Derailleur Adjustment: an Illustrated Guide

Thank you once again everybody for the advice on how to adjust a derailleur. I am pleased to announce, that with your help, it is done.

To recap the problem I was having: When downshifting to the lowest gear, there was nothing stopping the chain from going past it and slipping off the cog. Here is how we corrected this:

Mechanic

Assistant Mechanic

The all-important tool

The derailleur. This is a rear SunTour Vx derailleur from the late 1970s. Note the two screws on the left.

A side view of the screws.

And here they are close up. Notice the letters "L" and "H" next to the screws. The "L" indicates low gear (the largest cog). The "H" indicates high gear (smallest cog). To stop the chain from going past the largest cog when downshifting into the lowest gear, tighten the "L" screw.

Here is the screw, being tightened. Conversely, if you find that the chain does not travel sufficiently to reach the largest cog when shifting to your lowest gear, you need to loosen this screw a bit. And if you are having this problem when upshifting to the highest gear, simply do the same thing to the "H" screw.

A close-up of the procedure. This takes very little time.

After the adjustment, test the derailleur: first by manually spinning the pedals as you shift, then by test-riding the bike.

Here I am, having happily shifted into the lowest gear without the chain coming off.

All done, and ready for the steepest hills. A big Thank You again to dukiebiddle, cyclemaniac, somervillain, and all the others who kindly offered advice and posted links. Your support is very much appreciated.

Some classic derailleur adjustment instructions, using more conventional tools:
. Sheldon Brown's thorough article on "derailler" adjustment
. The Bicycle Tutor's instructions and video

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Creative Encounters: Bicycle "Self-help" Workshop

Located in the WUK center for workshops and culture in Vienna, the Fahrrad Selbsthilfe Werkstatt (Bicycle Self-Help Workshop), functions on a similar premise as co-ops like Bikes Not Bombs in the US: You pay a small fee for the afternoon, and one of the mechanics on staff helps you fix your bicycle or assemble an entirely new one using the parts available at the shop.

But the unique thing about the Fahrrad Selbsthilfe Werkstatt, is that here you are likely to see bicycles like this:

or like this:

or like this!

The workshop specialises in tall bikes and various other remarkable constructions, the likes of which you are not likely to see every day.

Though the floorspace is small, they make excellent use of the extremely high ceilings. Rows upon rows of frames, wheels, and partially assembled bicycles of different vintages, hang suspended above the visitors' heads. The resultant arrangements are quite beautiful.

Wheels and a station with tools...

forks...

cranks and pedals...

small parts...

Of course the majority of those who come in, are looking for help with "normal" bikes and are not assembling the sort of eccentric constructions shown above.

The mechanics are very helpful, and the atmosphere is mellow and friendly. A wonderful place to be, even just to watch. If you are a cycling enthusiast visiting Vienna, you will enjoy a visit to the Fahrrad Selbsthilfe Werkstatt.

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