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Is loose Front derailleur causing ghost shifting -and is this bike fixable?

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Is loose Front derailleur causing ghost shifting -and is this bike fixable?

Old 05-16-16, 09:45 PM
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sac150
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Is loose Front derailleur causing ghost shifting -and is this bike fixable?

I purchased this bike new in 1994-1995. Now itís worth much other than sentimental value. It has a steel frame (chro moly), Shimano Altus front derailleur, and Shimano Acera X rear derailleur. The front derailleur has 1-2 mm of play in all directions. The rear one is scratched from an accident.

The problems are twofold: (1) it will randomly ghost shift under pressure on the rear 1 - 7, usually when Iím accelerating; (2) the chain will randomly lose all resistance, throwing me forward 6Ē-8Ē before catching again, while making a grating noise Ė sometimes this also happens momentarily with very little loss of resistance, usually under acceleration. I donít know if this is the front or back.

Question Ė is this something that replacing the front derailleur could fix, or is there likely some other problem? And how much time and money would I be looking at to fix this?

About the history - I was using this consistently for short commutes to work for the last 6 years, until this problem came up and my fiancťe made me buy a new cyclocross bike. I like this bike because itís built like a tank and can withstand abuse that would sideline most bikes built in the last decide; nobodyís going out of their way to try and steal it; and Iím not worried about it getting dinged falling down in the train or other people putting their bikes against it. Itís been in several incidents:
(1) in 8th grade I crashed it into a stop sign, the front handlebar absorbed the impact
(2) in college I slide out at a corner and the curb broke my slide- since then it has a hole in the seat, a scratched handlebar, and a scratched rear derailleur;
(3) in grad school the front hub collapsed jumping off a crub, sending the ball bearings into the street. I purchased a used tire on ebay with the same equipment, pulled the hub, and replaced it;
(4) more recently, a pedal broke in half, and I replaced both with steel pedals.


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Old 05-16-16, 09:55 PM
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Your shifting issues could be a "stretched" chain. There are online instructions for checking this with a ruler. The chain is a consumable item, and having to replace it after 10 years of use would not be shocking. As for the list of incidents, it sounds like the typical life of a commuter bike.
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Old 05-16-16, 10:03 PM
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I'd say there is a 99% chance that your chain and/or rear small cog is worn out; changing the front derailleur won't do a darn thing. For one thing, you should never use the 1/7 combination. That is a cross chaining gear; it puts more stress on the chain, and there are other gear combinations that have a similar ratio without the issue of poor chain line. Also, when you use the 1/7 combination, you are using the small chainring in front, and the small cog in back. Since they are small, the pedaling pressure is spread over fewer teeth, wearing those parts out faster.

To fix your bike will require probably a new chain and cassette, about $25-30 in parts, plus labor. You can do it yourself, but the cost of tools would be the same as the cost to have someone else do it. Of course if you buy the tools, you can do more of your own maintenance in the future.
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Old 05-16-16, 10:11 PM
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I think the rider really needs to understand wear and life span of parts.

First thing I think when reading the rider's description is whether he knows the difference between shifting (as in the chain moving to another cog) or chain/cog sipping (where the chain links can't engage the teeth fully enough to not slide over the teeth tops). Big difference in feel and solution.

Mere looking at the cassette/freewheel during said problems will show whether the chin is moving to another cog (as in shifting) or riding over the tops of the same cog's teeth (as in skipping).

So which is it? Andy.
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Old 05-17-16, 09:24 AM
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Originally Posted by Andrew R Stewart View Post
... the difference between shifting (as in the chain moving to another cog) or chain/cog sipping (where the chain links can't engage the teeth fully enough to not slide over the teeth tops). Big difference in feel and solution....
My thoughts as well. Seems more likely to me the rear derailleur is not well-aligned, so it is throwing the chain side-to-side. If that's the case, a few twists of the barrel adjuster should be sufficient.

OP, get your bike in a position so you can eyeball down the chain from behind while reaching forward and pedaling with your right hand. That might mean up in a stand, or maybe turn your front wheel 90 degrees and stand the bike up on it.

Shift the rear all the way high (small cog). Then operate the shifter one click (in the easy direction, i.e. towards one larger cog, the 2nd smallest).

Slowly operate the pedal while sighting down the chain and paying special attention to how the upper pulley of the rear derailleur directs the chain onto the cassette.

The barrel adjuster where the cable enters the rear derailleur, give it a quarter-turn at a time counter-clockwise (it is probably spring-loaded, you may have to pull it back to engage it), and watch it tweak the derailleur (and thus the pulley and thus the chain) to the left slightly. Or turn clockwise and everything tweaks to the right.

Use the barrel adjuster to make sure that the chain ends up centered as precisely as you can on that second cog.

Hopefully that solves your ghost-shifting. If not, then it is quite likely your chain and/or cassette (or probably freewheel, for a 7-speed) are worn and need replacing. It's been over 20 years, that would not be surprising.
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Old 05-17-16, 09:27 AM
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Originally Posted by RubeRad View Post
...operate the shifter one click...
PS if your shifter doesn't click, it's a 'friction' shifter, and the problem is either your (lack of) skill in shifting the derailleur to be well-centered on each cog, or worn chain/cassette/freewheel.
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Old 05-17-16, 06:26 PM
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Originally Posted by RubeRad View Post
PS if your shifter doesn't click, it's a 'friction' shifter, and the problem is either your (lack of) skill in shifting the derailleur to be well-centered on each cog, or worn chain/cassette/freewheel.
Not always the total truth but usually both comments are true.

There are many friction shifters with 'clicks' in them. From cheap thumb shifters that are trying to emulate an indexed on on the big box sales floor to truly neat ratchet/clutched ones like Sun Tour Power shifters. But these all act as non indexed controllers.

Poor friction shifting techniques or off indexed adjustment (which can be pretty close to correct even with a bent hanger, for those who place bent hangers on a pedestal) are not the only reasons for a chain hunting between cogs. Things like a guide pulley that wobbly from a worn bushing of distorted plastic on the bushing, a cog set with so much "float" or bearing slop that it shifts side to side, bent cog teeth, bent cog plates, chains with twisted links and more.

Granted the above possible issues are not as common as others they can and do happen. One of the aspects of an experienced wrench is their range of understanding. We have to look for the obvious first but be open to the unusual too. Andy.
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Old 05-17-16, 08:27 PM
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I've never seen a front derailleur inadvertently throw a chain off the big ring. Something has to release the cable tension. If the shifter is indexed, something or somebody is shifting down. Or if it's a friction shifter, the friction screw is too loose to hold the gear.

I have seen downshifts from incorrect chain lines, the bottom bracket spindle being too long and the chain dropping off the big ring when cross chaining. I've also seen downshifts from the chain ring being bent or having bent or otherwise damaged teeth. And I've also seen chains with bent links perform acceptably until shifted onto the big ring. Examine rings and chain for damage. Of course, concerns about worn chains apply, too.

The rear derailleur handles the chain after it has left the ring. It's more likely to affect how the chain interfaces with the next component in line, the cassette cog.

Last edited by oldbobcat; 05-17-16 at 08:33 PM.
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