Sportbike World banner

1 - 20 of 32 Posts

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #1
I have this odd sort of situation that's been going on for quite a while and I'm not sure what to make of it. It was exasperated in my last track day.

When the bike is cold, the front brakes work spectacularly. After a while or on a hot day, when the bike slows to say 20mph and the front brakes are applied, the front brakes chatter, very much like the rotor is warped (continuous, pretty consistent skipping). This is not seen in the cool mornings even at low speed.

Since I just pulled the front wheel off for a tire change, I loosened and re-torqued all the rotor bolts to spec, hoping this would resolve the issue; I haven't had a chance to ride it since the change.

Anyone have any thoughts on what might be happening? Could the rotors be perfectly flat/straight until they heat up, and then warp? If so, I presume my only option is to replace them, but how do I avoid this situation in the future? What are some possible causes?
 

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #2
Well, after some looking into it there are a few people who had suggested using a combination of a buffer (sand paper, really) and then a rag to wipe away remains. The posted theory was something about tiny particles collecting in rotor pores.

I've never had to do this on a car and didn't on my first bike. However, I gave it a shot and its markedly better. WTF? Anyone have any thoughts on what's really going on here?

Its not completely better and some have suggested pulling of the pads and running them over the buffer on a completely flat surface too, which I might try to see if it resolves the issue completely. when I have time.
 

·
Registered
Joined
·
8,798 Posts
Are you certain you did not get any oily fluids on the pads?

Edit: If not, it sounds like you glazed them. After sanding the pads, take care to re seat them properly
 

·
Registered
Joined
·
210 Posts
Well, after some looking into it there are a few people who had suggested using a combination of a buffer (sand paper, really) and then a rag to wipe away remains. The posted theory was something about tiny particles collecting in rotor pores.

I've never had to do this on a car and didn't on my first bike. However, I gave it a shot and its markedly better. WTF? Anyone have any thoughts on what's really going on here?

Its not completely better and some have suggested pulling of the pads and running them over the buffer on a completely flat surface too, which I might try to see if it resolves the issue completely. when I have time.
Your pads got glazed. I am going to assume you have been playing on the track... It'll happen from time to time; no big deal.
 

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #5
Thanks for the glazing comments. Its always had some chatter since I bought it used, so I'm wondering if the newb who owned it before me glazed them on the track. Surely I helped that along :eek:
 

·
Registered
Joined
·
210 Posts
Thanks for the glazing comments. Its always had some chatter since I bought it used, so I'm wondering if the newb who owned it before me glazed them on the track. Surely I helped that along :eek:
Just keep an eye on it. If it does it again, pony up for the new pads and be done with it.
 

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #7
I'm going to give the sand-paper a shot but putting out for new pads isn't a big deal. Got a nice travel reimb coming from the company for some travel on the bike.
 

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #9
I tried the sanding of both the pads and rotors and still have some high speed chatter, which isn't acceptable. Now the hard question is whether to change the pads (which have LOTS of material left on them) or the rotors. I'm leaning toward the rotors because the chatter varies each time I stop, though rotor changes usually are required when you have runout (shown as pulsing on the brake lever).

The reason I wonder about the rotors is that I change that front tire pretty often when going between track and street and think its possible it got a jarring somehow. However, I did the pencil test to see runout on the rotors and simply didn't see anything significant.

Rotors would be $115, pads look like they're $53 at the Toy Store. Anyone got a recommendation for place to start?
 

·
Registered
Joined
·
8,798 Posts
Before you go off spending money, why don't you measure the run out on the rotor?
 

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #11
Because the tool to do that runs ~$100 (or just shy) and it is highly unlikely I would ever need it again. I don't know anyone who has one and you can't borrow one from AutoZone.
 

·
Registered
Joined
·
210 Posts
That's a very good idea! I've had some brake issues in the past and was able to fix them with a rubber mallet. I've seen rotors sometimes get out of whack and get stuck in a crooked position. I think what was happening was that the buttons on the carrier are crap and do not allow the rotor to float the way it should. If it gets out of line, it is possible that it could stay that way until you beat it into submission. I know it sounds a little hokie, bit it happens. I put my bike on a front stand and checked the runout. Wherever it was out of line, I tapped it back in with a rubber mallet. I never had a problem after that.

