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Discussion Starter #1
1986 VT500c rider. Noticed this since I got it a few months ago but it doesn't normally effect me too much. Bike rides fine up to about 75 mph and I try not to speed very much but I've noticed once I go past 75 and the bike becomes very shaky. Especially around 85 or so there's a very noticeable shake. It isn't a tire pressure issue and maybe it's normal but it doesn't feel like it should be. My dad who's been riding for a long time says my tires look good so I haven't worried about changing them yet.
 

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What's the date code on the tires? You make it sound like they're older. If they are, I sure as hell wouldn't be running 85mph down the road. Might also be a balance issue or a wheel bearing. In any event, worth checking out.
 

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If the bike sat awhile, the tires may be flat spotted, if not they may need balanced. Also, you may not be able to tell by looking if they are flat spotted.
 

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Discussion Starter #5
What's the date code on the tires? You make it sound like they're older.
I didn't know about date codes before this. Front tire is from 05 and rear is from 07. I'm no tire expert but to me they looked a lot newer than that. Will definitely look into a new set very soon and avoid higher speeds.

Sort of normal.
Tires can make a big difference as can weight and the distribution on the bike.
Here is an nice old video for your perusal.
I've experienced a little wobble and weave as well and maybe it's harder for me to tell while riding but what I get when reaching around 85 feels a lot more shaky then wobbly if that makes any sense.
 

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OK that does clarify it a bit.
It could be tire balance, or a rim out of true.
The tire balance will be fixed with the tire replacement and the rim can be checked at the same time.

Another thing to check is the metal cross brace between the lower legs of the forks.
They have been known to crack through allowing independent movement of the fork lowers.
 

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OK that does clarify it a bit.
It could be tire balance, or a rim out of true.
The tire balance will be fixed with the tire replacement and the rim can be checked at the same time.

Another thing to check is the metal cross brace between the lower legs of the forks.
They have been known to crack through allowing independent movement of the fork lowers.
Bingo! Some Hondas are noted for that, like the Magna V45 and V65's.
 

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Another thing to check is the metal cross brace between the lower legs of the forks.
They have been known to crack through allowing independent movement of the fork lowers.
I know that on my vt500 that brace is cast aluminum and doesn't look very strong. Finding a new one may be tricky but making a new one would be quite easy for anyone with some basic metal fab tools.
 

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Discussion Starter #9
Another thing to check is the metal cross brace between the lower legs of the forks.
They have been known to crack through allowing independent movement of the fork lowers.
The brace directly above the front fender? Mine does have s crack in it now that I checked, doesn't look major but possibly contributing to the problem?
 

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Maybe a contributing factor, it is there to stop the forks moving separately due to harmonics at high speed.
That is a pretty typical crack for them, caused by the stress of what they are meant to stop.
They are no longer available from Honda, but you may turn up a good one used.
I believe people have made replacements from aluminum bar stock in the past, but it looks like a fair bit of work for what initially seems like a simple piece.
I'd stay away from high speed runs or aggressive cornering without replacing it.

There are people running around on bikes with nothing holding the lower legs together other than the axles.
I look upon those people as foolish unless the bike is just used in town for coffee shop runs or taking poses.
If they didn't need them manufacturers would not have put them on there. On some bikes the fender mounting hardware does the same job.

I'm sure somebody will pop in and say "I've ridden thousands of high speed miles without one."
I wouldn't.
 

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Discussion Starter #11 (Edited)
Maybe a contributing factor, it is there to stop the forks moving separately due to harmonics at high speed.
That is a pretty typical crack for them, caused by the stress of what they are meant to stop.
They are no longer available from Honda, but you may turn up a good one used.
I believe people have made replacements from aluminum bar stock in the past, but it looks like a fair bit of work for what initially seems like a simple piece.
I'd stay away from high speed runs or aggressive cornering without replacing it.

There are people running around on bikes with nothing holding the lower legs together other than the axles.
I look upon those people as foolish unless the bike is just used in town for coffee shop runs or taking poses.
If they didn't need them manufacturers would not have put them on there. On some bikes the fender mounting hardware does the same job.

I'm sure somebody will pop in and say "I've ridden thousands of high speed miles without one."
I wouldn't.
I'll look around for a good used replacement. I work in a fabrication shop but we're more setup for building structural supports and don't work with any aluminum. If I have too much trouble finding replacement maybe I could see about fabbing one up from stainless steel?

I've found a few for earlier models but as far as I can tell the 83 to 86 likes have the same part number.
 

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The brace directly above the front fender? Mine does have s crack in it now that I checked, doesn't look major but possibly contributing to the problem?
The 83 thru 86 Honda Magnas have been known to catastrophically fail at high speeds with severe tank slapping and the bike going down. I have one of these bikes. If yours uses the same brace, GET IT REPAIRED ASAP!!!
 

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Discussion Starter #14
The 83 thru 86 Honda Magnas have been known to catastrophically fail at high speeds with severe tank slapping and the bike going down. I have one of these bikes. If yours uses the same brace, GET IT REPAIRED ASAP!!!
Looks like at least the 84 and 85 magmas used the same one as the shadows according to one site. Found one on eBay that should work. I kind of wish I could find an aftermarket one instead of just buying another 30 year old part that will probably just fail again.
 

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The part is really nothing special to make. If you can draw it up or take the part to a shop, they could make one easily.
 

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The part is really nothing special to make. If you can draw it up or take the part to a shop, they could make one easily.
Yeah I've already made a fuse box cover out of some stainless and like when I can make things myself. I may pull it off and see what I can do if I have any free time at work.
 

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I'm no engineer, but I'd bet you could fab up a hollow section and plate over the openings, where you had to cut it to profile and it would not weigh much more than the aluminum and would probably be stiffer. The thing that bothers me about making one out of stainless bar of the same profile would be the additional unsprung weight, but I may be overly cautious, it may not be that heavy of a chunk and might work out just fine.
 

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You also should check your rear shock bushings
 

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You also should check your rear shock bushings
That's a good thought, there is a fair chunk of mass back there that can have a profound effect if not properly damped.
Bad bushings can act as if there was not shock at all for a small amount of travel and that might be all it takes to trigger the shake at speed.
 
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