Triumphrat

grapeman · 04-27-2010, 08:55 PM

All,
I need some help. When riding over 50 mph the bike has a weird vibration. To describe it, it feels like go over a series of small bumps. The "bumps" last for about 1 or 2 seconds then it stops for about 3 or 4 seconds and does it again. The road is smooth asphalt, with no visible imperfections.

The bike is a 2006 Speedmaster with 2k miles. The bike was purchased over the winter as a project. At the time of purchase, the dealer indicated there was nothing wrong with the bike.

Since purchase I have swapped out the cast wheels with America lace wheels. The wheels where taken apart and rims powder coated. The wheels were then laced and trued by a 20+ year pro.

In the process of swapping the wheels, I reused the cush drive, final sprocket and carrier, axle's and axle spacers from the speedmaster setup.

The front tire was replaced first with a Metzler ME880 (for about 60 miles) and then with a Avon Venom. The back tire is the original Metzler ME880 with 2k miles.

Wheels and Tires were balanced at the local bike shop on a machine. The front took an ounce and the rear was one and a half once.
Since having the tires balanced I removed the front and had it re-trued and balanced by hand. The hand balance method resulted in no weights being added (and some griping about the machine balance quality by the same 20+ year pro).

Progressive springs have been added to the fork tubes. The compressed part of the springs are at the top (to keep the fluid level the same).

The front bearings have been replaced.
The wheels have been aligned back to front and rechecked.
The steering head bearing load has been adjusted (may be a smidgen to tight now - but adjusting had no effect)
The brake rotors have been checked for run-out. The front is on the edge of needing replaced at .012".
The chain has been adjusted and rechecked.
Wheel weights have been removed from the rear tire, with no-effect.

Need some help here fellas, what could this be?

marc hanna · 04-28-2010, 02:05 PM

It sounds like you're describing a chassis vibration issue but it's not exactly clear.

Such a slow repeat rate at that speed would suggest more of a carb balance or timing issue.

At low speeds tight spots in the chain or bad sprockets can create these types of issues, but at high speed these would be perceived as harsh vibration.

A bad tire can get very shaky when accelerating but then re-stabilize at a higher speed.

Is your issue more of a vibration or a distinct shake?

grapeman · 04-28-2010, 03:56 PM

It is not a shake. It is more of a vibration. Like going over rumble strips.

Carbs have been balanced.

The chain does not appear to have any tight spots. Back sprocket looks ok. Have never looked at the front one.

desmo955i · 05-07-2010, 04:36 PM

OMG! I have that exact same issue!!! It happens to me while riding 2 up. My passenger doesn't notice it. Doesn't matter the road surface, air pressure or rear shock preload. Only happens between 50 and 65-ish, seems to disappear above 70. Bike is in great shape, 2007 less than 10k on the odometer.
I don't have an answer for you. But your not alone

marc hanna · 05-07-2010, 04:44 PM

It might be a bad tire then. If it appears at certain speeds but you can accellerate through and it goes away, this is a symptom of an out of rounds or poorly balanced tire.

mag10 · 05-08-2010, 07:59 AM

I second the chain and sprockets suggestion. you mentioned teh cush drive, but how is the chain? a lumpy chain (one with tight spots) will create very interesting harmonics at select speed ranges, that you can get past by speeding up.

I used to ride with a guy who had 'discovered the bikes harmonic' as he put it. It was an old honda 750-4 that shook horribly between 40 and 60mph. he would speed up quicky to 60 to get past it and then use his 'late braking technique' to slow down past the vibration. After 2 very stubborn summers he finally gave up a replaced the chain. It fixed the vibration but he always said it took the challange out of riding.

grapeman · 05-08-2010, 08:50 PM

I have looked over the chain several times. If it has a tight spot I can not find it. The rear sprocket looks good. Never have eye-balled the front sprocket yet.

My current thinking is that the front forks are having trouble. Either stiction issues with the seals or something in the internals that is causing trouble.

Going to rebuild the front forks next weekend.

Army Mom · 11-23-2012, 05:34 PM

I just bought a 2004 Speedie and took it out for its first ride. I also noticed a series of bouncing on relatively smooth highway. I thought perhaps it need a wheel balancing. The bike also has a vibration at low speeds which is a mild vibration that disappears at higher speeds. What appears to be an out-of-balance front wheel is what drives me crazy. It has me afraid to go much over 65 mph. I've never had wheels before now - always laced. I would appreciate anyone's advice on how to determine what's the matter with my new bike. It only has 1,650 miles on it, even if it is a 2004 model.

Verde · 11-25-2012, 03:28 PM

Hi, Army Mom,

I assume you've checked it, but keep an eye on the tire pressure. If mine is just a tad low my America feels really loose.

As far as the possibility of being tuning related, since it's such low millage for that year bike the carbs may be a little gummed up from long periods of disuse. If it idles and runs fine, then I won't worry too much, but maybe put some "seafoam" brand gas treatment through it on the next tank of gas.

One thing that can cause weird behavior at cruising speed is the carb vent tube dangling in the breeze. Read through this one and make sure you get the right tubes(while you're at it though you might as well drain that airbox tube that got mixed up later in this thread): http://www.triumphrat.net/cruisers-a...ml#post2387328

Army Mom · 11-25-2012, 07:11 PM

Hey, Verde, thanks for your input. Since posting this, we've checked the front tire and discovered that it has a flat spot about 18" long. Although I haven't had a chance to replace the front tire, it appears that this is a problem, hopefully the only problem. Because the bike is 8 years old with only 1,650 miles, it obviously has been lerft to sit for long periods of time. We had a friend stop by and lament that he wouldn't want to run an 8-year-old front tire. Now we're waiting for our favorite bike shop to reopen on Wednesday to replace the front tire. The bike truly runs great, though. I'm very pleased with my beautiful new bike. I've named him "Sanity."