JohnnyV

Hey guys...

I'm lost. I have a front end shimmy under heavey breaking. I CAN'T find it.
befor I go any further; yes i have,

checked the brakes (I trued the rotors to 3thou),
all 8 pistons are in good working order,
I scuffed up the rotors and pads,
the axle & rim are straight and true,
new sneakers (Michelin pilot) balance with a 10th of a gram,
the stem has been pulled apart, and bearing check and greesed,

yet I still am getting a big shake under heavey breaking. under power its not so bad but is still there. I can see the lower end of the fork leg, vibrating drastically a few mm.

any suggestions are welcome...

I'm thinking fork leg bushing?

anyone?

gboezio

The bearing should have been changed and properly torqued, following the manual procedure down to the letter, anything else than this would spelle like incorect preload and a possibly notched bearings.

comedo

Are the front wheel bearings good? You've probably checked them already when you had the front wheel off the bike for the tire change and brake maintenance. Does the frequency of the vibration vary with road speed? Is there any play in the front end when you raise it off the floor?

Tweety

How much do you weight and is the fork stock?

nuhawk

Stock front brakes suck! First mod I did!

If you weigh more than 180 they really suck. The shocks do too!

If you weigh more than 200 the stock front forks are inadequate.

1 mm loose in the neck can upset the whole bike's geometry.

Make sure you're on good rubber at proper inflation.

JohnnyV

bearing are good... replaced earlier.
the stearing head was ripped apart, inspected, and repacked.
Rubber is brand new... michelin pilots (balanced within a tenth of a gram).

weight: I'm 220lbs... however, my friend who owns a race shop (racetech suspension dealer) weighs 175, and the bike was doing the same thing. He's stumped as well.

I have pulled the folks off. I think the only explanation the folk bushings.
any input?

Circuit_Burner

Bent wheel?
best way to check wheels if they have been whopped, is to remove all wheel wieghts and if the tires fresh, put it on a balancer. If it wobbles, remove the tire and test.
If it wobbles its the wheel, if it stops wobbling its the tire.
A large number of new tires are actually "blems" , sold at a discount because of slight manufacturing flaws.
Mostly blems are good tires that have cosmetic flaws, but never assume they dont have internal issues with de-lamination between the different ply layers.

JohnnyV

nope... the rim is true, the rubber is brand new.
the only thing left is the fork. the vibration and the deflection is massive.

Thumper

I have had mine do this a couple of times after replacing the tire with a brand new one. Each time the tire was beaded correctly and balanced perfectly.

Each time i dismounted the tire and remounted it, then re-balanced it and the problem was solved.

Circuit_Burner

Balance and trueness are two different variables tho.
Be sure to use a balancer to verify or you might go around in circles chasing this problem.
Also, Blems are sold as regular tires at many shops( more profit ) so, the balance testing is the only way to catch them.

Ive seen forks that were put together wrong with missing, mismatched or damaged components down inside the tubes that shook like this.
But that was a bike that was thrown together quickly to sell by a local low-end bike dealer I wouldnt trust to check tire pressure.

Hawkrider

When did this start? What changes were made to the bike when it started?

Assuming tires are good (balanced and round) and brakes are good (good runout, no high spots) then you may be correct about worn bushings. It's pretty unlikely though. I didn't replace mine until 40000 miles, and I really didn't need to, but I was in there and they showed some signs of wear.

Had a wheel bearing go out on my CBR1000F. That caused a HUGE shimmy, but it wasn't just during braking. When the guy at the shop pressed them out they came out in pieces!

JohnnyV

found it... FORK BUSHINGS.


thanks for the advice.