[TheJackal]

Although I've got a 929, I'm posting in this forum because I rode my Dad's '02 F4i today and I think its got a problem with the front forks!

My Dad always complained about vibration coming from the front when he applied the brakes so we both thought that it could only be the discs which were warped. Had them checked out by the dealer and after measuring with a caliper, they were within spec.

After having properly () ridden the bike, I'm not so sure that its the brakes, here's why:

- I only feel vibration/juddering (as if the discs were warped) when I'm light to medium-light on the brakes.
- As soon as I start braking heavily, the juddering goes away.
- After I've come off the brakes from heavy braking and I go over a bump/hole/whatever, I hear a "clunk" from the front.
- After, if I go over any more of the above, there's no clunk.

Any ideas on what it could be?

[Paddy]

It could be worn out wheel bearings but I still would rule out warped discs.
Do you have a way to lift the front off the bike so as to spin the wheel and
put something from the fork leg to the disc.You will see and hear if they warped.

Paddy.

[TheJackal]

I have ruled out warped discs because its been measured with a micrometer gauge by the dealer and the juddering doesn't always happen, like for example under heavier braking.

The juddering seems to disappear past a certain point as the forks dive, if the discs were really warped then the juddering would still be there

[Paddy]

I don't see how you can measure with a micrometer to check if a disc is
warped.You can only measure how thick the disc is.
Did you check the stearing(headrace)bearings.

Paddy.

[JohnDoe83]

Paddy is correct in asserting that a rotor's runout cannot be checked with a micrometer alone. A micrometer can check to see if the disc thickness is within spec, but it cannot determine if the rotor is warped.

Checking a disc's runout (or degree of warped-ness) requires a stable rotating platform and a solidly mounted dial indicator. This link is to a picture of a setup where a car disc is being checked. The principle is the same for motorcycle discs. Or any rotating part for that matter.

http://mysite.verizon.net/vze7aq8e/s.../frotor-ro.jpg

The symptom you describe of vibration during light to moderate braking at speed is a classic symptom of a warped disc.

If you do discover that the disc is warped, then you have two options.
1) Purchase and install new rotors.
2) If the rotors are thick enough then you can have them "Turned" such that they become flat again. Basically a machinist grinds off metal on a lathe until the rotors are flat.

You could potentially have a front fork problem in addition to a warped rotor. You should either get a dial indicator to check the runout or take it to a local machinist. Also find out if the fork oil has ever been changed. New fork oil can make a world of difference in the reaction of the front end under hard braking.

Good luck and keep us posted.

[TheJackal]

Just been again to the dealer and their thoughts echo mine, definately not the rotors because there is absolutely no kickback being felt through the brake lever at any speed. Not only that but the juddering being felt goes away under even heavier braking....if the rotors were warped then it would always be there at any speed, period.

Its been booked in for Wednesday and they're going to strip down the front forks because they think it might have something to do with some copper shims inside the forks, not too sure what they're on about without looking at a diagram of the forks.

[tmac]

im with paddy!....give the head bearings a tighten before you go .5 to 1 full turn should be enough?...see if that helps!

[jhonda41]

Originally Posted by JohnDoe83

The symptom you describe of vibration during light to moderate braking at speed is a classic symptom of a warped disc.

If you do discover that the disc is warped, then you have two options.
1) Purchase and install new rotors.
2) If the rotors are thick enough then you can have them "Turned" such that they become flat again. Basically a machinist grinds off metal on a lathe until the rotors are flat.

You could potentially have a front fork problem in addition to a warped rotor. You should either get a dial indicator to check the runout or take it to a local machinist. Also find out if the fork oil has ever been changed. New fork oil can make a world of difference in the reaction of the front end under hard braking.

Good luck and keep us posted.

and if it wasnt the brakes you might feel the shuddering under certain types of engine braking.

How are your tires?

-jh

[Fastrr]

First obvious thing to check is the tire for wear and proper air pressure. I've noticed a worn front tire causes some bad steering, turning, and braking issues...also can cause vibration.

It shouldn't be fork shims, i wouldn't think... i mean, what can change inside of a fork.. everything inside a fork is preset and stays in place. The only copper washers i know of on forks is for the the dampening rod bolt..where it bolts through to the fork leg to keep oil from leaking out. This copper washer is located where the wheel axle slides through the fork. Were your forks leaking any oil at the bottom of either fork leg? Being low on fork oil will cause problems.

As mentioned above steering head bearings being worn or lose can cause vibration and some weird feelings in the front end.

wheel bearings, again like stated, can cause vibration and wobble feeling in the front end. Makes the front end feel weird in corners and unstable.

That can be checked by lifting the bike up onto a front fork stand, unbolt the calipers and hang them out of the way. Place on hand on the front of the wheel, the other on the back and rock the wheel slightly to feel for any loose play.