CB700SC - Front end wobble

[SmokinFast]

On the way to the store today I decided to let go of the handlebars at about 40 MPH. The front end went into a wobble that got stronger and stronger. If I hadn't grabbed the bars quickly I would have lost it.

None of my other bikes do this. What should I look at to fix this?

[ariwhiteboy]

Could be a nuber of things...I'd start with the cheapest first. 

1. Improper tire pressure ( Front OR Rear will cause this )
2. Bad / Worn tire
3. Steering Head  or wheel bearings

Good Luck keep us posted.

[tomb raider]

Does it jiggle with hand's on ?? That's bad.. Mine did that till I put that fork brace on, not bad though..

[gammer]

I agree with Ari.
It could be one of many things. Start with the cheapest first.
Also, put the bike on the center stand, have someone lean on the back of the seat so the front tire lifts off the ground. Now turn the steering. Any lumps in the steering? There shouldn't be any. If there are lumps, then its a sign of worn steering head bearings (p.s. I just changed mine   )

Other causes (some already mentioned) in order of most likely to less likely:
- unbalanced tires
- uneven front fork oil levels
- tire air pressure
- worn wheel bearings
- Old, dry tires
- worn swing arm bearings
- riding on bumpy roads  

[jeff]

Do you have the preload cranked all the way to the hardest setting, on the rear shock? Raising the rear end of a motorcycle does weird things to the steering. Offroad motorcycles really get headshake with the rear up to high. The higher the speed the worse it gets. Some guys do it on purpose to tget the bike to turn quicker.

[Bad Boy]

The 700s is inherantly suseptible to this do to its quick steering geometry and 16" front wheel.  This is what I would do

Check for worn or unbalenced front tire.
Check for loose steering bearing, Bearing should be slightly over tightened to provide damper like resistance, procedure in Honda shop manual.
Install front forks so top of forks are flush with top of triple clamp, rear preload set at two for solo riding.  Raising the front or lowering the back will give more stability, slower steering.

If that doesn't fix it than keep your hands on the bars and should be no problem.

[SmokinFast]

Thanks everyone. I'll check all those items.

Some more info:
The front doesn't wobble if I have both hands on the bars, but it feels like it wants to. This worries me.

Unlike my previous two CB700SC project bikes, cornering on this one is scary.   Even at relatively slow speeds. One time it felt like the wheel came out from under me, and there was nothing on the road to cause a slide.

Of the 3 CB700SCs that I have worked on, this one was by far in the worst shape. It hadn't been ridden in at least 10 years before I got it. It looked like it died mechanically, not from an accident.

[happycommuter]

It hadn't been ridden in at least 10 years before I got it.

I know that in the automotive world, this is a recipe for wheel bearing problems.  Lube doesn't spread itself on a parked vehicle, bearing rust eventually occurs.

[Brittles]

I've got the same problem with my beater '85 and it's no surprise. It's got an almost bald front tire, fork seals leaking like a sieve, and neck bearings in bad shape.

I let go of my handlebars once at about 25 mph and it scared me to death. Can't imagine what it would be like at 40. Needless to say, I don't ride that bike anymore.  

[SmokinFast]

With the front of the bike lifted off the ground, the front wheel will flop from side to side under its own weight. Its not supposed to do that.

So I need to re-torque the bearing adjustment nut (its a 'castle' nut, not hex). Anyone know where to get the special steering stem socket ? Or some other tool that will work?

[jonwayneking]

My 86 does the same thing, but my front tire is worn from cornering and probably out of balance. I am waiting till I replace the tire before I tear into anything.

[benjithehunter]

Hey, just wondering how it turned out, I'm having the same problem, albeit mine feels a little worse than what you described, put brand new tires on and had the bearings quick checked by a mechanic (even have new ones on hand) but he said they were fine.  Hoping you're going to tell me it's just a steering bearing or torque problem, I'm thinking with all the manual shock adjustments something might be unbalanced (front or back) let me know!

PS- it looks like my rear grab bar is slightly out of wack which is what worries me.....

[tomb raider]

What is this ????

Re: CB700SC - Front end wobble
« Reply #9 on: July 11, 2010, 01:56:56 AM » Quote 

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With the front of the bike lifted off the ground, the front wheel will flop from side to side under its own weight. Its not supposed to do that.