Bicycle Mechanics - Front Derailleur Problem

In our family’s fleet of bicycles is a Trek 360 (1980”s). I am having much trouble adjusting the front derailleur. It will only shift up from the smaller chaining to the larger, but not down. I have tried adjusting the angle of the derailleur by the derailleur bracket attached to the front fork as well adjusting the tightness of the cable. This particular derailleur has only a single adjustment screw which seems to control only the outward movement. Could it need a new cable? I have spent hours trying to correct the problem and am about to pull out my remaining hair. Please HELP! :crash:

As usual, see
http://sheldonbrown.com/derailer-adjustment.html

and
http://www.parktool.com/repair_help/howfix_frontderailleur.shtml

Is the height of the mech OK.
Is the cable tight enough

You don't say what kind of derailleur it is (and I can't remember what came on those Treks) but it sounds like the return spring is broken or disengaged.

"Attached to the front fork"? You don't really mean that...

"Attached to the front fork"? You don't really mean that...

Although . . . if true . . . that would explain a great deal ;)

Hell, if true I'd want to learn how he got it to shift at all!

:D

Thanks for all the response! Oops, I did not mean the derailleur is attached the fork, rather the mechanism (clamp) directly over (in-line) with the chain is attached to the fork. Thanks.

Thanks for all the response! Oops, I did not mean the derailleur is attached the fork, rather the mechanism (clamp) directly over (in-line) with the chain is attached to the fork. Thanks.

Now I'm really confused!

Thanks for the response. I'm referring to Sheldon "Click" Brown's:

# Clamp Position
The most critical adjustment of a front derailer is its attachment to the bicycle frame. This must be set correctly before you attempt to adjust the limit stops. There are two variables, angle and height.

* Angle of the front derailer is judged by looking down on the cage from above. Modern front derailers have very subtly shaped cages, so it is not always easy to tell when the ideal adjustment has been made. In general, the centerline of the cage should be parallel to the centerline of the frame. Rotating the derailer so that the back of the cage is farther out will sometimes improve shifting to the small ring of a triple by preventing overshifting, but may cause increased need for trimming on the larger rings. It may also cause the crank to strike the cage.

Rotating the derailer so that the front of the cage is farther out will help reduce the need for trimming on the large chainwheel, and will provide crisper downshifting, but with a greater tendency to overshift on the inside. This may be appropriate on bicycles equipped with an anti-derailment device.

* Height of the front derailer is a principal factor in how well it will shift. Manufacturers commonly recommend 2mm clearance between the bottom of the outer cage plate and the teeth of the large chainwheel. This is a bit of an oversimplification. Best performance will result from the very lowest position that still just barely keeps the cage from hitting the chainwheel teeth.

The lower you can get it, the better it will shift, and the less you will need to trim the front derailer.

I've made those adjustments and it now will downshift, but it's very slow, three revolutions or even more. I have now literally spent hours working on this problem. :(

Have you tried lubing the pivots and checking the cables?

Have you tried lubing the pivots and checking the cables?

I absolutely agree with Wordbiker--this would be the first thing I would look at.

The derailleur return spring is what brings the derailleur to the smaller rings (it's your own muscle acting against the return spring that gets the der. to the bigger gears). (This same principle of der. spring vs. muscle power also applies to the gears in the back.) If the cables are old and gunked up...and the derailleur is old and gunked up, the force of the return spring isn't great enough to overcome the friction of the gunk. Lube the four main der. pivots with some good penetrating lube (I like Tri-Flow), and get some lube in the shifter cable housing. Unless you actually have something bent or worn out, this should do the trick.

By the way, cable tension would only be an issue here if it's too tight. Presumably not the problem here, since you've already been fiddling with the cable tension. (If the cable tension is too high, it would prevent the der. from getting all the way back down to the small ring.) Also, as the bike/cable ages, the cable will tend to stretch--hence will become too loose. Unless someone has explicitly overtightened the cable, I can't think of a natural situation where the cable tension gets too high.

(As always, when lubing stuff, wipe off all unneeded, excess lube, as it will attract even more gunk and you'll be back where you started.)