Replacing broken index shifter

[brianduffy]

So, I need a new bike since my other bike broke (long story, told in my thead about trying to true my front wheel). I bought a bike at Goodwill that I think will do the trick, a big-framed mountain bike/road bike hybrid that should accommodate a big guy like me without getting lot of flats or breaking axles or doing anything else flimsy.

Unfortunately for me, the reason I got it used for $30 was that its shifter was broken. The derailler looks fine, but when you turned the handle on the shifter, nothing happened, except that the handle turned. Most especially nothing happened to the wire attached to the shifter -- it didn't move a bit.

I did some reading and discovered that fixing a broken indexed shifter was a job that was considered somewhere between fiendishly difficult to impossible. One person who attempted it said he came away convinced that unicorn blood had been used in the original manufacture of the shifter.

No matter. I have a couple of old bikes sitting around I use for spare parts, and one of them had a functional indexed shifter. So I took the broken shifter off my new bike and installed the working shifter from the junker, installing a new derailleur cable while I was at it.

No joy, I'm afraid. The new shifter does indeed move the cable it is attached to, but not enough to make the dearailleur change more than one gear. I'd like to have at least four or five gears to play around with. I especially want the granny gears, for hill climbing.

The front derailleur -- well, I've never found them particularly useful, since they're almost never in working condition on used bikes, and tend to skip and slip a lot if they work at all. I generally set it at the easist gear it will stay in, and leave it there. But if I was able to get the front derailleur to work and use it as a three-speed, that might work, especially if one of those speeds was the super-easy granny gear

I was able to pull the derailleur across all six gears on the back wheel by hand

I was able to pull the derailleur across all six gears by hand so I know it is in functioning condition. But the derailleur cable does not appear to be capable of generating anywhere neaer the amount of force/leverage needed to make that happen.

One thing -- when I installed the new derailleur cable, I had to dump the original cable housing because it was way too long and the replacement cable wouldn't come out the far end of the housing. I replaced it with the cable housing from my junker bike that I got the shifter from. It's too short, really, with about nine inches of cable exposed between the end of the housing and the, um, entry hole for the derailleur assembly. The cable itself is just long enough, sticking out about three or four inches from the clamp that holds it in place on the derailleur.

I toyed with the idea that the problem was that the end of the cable housing had to be snug up against the barrel adjustment but dismissed it because my son's bike doesn't even have a cable housing, just naked cable, and it works just fine (except for the front derailleur, of course). It seems to me that if the cable housing were necessary to give the cable leverage to move the dearailleur, his bike shouldn't work at all, but it's been much more reliable than my road bike. But I could be wrong about that.

I thought about just buying a new derailleur or shifter/derailleur set to fix the problem, but my local bike shop sells nothing but high-end Campagnola shifters and such that cost so much I could make a good start on buying a pretty good low end road bike for just what the shifter costs. The big box retailers don't sell derailleurs or shifters. Is there anyplace I can get decent replacement parts at a reasonable price?

Anybody got any ideas about what's going on (or not going on) here? How can I get this derailleur working? CAN I get it working?

 

[dabac]

...a big-framed mountain bike/road bike hybrid that should accommodate a big guy like me without getting lot of flats or breaking axles or doing anything else flimsy.

Unfortunately appearances can be deceiving, last junker I resurrected into beater status had an 8-spd freewheel. The bike looked sturdy enough, but freewheels leave more axle unsupported than freehubs - not what you want if you're a heavy rider.

...I ..installed the working shifter from the junker, installing a new derailleur cable while I was at it.

No joy, I'm afraid. The new shifter does indeed move the cable it is attached to, but not enough to make the dearailleur change more than one gear.

I was able to pull the derailleur across all six gears by hand so I know it is in functioning condition. .. here? How can I get this derailleur working? CAN I get it working?

So you have a der that can be moved by hand, and a shifter that pulls cable, and they're not working together at all?

Some pics would help, both of the bike you're working on and the odd setup you're describing on your son's bike.

Obviously you must be losing that movement somewhere along the way, and by your description I suspect that there's something wrong where your cable housings attaches, either to the frame or at the der. Start at the shifter, follow the cable down, ensure that the cable housing really is secure at all the cable stops it passes through. Work the shifter, see if something is sliding that shouldn't be.

It's also a bit odd that you found your new shifter cable almost too short, there's something going on there too. Maybe the routing was "improved on" by the previous owner?

 

[John M]

What are the brands of the shifters and derailleurs in question here?

Sounds like you are using a grip shifter (twist style as opposed to a trigger style). Most grip shifters are SRAM brand, and SRAM makes two kinds, one for use with SRAM derailleurs and one for use with Shimano derailleurs. The different brands of derailleurs vary in the amount of cable pull required to move the derailleur sufficiently to actuate a shift--also called the actuation ratio.

I think that you may have a mismatch between the shifter and derailleur.

Craigslist or eBay are good places to get used parts for good prices, but you have to know what you need.

 

[kdelong]

You might at least try to mess with the old shifter. After all, you can't break it! The big thing is to take it slow and don't let it fly apart on you. And remember where the springs and balls go.

 

[garage sale GT]

Yes the cable housing does have to be snug against the adjuster, unless there is a cup in the frame to mount it to. If there is a barrel adjuster, that suggests the derailleur is designed for a full-length housing or perhaps a short housing running between frame ferrule (cable-end cup) and derailleur. If you post pics be sure to show your cable routing.

Try bikepartsusa or niagaracycle.com for inexpensive shifters if something's really broken.

Last, your rear wheel is probably not much stronger than Dabac's, being a 6-speed freewheel. The lower end bikes typically just bend the axle instead of breaking it because it's softer, cheaper steel. Then the bearings wear out, drag goes up, and the wheel starts to wobble without even spinning. I hope you service the thing; keeping adequate preload on the rear cones can prevent a bent axle.

 

[dabac]

What are the brands of the shifters and derailleurs in question here?

Yeah, that would be helpful to know too.

... The different brands of derailleurs vary in the amount of cable pull required to move the derailleur sufficiently to actuate a shift--also called the actuation ratio.

But he wrote: The new shifter does indeed move the cable it is attached to, but not enough to make the dearailleur change more than one gear.
And I can't think of any combination of parts that alone would be able to cause such poor function.

I think that you may have a mismatch between the shifter and derailleur.

That may still very well be the case, and if all he'd been complaining about had been sloppy shifting, or the driveline running fouled on certain gears then that might have been the end of it. But considering what he's written there has to be something more going on. AFAIK any 6-spd shifter together with any der would at least shift over more than one sprocket. Different actuation ratios aside, there has to be a lot of system slack somewhere to lose that much wire travel.