'91 K75S hop and wobble

[kurtk75s]

Good suggestion.  It might come to that.

The first time I changed tires on my RT,  after breaking the bead I went to remove the tire and f-Ing dyna beads scattered all over my garage floor.  I was not happy.  So there is source of my prejudice against dyna beads.  I’ve never had a balance problem in the last 33 years so I just thought they were a solution looking for a problem.

I’ve convinced myself that it is a problem with either:  wheels, tire, front suspension.  The rear shock is still a possibility but will be a last resort.

Dyna beads are relatively cheap to try, though.

[kurtk75s]

PMP,  I will do each independently.  The only thing I will double up on is:  when I have the wheel off, I’m going to rotate the one of the brake disks 180 degrees as well.  Changing the oil will only take a few minutes.  Fork springs only slightly longer.  I’m getting pretty quick at disassembling and reassembling both the front and rear end of the bike thanks to this issue.  I think my last tire change and balance took less than an hour for both wheels!

Regarding fluid level.  I may experiment with that AFTER the springs if I still have issues. 

As a side note:  I’ve started my winter project which is a frame up on an R90/6.  I’m going much farther with that project because all of the seals need to be replaced.  It only has 15k miles but sat in a barn neglected for 30 years.  I am approaching it as an educational exercise.  The K75 was too nice to really dig into.  I can’t make the airhead worse than it is 😁.

[alexg]

I read with interest this trail. Since your wife commented about the hop being under the seat, could it be that you have a stiff U-joint? That would be really bad for the splines too.

Alex

[milq]

Have you checked the swingarm and bearings for play or stiffness? Just tossing stuff out there.

[daveson]

Probably all's I can toss in.

Don't remember if it's at the same speed in another gear. In a lower gear if it's still happening at the same speed, could point to suspension. If it's revs related, could point to the drivetrain.

Could a dynamic balance do the trick.

Maybe get to the trouble speed on the centre stand, might help to eliminate some stuff, dunno if that's been mentioned yet.

[kurtk75s]

Thanks for the comments. 

1.  If the U joint is bad I’ll be pissed because this is a brand new $$$ driveshaft.  I think my wife may have noticed the bounce because the bad rear shock was amplifying it from her perspective.  When I run the bike on the center stand, it appears to be smooth so that is why I think it is tire, wheel, or suspension.

2.  At the Green Mountain rally, a friend also suggested swing arm bearings as something to look at if all else fails.  I was going to ask this group if anyone has experience with swingarm bearings going bad - what are the symptoms?  My friend is a very experienced professional mechanic, Connecticut airhead air Marshall, and has restored a number of beautiful bikes.  He said that he had a similar hop on an R100 and he never figured out what it was.  It eventually went away.  That didn’t give me a warm fuzzy feeling.

3.  The symptom is the same no matter what gear the bike is in or if the clutch is pulled in.

This is a crazy situation where I have multiple issues compounding each other.  I always assume that if something is wrong after I work on it, it is related to something that I touched even if it is seemingly unrelated.  So far this hasn’t been the case with this problem.  The shock and steering bearing looseness were things I hadn’t messed with. 

[daveson]

You might get an opportunity to swap the final drive. Or other bits. I know trial and error isn't the proper way but that's what I sometimes do.