Brake Caliper Problem - Wrist Twisters
 
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post #1 of 16 Old 07-02-2007, 09:42 AM Thread Starter
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Brake Caliper Problem

I have my bike mostly assembled from the accident, might post pictures later. There is one part that concerns me: the front left caliper. I took the bike for a ride, accelerates/brakes strong, runs straight without any vibration, but the brakes were making noise.

I noticed a smooth ring on the inside of the left rotor, and took the caliper off. The caliper has been ground down where that mark was. What would cause this? They are the stock brakes on F4i forks, but only one side does it. They seem straight, but I had to add a washer as a spacer to stop the scraping.

Is there anyway to troubleshoot the rotor/caliper to tell if it's slightly out of line? As I said, everything looks straight, and the problem happens full rotation so it's not a warped rotor problem. I'll try to get pictures later, as I'm sure they'll help.

Note that I'm not riding the bike until I figure this out and fix it, and I'm taking the MSF course this weekend as well (to try to prevent future accidents and learn better technique). Having a recalled front tire doesn't help either.

03 919 (most of it anyway)
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post #2 of 16 Old 07-02-2007, 07:55 PM
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Bent caliper mounting tabs,bent Axel causing twisted fork tube.
Without seeing it, it's hard to say.

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post #3 of 16 Old 07-03-2007, 05:07 PM
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hard to guess, the manual says measure caliper to rotor clearance with a feeler gauge, so its got to be assembled just right.

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post #4 of 16 Old 07-03-2007, 07:34 PM Thread Starter
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I'm guessing the bent axle is the most likely problem. Can't hurt to replace it anyway for around $30

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post #5 of 16 Old 07-03-2007, 08:08 PM
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could the piston be stuck?

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post #6 of 16 Old 07-03-2007, 08:22 PM Thread Starter
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Na, the piston moves no problem. The part that is fixed (non-piston side) is the side that is scraping.

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post #7 of 16 Old 07-03-2007, 09:56 PM
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Welcome to the wonderful world of Frankenbikes!

Okay, now I'm confused. Neither the F4i nor the 919 has single acting calipers -- both have two pistons on each side of the rotor. If the caliper body is contacting the rotor it is probably due to the wheel being slightly offset to one side, likely if the F4i forks are installed in the 919 trees. Since the primary wheel spacer (the one which bears against the fork slider and is cinched down by the nut/threaded portion of the fork slider) is on the right side, that caliper will line up with the rotor under any circumstances. The left side, however, may not due to a difference in the width of the 919 trees compared to the F4i trees as this side does not have a spacer bearing against the fork to allow fine adjustment to prevent binding. Naturally, this assumes the fork legs/trees are a mix-n-match. If this is the case, shimming the caliper mounting eyes is a valid fix, but does not address another condition -- the front wheel being out of line with the rear. Ideally, you should use a slightly wider wheel spacer to properly center the wheel but then you will have to shim the calipers on both sides for proper centering. Of course, everyting would line up perfectly if you used the F4i trees, but then you would have to contend with cobbled up handlebar mounts or clipons, different or missing mounting points for most everything, not one 919 instrument cluster / ignition switch / headlight support / whatever in the right place. And on and on.

If you can live with the offset wheel and shimming just the one caliper then you would be bucks ahead to do so. If not, then it's time to get creative.
Glad to hear it's back on the road, now just press the lapels and you're done.

Rob

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post #8 of 16 Old 07-04-2007, 08:23 AM Thread Starter
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I read here that the F4i forks were a direct swap, so I assumed they would be fine. The only part claimed not compatible is the 919 fender, which is pretty easy to modify to fit. I'm going to replace the axle anyway, it's cheap and it was a little hard to get in/out of the forks, so there may be a slight bend I didn't see. If you saw how the old forks were twisted, it would be surprising if it was bent.

As for the calipers, I removed the inside pad (closest to wheel) on the left side caliper and didn't actually see a piston in there, just a spot for a piston. Did the 03's have 2piston calipers?

