[waxfigure]

I took my CPO m235i (38k miles) on a canyon run at Angeles Crest highway last weekend.

After going up and coming back down from the canyon, around 20 minutes into the run, there was a noticeable change in the brake feel where I would have to press the brakes almost all the way down to get the car to stop when it was working perfectly right before.

I stopped the car for about 10 minutes, then the brakes kind of came back to normal (I also didn't drive aggressively enough to actually test it again).

As a previous scion frs owner, I would drive aggressively through the canyon for almost an hour and I would only notice maybe 30% brake fade.
The m235i feels A LOT heavier - which seems to contribute to the brake fade.. after 20 minutes into driving, I felt about 60~70% loss.

Is it normal for the brake feel to disappear so soon after aggressive driving with the m235i?
or is this because my brake pads are probably aged and needs to be replaced?
For those who canyon / track / autox, what are your thoughts on the OEM "M" brakes that these cars come in?

[overcoil]

Yeah the power and weight of car can overwhelm the brakes and many cycles of heating probably effects the pads and fluid.

Chk the braking forum for pad suggestions.

[dradernh]

Originally Posted by waxfigure

The m235i feels A LOT heavier

The car is an overpowered tank; it's completely different than the twins.

If you're going to lean on the car, you'd be wise to upgrade both your brake fluid and your brake pads.

Originally Posted by waxfigure

...there was a noticeable change in the brake feel where I would have to press the brakes almost all the way down to get the car to stop when it was working perfectly right before.

If you were running over bumpy pavement, it's possible that you experienced pad knockback. That condition produces a very soft pedal along with little braking effect, and it goes away after you use the brakes again. Its effects can be eliminated by lightly tap-tap-tapping the brake pedal after running over something that's causing the knockback. That tapping will move the pads forward and into their proper position.

The Anti-Knockback Springs section in this Essex Parts page explains knockback better than I can: https://www.essexparts.com/essex-des...87M2f80M3f82M4.

[Maynard]

Or perhaps just lightly boiled them, and they cooled off? Especially if that is old brake fluid (CPO doesn't always mean they update e/t, just 'check it'). You'll also really work the brakes double time if traction control is on, so the twisties can really heat them up.

[waxfigure]

Originally Posted by Maynard

Or perhaps just lightly boiled them, and they cooled off? Especially if that is old brake fluid (CPO doesn't always mean they update e/t, just 'check it'). You'll also really work the brakes double time if traction control is on, so the twisties can really heat them up.

Can I assume that sport + turns the traction off? in that case, it would be the fluid that is causing the issue?

Also, when you say 'you work the brakes when the traction is on', does that mean this car's stock diff is brake based?

[Maynard]

Originally Posted by waxfigure

Can I assume that sport + turns the traction off? in that case, it would be the fluid that is causing the issue?

Also, when you say 'you work the brakes when the traction is on', does that mean this car's stock diff is brake based?

First is a no - Sport and Sport+ each reduce the amount of traction control, but you have to go to full 'DSC-off' to get rid of (most of) the nannies - you get this by holding down the button longer, until you get the traction off screen. I honestly get confused by the terminology of TCS-off vs DTM, but it is the long push. I'm told there are still a few emergency nannies that can only be coded out (good thread on that elsewhere, if you want). All of the traction control and LSD work through the brakes to some degree, but I think they can also reduce power and divert torque front-rear; I know it is common to wear out rear brakes first due to this (mine did, at just under 20k). FWIW, I would not totally disable the TCS on the road; even at an HPDE, the smart advice is to leave it in sport until you notice it, then move to sport+, eventually off once you gain more experience (I'm still running sport+ on track myself).

I would always suspect fluid first, unless it was fairly fresh (it is a very common maintenance item for shops to skip, since almost nobody will care or know how to check it); factory pads also crap out rapidly once they get over their heat range, and I think this should leave visible signs on the pads/rotors (and they wear very fast). The pad knock noted above is also quite possible, but IIRC that will correct almost immediately (just one soft press, then it is fine?). Factory pads aren't great for really heavy duty street or track work, but I'd think it would be hard to overwhelm them on the street (coming down a long steep winding canyon could do it, though). Lately I rely on Zeckhausen for brake advice, you may want to call them for recc's (and good prices) on pads and fluid'; they spent about a half hour with me, and their advice was quite helpful. https://www.zeckhausen.com/catalog/