Excessive Chassis Vibration

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Re: Excessive Chassis Vibration

Post by Mr Wazzock » Mon Feb 17, 2020 9:08 am

Wheels been balanced? Or not?

'Cause you mentioned new tires and tubes..... rim weights, if any, may now be in the wrong place(s) or not necessary / too few / too many delete as appropriate...
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Re: Excessive Chassis Vibration

Post by Mr Wazzock » Mon Feb 17, 2020 9:10 am

Appendix: got any tire sealant in, that can gloop up in a lump or need time to distribute around the tube evenly, while in the meantime make the tire like a wobbling weight. Just guessing
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Re: Excessive Chassis Vibration

Post by cookiemech » Mon Feb 17, 2020 9:38 am

I carefully balanced wheels. Never any sealant or liquid "balancers". These tires/wheels take more weight than other makes, between one and three ounces each.
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Re: Excessive Chassis Vibration

Post by Mr Wazzock » Mon Feb 17, 2020 11:22 am

OK, just a thought.
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Re: Excessive Chassis Vibration

Post by cookiemech » Mon Feb 17, 2020 1:30 pm

Took it out this morning to an appointment; it was about 23°F with ice fog, just lovely. I'm not sure what I learned on the 20 mile trip there or the 30 mile trip back. At 50 mph on a flat straight road in 4th gear, I pulled in the clutch and hit the kill switch. Most of the vibration was still there, just diminished slightly. There is more vibration under throttle application than when coasting. I tried running at 50 mph in both 3rd and 4th gear. I think the vibration is very similar, but of course everything sounds different at different rpms due to the gear selected. I tried to quantify the vibration level by looking at the mirrors; it seems the same in either gear.

The nature of the vibration is almost as if there is a "beat frequency" component to it. Like there's a rhythmic shudder superimposed on the general and constant high level of vibration. It really feels like a driveline vibration, like a bad U-joint or driveshaft way out of balance. But all three U-joints are fairly new, and even with the original (bad) U-joints, the vibration was pretty similar. And those U-joints were bad enough that they were actually sloppy.

Think I'll go out to the garage this afternoon and look everything over some more. That will likely just result in more head scratching . . . I suspect I'm not seeing the forest for the trees, which has happened to me more times than I'd like.
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Re: Excessive Chassis Vibration

Post by jaybird » Mon Feb 17, 2020 1:48 pm

My apologies if this has already been discussed but, have you checked the sidecar driveshaft for a bend or woop? That could/would cause what you are describing.

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Re: Excessive Chassis Vibration

Post by Wildhorse Cafe » Mon Feb 17, 2020 2:04 pm

Insugest putting the drive wheel up in the air and run the drive train up to speed and see what you can see.
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Re: Excessive Chassis Vibration

Post by chaos2 » Mon Feb 17, 2020 2:54 pm

I was going to suggest running on the centerstand also. You mentioned the tires needed more weight than usual to balance, that could be a sign of them being out of true radially.
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Re: Excessive Chassis Vibration

Post by cookiemech » Mon Feb 17, 2020 3:39 pm

Thanks to everyone who suggested running it with wheels in the air. Now we're getting somewhere.

Bike on centerstand, jack stand holding sidecar wheel up. Ran in all gears and then engaged 2WD. Oh, boy. The 2WD shaft has a good 1/8 inch runout and in 4th gear at idle makes some noise. Also noted that perimeter of donut does not run true at all. Normal? Also pusher tire has one small area of significant radial runout. And sidecar tire has some lateral runout.

I know what to do with the wheels, but can the 2WD shaft be straightened? Is my donut bad just based on the appearance of runout?
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Re: Excessive Chassis Vibration

Post by Mr Wazzock » Mon Feb 17, 2020 3:50 pm

Can you just remove the 2WD shaft and ride it without, just to prove if that's the problem?
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Re: Excessive Chassis Vibration

Post by cookiemech » Mon Feb 17, 2020 3:54 pm

Is that possible? Unless you remove the U-joint from the yoke at the sidecar wheel, I don't see a way to do it.
1982 BMW R100T
1994 BMW K75RT
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2009 Kawasaki KLR 650
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2017 Harley-Davidson Road Glide Ultra
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Re: Excessive Chassis Vibration

Post by Mr Wazzock » Mon Feb 17, 2020 3:59 pm

Complicated then. :D

But yeah I suppose.
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Re: Excessive Chassis Vibration

Post by cookiemech » Mon Feb 17, 2020 4:38 pm

It's just that I recently replaced that U-joint (and the others) and it wasn't easy. I'm afraid I will damage something if I remove it.
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Re: Excessive Chassis Vibration

Post by windmill » Mon Feb 17, 2020 5:17 pm

cookiemech wrote:
Mon Feb 17, 2020 3:39 pm
can the 2WD shaft be straightened?
Yes,
I've bent it really good a couple of times, and straightened on the spot with careful use of a jack.
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Re: Excessive Chassis Vibration

Post by jaybird » Mon Feb 17, 2020 5:51 pm

windmill wrote:
Mon Feb 17, 2020 5:17 pm
cookiemech wrote:
Mon Feb 17, 2020 3:39 pm
can the 2WD shaft be straightened?
Yes,
I've bent it really good a couple of times, and straightened on the spot with careful use of a jack.
+1
It can take some work and ingenuity to get them anywhere near perfect though.

Happy trails,
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