Pulsing Front Brakes

[Speeda]

My brakes started pulsing at high speeds just before entering turns but wasn't as noticeable at low speeds. So I ordered new rotors but kept the old brake pads because they had a lot of meat left on them. Took it for a test drive and I still felt the pulsing, except the opposite, now at high speeds. I'm fucking pissed because the new rotors cost me a bundle and didn't solve the problem. Everything is tight in the head and caliper and torked to spec. The only thing I haven't done is bleed the brakes. Could that be the issue? I would like to resolve this as soon as possible. Any Ideas?

 

[stan23]

I would change the pads.. The pads may have uneven wear from the old warped rotors.

Also check the steering head bearing to make sure it's torqued to factory specs.

 

[gixxerjeff]

Warped brake rotors....^^^ what he said.

Edit: read the post too fast. Didn't see the rotor comment.

 

[eldiabloe1]

To be sure it isn't the rotors do a quick run out check. You can put the bike up on stands and use a can of WD40 with a straw to check run out. Basicly sit the can down next to the tire and point the tip of the straw at the rotor. Let the straw sit as close as you can to the surface of the rotor without touching it and then spin the tire. If the rotor is warped you will see it. If that show your rotors are good then toss the pads. The pad contact surfaces are matched to the old rotors as stated by Stan. The process of bedding in brakes basicly matches the face of the pads to any imperfections in the surface of the rotor. Trying to fit them to a new rotor can cause problems because of the previous pad wear. What rotors did you purchase?

 

[Speeda]

Hey guys thanks for chiming in. So the warped feeling started immediately, with the old pads, so I bought new pads and installed them. The old pads barely made a scratch on the new rotors. What my mechanic said was maybe that the caliper pins may need lubrication so they can move back and forth. I'm going to try the straw maneuver, and se if the rotors are screwed. Still pending!

 

[gixxerjeff]

Ten bucks says you're gunna need rotors.

 

[ST Guy]

FYI, a dirty spot on the rotor will cause what most people will describe as a pulsing, and it has nothing to do with a warped rotor.

A warped rotor can usually be felt in the brake lever. But regardless, the only way to tell if the rotor is actually warped is to use a dial indicator and take a reading on the rotor.

A dirty rotor, one where there's a small area that is contaminated or different in some way will produce an alternating increase and decrease in the braking force simply because as the rotor turns, the pads alternately are gripping a higher coefficient of friction area and then a lower one. The lower one usually being the contaminated area. Rotors with this problem can often be cleaned. Try brake cleaner first. If that doesn't work, brake cleaner and Scotchbrite pads.

First, though, you need to rule out true warpage. And unless you're really, really used to seeing very tiny differences in things, putting a small tube up against the rotor and watching he gap won't tell you anything. You're eye can't tell the difference. Sometimes rotor warp tolerence is in the range of +/-0.003". That's about the diameter of a human hair. So, measure the rotor properly. If it checks out, then it's a dirty or otherwise damaged rotor.

And bleeding the brakes won't have anything to do with it one way or another.

 

[Speeda]

Thanks for the reply, the last statement made a lot of sense, because when I took the old pads off there was a inconsistant residue on the rotors. How it started was I installed the rotors, put the calipers back on and went for a test ride. There was no warped feeling at first but as I pulled in the driveway and headed for the garage there was a slight feeling of which I attibuted to the pads wearing in. I did notice a black residue on the rotors though but, I felt after a few rides that would automatically go away. I coud in fact still have bent rotors, but as I mentioned, I was having the same issue with the origional rotors. I'll try anything at this point and last resort replacing the rotors.

Good feedback, thanks!

 

[clutchslip]

ST Guy's post was good.

However, you have not mentioned any other normal maintenance, except tight bolts. If your caliper is not function properly, it will cause this sensation. Did you clean the rotors? Are the caliper pods working correctly? Etc. I would go through all the basic maintenance issues before replacing rotors, which are expensive. And in my experience, rarely warp.

Edit: In addition, if the pads are contaminated, they, too, will cause this sensation.

 

[frozenduc]

My brakes started pulsing at high speeds just before entering turns but wasn't as noticeable at low speeds. So I ordered new rotors but kept the old brake pads because they had a lot of meat left on them. Took it for a test drive and I still felt the pulsing, except the opposite, now at high speeds. I'm fucking pissed because the new rotors cost me a bundle and didn't solve the problem. Everything is tight in the head and caliper and torked to spec. The only thing I haven't done is bleed the brakes. Could that be the issue? I would like to resolve this as soon as possible. Any Ideas?

DO you have new rotors on or the old ones.
If the old ones take them off and use this rotor hone to remove pad residue.

 

[kiltwearinfool]

+1 on STGuy's post. And the advice about ensuring your caliper pins are clean & lubed.

