front shake/pulsation on the brakes - Sportbike Forum: Sportbike Motorcycle Forums
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post #1 of 29 (permalink) Old 07-12-2006, 12:21 PM Thread Starter
 
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front shake/pulsation on the brakes

I noticed the last time out on the track that I was getting a pulsation up the handle bars when I was hard on the brakes. I was thinking it could be either the balancing being off or the rotors getting warped. I took the front tire in to get balanced and it was off by 10oz, pretty minimal, the service tech mentioned that what I am feeling is caused by my front tires being cupped, and that if my rotors were warped they my brake lever would go all the way down and then have to pump the pressure back on the calipers.

so...

1. I've never heard of shakes being caused by cupped tires.. could this be the reason?

2. The tech's explaination of warping rotors seems to me to be the severe type of warping similar to when i left my disc lock on the rotor and messed it up. I'm thinking more along the lines of when rotors start going bad on cars and the pulsation starts.

I have a new tire at home and EBC Pro-Lite rotors sitting there ready to go on, but I dont want to replace anything prematurely

Can anyone shed some light on this for me?
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post #2 of 29 (permalink) Old 07-12-2006, 12:34 PM
 
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Your tire balance was off by TEN ounces? Each one of the wheel weights I use is a quarter of one ounce. So you're saying your tire is out of balance by 40 wheel weights. This doesn't sound right.

Does it pulse with the same frequency as your tire is spinning (one pulse for every rotation) or is it a faster frequency pulsing?

If you lean slightly and brake does it pulse worse?

If you put your front wheel up on a stand do your rotors look true while spinning the tire?

Are your bearings good?

Sometimes these things take some investigation.
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post #3 of 29 (permalink) Old 07-12-2006, 01:06 PM Thread Starter
 
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Quote:
Originally posted by Bluto
Your tire balance was off by TEN ounces? Each one of the wheel weights I use is a quarter of one ounce. So you're saying your tire is out of balance by 40 wheel weights. This doesn't sound right.

Does it pulse with the same frequency as your tire is spinning (one pulse for every rotation) or is it a faster frequency pulsing?

If you lean slightly and brake does it pulse worse?

If you put your front wheel up on a stand do your rotors look true while spinning the tire?

Are your bearings good?

Sometimes these things take some investigation.
Maybe he said it was off by 1 or .1oz, regardless he said it was minimal and should not have caused a pulsation that bad.

The rotors look true to me when I spin the wheel, but if it is just starting to go it might be the reason why.

The only time i really notice it is when I'm braking into turn one so i'm trying to slow down from 120+ to set up for the turn.

I'll check the bearings before i mount the tire back up tonight.

Next time i go for a ride i'll see how it feels when i brake in a turn.
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post #4 of 29 (permalink) Old 07-12-2006, 01:24 PM
 
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I hear ya. You hate to start replacing stuff if you don't have to. Seems to me at those speeds problems show up that you don't see at 60mph. If you figure out what it is I'm curious to know. If you need a hand with balancing we can hook you up as well. Get that wheel within a quarter gram.
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post #5 of 29 (permalink) Old 07-12-2006, 01:31 PM
 
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BTW as an added note. When you're tires are going bad or are bad it causes all kinds of weird problems.

I was getting a weird tank slapperish vibration when I let go of my bars. At certain speeds when the throttle was locked the bars would ocilate left and right to the point it would almost go into a tank slapper. Replaced the front tire...problem disappeared completely. I thought my front or rear wheel was out of alignment...turned out to be the tire.

Your tire deflects quite a bit when your braking heavy...especially when running reduced pressure like you do at the track. If there's a bad spot in the tire or bad cupping spot I bet you feel it under load.
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post #6 of 29 (permalink) Old 07-12-2006, 01:39 PM
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I doubt your tires are couped, i believe your running pp's, and when i saw you at the track it looked like your tires were very new, I am not sure how much you ride, but i doubt they are that worn down.

I would replace the rotors and pads and see if thats the problem.

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post #7 of 29 (permalink) Old 07-12-2006, 02:04 PM
 
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You've got two options:

Start spending money replacing shit trying to get to the root of your problem.......

Oooooooooooooooooooooooooooooooorrr.......

You can call one of your two friends (or both) who attended and graduated from MMI.......................
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post #8 of 29 (permalink) Old 07-12-2006, 02:41 PM
 
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Flip, the pulsing you're feeling could be the result of 1) loose head bearings, 2) tires, 3) glazed brake pads, 4) wheel balance, or 5) warped rotors.
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post #9 of 29 (permalink) Old 07-12-2006, 04:59 PM Thread Starter
 
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Quote:
Originally posted by KM2006
You've got two options:

Start spending money replacing shit trying to get to the root of your problem.......

Oooooooooooooooooooooooooooooooorrr.......

You can call one of your two friends (or both) who attended and graduated from MMI.......................
Good point i'll try one of them tonight.

I did ride it tonight after I got my tire reinstalled after balancing. i stayed on the throttle and pulled my brake lever in a little bit and felt the pulsation right at the lever.

Last edited by flip f4i pilot; 07-12-2006 at 05:07 PM.
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post #10 of 29 (permalink) Old 07-12-2006, 05:20 PM
 
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Im goin with rotors. 5 bucks on rotors.

When you have a deep spot in a rotor on a car, the same thing happens, only its in the foot pedal. Replace them bad boys.

Betcha it clears right up.
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