All of this is predicated on the fact that you have a dial indicator though. Without is, there aren't too many ways to find out if your rotors went silly on you.
 

·
Registered
Joined
·
8,798 Posts
Personally, I consider tools to be a great investment, but I see how that wouldn't fly for everyone. If you were any closer, I'd bring one over so you could use it.

The symptoms you are describing sound a bit fishy for a warped rotor. With a warped rotor, pulsing should be very consistent. Yours first only appears at low speeds, then only appears at high speeds, and is temperature dependent. On top of that, it seems to be affected by sanding. And while a bad rotor could, somehow, be responsible for all this, it may well have nothing to do with it. And if that is the case, you will spend $500 trying to save yourself $150.

As for the idea of fixing rotors with a rubber mallet? Well as scary as it sounds, if you are about to throw it away, i guess its worth a try.

btw, here is a link to a cheap dial indicator on ebay
http://cgi.ebay.com/ebaymotors/7-JEWELS-DIAL-INDICATOR-HOLDER-SAE-TEST-0005-NEW_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1205Q7c39Q3a1Q7c66Q3a2Q7c65Q3a12Q7c240Q3a1318QQ_trksidZp3286Q2ec0Q2em14QQhashZitem250318010493QQitemZ250318010493

You don't need a top of the line tool for this job. I believe maximum allowable runout is 0.010", so there is no need in a tool that measures tenths of thousands. Just remember to measure multiple times, so you don't get some fluke throwing your numbers off.
 

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #14
Thanks a tone for all those thoughts. The brakes are very strange in behavior and not very repeatable. I spread my net wider and found a friend-of-a-friend who has a gauge, but he has to dig it out of his unpacked garage. I'm trying to decide if he'll find it before spring :rolleyes:

Just gotta remember, beggars can't be choosers.
 

·
Registered
Joined
·
210 Posts
Thanks a tone for all those thoughts. The brakes are very strange in behavior and not very repeatable. I spread my net wider and found a friend-of-a-friend who has a gauge, but he has to dig it out of his unpacked garage. I'm trying to decide if he'll find it before spring :rolleyes:

Just gotta remember, beggars can't be choosers.
On a side-note; have you checked your steering head bearings? Sometimes that will make the front end chatter a little bit.
 

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #16
Good question. I didn't specifically test for that but would think I'd get that at times when I didn't use the brakes, like accleration, slowing, and non-smooth turning. Maybe not and I'll check it. I had already checked the wheel for play and there is none, so I'm quite certain the wheel bearings aren't an issue.
 

·
Registered
Joined
·
210 Posts
A loose steering head bearing can be tricky to find. In my experience, I have found that it has inconsistent symptoms. If you tap the front brake at slow speed, you might be able to feel movement. If you do, you now know your problem.
 

·
Registered
Joined
·
8,798 Posts
How do you check the steering head bearings?
 

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #19
I remember seeing a section in my Clymer's for my last bike, so I'm going under the assumption there's a section in my factory manual for the 636. Here's what I pulled off of kawiforums:
Steering head & swingarm bearings: Lift wheels off floor, grab lower fork legs and pull and push to feel for play; repeat at rear. Turn fork to feel for detents in bearings.
 

·
Strength and Honor
Joined
·
6,144 Posts
Discussion Starter #20
Alright, I did what I could to check for runout and it was like 5 thousandths, IIRC. Was a mother to do with the freakin' gauge dropping into the vent holes :mad:

Just keep an eye on it. If it does it again, pony up for the new pads and be done with it.
I think I'm going to do this. I have read spectacular things about Vesrah from club racers and think this might be a good option. Any others I should be checking out? Changed the brake fluid to make sure I wasn't getting some weird boiling action as the brakes got warm and that didn't seem to help at all. No bearing issues either.
 
1 - 20 of 32 Posts
Top