The craziest thing..........
 

Been riding since the early 1980's and had a first time weirdo experience.

Been commuting on a Benotto (1981) for a few weeks, keep tires pumped to 100/120 (120 fresh pump, get to 100 or so before re-pump).

Cruising in to work, and I cannot control the bike- twitching worse than a 1980's nightmare steed with a 90 degree head angle and straight forks.

Everything checks out, this is strange. I have already been close to getting wiped out twice since riding her.

The seat tube to BB repair is fine, wheels are true and centered, headset is adjusted perfect, nothing is loose etc.

This bike is now named "Christine", it is trying to kill me!

:D:(

is this the classic "speed wobble" that rears ugly head during high speed descents, or does it occur under different circumstances? Depending on your answer I'd check:
1. overall frame alignment
2. fork trail
3. could be frame geometry that you'll never be able to alter, but you say it's been repaired?

I will get it into the stand today at lunch to check geometry. I rode it for over 3 hours on Sunday, and it felt great, in fact, I was telling my brother how great those 80's Benottos feel............

Rode the Pinarello Monday, the Faggin yesterday, then got back to the Benotto.

Not high speed shakes, but just like the wheels were seriously out of alignment, it was the strangest sensation. It felt like it was on a Velodrome banking, and any correction (steering input) was magnified.

I will post a pic after she gets on the stand.

At what speed did this occur?

-Kurt

All speeds, when I stood up to get in the left turn lane, she darted hard into incoming traffic. Even on the bike path it took effort to keep it tracking.

Is the front hub slightly loose?

Hubs check out.

It might be that this frame geometry is ultra sensitive to misalignment (horizontal DOs) so I will really get it dialed at lunch and see what happened. It does not appear that anything moved, but I will check with a string etc. I have ridden misaligned junk and taco'd wheels, but this sensation is subtle and powerful, almost as if there is a counterweight on the wheel.

Loose headset?

I'd also check the frame/fork for cracks. Possibly a cracked steerer tube.

spokes loose on one side?

That's my guess. Pull the fork and check the bearings in the head tube real good. Could be a single bearing that chipped or broke and is working it's way around the race causing problems when everything lines up with the missing chunk in the bearing. One of the bikes I scavanged for parts this summer had a bad single ball bearing in the bottom bracket.

Sounds like something is getting to a loose point, causing havoc, then setting itself tight again before you can track it down.

Hate to say it but it sounds like a frame issue to me, as in damage.
I'd check for cracks at all the joints, specifically I'd look at BB chainstay joints,
and seatstay seat tube joints.

Marty

Do you believe in ghosts?

I might now.............

Tearing her apart, so far steerer/bearings races etc. are sound and headset cups square to head tube etc.