Topic: Speed wobble at 40mph gone at 50mph!!??

[andy750]

Ok this is a new one for me...on my cafe CB750K2 if I let go of the handlebars at 40-45mph I get a serious headshake and have to quickly grab the bars. This is not present at 30mph or 50mph (havent tried above 50mph yet). My first thought would be steering head bearings but wouldnt that cause the headshake at all speeds? Just curious if it could be something else? Something simple and easy to fix before Laconia this weekend?? 

thanks for any suggestions,
Andy

[bryanj]

Yes it would, the Yamaha Elsie was VERY prone to that, but also check wheel ballance/bearings

[tmht]

Wheel balance?
Loose spokes?
Tire (tyre for the Scottish among us) pressure?
Wheel True?
Wheel bearings?

If you can get the front wheel off the ground, you should be able to feel for any free play or notchiness in the steering head bearing. The others should be pretty self explanatory checks.

[clarkjh]

Loose nut stearing , I mean loose stearing head nut.

James

[nickjtc]

That used to happen on my VFR at about the same speed. Everything was fine on the bike so I put it down to an idosyncracy.....and  made a habit of not letting go of the'bars!!

[CrisPDuk]

   @ James

Thats something out of rotational balance that is, at that speed it's more than likely to be something to do with the tyre or rim. Have you locked the front up recently, or clipped a pot hole and nipped a tyre edge off?


It's a very common phenomenon on cars belonging to women
It occurs during parking manuouvres when they run the wheel rims down kerbs and knock the clip on balance weights off

I think I'm going to need to get my flame suit on now

[CrisPDuk]

PS: You'll find that the vibration re-appears at around 80mph and 120mph but I wouldn't recommend you go looking It's scary as feck in a car

[clarkjh]

PS: You'll find that the vibration re-appears at around 80mph and 120mph but I wouldn't recommend you go looking It's scary as feck in a car

Mine starts at about 90 on the speedo, but I'm thinking its the back tire(tyre).  Haven't had the "Brass B@lls" to push it past it.   The old girl would do the "Ton" very easy if it wasn't for that.

James

[SteveD CB500F]

That used to happen on my VFR at about the same speed.

Me too.

My front tyre (BT020) was badly "feathered" ie not worn out but worn irregularly.

New tyre. No wobble. (went for Pirelli Diablo Strada though as better tyre for a sports tourer)

[andy750]

Thanks for all the helpful suggestions -should have mentioned that I have a brand new tire (well with 500 miles now) - BT45 Bridgestone. Anyway you have all given me some things to check out so Ill have a look and see.

cheers
Andy

[Jerry Rxman Griffin aka MuthaF'er]

Andy,

Did you have the new tire balanced correctly? Right air pressure?

[bwaller]

Did it ever shake its head before the different tire or is this new? That's partly why I added a steering damper back in the day, mine was always that way.  Could be a rim slightly offset that's made worse by a tire with better grip??

Will you be at the track or just hangin at the Weirs?

[snyquist53]

i have heard of metzler tires having a recent problem like this.  i guess a busted chord or something in the tire would make this happen.  check for balance , check to make sure all your triple tree bolts are tight.  i seriously doubt it would be in you steering, unless your whole front end is clunking when your start and stop (seriously loose headset)  my buddy with the metzler got a bunch of new parts from harley untill they finally figured out that even though the tire balanced good it still caused a violent shake around 35 to 40. 

[andy750]

Thanks guys Ill check the tire pressure tonight but I am wondering if its the tire not being balanced - anyway with all these good suggestions Ill work through them. Did it shake before the new tire (BT-45)? Its been 6 years since the bike ran last and I rebuilt it ground up over the course of last year and so cant quite recall how it ran before this. It also has 48,000 miles on it which made me think of steering head bearings but I take the point that if it was this it would occur at all speeds and it dosent. It could also be the rim being slightly offset but Ill need to prop it up to look at this. Thanks for that.

On better news I was having trouble with my newly rebuilt carbs - not getting much acceleration/lack of power despite new carbs kits, cables etc and appeared to me to be running a tad lean. Last night changed the jets from 110s to 112s and after a short (4mile) test drive seems to have made a big difference with better acceleration which on a cafe bike is what its all about ;-)

"Will you be at the track or just hangin at the Weirs?"

Bwaller -plan is to ride up from Boston leaving around 7.30am and head up I93 jumping onto Rt 28 after the NH border. Ride to Weirs beach, hang around there for an hour or less (get a t-shirt and then go as last year it wasnt that exciting), and then ride over to the White Mountains via the Kangamangus to Conway and then back via rt 302?? to I-93/Rt3 and head south on the backroads back to Boston. If you think you`ll be at Weirs beach I can give you my cell # if you want to meet up. Ill be riding with another guy.

cheers
Andy

[bwaller]

Andy,

No I don't bother with Weirs Beach any more, too hard on the ole 750 clutch! I'm heading to the track Saturday late morning, but we might be able to hook up somewhere. I'll get back for your cell#.