Brake Pedal Pulsation -- is it a safety issue?

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Had a debate with another tech about this one.

If your vehicle exhibits brake pedal or steering wheel vibration/pulsation when slowing from high speeds, is it a safety issue?

He says yes because the disc thickness variation may cause an increase in stopping distances.

I disagree - I think at worst, you may have slightly reduced control due to the shaking/vibrating steering wheel. So IMO, it is more of annoyance than a safety issue.

What do you folks think?
 
If severe i think it could be a safety issue, with non abs, it would be hard to modulate the brake pedal to just under lockup with all that pulsation feedback. I'm not sure how it would affect abs.
 
yes, because it can also mean or lead to one side of the pad is wearing more. It can also make that pad wear through faster and harder to know when that pad fails. So maybe it's good now, but when worn through and your brakes may fail completely it'll come all of a sudden cause you're used to loss of control when pressing the brakes .

I agree also that if it is shaking the steering wheel it is exerting left and right forces against the wheel. This reduces the physics of your inputs being able to execute and reduced actual control; It also puts extra wear on the steering components.
 
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I feel like it's a safety issue because you always have to remember to tightly grip the steering wheel. What if you forget to tightly grip the steering wheel and you're on a less than perfect surface?
 
Yes, I think it extends the stopping distance and it can cause an inexperienced driver to release pressure on the pedal.
 
Originally Posted By: qdeezie
I feel like it's a safety issue because you always have to remember to tightly grip the steering wheel. What if you forget to tightly grip the steering wheel and you're on a less than perfect surface?


Hmm, that's a great point that I had not thought of.

Given the responses so far, I'll probably reconsider my position going forward.
 
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Reduced braking effectiveness, since the pad is not fully contacting the rotor at all times as it would if the rotor was a flat surface.
 
Im assuming that the rotor is rigid enough that the feedback that you're feeling is the pad being pressed back (piston into its bore) on the high points, and the pad going down against the rotor on its low points? IOW, the pad is flexing to the rotor, not the other way around?

If this is the case, then Id say that it is not a safety issue, as it is felt due to compliance of the caliper piston to the irregularities, while maintaining a certain pressure.

If that is the case, then the friction is roughly constant and it is just feel.

Otherwise, it might be a safety issue.
 
Well I notice this phenomenon when I'm going 100 mph trying to slow down to 55 to make a comer. Now in regular instances of say from 75 to a lower speed or from 65 to a stop the vibration is non existent. In the first instance I am thinking it is just rotors getting very hot attempting to slow down from a very high speed.
I do wonder though if I may well need new rotors before too long. They are original. But again, in 98% of the time there is ZERO vibration.
 
I would default to a safety issue until an investigation proves it is a harmless mechanical issue.

Consider mid to hard braking on a reducing-radius curve with and without the pulsation. If the condition was benign yet caused inadviseable driver input you could easily find the vehicle crossing from the inside to outside (oncoming) traffic lane.

I'm a little anal when it comes to tires / wheels / brakes / suspension to the point where that is the first thing I address when I buy a used vehicle (let's see here .... Hmmmm ... yep, that would be *all* of my vehicle purchases) before I consider any power improvements.

Maybe not the average owner's priority list but it really works well for me. I'd look into it and probably fix it even if not a safety issue. YMMV.
 
Originally Posted By: bbhero
Well I notice this phenomenon when I'm going 100 mph trying to slow down to 55 to make a comer. Now in regular instances of say from 75 to a lower speed or from 65 to a stop the vibration is non existent. In the first instance I am thinking it is just rotors getting very hot attempting to slow down from a very high speed.
I do wonder though if I may well need new rotors before too long. They are original. But again, in 98% of the time there is ZERO vibration.


That is severe braking demand, many times the heat load of a 70-0 stop. You can buy paint that changes color at a given temperature. If you are willing to investigate further you could try and determine what rotor and caliper temps you are generating. That might lead to a decision to increase pad swept area, rotor diameter, or calliper piston count.
 
If the pulsation is from the varying thickness of the rotors, that is not a safety issue.
Sounds like one of those scams the dealerships pull on clueless normal people.
 
It's either a warped disc, or your ABS cycling.

Disconnect all your wheel speed sensors and go for a drive, then you'll know if it's wheel speed sensors or abs pump.
 
It is a safety issue as you can't threshold brake as effectively, eg, use almost all the friction without locking the wheel up. ABS doesn't really matter, as when that kicks in, you've already over-driven the circumstances. In fact I'd be curious about what frequency of pulsing it can provide per rotation at various speeds vs the "high spots" or "sticky spots" (if a pad transfer is involved).

Half the rotation of the wheel isn't being done with maximum clamping force.
 
On normal, dry pavement it's just an annoyance. But in the winter on icy roads it is a significant safety hazard if the brakes don't grab the rotor evenly and smoothly.

But either way it should be fixed.
 
On a non-ABS car, rotor warp will tend to increase the chance of wheel lock up during a hard stop in the rain. A panic stop in the dry may also experience more lock up. Not a major safety issue, just be more careful if the warp is severe. Rotors are pretty cheap these days. Break new ones in gently.
 
It depends on circumstances at the moment of use. I was living with rough, rumblely oem brakes because there was at least 50% pads left. Early this year, I had to do a panic stop and nearly didn't make it. A few weeks later I had new pads and rotors.
YMMV
 
Originally Posted By: The Critic
Had a debate with another tech about this one.

If your vehicle exhibits brake pedal or steering wheel vibration/pulsation when slowing from high speeds, is it a safety issue?

He says yes because the disc thickness variation may cause an increase in stopping distances.

I disagree - I think at worst, you may have slightly reduced control due to the shaking/vibrating steering wheel. So IMO, it is more of annoyance than a safety issue.

What do you folks think?
"Full time ABS".
 
After reading the replies, I decided to go ahead and do the brakes on the gf's dad's ride for him. I put in updated dealer pads (per the TSB), Centric 120 series premium rotors, a new OEM fit kit (abutment clips) and confirmed that rotor runout is less than 0.001" on both front corners after installation.

The problem appears to be mostly solved, but there is still some pulsation coming from the rears; I'll get to that some other time.

Originally Posted By: HerrStig
"Full time ABS".


Good one.
lol.gif
 
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