One more thing to add to the bag of diagnostics and "didja try": On floating discs, be sure the bolts between the disc and carrier are clean and free of brake dust. I had a similar problem on a bike a few years back, one mechanic said I needed new rotors and pads. When I took it in for service, a different mechanic tried cleaning the carrier bolts with brakleen, and that did the trick. $4 fix, gotta love it. Apparently the brake dust builds up over time and prevents the rotor from freely centering itself in the caliper when the brakes are applied. Brakleen is now part of my regular maintenance and pre-trackday prep routines

 

[Nemesis]

Good posts guys!

IME every time I felt pulsating or rather crazy chatter in the front brakes it was because I failed to torque down the pinch & axle bolts after a tire swap. Another was I was going ballz out hard braking in the first lap when I should be light brakes on the first lap or so. After that I never experience chatter/pulsating brakes.

Again, this is purely my experience.

 

[planegray]

+1 on STGuy's post. And the advice about ensuring your caliper pins are clean & lubed.

One more thing to add to the bag of diagnostics and "didja try": On floating discs, be sure the bolts between the disc and carrier are clean and free of brake dust. I had a similar problem on a bike a few years back, one mechanic said I needed new rotors and pads. When I took it in for service, a different mechanic tried cleaning the carrier bolts with brakleen, and that did the trick. $4 fix, gotta love it. Apparently the brake dust builds up over time and prevents the rotor from freely centering itself in the caliper when the brakes are applied. Brakleen is now part of my regular maintenance and pre-trackday prep routines

I can't figure out what part(s) you're talking about cleaning..

is it the buttons on the rotors ? surely not the bolts that hold the rotors to the wheel hub ? maybe the pins that the brake pads slide back-n-forth on ?



thanks in advance

 

[ST Guy]

In addition, if the pads are contaminated, they, too, will cause this sensation.

Actually, they won't.

If the contamination is localized in one or more spot on the disk, then as the disk sweeps through the pads, areas with more or less friction are gripped by the pads and thus, you get the pulsing feeling.

However, if there's a contaminated spot on the pad, it's always in contact with the rotor, regardless of the position of the rotor, and thus, there's no alternating between areas with more or less friction.

 

[frozenduc]

I can't figure out what part(s) you're talking about cleaning.. is it the buttons on the rotors ? surely not the bolts that hold the rotors to the wheel hub ? maybe the pins that the brake pads slide back-n-forth on ?

Good thought.
OP: Give the buttons 1/4 turn. Sometimes they stick and won't allow the disc to move around like it should. I use a snap ring pliers and expand it on the ID and give em a twist.

If your bike doesn't have floating rotors ignore my suggestion.

 

[Matt.Lai]

I once had the exact same experience you had. I changed everything at least once (rotors, pads,brakelines), including the use of new parts. Everything was torqued to spec, the pins were flawless and I was one stumped chimp. I even had Galfer send me yet another new rotor!

My brain kept saying: it couldn't be the fluid. . . fluid doesn't cause any sort of pulsing that I'm experiencing. Nothing I've read or nobody I ever spoke to said that brake fluid could cause this issue. ITS NOT THE BRAKE FLUID. ITS NOT THE BRAKE FLUID. IT CAN'T BE THE BRAKE FLUID.

And I continued to try different parts combinations and did some mild bleeding, all to no avail. Finally, at whits end, I completely flushed the hydraulic system and re-bled. New fluid top to bottom. Guess what. NO MORE PULSING. It was the brake fluid. A very surprising conclusion, as far as I was concerned.

Flush, refill and bleed. Its a simple strategy of "eliminating the obvious." It may not be the cause, but you might be surprised. I was.

 

[ST Guy]

I once had the exact same experience you had. I changed everything at least once (rotors, pads,brakelines), including the use of new parts. Everything was torqued to spec, the pins were flawless and I was one stumped chimp. I even had Galfer send me yet another new rotor!

My brain kept saying: it couldn't be the fluid. . . fluid doesn't cause any sort of pulsing that I'm experiencing. Nothing I've read or nobody I ever spoke to said that brake fluid could cause this issue. ITS NOT THE BRAKE FLUID. ITS NOT THE BRAKE FLUID. IT CAN'T BE THE BRAKE FLUID.

And I continued to try different parts combinations and did some mild bleeding, all to no avail. Finally, at whits end, I completely flushed the hydraulic system and re-bled. New fluid top to bottom. Guess what. NO MORE PULSING. It was the brake fluid. A very surprising conclusion, as far as I was concerned.

Flush, refill and bleed. Its a simple strategy of "eliminating the obvious." It may not be the cause, but you might be surprised. I was.

Please explain how it could possibly be the brake fluid. I say your experience was coincidence and the actual cause was something else.

 

[clutchslip]

Actually, they won't.

Actually, they can. Been there. Done that.

 

[LongGoneJohn]

Please explain how it could possibly be the brake fluid. I say your experience was coincidence and the actual cause was something else.

I believe it.

Fluid breaks down, and when it does, you can get all sorts of wonky issues.

 

[gixxerjeff]

I believe it.

Fluid breaks down, and when it does, you can get all sorts of wonky issues.

Meh....a spongy lever maybe, but pusling? Naw, that's a pad/rotor thing.
St guy makes a lot of sense.

Extra points for the use of the word *wonky* though.