Brake Question - pulsing

[bikerboy337]

So I'm trying to figure out whats going on... have a fairly new set of wheels that i just started using again. Problem I'm having is a pulsing as i brake. I've swapped brake pads, cleaned them and all is good with teh brakes/pads. I've inspected the rims, no noticable bumps, hops, out of true, etc. I haven't put it in a truing stand, but i've spun it with a tool just off the rim and there are no wobbles/hops that I can identify...

any idea why i might be getting a pulsing when i brake? its my front wheel by the way...

any thoughts would be appreciated. Going to drop off at my LBS this afternoon... but wanted to see if anyone had any ideas...

thanks...

[AngryScientist]

it almost has to be some irregularity in the rim. slight concavity or something you might not see without a truing stand can definitely cause braking pulsations.

[christian]

Can you put it on your other bike to try to isolate whether it's the brakes or the wheel or something else? Do that and report back.

[bikerboy337]

Agreed... as i was typing the original questions this morning... i realized that I haven't swapped wheels between frames... so that will be my next step... i just took a flat edge screwdriver and held it just off the rim and spun... no noticable wobble, dips, etc that i could notice

i'll swap the wheels and report back...

fun stuff...

Thanks! :beer:

[keevon]

Did you toe-in your brake pads? I can usually eliminate pulsating this way.

A credit card positioned under the back 2-3mm of the brake pad seems to be just about right.

[yashcha]

Is it a Kinlin rim?

I just took apart my wheel built with a kinlin 300 rim because it pulsed so badly that the whole front end would shake during braking. I have heard of many others complaining about this issue as well. The problem with my rim is that there are several sections where the rim width meaures narrower than the rest of the rim.

My solution was to replace the rim with a Velocity A23 .

[MattTuck]

Can you put it on your other bike to try to isolate whether it's the brakes or the wheel or something else? Do that and report back.

I like this... sounds very scientific. :beer: :beer: :beer:

[Joachim]

Not sure what headset you have on there, but sometimes a loose headset can cause pulsing when braking.

[christian]

Not sure what headset you have on there, but sometimes a loose headset can cause pulsing when braking.
You are a scientist, yet you are jumping, nay, leaping, nay bounding madly to conclusions. I think this is a likely scenario, too, but let's get there methodically! :)

[Joachim]

You are a scientist, yet you are jumping, nay, leaping, nay bounding madly to conclusions. I think this is a likely scenario, too, but let's get there methodically! :)

What can I say, I had a cup of coffee and threw all reason out the window during a time of complete and utter madness.

[bargainguy]

Rim weld that isn't finished properly. I once spent hours chasing my tail (truing, repacking hub etc.) until I figured it out.

Don

[bikerboy337]

Thanks for all the thoughts folks... these are Campy Zondas by the way...

i'll test a few things out tongiht before I take it to the LBS tomorrow....

I'll update once I figure it out...

Definately not the headset.. have a CK headset, plenty tight... I had that thought too though...

We'll see!

[Ken Robb]

Make SURE there are no contaminants any where on the rim. Something you can't see or even feel with your fingers can cause a variation in coefficient of friction and lead to pulsing brakes. I use aerosol brake cleaner for automobile brakes to be sure I get everything off.
I'm assuming you mean the brakes seem to grab and release a little while you maintain steady pressure. If you get pulsation through the brake levers it must be a mechanical problem. I wonder if there can be a weak or thin place in the rim that "gives" a little under pressure from the pads.

[mister]

brake pads are probably worn enough to cause this chatter
replace them or try toeing them in like previously mentioned

[bikerboy337]

THIS... is one of my other thoughts... i'm going to be cleaning the rims tonight as well... making sure they're nice and clean... there is a good bit of brake pad on the rim from a set of campy pads i had on this bike... swapped to kool stop as i like em better, but i'll clean off the residue thats left...

Make SURE there are no contaminants any where on the rim. Something you can't see or even feel with your fingers can cause a variation in coefficient of friction and lead to pulsing brakes. I use aerosol brake cleaner for automobile brakes to be sure I get everything off.
I'm assuming you mean the brakes seem to grab and release a little while you maintain steady pressure. If you get pulsation through the brake levers it must be a mechanical problem. I wonder if there can be a weak or thin place in the rim that "gives" a little under pressure from the pads.

[Vientomas]

Is this correct?:

1. Owned wheels for a time and have used them previously with no problems.

2. The only recent change in parts to the bike you used the wheels on are new brake pads.

The problem would appear to be related to the new brake pads. Replace new pads with old and see if problem continues.

No problem with old pads then it looks to be a new pad or old pad residue issue. Did you replace the pad only, or the carrier and pad. If you replaced the carrier and pad, your toe-in may be off. If you only replaced the pad then old pad residue may be the culprit.

Good luck!

[hokoman]

call me crazy, but i had that problem with a steel fork once. the thing would deflect when i applied the brakes and made me think that i was having pulsing/ :) braking issues - i swapped to a carbon fork and it was gone. i know this is out of left field, and others will shake their head... but that's my story and i'm stickin' to it.

[mister]

^ yeah i've had that too

but the fork is not the cause of the brake chatter and switching the fork does not solve the problem
the chatter is still there, it's just damped differently with a carbon fork vs a steel fork

[rustychisel]

if you can't see and feel a wheel pulsing, and it's brake related (rather than say a sticky dragging hub seal, a flat-spotted bearing... etc) then perhaps you've knocked the brake shoe out of adjustment so that the block rubs off the rim and is clipping the tyre...?

[thwart]

I've had this happen, and then the next ride the front brake popped right off and landed in my hand, still attached to the cable and housing... I'd loosened it to adjust the centering and not re-tightened it properly.

And no, I never found the fastening nut... :rolleyes:

[bikerboy337]

Think i've solved it, not sure how this happened though...

the rim had several small spots on it where specks of rim were raised... small, pieces of sand sized pieces of the rim were raised... i was able to use the red automotive wool to remove the spots on the rim and remove any pad debris that was there... haven't been able to ride them as of yet, but the rim surfance is super smooth now and it appears that the hop/pulsing is gone...

not sure how these little burrs happened, I'm guess i must have had some debris in the pad for a small time and it caused a few burrs to form on the surface... the pads are clean now, so not sure if that was it, but thats my guess...

I could only feel the little burrs if i ran my fingernail along the rim, but they were there and in the spots where i was getting a pulse (2 different locations)

thanks all for the thoughts!