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

[mrgizmo04]

You can never fully escape taper. I had some slight taper on my st40 kit, I had taper on 996 kit, I know people get taper on AP kits as well. I haven't seen radial taper much though.

With brass guides you have to relube them pretty frequently. Yours almost look like they get jammed and don't slide freely and then they twist the whole caliper.

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[Pklauser]

Here's my taper for reference. IMO as bad if not worse than the rubber guides.

[George Hill]

It does have some slight radial taper but nothing as much and significant as photographed.

Yes, rubber guides and this is a 330 rotor/caliper, but the uses the same M3 pad. The car does have an S54 and will do 140+ at CoTA so I feel it is relevant. I had stayed with the rubber guides as I was concerned with stiction from brass guides, but I can't imagine it would be worst than this, lol.

After seeing these pads though I am now looking into changing my braking setup and will likely go with a radial mount caliper.

[Pklauser]

Yea Bimmerworld actually says to forego the spring clips with their guides. Appreciate that comparison! I'd say those look nearly identical to my taper. Mine also have radial taper, from the inside of the rotor to the outside, not sure if you have that as well. Are you tracking with the rubber guides?

[George Hill]

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.

I would agree, the spring clip helps counteract this but the solid guides I would think shouldn't need.

I am no expert on the solid guides so I don't have an opinion on them in this situation. But just as an interesting note on pad taper or to compare these are my DTC-60s with stock rubber guides, lol.

[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.

[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]

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.

[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]

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.

[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]

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

[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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[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]

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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