Shake During Deceleration?

[Guest]

Hi all,

I've noticed lately that when I start to decelerate from a cruising speed of 60ish that there seems to be a certain speed that the bike shakes or kinda bounces it seems. It will do this for a few oscillations and then return to normal. It can be seen in the front forks if you look carefully, almost like the neck on the frame is flexing. Or maybe the forks are just bouncing and that's how it looks to me on the bike. I just replaced my rear D404 with a Shinko 230 (front is still a D404 for now) and I can't seem to remember if the bike did this before. Either way the problem has either been aggravated by the new rear tire or swapping the rear tire caused it. I've checked the rear wheel alignment and the chain multiple times and can't find anything wrong. If I roll into the throttle a little bit when the bounce starts it immediatly stops.

So what gives? Maybe time for new fork springs? The forks are the only thing I haven't rebuilt on this bike except for changing the oil

 

[NavyDad]

Steering head bearings need replaced or torqued properly?

 

[Guest]

Steering head bearings need replaced or torqued properly?

That would be my guess.

 

[Guest]

I'll have a look at the steering bearings, I did replace them 6 months ago. But to me that doesn't seem like the problem, I can let go of the bars when it does this and I get no headshake. It just sort of bounces, very different than any common problems I've experience before.

 

[cowboyup3371]

I would get rid of that Dunlop up front first

 

[steve murdoch]

As Cowboy mentioned having a Dunlop paired with a Shinko might be a problem.
Having a touring tire paired with a cruiser tire might be a problem.

Is the new rear properly bedded on the rim? Proper tire pressure in both rims?

I used to get a subtle front end weave when the air pressure would drop in only one of the fork legs.

 

[Himer]

In my case I had shake on deceleration and handlebar shimmy on high speeds and the cause were leaked swingarm shocks. In my country most people do front forks rebuild and they completely forget the back, which often leads to crash.

 

[Guest]

While you're tinkering, check the swing arm for looseness. I had an old Cb750 than had the same symptoms, finally tracked it down to that.

 

[Mr.humbucker]

Wheel bearings perhaps? I had one go, replacement is pretty easy with a good blunt punch and replacement bearings are about $40 for a pair. Lift the front wheel off the ground and try to flex the wheel at the axel or whatever you call it here and see if there is any play.

 

[bonanzadave]

steering bearings, I did replace them 6 months ago.

Id be curious about that project. Were the forks installed when you replaced the bearings ? How did you set the bearing torque. Might just need to be snugged up. Make sure one set of fork pinch bolts (top or bottom) are loose before you tighten the head bearings.

Yes. Get some new fork springs.

 

[Guest]

Id be curious about that project. Were the forks installed when you replaced the bearings ? How did you set the bearing torque. Might just need to be snugged up.

Yes. Get some new fork springs.

I basically went through the bike 6 months ago. New wheel bearings front and rear, steering bearings. Took it down to the frame except for the engine and painted most of the frame. Upgraded to the all balls bearings and tightened them with the forks out till it felt right to me; a slight drag turning side to side.

I planned to replace my dunlup shortly after the rear. I didn't think that would cause a bounce though?

Tire pressures are good and with the wheel on a truing stand it seems the rear tire bead is perfect all the way around

 

[Guest]

Well looks like I was wrong to begin with. I ended up tightening up the steering bearings and it got rid of most of the shake. I still get a little shake every once in a while but it's so little that it's hard to tell if it's my bike or the road. What causes the head bearings to come loose? Or is it just wear and you have to tighten them every so often?

 

[Big T]

Wheel bearings perhaps? I had one go, replacement is pretty easy with a good blunt punch and replacement bearings are about $40 for a pair.

I know Canadaians pay a lot for some things, but that's 250% of what we pay here. Local bearing shop has them at $8/each

 

[Mr.humbucker]

Maybe I should move there ... the point is they're a relatively cheap and easy fix whether they're $16 plus tx US or $40 Cnd a pair ($31 USD). Good. To hear the problem is solved for the vibration.

Big T - what model of GS850 1981 are you offering up in your signature block for a project?

 

[tom203]

" Make sure one set of fork pinch bolts (top or bottom) are loose before you tighten the head bearings."

Dang me, I failed to loosen one and was unable to figure out why my head bearings seem so tight. (I had a slight low speed handlebar wobble.) Today, I corrected my error and wobble was gone. Thanks!

 

[Guest]

After riding the bike some more I'm not quite sure the steering head bearings fixed it. It seemed better at first but now is shaking again. Im heading out to check if they came loose now. But I think I'm going to settle at the conclusion that either:

The rear wheel is out of balance, or

The mismatched tires are causing it

It seems to be just below 60 mph every time when decelerating, leaving me to think it is out of balance.

 

[willie]

Happened upon this thread and couldn't agree more with the advice to get rid of the Dunlop tire. I had a head shake problem with an 1150ES many yrs ago. Checked everything including having the frame examined on a laser table. I was a big fan of Dunlop at the time and a fresh front Sport Elite would cure the problem, for about 500-750 miles. Then, the problem would return. I couldn't believe it would happen after so few miles but it would with every new Dunlop.

 

[RichDesmond]

After riding the bike some more I'm not quite sure the steering head bearings fixed it. It seemed better at first but now is shaking again. Im heading out to check if they came loose now. But I think I'm going to settle at the conclusion that either:

The rear wheel is out of balance, or

The mismatched tires are causing it

It seems to be just below 60 mph every time when decelerating, leaving me to think it is out of balance.

It's not the steering head bearings.
What you're feeling is a decel wobble, very common phenomenon. You can make it go away by tightening (actually overtightening) the steering head bearings, to the point that they start to act as a friction steering damper. Not a good solution.

Root cause is generally one (or both) of two things. The first is the front tire. Most front tires when they're worn, and some when they're brand new, will lead to it. I've had two different tires on my Strom that were horrible for the decel wobble, a Tourance and a Conti Road Attack. Went back to a Pilot Road and all was well.
The other is a worn rear shock. As the miles add up the rebound damping in the shock deteriorates and allows the rear of the bike to cycle up and down. That motion feeds forward to the front of the bike and starts the oscillation.

 

[Guest]

It's not the steering head bearings.
What you're feeling is a decel wobble, very common phenomenon. You can make it go away by tightening (actually overtightening) the steering head bearings, to the point that they start to act as a friction steering damper. Not a good solution.

Root cause is generally one (or both) of two things. The first is the front tire. Most front tires when they're worn, and some when they're brand new, will lead to it. I've had two different tires on my Strom that were horrible for the decel wobble, a Tourance and a Conti Road Attack. Went back to a Pilot Road and all was well.
The other is a worn rear shock. As the miles add up the rebound damping in the shock deteriorates and allows the rear of the bike to cycle up and down. That motion feeds forward to the front of the bike and starts the oscillation.

I think you're definitly on the right track, I was talking to some of the guys over on the Honda SOHC4 forum and those bikes and particular are very sensitive to the new style tread patterns. I've ordered a Shinko 230 for the front as well. I'll report back when I get it installed

 

[RichDesmond]

I think you're definitly on the right track, I was talking to some of the guys over on the Honda SOHC4 forum and those bikes and particular are very sensitive to the new style tread patterns. I've ordered a Shinko 230 for the front as well. I'll report back when I get it installed

Just keep in mind that as the shock damping fades over time, the bike will exhibit this tendency more and more, until eventually it will do it to some extent no matter what tire you have.
As for tires, I think it has less to do with tread pattern and more with carcass stiffness and damping characteristics.