Severe pulsing in front brake lever

Bike in question is a 81 KZ1000 CSR, triple disc, two front / one rear. The bike has just undergone a 7 month down to the frame rebuild. From the very first ride out of my garage and the very first application of the front brakes, the bike hobby horses under braking and the front brake lever visibly pulses a 1/4" or more even under a very firm 2 finger squeeze, it will move your fingers no matter what! It is bad!

If you use only the front brake to come to a stop, it's as if the front brakes catch and release and the front end bounces wildly to an unpredictable stopping point, even with a light application. At higher speeds it is not as bad but I belive it is just due to the frequency of the pulsing being higher, but the felt pulse in the lever is just as bad. When the bike is up on Pit Bull stands, the front wheel spins freely, but you can hear the drag as the wheel passes a certain spot, and it often stops abruptly when it has slowed to nearly a stop and passes the bad spot. Again spinning the tire by hand rapidly and eyeballing the rotors, they look true. They also appear to be bolted flat to the hub.

The rear works perfectly.

The braking system was totally rebuilt and I am trying to track this down before spending any more money. The stock rotors were turned at a local machine shop on a flywheel machine using a brand new cutting bit. They looked beautiful with the swirl marks from the cutting. They looked smooth as glass! I would never have believed there could be any issues with them!

All calipers were stripped bare, powercoated, flushed with endless amount of brake cleaner and care prior to reassembly and rebuilt with K&L seal kits and NOS OEM pistons. The pads are new Ferodo. The sliding pins with rubber bits that the caliper rides on looked perfect and were lightly greased. The front master cylinder is a 2002 Kawi ZX9R. The rear master is a 2002 CBR954RR. The lines are all HEL stainless custom length jobbies.

Now with such a huge pulse I would think warped rotors. I borrowed a dial indicator from work but I cannot get the bike (hung from Pit Bull stands) and the indicator stable enough to get a good reading. I am going to try to get an outside micrometer tonight and mic the rotors in several spots and radiuses. I believe it to be a low spot in one of the rotors.

Does anyone else have any ideas? I thought about maybe removing one of the two front rotors, and putting somthing in between the brake pads of the caliper without a rotor and going for a 20 mph test drive in my apartment complex to further diagnose the problem.

I would love a suggestion! I have got about 300 miles on the bike since rebuild, and i basically only used the front brakes at high speeds, and then had to transition to rear brakes as i came to a stop to avoid the bouncing front end and unpredictable stopping point. They were farily strong at higher speed but the shudder they induce cannot be safe. I wouldn't touch them in the wet! BOOM, faceplant!

I would have thought that you would have a rotor visibly bent to get this bad of a pulse.

Any idears fellers...?



Thanks!

sheik*yerbouti wrote:

. . .front brake lever visibly pulses a 1/4" . . . you can hear the drag as the wheel passes a certain spot, and it often stops abruptly when it has slowed to nearly a stop and passes the bad spot. Again spinning the tire by hand rapidly and eyeballing the rotors, they look true . . . They also appear to be bolted flat to the hub . . . The stock rotors were turned at a local machine shop on a flywheel machine using a brand new cutting bit. They looked beautiful with the swirl marks from the cutting. They looked smooth as glass! I would never have believed there could be any issues with them!
. . .Now with such a huge pulse I would think warped rotors. I borrowed a dial indicator from work but I cannot get the bike (hung from Pit Bull stands) and the indicator stable enough to get a good reading. I am going to try to get an outside micrometer tonight and mic the rotors in several spots and radiuses. I believe it to be a low spot in one of the rotors.
Does anyone else have any ideas? I thought about maybe removing one of the two front rotors, and putting somthing in between the brake pads of the caliper without a rotor and going for a 20 mph test drive in my apartment complex to further diagnose the problem.

I would love a suggestion! I would have thought that you would have a rotor visibly bent to get this bad of a pulse.

Any idears fellers...?

I have a few.

I bolded what you said, to affirm your suspicions.

It's a rotor issue, but not neccesarily warp.

When you put the rotors on, did you use a torque wrench to set bolt tension identically? Clean the mounting bolt threads, so that they all pulled down evenly while mounting the rotors?

Rather than pull a wheel to pull a rotor for testing, I would disconnect a caliper, and wire it aside, placing some kind of block between the pads on the disabled caliper to keep the inactive side from spitting out parts.

That will maybe isolate one side of the bike as to a bad rotor issue. Don't retorque anything until you find which side is warped.

Because you had the rotors machined, it isn't likely in my mind that there is a problem with them.

Offhand, I don't know how thick a human hair is, or a sheet of notebook paper. But that thickness varience could give you a warp you would never see. A loose mounting bolt or a mounting surface that wasn't true would give you the same symptom.

There is a possiblilty that the mounting area between rotor and hub has induced the warp, due to overlooked rust, corrosion, or dirt of some kind when the rotor was mounted.

As far as the dial indicator, I think if you were to turn the fork to full lock, and then test while holding it against the stop, you might find a reading you could work with.

Hope some of this gets you started on a path to a sucessful stop. . .

i think id check runout of both rotors and the wheel itself. maybe you got a wheel bearing that isnt seated quite right and when you apply the brakes its being pulled to center?? this is a maybe...steve

hey guys thanks for the replies...

well i've dropped the front rotors back off to the same machine shop and i talked over the issue with the owner.

he said he would jig them up and indicate them tonight or tomorrow, so hopefully that will tell me somthing.

i did torque them to spec with clean mating surfaces, and freshly wire wheeled bolt threads. as there are only 4 bolts per rotor i just did a figure 4 tightening pattern. when i loosened them all, they were all the way down flat and tight plus loctited. the hubs were blasted and freshly powdercoated so the mating surfaces looked like a brand new piece of aluminum.

it was so severe, pulse doesn't even totally describe it. imagine that the front brake lever is geared to the front wheel and the brake lever moves in and out in perfect time to the wheel rotation speed.

i found EBC full floating rotors for my 81 CSR parts MD4080LS / RS for about $169 each. If this machining redo doesn't do it, I'm just going to buy the new rotors. After an $8,000 cafe build, whats $340 to be able to pound the front brakes with utter confidence. plus they'd be full floaters...

thanks for the ideas guys, if reground rotors or new rotors don't fix it, i'll be trying any and all suggestions (and crying tears of twenties on my EBC rotors...)

