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Buell Forum » 1125R Superbike Board » Front brake pulsation after low side that didn't touch the brakes at all? « Previous Next »

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Thefleshrocket
Posted on Monday, May 10, 2021 - 04:30 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Last fall, I lowsided my 1125R at Deals Gap. (I overcooked it between corners, braked hard while upright, slowed down enough, but ran off the road at about 20mph as I couldn't get leaned over quickly enough to complete the turn.) Left side pod took some rash, and the subframe got tweaked (I think the passenger peg must have hit something that tweaked the subframe), but other than that, there was no damage. Bike was rideable, and I finished out the weekend on it.

Problem is that the front brake has a pulsation now, that wasn't there before. When free-spinning the front wheel off the ground in my garage, the front brake has consistent friction throughout almost the entire rotation, but then for one small spot, there's a lot more friction. It's acting like a bent brake rotor, but neither the wheel, nor the rotor, nor the caliper, nor the fork sustained any damage that I am aware of.

I loosened the mounting hardware, spun the wheel a few times by hand, and then tightened it, but that didn't seem to have any effect. To be fair, the bike still has the original brake rotor mounting hardware--I have never replaced it. What should I do next for troubleshooting, short of just replacing the rotor and the rotor mounting hardware?
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Two_seasons
Posted on Monday, May 10, 2021 - 05:10 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I would again loosen the hardware at the front wheel. Loosen the lower clamps of the triple tree. DO NOT LOOSEN the upper clamps of the triple tree.

Then put a rear stand on the bike.

From there you'll want to mount the bike. Standing on the foot pegs and with the front wheel as straight as you can, position your body weight over the front forks, then push down several times using your body weight and the handlebars. Retighten the lower clamps, then the wheel.

More than likely, you forks are tweeked, but not bent. Used to happen to me when I rode dirt and crashed!

(Message edited by two_seasons on May 10, 2021)
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Skrip
Posted on Monday, May 10, 2021 - 05:10 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Sounds like the wheel is slightly bent. I'd get a dial indicator attached to the fork and check the wheel. The rotor should be removed and place on a flat surface and inspected with a feeler gauge. Lateral runout is .0248 in. Hopefully it's just you rotor.
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Thefleshrocket
Posted on Thursday, May 13, 2021 - 10:26 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Thanks, guys. I'll give those suggestions a try.
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Thefleshrocket
Posted on Wednesday, June 16, 2021 - 02:01 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I got a dial gauge and ran some tests. With the front wheel lifted off the ground, there was one point on the brake rotor with 0.005" runout. The rest was almost nothing.

When checking the wheel, there was one point with 0.013" runout. There were a few parts where it varied around 0.003" to 0.005".

With the rotor off of the bike and on my (hopefully completely flat) countertop, I used the thinnest feeler gauge I had and could not get it under the rotor anywhere along its perimeter.

If the rotor or wheel were bent enough to affect the brakes, wouldn't that knock the pads back into the caliper a bit, and cause the lever to get spongy? Because that's not happening.

I also totally removed and cleaned the rotor mounting hardware. Some of the mounting points had old excess blue Loctite, which I figured might have gotten wedged in there and caused the rotor to feel funny, but cleaning it out didn't fix it.

Also while riding, I noticed that braking at low speed, like under 20mph, the grabby point is almost unnoticeable, but at higher speeds, like over 30mph, it's more noticeable and gets progressively more noticeable at higher speed.

I guess I need to retry the runout test and see if the runout points coincide with the grabby point on the rotor.
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Skrip
Posted on Wednesday, June 16, 2021 - 07:32 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

If they were bent really bad I'd say yes. It doesn't take a lot to feel a pulse. Especially on these huge hula hoop rotors. It sounds like you're on the right track though. Curious, did the runout on the wheel coincide to where the runout of the rotor was?
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Thefleshrocket
Posted on Tuesday, June 22, 2021 - 09:53 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

There is one part where the rotor's runout is about 0.005". I made a mark on the rotor where the runout peaks at 0.005" and another mark where it begins decreasing. Interestingly, the two marks are about as far apart as the swept area covered by the brake pads. IE, if I spin the wheel, when one mark is becoming visible from under the caliper, the other mark is about to disappear under the caliper. Spinning the wheel, this is clearly where the "hang up" is in the rotor's rotation.

So I checked the wheel itself, and its runout is about 1/4 of a rotation away from where the rotor's runout is. But, I have already removed and reinstalled the rotor, and probably didn't put it back in exactly the same position. That said, the wheel's runout is between two rotor mounting points, and only peaks for at best a couple inches.

It's almost like the pads left a deposit on the rotor at the point of the hangup, and that's what's causing the pulsation but.. I've never had motorcycle rotors get deposits on them, and I was off the brake entirely when I low-sided, so I don't think I squeezed the brake lever hard enough to leave deposits. But.. maybe I should take the bike out and re-bed the pads and rotor. Now that I think about it, when I was lifting up the bike, I was most likely gripping the front brake lever. The brakes must have been hot at the time, and I bet I was gripping the lever really hard. So.. maybe deposits on the rotor isn't all that unlikely.

If that doesn't work, I'll try a replacement rotor next.


(Message edited by thefleshrocket on June 22, 2021)
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Two_seasons
Posted on Wednesday, June 23, 2021 - 06:03 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Before you go out and try to re-bed the pads or go purchase a new rotor, try this...

Get some Scotchbrite pads, red or green, lift your front tire off the ground, and while holding the Scotchbrite pad between thumb and forefinger, spin the front wheel so the rotor is spinning between your forefinger and thumb. As much pressure on the rotor as you can muster. You'll use up the Scotchbrite pad fairly quickly.

Do this until you have a bright and shiny rotor. It may take a while, but it's as good as a rotor hone if you are patient.

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Thefleshrocket
Posted on Tuesday, June 29, 2021 - 10:32 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Guess I should have checked this thread last night.. instead of Scotchbrite, I went out and rebedded the front brake last night. The pulsation was unnervingly bad at first--like the whole mirror assemblies were vibrating up and down what looked like a couple inches in each direction--but I made progress to where the pulsation is mostly gone. I must have done 30+ braking events. I put the bike back up on the stands in my garage with the intent of checking to see if the raised section was (mostly) gone. I'd figured I would have a go at that particular section with some sand paper, but if you guys think that Scotchbrite over the entire surface of the rotor is a better idea, I'll do that instead.
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Two_seasons
Posted on Tuesday, June 29, 2021 - 03:38 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Or a rotor hone will work, but then you have to pull the wheel.

Hope you get it all out.

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Thefleshrocket
Posted on Thursday, July 15, 2021 - 05:12 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I did Scotchbrite galore, no improvement. For the heck of it, I used the dial indicator on the outside edge of the rotor, and the inside edge. Sure enough, there is more runout at the outside edge than there is at the inside edge. Conclusion--rotor is warped or bent. I ordered a new-to-me used rotor which arrived yesterday. I cleaned it thoroughly and will install it over the next couple of days.
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Two_seasons
Posted on Friday, July 23, 2021 - 05:23 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

keep us posted flesh
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