AP Racing, Freaky Parts, 996, Cooling? School me on BBK to help pad consumption

[Pklauser]

Valid question, DSC is totally off when I'm on track.

On the ABS side of things, let me explain with a general update. I just spent three days on Summit Point Main, where I was experimenting more with double-tapping the brakes to fight knockback. Double-tapping has made a huuge difference in my braking, and is helping me stay out of ABS. My assumption is that the knockback in the front was causing the rear to lock up, getting me into ABS. Heck, since double-tapping the pedal, I had to adjust my heel-toe since the pedal is now that much higher in the braking zone.

Hence my focus now shifting a little more towards my taper issues, since those are surely exacerbating the knockback.

As far as DTC70s being the bitiest pads in the world, yes they are bitey, but I disagree with the sentiment that they're un-modulatable. I had no problem staying out of ABS with them in the rain this weekend once I started double-tapping the brake pedal.

The other change I'm about to make to the car is suspension. On Dominion a couple weeks ago, a fairly rough track, I really started to feel how the (PO's 😛) H&R springs were letting me bottom out under braking, again leading to ABS activation as the car skipped across bumps in the braking zone. I'm thinking if I get some suspension travel, and can reduce my pad taper some, the subsequent reduction in ABS will help things last a little longer.

[Estoril]

I quietly wonder if your pad taper issue is coming from the initiation of pad doubletap.

[Pklauser]

I quietly wonder if your pad taper issue is coming from the initiation of pad doubletap.

Meaning the taper is being made worse by double tapping the brake pedal? For what it's worth I've been tapering pads since before I was doing the double tap if that data point helps clarify anything.

[mrgizmo04]

Double tapping is the right way to prevent knockback. First one straightens out the pad and seats the pistons square.

But, you are still running stock calipers and getting knockpack/taper, that points me to need to swap your wheel bearings. With brass guides your caliper actually sits pretty firm, but rotor oscillates due to tired bearings. I haven't heard of knockback on stock calipers, even from very spirited hpde guys and spec racers.

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[Pklauser]

Could be. Bearings feel tight to me, granted I'm not loading them up the way a corner would.

My other theory-in-progress is that I'm stuck in a taper cycle. I haven't changed rotors and pads at the same time yet. I think there's a possibility that: rubber guide bushings tapered my rotors -> tapered my pads -> new rotors, same pads -> tapered my rotors and so on.

This evening I plan on pulling the pads and seeing the amount of movement the caliper has with the brass guides to run that by the hivemind.

[mrgizmo04]

Rotors are much stronger material being cast iron than pads, which use different compounds/fillers/binders, so they are unlikely tapered, pads will taper. If you constantly run same track in same direction (cw vs ccw) you can check where the taper happens and see if it directionally makes sense, like clockwise tracks would shave more off the top of the outer pad on left side of the car.

Shaking wheel by hand can surface a really serious problem, but not enough to show deflection the way they get loaded up on track.

Over time I developed knockback on my Stoptech kit when I ran it, even though nothing in my setup/speeds changed. Wheel bearings felt tight by hand. I checked all the other parts for play/tightness and decided to replace the bearings, given they were the last part that I hadn't replaced on the car. Knockback solved.

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[Nate047]

Maybe this is a dumb question, but aside from a spongey pedal feel, what other symptoms would you get from pad knock back?

[mrgizmo04]

You go to jam the brakes and they aren't stopping with a prolonged pedal travel. It's a feeling a bit in between a cooked brake pad, where pressure is still somewhat firm but the pad just isn't grabbing, and a boiled fluid where pedal gets long but it kinda grabs with longer pedal. Somewhat scary to experience. You know it's knockback and not pad/fluid issue if you tap the pedal on next straight and then you jam the pedal and brakes act normal again on next turn.

This can be due to looseness in the caliper that forced it to flex and push/retract the pistons more than they should or loose bearings that force the rotor to press the pad/pistons to depart from rotor surface. Can also happen if you like to ride burms, partially why I don't enjoy Laguna (and only track I experienced knockback at).

The other solutions (in addition to left foot tapping on straight) to solve knockback are fully floating rotors (loud) or adding springs behind the pistons.

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[Pklauser]

The reason I suspect my rotors are tapered is that when I put on my street pads, I end up with a rust ring in the center of the outside face of the rotor. The street pads themselves do not appear tapered. Another interesting data point against wheel bearings, not saying they aren't contributing at all, is that my pedal is garbo even just going straight down the road without double-tapping.

On the subject of brass bushings. This is how much movement the calipers have on the Bimmerworld brass bushings. Maybe I'm misunderstanding something, but this seems like a lot, and doesn't seem like they would do a great job of preventing taper.

https://youtube.com/shorts/f9TZ4fejAy0?feature=share

[Estoril]

The reason I suspect my rotors are tapered is that when I put on my street pads, I end up with a rust ring in the center of the outside face of the rotor. The street pads themselves do not appear tapered. Another interesting data point against wheel bearings, not saying they aren't contributing at all, is that my pedal is garbo even just going straight down the road without double-tapping.

On the subject of brass bushings. This is how much movement the calipers have on the Bimmerworld brass bushings. Maybe I'm misunderstanding something, but this seems like a lot, and doesn't seem like they would do a great job of preventing taper.

https://youtube.com/shorts/f9TZ4fejAy0?feature=share

Obviously you have a serious caliper mounting problem to be found and resolved. That setup doesn't belong on the street, let alone the track.

I was instructing at SP ~5 years ago when we started having a clunking sound like that upon braking. Parked it and saw the movement. He was done until it was solved.

What caused you to leave OE calipers?

[Pklauser]

Obviously you have a serious caliper mounting problem to be found and resolved. That setup doesn't belong on the street, let alone the track.

I was instructing at SP ~5 years ago when we started having a clunking sound like that upon braking. Parked it and saw the movement. He was done until it was solved.

What caused you to leave OE calipers?

To be clear, these are OE calipers with Bimmerworld brass bushings. In this video there are no pads installed, this was done to illustrate the tolerance in these brass bushings. With pads, I can't wiggle the caliper as easily or as much as that, since the pad helps shore up the caliper. I'd be willing to bet the OE bushings with no pads has similar movement. My point is just that the brass bushings still allow for a lot of flex.

[heinzboehmer]

The reason I suspect my rotors are tapered is that when I put on my street pads, I end up with a rust ring in the center of the outside face of the rotor. The street pads themselves do not appear tapered. Another interesting data point against wheel bearings, not saying they aren't contributing at all, is that my pedal is garbo even just going straight down the road without double-tapping.

On the subject of brass bushings. This is how much movement the calipers have on the Bimmerworld brass bushings. Maybe I'm misunderstanding something, but this seems like a lot, and doesn't seem like they would do a great job of preventing taper.

https://youtube.com/shorts/f9TZ4fejAy0?feature=share

Sliding pins are torqued? That's a ton of movement

[Pklauser]

Sliding pins are torqued? That's a ton of movement

Yuuup. Same thing in the rear. I noticed this when installing as well and thought maybe the rigidity relied on the pad or something. Seeing my taper, I'm now starting to think the effectiveness of these is overblown. Not really sure what to think tbh. Still contemplating trying the IE longer ones.

[Estoril]

You should seriously consider not using any shop that allows your car through pre-track Tech inspection with that serious of a problem. No way they should be signing that form.

[Pklauser]

You should seriously consider not using any shop that allows your car through pre-track Tech inspection with that serious of a problem. No way they should be signing that form.

I'd put money that most all stock calipers, brass or (especially) stock bushings, have this movement to some degree when there are no pads installed.