Brake pedal vibrations?

[Drifter995]

Ok, so, trying to figure out exactly what is causing this...

I'm fairly sure it's not rotor or pad related, but I'll give you the story anyway:

What the car does:
The pedal is fine for a while, mostly under normal driving and braking, however, sometimes it'll pulsate. Usually when presented with high load (ie, fast braking, braking from a high speed quickly, braking down hill)

The story:
So, I took the car into the mechanic to get it's service done, and I'd said I was after some slotted rotors for the sake of it. He said he'd have a look at my rotors, and see if they needed replacing, just because it'd be cheaper to machine them, then get slotted rotors (they were vibrating and being crap. The stock ones I mean). So, got a call later saying they were below minimum machine line, and that I was go for slotted rotors if I wanted. I said sure, and he said he'd chuck some better pads in as well (I mentioned track days earlier) suited for track work. Anyway, got them in, slotted dba rotors and some form of pads (unsure on what). They bed them in for me.

Hit up the track a few weeks later, got the hang of braking stupidly late. Was braking amazingly. Made sure not to sit on the brakes after a track event, so I didn't warp the rotors. Everything was fine before, during and after the event, and for a few days/ weeks.

After a while, it started vibrating during normal driving (mostly during more spirited driving, and sometimes just normal driving), but, not all the time. A lot of the time, it wouldn't vibrate at all.

Still does it on and off.

I've been told it could be due to the brake lines, and that upgrading to braided lines might be a good option, and should fix it, but I'm unsure. Car is overdue for a service, and he'd be a good person to ask, just want to make sure I get an idea of it, so we don't machine the rotor, if that's not it (which, it sounds like it isn't. And, by logic, it shouldn't be. Especially if it's on and off)

Ideas?
Rekon it's the brake lines? It does have stock lines in, which are a bit old iirc. Had a wheel alignment recently, some bushes are worn, but I can't see that affected slow and fast braking sometimes, not all the time. When it happens, it happens on both low and full brake. More prominent on stronger braking

Thoughts?

[Hondarally]

I can't see how it would be brake lines. Sounds like DTV (google it). It's likely that when they installed the new rotors, they didn't check them for runout (face runout needs to be less than 0.1mm, which you can't see by eye - you need a dial gauge). A small bit of dirt / rust flake under the rotor mounting case can cause this level of runout (I've done some testing with installing rotors, and it's amazing how much effect a small bit of dirt can have on rotor runout). SOme cars get it, others don't. Usually it will be ok for a while, then the problem comes on over time.

What happens if there is excessive runout (or a warped disc - don't rule that possibility out if they've been uber hot) is that part of the rotor might be touching the pad as the wheel rotates. This can wear that part of the rotor slightly, which then gives you the shuddering effect. On this same theme, the rotors build up a layer of pad material on them through normal use (bedding in the brakes achieves this film transfer). If this is worn away in places, then this gives differing friction coefficients in different parts of the rotor, which will lead to the shudder again.

If it is DTV, then machining the rotors will fix it. However, it the rotors are warped, or not installed correctly, then the problem will come back.

What brakes are they, anyway?

Oh, and finally, don't waste your money on slotted rotors, they do nothing for performance, and in fact remove the sintered / conditioned surface of the brake pad leading to diminished performance of the brake pads.

[amant02]

Okay so imam go against Hondarally here.

Slotted rotors way to go. I have found that you can abuse the pads for longer. Left foot braking is much easier. Helps the pads stay consistent. \
Plus them looks

Currently using DBA T2 + DS2500 + Braid lines.


Do your problem. - Check the screw that holds the rotor in?

What I do with these - I use 3/4 fitting on my impact so I can fit a large screw driver inside there. Hand tighten 1st make sure its on flat. You may have to clean the hub or mating surface with some sand paper. Then lightly use the DIY IMPACT SCREW DRIVER Technique. Careful not to tread it.

Also + 1 for braided lines. Don't jew on the brand. Its brakes that we talking about here.

[Drifter995]

Okay so imam go against Hondarally here.

Slotted rotors way to go. I have found that you can abuse the pads for longer. Left foot braking is much easier. Helps the pads stay consistent. \
Plus them looks

Currently using DBA T2 + DS2500 + Braid lines.


Do your problem. - Check the screw that holds the rotor in?

What I do with these - I use 3/4 fitting on my impact so I can fit a large screw driver inside there. Hand tighten 1st make sure its on flat. You may have to clean the hub or mating surface with some sand paper. Then lightly use the DIY IMPACT SCREW DRIVER Technique. Careful not to tread it.

Also + 1 for braided lines. Don't jew on the brand. Its brakes that we talking about here.

Figured it doesn't sound like warping, as it's on and off, not constant, as a warped or not properly installed one would suggest.

And yeah, slotted rotors seem to have much better cooling, and I'd assume a touch more bite from the slots. If they were pointless, they wouldn't be used so heavily for performance use. But, they are pointless if you haven't upgraded pads, which I did.


