Front end bounce

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chuck 56 pan
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Front end bounce

#1

Post by chuck 56 pan »

Good day folks, I did some maintenance this spring, bike runs better than ever. engine is real smooth now and really rides nice except for a bounce in the front. This bounce showed up all of a sudden and was the main reason for new tires, bearings and wheel truing, I had also replaced the neck bearings and fork fluid over the winter. oddly the bounce is still there, it comes in around 35 mph and goes away around 50. I will revisit the neck bearings, they are on the loose side but have no detectable play in them.
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Re: Front end bounce

#2

Post by RUBONE »

You mention new tires, truing and bearings, but don't mention balancing. Was it done? what tires are you using. And is the fork oil the right viscosity and level?
chuck 56 pan
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Re: Front end bounce

#3

Post by chuck 56 pan »

Hello RUBONE, I did balance and used correct fork oil and amount. So to update, I did the worst thing. I Just made two adjustments at once so I dont know right now which one took care of the problem. I tighten up the neck bearings and then dropped the tire psi from 27 to 12 in the front and 14 in the back. The new tires are Avon safety mileage MKII 5.00 x 16 front and back. The bounce is gone. I will put the tire psi back up and go for another ride.
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Re: Front end bounce

#4

Post by chuck 56 pan »

I did confirm lowering the tire psi eliminated the bounce in the front end, not sure why but I tested it twice and got the same results. I might call Avon and ask them about running their tires like we did in the old days. I have read on here that modern tires should run higher pressures, for some reason thats not working on my bike. Perhaps my sliders are wornout and the lower pressure is masking that. no leaks of fluid though and no detectable slop in them.
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Re: Front end bounce

#5

Post by Excalibur »

Even though I hear those Avons are made with an updated rubber compound, it doesn't surprise that they behave better with lower pressure. I've never run one but isn't the carcass of those older designed tires likely to be stiffer than a modern tire?
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Re: Front end bounce

#6

Post by panfreak »

In my opinion, a tire shouldn't bounce like that no matter what end of the scale your pressure is at. Isn't having to run it hi/low to avoid bouncing just a way of masking the real problem i.e. shitty tires? I don't fuck around if I suspect any issue at all that might be wheel related, I've lost a tire at speed and it's really not fun.
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Re: Front end bounce

#7

Post by Bigincher »

Not to discount anything said, but I had a friend with a '57 with the same issue. Lowering the air pressure solved it. Generally speaking, an issue with the fork bearings can cause wobble, tire pressure or balance issues can cause bounce.
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Re: Front end bounce

#8

Post by Excalibur »

Another thing worth checking is the tire run-out. Book says up to 3/64" is allowed and has a good write-up about it.
I once adjusted front tire run-out on a lightweight dragbike. For that bike I'd found the lightest H rated treaded tire available. They are rated to 130mph and we were doing 119mph as best speed in the quarter.
I mounted the wheel on a fixed center and spun it by hand against an electric sander. I gradually micro-adjusted the sander closer a few thou at a time. It was surprisingly quick and easy.
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Re: Front end bounce

#9

Post by chuck 56 pan »

On my ride to work today, I took more notice to whats happening up front, There is still a little bounce at times, very brief unlike before when I had increased the air in the tire. What im seeing is forks have no or very little dampening . The bike just goes bouncing down the road, not sure why its speed related though. Was doing this before and after new tires, bearings, truing, and balancing. Appreciate your comments. Do you folks recall the the movie Easy Rider? there are some scenes of the capt America bike doing the Bounce, Think back, do you see it?
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Re: Front end bounce

#10

Post by Gotnoclass »

Sounds like you need to replace the bushings on the fork lowers. When was the last time you replaced them?
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Re: Front end bounce

#11

Post by chuck 56 pan »

Gotnoclass wrote:Sounds like you need to replace the bushings on the fork lowers. When was the last time you replaced them?
other than neck bearings all I have done to the forks was change the fluid, 7 oz of type B in each leg.
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Re: Front end bounce

#12

Post by Bigincher »

Changing the slider bushings is a tough job that requires special tools. I wish I was set up to do it, I've got a couple sets of sliders that need it.
Chuck56, have you ever checked the condition of your bushings? Next time you drain the fork oil, remove the tube caps and the inner spring. (Careful when removing the caps.) Then remove the front wheel. You can then grab each individual slider and try to move it forward and back and side for side. If you notice any slop, the bushings should be replaced. Like I said, it's quite a job. I'm also not sure what the symptoms would be of bad bushings. Probably a lot of different things.
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Re: Front end bounce

#13

Post by Gotnoclass »

Bigincher wrote:Changing the slider bushings is a tough job that requires special tools. I wish I was set up to do it, I've got a couple sets of sliders that need it.
Chuck56, have you ever checked the condition of your bushings? Next time you drain the fork oil, remove the tube caps and the inner spring. (Careful when removing the caps.) Then remove the front wheel. You can then grab each individual slider and try to move it forward and back and side for side. If you notice any slop, the bushings should be replaced. Like I said, it's quite a job. I'm also not sure what the symptoms would be of bad bushings. Probably a lot of different things.
I had mine done at Bill's Custom Cycle. Did an awesome job. He has the special puller and tools for the job.
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Re: Front end bounce

#14

Post by Excalibur »

I found this post over on Caimag Look at post #3. Maybe the same issue?
Chuck, can you describe better the bounce problem? Like is it pumping the forks, pattering on the road or flexing the forks back/forth? Do bumps set if off? Does applying brake or throttle change anything?
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Re: Front end bounce

#15

Post by Bigincher »

Gotnoclass wrote: I had mine done at Bill's Custom Cycle. Did an awesome job. He has the special puller and tools for the job.
Bills is a long way from me. I think I can find someone closer, when the time comes.
Thanks for the heads up.
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