weird steering problem

I've got a mid-90s Rockhopper for a beater with a threaded rigid fork.
Sometime ago it developed this problem in which the bike will steer to the
left by itself, as though being pulled. I thought maybe it was the beat-up
Mythos XC front tire w/ uneven treads (one or two big bald spots from
absurdly hard braking that tore off the knobbies), so I replaced it. I
checked the cable housing to make sure they weren't too short. Demonic
possession aside, what could be the problem? I am wondering if the threaded
headset's got something to do with it, but don't know exactly what. Any
ideas?

On Sun, 03 Jul 2005 22:02:36 GMT, "ellis" wrote:

I've got a mid-90s Rockhopper for a beater with a threaded rigid fork.
Sometime ago it developed this problem in which the bike will steer to the
left by itself, as though being pulled. I thought maybe it was the beat-up
Mythos XC front tire w/ uneven treads (one or two big bald spots from
absurdly hard braking that tore off the knobbies), so I replaced it. I
checked the cable housing to make sure they weren't too short. Demonic
possession aside, what could be the problem? I am wondering if the threaded
headset's got something to do with it, but don't know exactly what. Any
ideas?

Check the centering of the rear wheel. Check the tightness of the
rear wheel's skewer or axle nuts. Check the chain stays and seat
stays for cracks. Check the fork for bent legs. Check the frame's
straightness uisng the string method (from one rear dropout to the
other, around the head tube; both strings shoud be about the same
distance from the seat tube as they pass by it). Check the headset
for looseness; set the front brake and rock the bike fore-and-aft;
there should be no clunking in the headset, and no apparent motion top
or bottom. I suspect that one or another of these checks will show a
problem, but there are other possibilities as well.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.

ellis wrote:

I've got a mid-90s Rockhopper for a beater with a threaded rigid fork.
Sometime ago it developed this problem in which the bike will steer to the
left by itself, as though being pulled. I thought maybe it was the beat-up
Mythos XC front tire w/ uneven treads (one or two big bald spots from
absurdly hard braking that tore off the knobbies), so I replaced it. I
checked the cable housing to make sure they weren't too short. Demonic
possession aside, what could be the problem? I am wondering if the threaded
headset's got something to do with it, but don't know exactly what. Any
ideas?

A possibility is that the headset bearing is "indexing" due to wear or a trauma.

You may be able to feel this by lifting the wheel off the ground while you
slowly turn the bars.
If the headset has cups then mark them at the front with a marker.
Take headset apart and inspect cups and steerer bearing surfaces and top nut
for wear.
Cheap way is to swap the cups top to bottom and rotate them about 90 degrees.
But since you have it apart and these parts are cheap then best replace the
knockout cups and the bearings.
(If the bearings are held in races carefully note which way they face to avoid
reassembly confusion).

Rob

ellis wrote:

I've got a mid-90s Rockhopper for a beater with a threaded rigid fork.
Sometime ago it developed this problem in which the bike will steer to the
left by itself, as though being pulled. I thought maybe it was the beat-up
Mythos XC front tire w/ uneven treads (one or two big bald spots from
absurdly hard braking that tore off the knobbies), so I replaced it. I
checked the cable housing to make sure they weren't too short. Demonic
possession aside, what could be the problem? I am wondering if the threaded
headset's got something to do with it, but don't know exactly what. Any
ideas?

Stop at any competent LBS and watch as they check both
wheels with a dishing gauge then slip alignment gauges into
your frame and fork.


--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971

"ellis" wrote in message
...
I've got a mid-90s Rockhopper for a beater with a threaded rigid fork.
Sometime ago it developed this problem in which the bike will steer to the
left by itself, as though being pulled. I thought maybe it was the
beat-up
Mythos XC front tire w/ uneven treads (one or two big bald spots from
absurdly hard braking that tore off the knobbies), so I replaced it. I
checked the cable housing to make sure they weren't too short. Demonic
possession aside, what could be the problem? I am wondering if the
threaded
headset's got something to do with it, but don't know exactly what. Any
ideas?

Fork legs twisted/bent/otherwise offset would be my guess.




Shaun aRe

"Werehatrack" wrote in message
...
On Sun, 03 Jul 2005 22:02:36 GMT, "ellis" wrote:

I've got a mid-90s Rockhopper for a beater with a threaded rigid fork.
Sometime ago it developed this problem in which the bike will steer to
the
left by itself, as though being pulled. I thought maybe it was the
beat-up
Mythos XC front tire w/ uneven treads (one or two big bald spots from
absurdly hard braking that tore off the knobbies), so I replaced it. I
checked the cable housing to make sure they weren't too short. Demonic
possession aside, what could be the problem? I am wondering if the
threaded
headset's got something to do with it, but don't know exactly what. Any
ideas?

Check the centering of the rear wheel. Check the tightness of the
rear wheel's skewer or axle nuts. Check the chain stays and seat
stays for cracks. Check the fork for bent legs. Check the frame's
straightness uisng the string method (from one rear dropout to the
other, around the head tube; both strings shoud be about the same
distance from the seat tube as they pass by it). Check the headset
for looseness; set the front brake and rock the bike fore-and-aft;
there should be no clunking in the headset, and no apparent motion top
or bottom. I suspect that one or another of these checks will show a
problem, but there are other possibilities as well.
--
Typoes are a feature, not a bug.
Some gardening required to reply via email.
Words processed in a facility that contains nuts.



Thanks for the suggestions!