As for lines, was pointed towards goodridge. Will check the screw holding the rotor in, and see what that's like

[amant02]

Yeh I got goodridge way to go. Direct fitment. Looks a lot better then the rubber hose.

Also stronk recommend to buy the flarenut wrench. Like 12 bux at repco. The nut that secures the solid line to the flexible line is a flare nut. Using normal open wrench will tread em when torqued on heavy.

PS: I have a gut feeling your rotors could be warped. Cos what you have described was the exact feeling I got in the camry before rotors required changing due to being wrapped.

[amant02]

It used to be on and off, then one day it didn't go away. We change rotors and back to normal. But this was after about 110k KM on factory pad and rotor. Daily driven for business by mature old age man.

[Drifter995]

Hmm. Ah well, i'll take it in and get the mech to have a look and gauge them and what not. Definitely seems odd that they'd be warped and off and on...

[Hondarally]

Another internet myth. Warped rotors don't cause the pulsating. It's the effect of the warping that can lead to it, and yes, this can come and go as the layer on the pads and rotors changes over time (partly caused by the slotted rotors). Warped rotors would just slide your caliper, but this won't cause the pedal to pulsate. It's the DTV that causes pulsating.

Funny that everyone I know who's put slotted rotors reports that they feel so much better (placebo much)? However, when the rotors get put on the brake dyno, they show inferior performance. Discussing this with a guy who tests these for a living (is involved with R&D for a large brake manufacturer) they couldn't even match the minimum acceptable performance levels with slotted rotors during the design and testing phase. Why did they want to develop the range if it's inferior? For the bling value of course. Everyone knows that slotted brakes must be better, so this large manufacturer developed their own range, purely so that they can have a share of the "performance" market (despite proving in testing that they are inferior to their standard solid stuff).

I know a lot of people have invested heavily in slotted brakes, and of course retailers are going to push them because they're dearer. I'd rather believe real world testing from the engineers who actually develop these things, thanks.

The screw is only to locate the rotor without the wheel in place. With the wheel bolted on, the rotor is clamped on to the hub by friction. Those screws do exactly nothing at that point in time.

[Drifter995]

Another internet myth. Warped rotors don't cause the pulsating. It's the effect of the warping that can lead to it, and yes, this can come and go as the layer on the pads and rotors changes over time (partly caused by the slotted rotors). Warped rotors would just slide your caliper, but this won't cause the pedal to pulsate. It's the DTV that causes pulsating.

Funny that everyone I know who's put slotted rotors reports that they feel so much better (placebo much)? However, when the rotors get put on the brake dyno, they show inferior performance. Discussing this with a guy who tests these for a living (is involved with R&D for a large brake manufacturer) they couldn't even match the minimum acceptable performance levels with slotted rotors during the design and testing phase. Why did they want to develop the range if it's inferior? For the bling value of course. Everyone knows that slotted brakes must be better, so this large manufacturer developed their own range, purely so that they can have a share of the "performance" market (despite proving in testing that they are inferior to their standard solid stuff).

I know a lot of people have invested heavily in slotted brakes, and of course retailers are going to push them because they're dearer. I'd rather believe real world testing from the engineers who actually develop these things, thanks.

The screw is only to locate the rotor without the wheel in place. With the wheel bolted on, the rotor is clamped on to the hub by friction. Those screws do exactly nothing at that point in time.

Actually had a look at dtv then, assuming it's disc thickness variation, that actually makes sense. But at the same time, doesn't. Does seem weird that it'd happen from anything other than almost locking up the brakes, or very brief hard stopping (less than a full rotation)

[Drifter995]

As for slotted rotor debate. It is true there is less surface area, to reduce effect in a sense, but at the same time, they are much better cooled, and would be much better under heavy load for that reason. More than likely means harsher braking would be allowed, and fade would be avoided. I'd assume they'd be made of a different material to suit tougher pads

[Hondarally]

The problem is that the pads develop a layer of sintered material on the friction surface, which has a better friction coefficient than the parent material. Slotted rotors shave this material off the pad, effectively reducing the pads friction coefficient. The brakes tend to work more by abrading the pad than friction coefficient. Also the cooling effect of the slots would be negligible if anything.
The science behind braking systems is a lot more complex than most realise. I've spoken with brake specialists who have no idea about how braking systems work. They just know how to select components out of a catalogue and bolt them onto your car.

The problem is usually when people fit slotted rotors they are either:
A) replacing old shagged rotors
B) fitting new upgraded pads as well
C) replacing brake fluid.

any of these will improve braking performance, which people will inevitably attribute to the slotted rotors.

[Baby Face]

I had read about this phenomena as well, where ppl actually believed slotted or drilled or dimpled were more superior.
when these rotors have less mass and ability to store. believe the main reason for having slotted or dimpled is because some pads expelled a gas and the gas would push against the pedal so the dimples or holes helped by giving the gas places to be stored.