hi speed decelleration vibe?

[pago cruiser]

Happens when closing the throttle fast from maybe 70-90.   

This has been ongoing for awhile, maybe 5000 miles.  About what I get out of a rear tire.

The bike has about 65k.  Replaced the u-joint maybe 2000 miles ago.  It helped...  a bit.  But it was not a solution.  Now it's getting worse.

Pulled the rear end and driveshaft.  Wheel flange is good.  Ring gear is good.  Engine splines are good.  Pinion gear is... almost good? .

   

Lots of lube inside, but definite wear.  41.3 mm on the OD of the new splines, call it 41.1 on the OD of the used splines.





Can 0.2mm cause this vibration?  If not, I'm out of ideas... ???

One hint maybe though?  In the last year the bike has sounded...noisier than usual when fired up when cold.  Mechanical noise.  This developed over time as well.  I am sure it's unusual, as the Hack Valk does not do it.  Maybe tranny?  But as soon as I put it in gear and take off the noise stops.  I never made a connection until just now.  But if the problem is not final drivetrain, maybe its related?

Ideas welcome.   

[Jess from VA]

Warped rotor should be felt on braking, not brakeless decel.  But it could be brakes, floating rotors.

Wheel bearing maybe, but not 5000 miles before destruction.

A high speed/rpm miss?  A plug, wire, timing, carb synch, valve adj, ignition, one tooth off on timing belt issue?

A slight defect in a tire where balance issue only shows up at high speed?

Clutch (rivets)?

Have you tried to duplicate the symptom, then pulled the clutch after throttle drop, to see if the vibe stops?

Hip shooting.

Describe the vibe better please.  A shake, a buzz, a humm, do you hear it and feel it?

[pago cruiser]

Jess -thanks for the quick reply.

Not rotors.  Brakes not engaged when it occurs.
New bearings all around.  Maybe 15000 miles on all.
Never does it except in that condition.  Hi speed decell.  Decell from 60 or less, no vibes.  If it is vibing, accellerate and it goes away.  Ease the throttle slowly, no vibes. 

Have not tried pulling in the clutch when it's doing it.  As soon as I reach about 60-50 it goes away.  But this test will now have to wait until next weekend when I get it back together.

Think I'll put the new driveshaft in anyhow.  Any thoughts on the .2mm wear in the splines OD?  I don't know if this is a sign or not. 

It's just... felt vibration.  Lower frequency, almost a shudder.  Not like old-skool Triumph handlebars when cruising along at 65 mph - I would call that higher frequency.   Felt in handlebars, footpegs, and butt ...  If you have ever been in an earthquake, it is kind of like the start of one.  You wonder what is going on, then you see things oscillating in place, then you figure it out and head for a doorway (used to live in SoCal, so I'm not sure than analogy will work... ).

To me it felt like a u-joint.  But unless that new u-joint went bad in a couple hundred miles, pretty sure that ain't it.

As the u-joint did not fix it, I was betting on the pinion gear.  Embarrassed to say, I had not checked that since I bought the bike, maybe 15000 miles and 3 tires ago.  Trusted the PO's info - turned out it was indeed well lubed.

[BnB Tom]

  I've never heard of worn out wheel dampers causing the vibration you describe but they are definitely worth looking at while you've got it apart. 
 

[pancho]

"It's just... felt vibration.  Lower frequency, almost a shudder.  "  

I'd first put an ounce of ceramic beads into each tire, and check the head bearings.  I don't think it is coming from the small amount of wear in the drive line/pinion cup joint, but I also would put the new one in to rule it out.


Just sounds more like a chassis or wheel problem than a drive train issue.

[DK]

It could be the lash between the ring gear & pinion since it occurs when the load on the drive shaft is reversed when decelaeration occurs and the gear teeth become loaded on the alternate side.

Judging from your picture it seems to me that the used pinion gear teeth are narrower / sharper that the new teeth. However, I'm not really sure of this from looking at the picture. If this is the case there is too much clearance.

Disengaging the clutch stopping the shudder further indicates this is a possibility.

See section 12-4 of the shop manual.

The foregoing is pure amateur speculation.

Dan

 

[Ricky-D]

Don't worry. It is the u-joint and that vibration does not indicate the u-joint is failing. It is because of the drive line and the way it is set up to run (by Honda) and there is little you can do about it.

When you let off the gas, you are incurring slack (relaxing) in the u-joint/drive shaft assembly that permits the assembly to float and cause the vibration. You might try a new spring on the drive shaft although I don't think that would do the job. The looseness is actually between the universal joint and the output shaft coming out of the engine. The spring can overcome this at lower rpm's but not while it is spinning faster at higher speeds.

It is possible to lessen this vibration by letting off the throttle in a more controlled deceleration. The more the action of acceleration/deceleration is jerky, the more you will experience the vibration and the more it will exacerbate the condition.

***

[old2soon]

First time I had that vibration head shake on decel turned out to be upper shock bushings. RIDE SAFE.

[Tfrank59]

I'm a simple fellow--could it just be your wheel's out of balance?  And 5k tire life doesn't seem right--did I misunderstand?  You should be getting at least 10k out of a rear tire, IMO.  I got 14k out of my last one, normal (city/hwy) riding conditions.

[Momz]

Check your upper shock bushings and your tire pressures.