Shake During Deceleration?

[The1970's]

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?

[gsrick]

Steering head bearings need replaced or torqued properly?

That would be my guess.

[The1970's]

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.

[05Astro]

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.

[The1970's]

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

[The1970's]

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!