Front gear issues - help b4 I go insane

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Front gear issues - help b4 I go insane

Postby heavymetal » Fri Mar 02, 2007 3:23 pm

I'm on the verge of insanity with this problem. I'm open to any suggestions. I've tried lots of things, but after todays ride, I'm ready to pick the bike up with my oil covered hands and heave it under a bus. :evil: :shock:

When I first brought my Mongoose Randonneur, the very first time I rode it and shifted down to the smallest chain ring, the chain fell off. The bike is not fitted with a chain anti-suicide plate. I thought "Oh here we go, one of these bikes", but being a new bike, some things needed adjustment as would be expected.

Not only does the chain come off when shifting to the small chain ring, it does it when going onto the large one. I have adjusted the derailleur stops etc.

Now this is what's driving me to insanity. I'm on the middle chain ring and want to change up to the large chain ring, sometimes it will not change up, sometimes it will, and other times the chain comes off. It is the same when shifting down to the smallest chain ring.

I thought this was dependant on where the chain was on the rear cluster, so I have been experimenting with shifting to the relevant front cogs only when the chain is on the same rear cog. I've recently fitted a chain anti suicide plate , so the chain doesn't come off when shifting down, but sometimes the bloody chain won't shift down. Other tiimes it will.

So for example to shift to the small front chain ring, I make sure the rear is on the third largest cog (I've tried all combinations and get the same results) and to shift to the large chain ring I make sure that it is on the third smallest rear cog. The results are different each time, it depends on what mood it is in.

I always back off power when pedalling and move the levers slowly, so it's not my technique. I think the bloody thing is possessed. Here is a list of the original specs and what I have done to it since. I'm still getting the same problems.

The bike came with Deore 9 speed RD, SRAM 8 speed cluster, Sora FD, Sora brifters and Sora cranks with a 30T-42T-52T chain rings. After wearing the bike in and adjusting things, I still had the same problems so I changed the brifters (I don't like them anyway) and fitted Shimano friction shifters. This didn't stop the problem.

Next I changed all of the chain rings for highly expensive stuff and a smaller granny, but the problem persisted. I've just recently changed the cranks for MTB cranks which are Shimano hollowtech with 22T-32T-42T chain rings. I've also fitted the anti-suicide plate.

I am still getting the same problems. I have the stops adjusted and have tweaked them in both directions, but still get 1. no change, 2. does change, and 3. chain comes off.

The last time I had a problem like this I had a cracked chain stay, but this is an aluminium frame and is quite rigid. The BB has no free play, the rear wheel is done up and the cranks are done up tight. The FD is also done up tight.

Anyone have any suggestions?

My options are

1. Change the MTB chain rings for something expensive,
2. Remove the FD stops altogether and really slowly change gears with the friction shifters,
3. Take it to a priest and have an excorcism done
4. Throw the bike under a bus
5. Give up riding
6. Admit myself to a psychiatric institution
7. Suck it and buy a Trek touring bike :D
8. Suspect maybe a bent link in chain and replace chain?
9. Throw Sora derailleur in bin and fit one chain ring.

PS : This is a long message, don't quote it as the thread will get quite long.
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by BNA » Fri Mar 02, 2007 3:39 pm

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Postby Bnej » Fri Mar 02, 2007 3:39 pm

Is the cable for the FD sticking? Does the FD move smoothly with no chain in the way?
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Postby heavymetal » Fri Mar 02, 2007 3:41 pm

Yes it all moves. I have at one staged replaced the cheap cables that the bike came with. The FD moves smoothly in both directions.
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Postby mikesbytes » Fri Mar 02, 2007 3:56 pm

At first I thought it was a post from Richard.

I've noticed on my bike that I'm more likely to have the chain come off when its dirty and/or worn.

I'm wondering if the leavers are set to a different width between the chain rings and is moving the chain too far?

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Postby heavymetal » Fri Mar 02, 2007 4:05 pm

mikesbytes wrote:I've noticed on my bike that I'm more likely to have the chain come off when its dirty and/or worn.