I'm sure it's the rotor.

I just had the same problem with my 400 rebuild. The rotor that I got with my new front wheel had a low spot on it - like almost a millimeter different. I would be bounce-bounce-bouncing to a stop, it was kinda funny, but annoying.

No biggie for me, being a single disk... I just pulled one off the shelf and threw it on... smooooooth as silk...

well the owner of the shop re-machined my rotors this AM and found them anywhere from .004 to .009 thousandths out of true. he thinks that his employees didn't have them flat against the machine and so they were kinda cut at a slight diagonal as compared to where they mount to the wheel hub.

for that small of an amount out of true, i would say this isn't going to fix that severe of a visibly pulsing lever *except* if they were 'on a diagonal' in relation to the mounting surface. if it was all parallel i could see feeling a some pulsing, but not making the brake lever move in and out somthing like a 1/4 to 1/2" like it's geared to the front wheel rotation, even under firm braking enough that you would think the calipers would slide on their pins and absorb some of that movement.

anyway i'm just about to head out on lunch and pick them up. i'll bung them back on ASAP tonight and go for a ride and find out.

i just can't imagine have a perfectly smooth lever of of nine-thousandths especially when the runout limit spec in the service manual is way more at 15-thousandths ... but i'm sure hoping!!!

will advise ...

sheik*yerbouti wrote:

...the hubs were blasted and freshly powdercoated so the mating surfaces looked like a brand new piece of aluminum....

Maybe misinterpreting the re-assembly information, but am wondering --

Is a layer of powdercoating now situated between the rotor and hub instead of the earlier metal to metal fitment? Am wondering if the varying thicknesses of powercoating on a previously uncoated mating surface has skewed the fitment by preventing perfect alignment of the rotor (disk) with the wheel. In other words, is the plane of the disk now slightly different from the plane of the wheel?

Patton wrote:

sheik*yerbouti wrote:

...the hubs were blasted and freshly powdercoated so the mating surfaces looked like a brand new piece of aluminum....

Maybe misinterpreting the re-assembly information, but am wondering --

Is a layer of powdercoating now situated between the rotor and hub instead of the earlier metal to metal fitment? Am wondering if the varying thicknesses of powercoating on a previously uncoated mating surface has skewed the fitment by preventing perfect alignment of the rotor (disk) with the wheel. In other words, is the plane of the disk now slightly different from the plane of the wheel?

i had thought of this as well. all mating areas of the disc to stock CSR hub were protected from the pcaot but were blasted. the powercoater ( www.streetwerkz.com ) was familiar with the potential for this problem because i told him just pcoat the whole hub evenly and he said no no no...gotta mask :)

the mating surface was hit with a quick blast of media so it is possible that it could be askew. but let's hope not because it's laced to about $675 of Buchanan's front wheel. i don't even want to ponder that... :eek:

the promising news is that my rotors are now picked up and are look great. he also milled off the high spots of the back side of the rotor that mates with the hub so they may help / may hurt. its clearly visible that the whole back was not hit, just the a few areas. he said "a thousandth or so"

the remaining front disc material is still at .230" where as the min thick stamped on them is 4.5mm ~ .177" so i'm ok there.

also the whole rotor is within a half thousandth of flat (.0005") as is the mounting area that bolts to the hubs...

we will soon see, i get off work at 5PM EST and should be taking a test ride by 10PM and you can bet your bottom euro / shilling / peso / dollar I'll be here singing the praises of a skilled machinist over a rookie machinist -- or crying in my Budweiser that my powdercoater fubar'd my hub that is now laced to...$600...of...(choke)...Buchanan's...(tear)....(drip)...front wheel...(sob)..... :huh: :S

This has been a thrilling read and I want to see what happens next GO RIDE YOUR BIKE, I want to know!

slickware wrote:

This has been a thrilling read and I want to see what happens next GO RIDE YOUR BIKE, I want to know!

thrilling for you, suspensful for me!! all this money and time, and she sure looks the part, but man i built it to rail the SE Ohio twisties, and I need me some front brakes!

the reassembly *will* happen tonight, but the testride may be in jeaopardy!

it's coming my way!!! ahhhhhh!!! :woohoo:

sheik*yerbouti wrote:

. . . the testride may be in jeaopardy!

it's coming my way!!! ahhhhhh!!! :woohoo:

Looks like the face of a green monster. . .

Hope your brakes ain't broke no mo'

If you still have the pulsing, I would work harder on setting up a dial indicator to measure the runout of the discs installed on the wheel, with the wheel spinning on the axle. That will narrow down which side is the problem. Always look at what you did that was new, first. You have two things: the disc resurfacing, and the new wheels. You should also make sure your wheel bearings are in A-1 shape. I can tell by your symptoms that it is not the calipers, or the caliper slides. I am betting on the discs, or the mounting surface to the wheels. You could have that mounting surface machined without ruining the wheels, but you may need to install a thin shim to make up the difference if it is significant. It will show up as the calipers being misaligned with the centerline of the discs.

One more thing: Is your axle straight and true? A bent axle could cause this problem.

Keep us informed. We want to know the answer to the puzzle!
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Post edited by: apeman, at: 2007/08/09 20:24