cdotbois

I've been riding in the rain a lot lately (though I don't know if that's related), and my rear gears keep automatically changing on me. I first noticed it while pounding up a hill, and then my bike decided to shift into a harder gear, completely destroying my rhythm.

At first, it was just like that, where it would happen when I put a lot of torque to the pedals. Usually while on the second cog, too, slipping down to the third where there is quite a large difference in teeth count.

I tried tightening the nut on the shifter. I have downtube friction shifters, by the way. But it didn't work exactly (so lately I've been tightening and loosening it while on the go, just to pretend like it'll be fixed). Now it just seems that the shifter is having problems trying to find the gears. It seems totally out of whack. Like I'll have to move the shifter farther than I remember to get to a certain gear, or that the distance the shifter moves in between gears is not even and feels sporadic. On top of that, I'm still having problems getting the chain to stay on 2nd, or now that I think about it, I had problems getting onto the smallest cog, too.

I'll go back again and look at the derailleur settings, while I wait to see what you guys have to say.

Thanks.

cdotbois

Also, down shifting requires a lot of force pulling back on the shifter.

Sci-Fi

Sounds more like you need to replace your cables and cable housings.

cdotbois

It could be, since this bike hasn't had that done before. How do worn cables and housings affect shifting? I know that cables stretch over time, but what sorts of problems does that cause exactly?

---

I greased the cable guide which seemed to help some, and that goes along with my rain riding theory with the water possibly washing out any grease that was there prior, but it still doesn't feel quite right. It's definitely not as smooth as my front shifter.

Rowan

Cables don't stretch under the loads they incur. The insides of the outer casings wear and the shorter route the cables follow gives the impression that they have stretched.

However, Sheldon Brown (as usual) has, I think, a dissertation on ghost shifting, or as he calls it, Autoshifting. Tis likely you need to clean and lightly lube the bottom bracket cable guide as your symptoms and causes all agree with what Mr Brown says. Link here: https://www.sheldonbrown.com/autoshift.html

Bikedued

Might not hurt to disassemble the shifter too, and give it a look. Sometimes there's a bushing or washer worn out or missing. This will cause the shifter to be very tight when tightened yet loosen while shifting over a short period. The rear derailleur cable could be sticking in the rear housing too. Changing the cable
and housing will probably solve many of the problems, as well as cleaning/oiling the rear derailleur.,,,,BD

Sheldon is the man!

forensicchemist

what type of shifters? Some vintage campy shifters were notorious for loosening / slipping where they mounted on the downtube. You had to constantly tighten the the screw holding the shifter.

raster

I would second new housing and cables. It costs about $15 for the whole shee-bang, and it's worth it.

Joshua A.C. New

I had a similar issue to this that turned out to be a battle-damaged derailleur. It just started getting a lot of slop at one point in one of the hinges. Everything looked OK, but when the chain tension was off, the wiggle was quite noticeable. It could be that when you're putting a lot of pressure on the pedals, it's pulling the derailleur out of place.

mikepoole

+1

I use friction shifters on my MTB commuter/utility bike, after a few days of wet weather the rear shifting gets flaky- cleaning & lubing the the cable guides underneath the bottom bracket cures the issue (until the next rain...)

Hmmm- maybe a plastic cable-guide-guard is in my future...

MichaelW

Take the shifter apart, noting the order in which bits come off, clean in soapy water and reassemble. Do not lube the shifter , you need to add friction, not remove it.

supcom

If your bike has downtube shifters and the cables and housings are original, then they are very likely to be pretty old and need replaced. It's a cheap fix, so do this first.

if that doesn't fix your problem, then move on to looking at things like worn derailleurs.

melville

Lube the cable where it runs under the bottom bracket. Lube the cable in the housing back by the rear wheel. Your 'started after a rainy ride' kinda points that way.

Check your frame for cracks. Had a ride where all of a sudden I couldn't tighten the shifter enough (rainy day, it was!) and didn't find the cracked dropout until after I'd changed the gearing for Mt. Washington. All night thrash to get my good stuff onto my winter bike.

carpediemracing 

I would disassemble and LUBE the pieces with appropriate grease.

If you have no grease, the various bushings etc can't slide. So you loosen the locknut - but then everything moves at once.

Greased bushings means predictable release tensions and smoothly moving pieces. Tightening the little turn thing on the outside will lead to predictable results - a shifter that moves as soon as you put a certain amount of tension on it but will not move otherwise.

However, it sounds like there are other issues. Like the previous replies state, I'd also check the cable, housing, under BB piece, and the general condition of the rear der, chain, and freewhee/cassette. Finally if the frame is damaged it could be flexing enough to allow the bike to shift.

Cut my teeth on friction Campy downtube shifters and meticulously kept them greased,
cdr

kenhill3

Get an old school Campy friction shifter with the little wings that fold out to tighten on the fly.

HillRider

Which you will have to do VERY often. These were the shifters that would not hold their adjustment no matter how hard you tightened the D-rings. Even the pros sponsored by Campy would replace the Campy shifters with Simplex Retrofrictions to avoid this.

I'm not sure the OP has a cable/housing friction problem. If it were, shifting would be difficult in both directions and there is so little friction that the bike ghost shifts. I expect the shifter itself is worn to the point that the friction surfaced are damaged.

cdotbois

Thanks for all the help so far. I'm a little swamped at the moment, so I haven't had any more time to look further into the matter, but I appreciate all your advice. I should be able to look at it again sometime in the next few days, and I'll update when I figure out the problem...because it will be fixed.

neilfein

I had the same issue with handlebar friction shifters; I ended up replacing the lever, since the shifter housing didn't disassemble.

melville

Cable friction is what causes ghost shifting! It happens when the drag in the turnaround casing PLUS the drag under the BB PLUS the derailleur spring tension is enough to overcome the friction in the shifter. If the turnaround casing were free moving, when the frame flexed the derailleur would move in the direction of a ghost shift toward a larger (more teeth) cog but would move freely back once the frame was returned to a neutral spot.

Note that a lot of the riders using Simplex shifters were riding very flexible frames--Vitus, ALAN, TVT, or small tubed 753. The big feature of the Simplex shifters was that they could have a whole lot of resistance in the upshift direction with a butter smooth downshift because the friction was on a one way clutch.

HillRider

It can but a worn shifter with damage friction surfaces can also cause it, particularly if the "ghost" always shifts in the direction dictated by the derailleur spring.

Some were and some were riding more rigid 531 and other stiffer tubing frames and had the same problem. It wasn't just frame flex it was a design defect in the shifters too.

I ran into the phenomenon when I had Campy Record DT shifters on a steel frame Bridgestone 400 that was anything but light and flexy. The shifters loosened over time and the bike would begin to ghost shift. Tightening the D-rings eliminated the ghost but only for a couple of weeks. Switching to Sun Tour Power Shifters (with same type of one-way ratchet as Simplex) made the problem go away for good.