I'm wondering if the leavers are set to a different width between the chain rings and is moving the chain too far?


The chain is clean and not worn. The levers are OK because the chain only comes off of an outer chain ring and they are friction shifters anyway.

I think I may have come up with a possible answer when doing some research.

Sora stuff is apparently low end Shimano road gear. This hollowtech stuff for the price I paid ($100) is probably low end gear. I have had a look at some high end gear and there are differences in the chain rings in that they have things in them to make shifting easier.

I looked at the Sora rings and the ones now on the bike and none of them have these funny little patterns and the odd twisted tooth.

I'm wondering if the chain is getting caught on the middle chain ring and causing the issues?
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Postby europa » Fri Mar 02, 2007 4:06 pm

mikesbytes wrote:At first I thought it was a post from Richard.


Shove off. I ride a Trek520 so, of course, there are no problems at all :P

I know you're running a suicide plate Kev, but would one of these work better? http://sheldonbrown.com/harris/derailers-front.html#352
The Jump Stop is the one I'm thinking of.

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Postby heavymetal » Fri Mar 02, 2007 4:08 pm

I have both of those chain anti suicide devices. I have an N Stop, which is currently stopping the chain dropping off of the inner cog. Due to the taper of the down tube at the bottom and the lack of room the plate is actually bolted to a sawn off Dog fang plastic one :shock:
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Postby europa » Fri Mar 02, 2007 4:10 pm

Well, it serves you right for riding a recycled coke can bike :D

I thought you'd just changed to an mtb chainwheel setup. Surely this would have solved the problems.

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Postby MJF » Fri Mar 02, 2007 4:10 pm

The stops stop it from shifting too far...

I'm guessing the chain guide is too wide. The Sora is meant for an 8-speed width chain, so that should be O.K... so I'm thinking the guide is either bent out of shape - or needs bending out of shape. Service instructions for the Sora FD are here.

My bike came standard with an Alivio FD (8 speed) with the rest of it being Deore LX 9-speed - no, I don't know why, but the LBS told me that's the way they are delivered. I've had the chain catch in the FD three times, bending it on two occasions. The LBS de-mangled it the first time with some channel-lock pliers... including narrowing the cage. I fixed it myself the second time. There is little difference in appearance between 'works correctly' and 'totally shagged'.
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Postby heavymetal » Fri Mar 02, 2007 4:13 pm

europa wrote:I thought you'd just changed to an mtb chainwheel setup. Surely this would have solved the problems.


That's whats got me nearing insanity as I haave changed to an mtb chain ring setup with new cranks and I still have the same issues.

I just went and stress tested the frame :shock: and I can't find any flex in the recycled coke can material :D
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Postby heavymetal » Fri Mar 02, 2007 4:17 pm

MJF wrote:I'm guessing the chain guide is too wide.


I'm thinking along those lines now as I was playing with it earlier and I could swear the cage is flexing as I changed gears. My bike also came with the Deore rear 9 spd with an 8 speed set up.

It's a bottom pull derailleur and every other FD I have here is top pull, so I can't change the FD for an experiment.
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Postby MJF » Fri Mar 02, 2007 4:18 pm

bicyclewa wrote:I'm thinking along those lines now as I was playing with it earlier and I could swear the cage is flexing as I changed gears.


Yep - mine does as well. They don't make them like they used to...
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Postby heavymetal » Fri Mar 02, 2007 4:21 pm

Thanks MJF, I think you have solved the problem. I've always had trim problems with the FD which is why I got rid of the brifters as they could only adjust trim in one direction.

I'll go and do some customisation of the FD and see if I can improve things, otherwise I might make a frankenstein FD out of some other FDs and put bits from each on and try it :D
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Postby heavymetal » Fri Mar 02, 2007 4:33 pm

Thanks guys for your help. I think I've located the problem.

The FD cage is indeed made out of recycled coke cans :D

It's a long reach cage, and I just tested it by changing under load and the cage has a real bad flexing problem. It's also bent in the wrong direction, probably by me kicking it today :shock:
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