Front Derailleur missing middle gear???

[stosh]

So I brought it back to the shop and they kind of fixed it. I have a 27 speed 2001 Trek 8000 and when I'm in the top or bottom FEW gears it will slip off the middle gear in the front.

I know that when it's at the top and the bottom of the rear gears it will have some problems. However, sometimes when I'm in the middle gears in the back and the middle gear up front it slips under pressure.


I'll probably take it back to the shop again this weekend. But does anybody have any ideas in the mean time.

[spincrazy]

Hey stosh,

You probably need a new chain and/or rear cassette. Your LBS probably just did a gear adjustment..........probably should have measured the chain for stretch and checked the teeth on the cassette.

The maintenance never ends..........

[muddywolf]

sounds like you need a new cassete and chain, maybe a new middle front ring to me too

[stosh]

I'm going to bring my bike into the shop sometimes this week. Maybe they can look at it again. I need a tune up and since it's free why the hell not.

[greasemonkey]

sounds like your chainline is off

have it checked by someone who knows how

[spincrazy]

About the chainline thing.......

I suspect mine may be off as well, now that you mention it.

My gears need a bit of a fine tuning right now, but, I am experiencing something that I've not gotten before, and that is that the chain is coming of my front rings when I back pedal in certain gear combos......seems odd. Could this be attributed to an off chainline?

I also tend to get a lot of chain suck and 'off' chains when on technical sections of trail where I am airborne. I am not in a small ring at that point, so I don't believe that it's due so much to chain sag......and I ride a hardtail.

Any ideas? By the way, where do you wrench?

peace

[oldfart]

Sounds like a worn out drive train to me. As the teeth wear and chain stretches, the chain does not mesh as welll with the teeth so the chain can more easily fall off when it gets bounced. Chain line will affect how easy it comes off. If your in the middle big for example the angle the chain makes at the rings may allow it to simply shift itself. Try this test. Put the bike in mid big or big and second from lowest, lean the bike to left and back pedal. Gravity might pull the chain over enough that it comes off at the front. To me that signals new drivetrain time.

How much time is on your drivetrain? If you ride hard in the pacific Northwest in conditions like Vancouver BC then you'd be lucky to get a season out of a drivetrain.

[gchavarr]

Something else you may want to look at is the middle ring. I had a similar problem with my chain falling off the middle ring under torque (sp?). I try and ride the middle ring the most, when I examinded the three rings, the middle was most noticably worn.

Took it to the LDS and they tried to align/adjust, but the chain kept dropping off under load. I bought and installed a new middle ring and have not had the problem since. Let us know how it goes.

[spincrazy]

My drive train is only about 3 months old.
I recently put on new cranks (Truvativ Stylo Team), new 9spd chain, and the rear cassette was replaced back in March. After a recent check, all is in order as far as components go.

I, or my mechanic, wrench on my bike on a regular basis......mostly me lately because now I know how, and the bike shops of course are a helluva lot busier than they were back in Dec. :)

Anyway, how do I check the chainline, and what would I do to straighten it?

peace

[stosh]

Originally posted by gchavarr
Something else you may want to look at is the middle ring. I had a similar problem with my chain falling off the middle ring under torque (sp?). I try and ride the middle ring the most, when I examinded the three rings, the middle was most noticably worn.

Took it to the LDS and they tried to align/adjust, but the chain kept dropping off under load. I bought and installed a new middle ring and have not had the problem since. Let us know how it goes.



Yeah I'm taking it in today and having them look at it again. I'll let you all know ASAP. I won't know till tomorrow when I can get out and ride it.

I don't think it's worn out already. I've put about 100+ miles on it I guess this year I guess.

I'll see what they say though.

Thanks for the help guys!

[stosh]

My center ring was bent. I guess they have had a few problems with the Bontrager center ring because it was made of steel and not an alloy so it isn't as hard.

ordering a new one FOC.

[oldfart]

Steel is harder than aluminum alloy. It may have bent due a design or manufacturing defect.

[stosh]

Originally posted by oldfart
Steel is harder than aluminum alloy. It may have bent due a design or manufacturing defect.


I think what he was saying is that it was a steel alloy. Don't know.
Maybe I got it backwards. Although I was trying to listen really well.

[oldfart]

Steel is an alloy as is all the aluminum we use on bikes and titanium for that matter. Alloy means a mixture of metals. Steel is an alloy of iron and carbon. Add chromium and molydenum and you get a lighter and stronger steel. Titanium used in bikes uses aluminum and vanadium to make it useful. Years ago there was a titanium bike called the Teledyne Titan. They all broke because they used pure titanium and I guess it was brittle. People often use alloy colloquialy to mean aluminum alloy. Not sure what goes into that alloy but I'm pretty sure pure aluminum would not be very good. Way too soft and maleable and hardly any fatigue life.

I remember making wicked "Iron Cross" emblems to bolt onto my bike. Kinda made a pedal chopper. Made them from sheet aluminum in metal shop in 10th grade. Fatigued and busted off in a week. Pretty sure that was pure aluminum. Any metalurgists out there wanna tell us the goods?

[Ranger]

Yo, oldfart (feel like I'm addressing my Dad...)

It's highly doubtful that you that you got a sheet of pure Al out of your shop class. Aluminium (like most usable metals) has things added to it in the smelting process to bring out certian aspects of the metal according to it's intended purpose. Another deciding factor in tensile strength and "flexibility" is how it is handled at the mill. Cold or hot rolled? Heat treated? Drawn or cast? Mechanichally or chemically aged?

This applies to tubesets. A good bit of info on our pal Aluminium can be found here: http://biketrail.318.nu/mek/metals/metal.asp

Another good basics inforamtional can be found here:
http://citybikes.com/bikes/frame_materials.htm

Steel is more my racket though. But I build armor with it and not frames so what I need for steel is worlds different than what Joe Framebuilder needs.

[oldfart]

excellent info bro. I'll read it when I get home from work.