I have a few questions about the problems I encountered. Rather than searching the Web for answers I've included my questions below, hopeful that forum members can share their knowledge. In addition to expertise on bicycles I'm aware that some members are scientists and engineers who might have fun pockets of information to share with the group.
I run Silver bar end shifters on my Sam Hillborne. Recently I left for a ride and once I got a few blocks from my house I realized the front derailer was rubbing the chain. When I went to trim the gear the shift lever slipped into the relaxed position and dropped the chain to the small ring up front. I tightened the wingnut to restore tension but there was no tension to be found. I had an idea of what was going on: the ratchet was clogged with corrosion, preventing the spring from engaging the pawl. I rode home in a very easy gear.
Back in the shop I loosened the clamp bolt on the front derailer to free the cable. When I went to pull the cable out of the shifter lever it wouldn't budge. The head of the shifter cable had chemically bonded to the lever itself. I removed the nuts and bolts that hold the lever to the bar-end shifter pod. I should note that I had previously replaced the external plastic nut cover with a brass counter-sink washer. I think the presence of the brass encouraged corrosion. I then struggled to get the cable out even with the lever freed from the pod.
I then noticed that the brass ferrule I'd used at the end of the shift cable housing had bonded to the bar-end pod. I now had two instances of dissimilar metals bonding together.
I snipped the shift cable, pinched the loose end with pliers and tried to wiggle and finesse it free. No luck! I tried to drill out the head of the cable, that also didn't work. I decided to abandon the shifter and salvage the innards for parts.
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Terrible pictures showing drilled head of shifter cable and snipped off cable stuck in lever.
I store my bikes in my shed, an unconditioned and uninsulated space in Virginia. It is very humid here. The spot where I hang my Hillborne seems to attract a lot of moisture and I really need to find another place to store that bike. Sometimes when it rains the handlebars feel damp and corrosion forms around the seatpost collar, on the chaingring bolts and the rear dropouts. The roof of my shed does not leak. I think the rust accumulation has to do with ventilation issues and related to the bicycle hanging between a door and a window, there must be some kind of draft situation going on and that spot is a real moisture magnet. I don't have the same problem with other bikes I hang in adjacent spots.
What causes the shifter cable head to bond to the lever? What materials are the shifter cable head and Silver shifter levers made from? Do the dissimilar metals encourage bonding when moisture is present? What causes the brass to bond to the bar-end shifter pod?
In my video about
repairing Pam's Silver shifters I mentioned corrosion as a potential problem with a Silver shifter that doesn't hold tension. Here was an opportunity to show the world! I was frustrated and eager to get it fixed quickly. Setting up to make a video really bogs things down.
I took the lever with the cold-welded shifter cable stuck inside and pried it open. Indeed, the spring was clogged with corrosion. The corrosion was chalky and white, resembling the type of build up sometimes seen on car battery terminals. With the spring clogged it won't push against the pawl which won't hold position on the ratchet wheel which won't allow the lever to hold tension to counteract the spring action of the derailer.
Thanks to board member Mike Godwin, who sent me some old Suntour levers to help repair Pam's shifters, I had some extra parts around. Shifter bodies (one good, one broken), spare cover plates and some ratchet wheels. I also had replacement springs I'd ordered from McMaster-Carr. I mated one of the Suntour levers from Mike with parts from my damaged lever and got them put back together. Pinching the parts together I could tell the ratchet was working. I set it aside to work on the shifter pod.
The brass ferrule had welded to the pod. I tried to pull it out with pliers. No luck. I'd encountered a welded brass ferrule before so I was relatively sure before I started that I wouldn't get it freed. I've heard that squelching is one method that sometimes works to free welded parts but I didn't have the means or patience to heat the parts. So instead I decided to saw off the ferrule and file it flush with the pod. I could run the shifter cable into the remnant of the ferrule.
With the ferrule flushed up I reinstalled the pod in conjunction with seating the shifter cable. I installed a new shift cable and re-installed the newly rebuilt shifter lever.
I have a newfound reluctance to use brass parts going forward. While my love of brass is well documented in my builds it has caused me several problems over a short few years. Twice my bar-end shifters have stopped working, I believe due to corrosion encouraged by the presence of brass and the contact between dissimilar metals. I have also twice had brass ferrules get welded to other parts. Here on the Hillborne it was the ferrule and the shifter pod. On my MB-2 it was a ferrule that welded to a Suntour brake lever.
Perhaps you can use brass parts if you live in drier climes or have better luck than I do. But I'm going to be phasing brass out of my bikes and builds from here out. Or until I move to the desert.