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post #9 of 16 Old 07-04-2007, 09:46 AM
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teksi
I'm sure that all of the stock 919 calipers are 4 piston.I'm very confused because you said "brakes strong". With a missing piston? Rob knows bikes. I can't wait to see some pictures!

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post #10 of 16 Old 07-05-2007, 05:33 AM Thread Starter
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Yea, I probably just overlooked it/didn't notice. Plus, if it was missing a piston I'd have no brakes at all. I'll try to get pics sometime soon, been pretty busy. I'll probably buy a new axle with the stock spacer, maybe try to find something else I can use for different increments of spacing too.

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post #11 of 16 Old 07-05-2007, 06:43 PM
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Quote:
Originally Posted by Teksi View Post
Yea, I probably just overlooked it/didn't notice. Plus, if it was missing a piston I'd have no brakes at all. I'll try to get pics sometime soon, been pretty busy. I'll probably buy a new axle with the stock spacer, maybe try to find something else I can use for different increments of spacing too.
Before you go & buy an Axel, Pull it out & roll it on a flat surface.
If it wobbles in the center or on the ends, It's bent,If not,don't bother to replace it & look elsewhere for the problem.
It would have to have a good bend in it to misalign a caliper.

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post #12 of 16 Old 07-08-2007, 05:28 PM Thread Starter
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Quote:
Originally Posted by xrmikey View Post
Before you go & buy an Axel, Pull it out & roll it on a flat surface.
If it wobbles in the center or on the ends, It's bent,If not,don't bother to replace it & look elsewhere for the problem.
It would have to have a good bend in it to misalign a caliper.
It rolls no problem. I was thinking a bend in the axle could be at the end (side w/o nut). I don't know what else it could be, but I'll keep looking.

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post #13 of 16 Old 07-08-2007, 07:40 PM
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Could you possibly take some pictures (big ones) from the front,side,top,bottom & any other angle you can think of. So we can look at it.
Maybe we can catch something you may have missed.

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post #14 of 16 Old 07-09-2007, 08:03 AM Thread Starter
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Quote:
Originally Posted by xrmikey View Post
Could you possibly take some pictures (big ones) from the front,side,top,bottom & any other angle you can think of. So we can look at it.
Maybe we can catch something you may have missed.
Sure. It might not be until Sunday as I'm going away tomorrow and won't be back til Saturday. I'll take pics with the caliper on and off, and I'll remove the fender for a clearer view.

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post #15 of 16 Old 07-17-2007, 04:19 PM Thread Starter
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No pics yet, but the wheel is definitely closer to the right side fork than the left. It's only around 1/16-1/8" off, but it's not centered.

When installing the front wheel, is there any technique to centering it or is it done strictly by the OEM spacers?

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post #16 of 16 Old 07-17-2007, 05:43 PM
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Quote:
Originally Posted by Teksi View Post
No pics yet, but the wheel is definitely closer to the right side fork than the left. It's only around 1/16-1/8" off, but it's not centered.

When installing the front wheel, is there any technique to centering it or is it done strictly by the OEM spacers?
The spacing on the right is strictly defined by the width of the axle spacer. A simple fix is to find a shim type washer of appropriate inside diameter and thickness to insert between the original spacer and the fork. This will at least tell you if the right side caliper will have to be shimmed slightly to maintain centering. Beware of deciding to just shim everything up and call it kosher -- a front wheel removal becomes a veritable festival of dropped and mixed up shims! (Very Ducati) An alternative is to go to a M/C salvage with a pair of calipers and rummage through their (usually) huge box of left over axle spacers -- if you are lucky, you will find one of just the right width/I.D./O.D. Of course, you could take your original spacer to a machine shop and say "I need a copy of this an eighth (whatever) inch wider." It wouldn't cost a bundle, but may take some time if they are busy.
Anyway, you get the idea.
Press on with this!

Rob

If it has already been done, it is safe to assume it is possible to do it.
On the other hand, if it has not been done never assume it is impossible to do it.
------- Rob --------
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