autoshifting (read FAQ and Sheldon's)

Derek King said:

This is on an older Specialized Sirrus, of unknown year using Suntour derailers. I cleaned and
lubricated the cable guide on the bottom bracket, according to suggestions on Sheldon Brown's
page. I also adjusted the rear derailer according to his guidlines, and tightened up the shift
lever (which helped briefly though it quickly loosens after use). I noticed the rear wheel seems
loose on its bearings... I can easily wobble it by hand. Would this contribute to upshifting
during hard pedaling? Someone at a bike shop said it could be that the gears are worn out. Not
expecting more than $100 in selling this bike, would it be cost effective to replace any parts
causing this problem? To this end, could someone recommend any reading so I can make the
appropriate choices on replacement parts?

Huh? "the gears are worn out" is not a technical analysis.

Yes, correct the wheel bearing problem before you have uneven wear of the cones. A loose bearing
touches only one ball at a time and so wears unevenly and more quickly.

Most friction downtube levers work better with a bit of oil on all the internal parts. Beyond that,
three possible solutions which come to mind.

1.Friction shifters need a mechanism to keep the parts from unscrewing when you move the lever.

Campagnolo's classic design has a (originally chromed steel but later nylon) washer just outboard of
the lever that engages two flats on the supporting post. Some Suntours use that design also. Early
with steel and late models with nylon. The flats in a nylon washer can be worn such that the washer
rocks and the outer screw loosens after a few shifts. That washer's replaceable.

2.Other designs use a tab on a cover plate just under the screw head. That tab must engage a slot
connected to something on the frame side of the lever. Suntour used that design as well. Look
closely and see if there is such a tab that is not properly engaged. Compare to the left side as
they are usually symmetric.

3.One of Suntour's many nice gifts to cyclists was the Power Shifter which incorporated a small very
effective ratchet. That ratchet pulled easily against the derailleur spring for a shift, yet
engaged with some resistance such that, when shifting the other way, the derailleur spring pulls
with you. Net result is a shifter that needs about equal force in both directions and almost never
slips. Until the ratchet cracks. Listen to the left shifter. If it clicks when pulled back there
is a ratchet. On disassembly not only the parts order, but the _ orientation_ is important. That
is, do not flip the washers when you reinstall. Ratchets may be found in discarded shifters. All
Suntour Power Shifts , road and MTB, used the same internal parts.

If not one of those three things, write back with the shifter model.

You asked about parts. If it is a down tube friction shifter, a new set with cables is $19.95 but
should not be necessary
--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

Derek King said:

This is on an older Specialized Sirrus, of unknown year using Suntour derailers. I cleaned and
lubricated the cable guide on the bottom bracket, according to suggestions on Sheldon Brown's page.
I also adjusted the rear derailer according to his guidlines, and tightened up the shift lever
(which helped briefly though it quickly loosens after use).

This is the whole problem. Keep it tight somehow or replace it with an indexed lever so it
stays put.

Quoted message said:

I noticed the rear wheel seems loose on its bearings... I can easily wobble it by hand. Would this
contribute to upshifting during hard pedaling? Someone at a bike shop said it could be that the
gears are worn out. Not expecting more than $100 in selling this bike, would it be cost effective
to replace any parts causing this problem? To this end, could someone recommend any reading so I
can make the appropriate choices on replacement parts? Thanks, Derek