightly and you might need to replace the pulleys to fix the problem. The easiest way to spot worn out pulleys is to compare yours to new ones in a nice big picture of a new derailleur online. Old pulleys have noticeably worn teeth compared to new ones.
Hope these tips result in a nice, quiet and smooth drivetrain!
Q: Hi Jim -
I have a carbon frame and I have been riding regularly in heavy rain. No matter how many times I turn the bike upside down (with the seatpost removed), I can't get all the water out. There's also a screw on the bottom bracket cable guide. I removed that to let the water out, but no luck. I've also let my bike stand for days at a time with the seatpost removed, in the hope that the water would evaporate. Also no luck. I have tried to blow air with my mouth in the frame's seat tube to see if I was missing a hole somewhere, but I was not able to. It seems pretty airtight. I would appreciate any suggestions to get the water out.
A: You might try using a hair dryer to blow hot air into/onto the tubes with any water or condensation in them. Storing the bike in a warm room might have the same effect, though it will take longer. You could also remove the bottom bracket, which is relatively easy if you have a newer external-bearing bottom bracket. You just need the right tool to remove the cups. Your local bike shop probably sells it. Once the cups are removed and the seatpost, too, the air should be able to pass through better and reach any moisture in the seat tube and it might have access to the other tubes to dry them out, too, depending on the frame construction.
It would also be worthwhile to try to figure out how the water is getting into the frame and trying to seal the entry points to keep it out. It might be that the water is being flung up onto the seatpost from the rear wheel and it's then running down the post and getting down inside the frame through the gap between the post and the frame, which is a common way water gets inside bicycles. You could try making a simple seal out of a section cut from an old tire inner tube. It needs to be a tight fit. Remove your seatpost and slip this "seal" over the seatpost. Then install the seatpost and tighten it at the right height again. Then pull the seal down and over the seat lug area so the bottom has a "shingle" effect and the water runs down harmlessly on the outside of the frame. To seal the deal further you could zip tie the top or even wrap it with electrical tape and then zip tie it. Something like this should seal out the water. Another approach would be to always ride with a quick-connect rear fender to keep the water from spraying up onto the seatpost from the rear wheel.
The good news is that the water shouldn't do any damage to your all-carbon frame, but if it gets in contact with any metal parts it can corrode them. But, at least the frame won't be harmed as a steel frame would by exposure to water inside the tubes.
Hope this helps dry out your frame and keep it that way,