SOLVED! 30 MPH Vibration & Noise - VTXOA
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post #1 of 40 (permalink) Old 04-21-2016, 06:53 PM Thread Starter
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SOLVED! 30 MPH Vibration & Noise

Rather than update the many posts in which I've participated I thought it would be simpler to summarize my experience in a new one.

The symptom: vibration and noise, specifically at 30mph. Severe enough to feel it in my legs and through the foot pegs. Wife gets on the back and the noise would disappear! I could not replicate the problem on the stand. I found about 6 other riders here with the same symptoms, but none were available to share their solution, or perhaps were never solved.

I've been at this for almost a year and have changed every bearing (wheel, steering, swingarm), the universal, fork bushings & seals, rear wheel flange, and tires. I ruled out the speedo housing, fuel tank, headlight bucket, tire inflation, brake rotors, calipers or pads, and heat shields. Basically, I have a new bike.

Solution: a few years ago I had replaced my OEM 1300 SHOWA shocks with used ones from an 1800. The 1800 shocks are just a half inch longer, slightly changing the drive angle. I replaced these with Progressive 412 4234C heavy duty 12" shocks and I am pleased to report that the vibration and noise has completely disappeared.

Regards,
Pete
Gaithersburg, MD
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post #2 of 40 (permalink) Old 04-21-2016, 10:55 PM
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Pete---congrats on eliminating your issue.
Longer 1800 shocks caused your problem.
Did you actually have a higher ride height with the 1800 shocks?
Wondering if it was the drive line angle or some resonance.

2005 1300c Red, Mustang seat, HK 2.5 straights. Leds for safety-front & back. 194,184 VTX miles
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post #3 of 40 (permalink) Old 04-21-2016, 11:28 PM Thread Starter
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Thank you Hans, I never felt like I was riding higher but I believe so. I had my son measure the shock length with me on the bike, and then again when my wife sat on the back. The difference came to roughly 1/2 inch more compression with the additional rider. I had thought about switching to Progressives anyway, so since I no longer had my original 1300 shocks, we decided it would be worth the additional $240 investment if it could possibly solve the problem. And it did!

I also thought of the possibility that our final drives might have some minor vibration at that speed, and that some shocks absorbers could act as an amplifier. I'm not sure how we could make a positive conclusion whether it was the length affecting drive angle, or a resonance. One local Honda dealer tech did say that when they installed snow blowers on the front of a Honda tractor (or ATV?) that it would change the drive train angle just a bit and "wreak havoc" on the universal.

Regards,
Pete
Gaithersburg, MD

Last edited by PoggiPJ; 04-21-2016 at 11:33 PM.
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post #4 of 40 (permalink) Old 04-22-2016, 02:18 PM
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I doubt the shocks were the actual cause of the problem, more likely they are just masking the real issue....like putting weight on the back.
Possibly jetting related, this can be the cause of weird harmonics.
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post #5 of 40 (permalink) Old 04-22-2016, 07:07 PM
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And here I was expecting to see that explanation that the blowing wind and whining problem was from the passenger...once they got off it stopped and couldn't replicate the issue.:P
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post #6 of 40 (permalink) Old 04-23-2016, 03:42 AM
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I'm glad you got it figured out, Pete.. That is a lesson for all of us.. Any modifications from OE can and mostly will have side effects.. Some we may notice, and some we may not.. Nice work!

03 VTX 1800 C ~ Mustang seat, Cobra pipes, Highway bar, Memphis shade Windshield, Viking hard bags, Honda Sissy bar, and Luggage rack..
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post #7 of 40 (permalink) Old 04-23-2016, 08:54 AM
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Congrats on your fix, I had what sounds like the same vibration & noise when slowing down and Progressive shocks fixed my problem also.
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post #8 of 40 (permalink) Old 04-23-2016, 10:55 AM
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Thanks for sharing Pete. Good lesson for the rest of us. BTW were your shock bushings still good when u pulled the longer shocks off?
Tony

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post #9 of 40 (permalink) Old 04-23-2016, 11:56 PM
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Actually I believe it was the longer shocks causing the issue. I'm not a motorcycle mechanic but I am a mechanic and have had engineering schooling. The same issue can present itself in autos and trucks as well. What happens is when elongate (raise) the rear ride height it changes the geometry of the bike effectively loading the front shocks and changing the front to rear weight balance. Drag racers do it on purpose to change to traction point of the rear by putting the effective weight just in front of the center of the tire instead of the actual center. So what occurs when your wife climbs on it relieves the front shock loading by moving the center of gravity of the bike back to where it was.
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post #10 of 40 (permalink) Old 04-24-2016, 12:06 AM Thread Starter
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Quote:
Originally Posted by grizzlygar View Post
Congrats on your fix, I had what sounds like the same vibration & noise when slowing down and Progressive shocks fixed my problem also.
Thanks Grizzly, That makes THREE of us with the same problem and same solution. There was one other gent's post that put the thought in my head.
Quote:
Originally Posted by fciam1 View Post
Thanks for sharing Pete. Good lesson for the rest of us. BTW were your shock bushings still good when u pulled the longer shocks off?
Tony
Yes, I had switched them to the green poly bushings. They were brand new. The Progressive shocks contain their own bushings.

Regards,
Pete
Gaithersburg, MD
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