Disc pulse.

[SteveD]

What is the reason that a disc (or rotor) develops a pulse?

It seems to be an issue with airheads. Is there something that can be done to avoid it occurring?

I have previously been told by a local cast iron disc manufacturer that heat will warp a disc due to a hot spot. The scenario given was when enjoying spirited riding and braking, then stopping but leaving the brake on...encourages the hot spot and warpage, hence the pulse. That's easy to avoid but is it the only scenario/answer?

[Motorhead]

warp comes for lots of reasons even time as metal ages

or heat treat methods not fullly followed I'd feel better with a thicker disc as use and warp can happen even if your system is long in tooth

there was some aftermarket that has some merit

[Jean]

The solid rotors are more likely to develop a pulse, Steve, as the holes in the later ones help keep them cool, as well as shed water, etc.
Rotors that have been ground or turned to minimum thickness are more likely to warp from heat just because they are thin, so that may be why Airheads are thought to be more likely to have the problem.
Stainless rotors may pulse if they have been turned and have areas that are not as smooth as adjacent areas. 300 series stainless steel is really bad to have micro-whiskers after machining. I think you can imagine how this would affect the pad-on-rotor action.
My rotors are maleable iron, not cast-iron, although they are made by a casting process. There is a BIG difference.

[Duane Ausherman]

I seem to be able to drive my cars for a long time without warping the discs. However, Linda can warp a disc in only a few days. I wish I knew how to get her to prevent whatever it is that she does.

All of our cars have at least one warped disc that I can feel a pulsing. I hate it.

[Major Softie]

I seem to be able to drive my cars for a long time without warping the discs. However, Linda can warp a disc in only a few days. I wish I knew how to get her to prevent whatever it is that she does.

All of our cars have at least one warped disc that I can feel a pulsing. I hate it.

That is really weird. It would be very interesting to know what it is she is doing that makes the difference.

It does make sense though. If things become warped just by being around her, it certainly explains Diane.

[Chuey]

Hi Jean, I always enjoy your posts.

Are you saying you have some aftermarket discs? I have a bike that I'm planning on replacing the discs on. I was thinking of the EBC floating type. Is that what you have? I wouldn't mind better braking a bit.

Thanks.

Chuey

[Jean]

No Chuey, no floating disks.
Just drilled, "cast" iron ones. If I don't ride often they get a fine dusting of rust that must be polished off with fine sandpaper. The holes make a buzzing sound on the pads (or is it the other way round?) that annoys some folks but I'm used to it.
And I don't know the supplier. My ex got them from his stash and we installed them about 20 or so years ago.
Dual disks on the front and stainless steel lines with small MC and I can lock the front wheel all too easlily.
How much better can you get? ( Are there different degrees of pucker-butt?)

[SteveD]

I seem to be able to drive my cars for a long time without warping the discs. However, Linda can warp a disc in only a few days. I wish I knew how to get her to prevent whatever it is that she does. Does Linda "ride" the brakes at all?

All of our cars have at least one warped disc that I can feel a pulsing. I hate it.

Since my chat with the ci disc maker I've developed a habit of a rolling stop. That means, when stopped, I move the car or bike forward a tiny bit and more than just once or twice, whilst stopped with the idea of moving the hotspot along the disc to reduce the chance of warping.

I have no idea if this is the main reason a disc warps. I suspect not, as even with that technique, I now have two (fr R & r) discs with a pulse.

Is there something in the way they get assembled onto the wheel that does it? It seems straightforward..place disc on the wheel, all surfaces clean, bolt on, tighten nuts to specified torque. What can go wrong?

I googled this question and here is one response I found.

This problem is most often caused by dragging the brakes from high speeds slowing down gradually and causing the brakes to heat up and then sitting at a stop with your foot pressed firmly on the brake when they are really hot...Another common cause of the brake pedal pulse is that a tire or wheel rim is out of round or a tire tread is seperating, or tire underinflation.

In looking at this question the other side of the friction is the pads. What effect will pad choice have on heat and warpage of the disc?

[Jean]

On the old disk-brake bikes, the MC set-up was critical to allow the pressure in the brake line to be relieved. If the MC piston actuator wasn't adjusted for a certain free play with a little gauge, the pads would drag on the disks and heat-up badly. Sometimes they could even lock-up when you were running along...most distracting.

Having enough free play in both the hand lever and at the foot lever to prevent actuation while 'covering" the brakes is important to prevent the pads from actually being in hard contact all the time.

Riding the brake pedal (in a car) could do the same thing. I think just touching the pedal is enough to cause the pads to drag more than float as they are intended.

[Major Softie]

On the old disk-brake bikes, the MC set-up was critical to allow the pressure in the brake line to be relieved. If the MC piston actuator wasn't adjusted for a certain free play with a little gauge, the pads would drag on the disks and heat-up badly. Sometimes they could even lock-up when you were running along...most distracting.

Having enough free play in both the hand lever and at the foot lever to prevent actuation while 'covering" the brakes is important to prevent the pads from actually being in hard contact all the time.

Riding the brake pedal (in a car) could do the same thing. I think just touching the pedal is enough to cause the pads to drag more than float as they are intended.

Of Course! So, a left-foot braker could definitely cause such a thing. What foot does the Mrs. brake with, Duane?