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Context:

I replaced all four pads and rotors on my 2001 VW Passat (~140k miles) about 4 weeks ago, with PowerStop Z23 pads and rotors. During bed-in, I took the car down a steep hill, and got a lot (too much) heat in the brakes. This was after about 10 accelerations, and 10 stops back down to ~20 mph on a steep downhill. As I got to the bottom of the hill, I lost braking entirely, and while the pedal still had pressure, it felt like braking against a repelling magnet, in that pushing the pedal could barely slow the car.

My assumption is that was a perfect example of brake fade, and after letting the brakes cool for 15 minutes, full braking performance returned.

Actual Problem

Fast forward 4 weeks, and I took a trip up into the mountains - note that the brakes were fine on the way up, and I didn't do any "performance" braking on the drive. Took the car out first thing in the morning, and I got the exact same pedal feel, and lack of breaking performance that I described above, except with cold brakes. I started the car, and the brake pedal immediately felt like I described above - not falling to the floor, but not firm. Pumping the brakes didn't change the pedal feel. I drove very cautiously for a few minutes, tested the brakes a few times, and after ~5 min of driving they started to feel normal again, and didn't have any further issues on the trip.

I also noticed a small amount of brake fluid sitting on top of the reservoir under the hood, although there is no apparent leak.

Is it possible this problem is caused by the reservoir being overfilled? (I did leave it open and remove excess fluid when resetting the pistons, however, it is still very full). Or is it possible that the original event during bed-in and this are related, and a sign of a bigger problem, like a failing master cylinder? Is it possible the brakes need to be bled? I would think it would be a persistent issue if they do, but I don't know for sure.

Also from this post on PassatWorld:

This was due to a reservoir breather blockage. Possibly caused by overfilling, the fluid could block the strainer holes and the gap around the strainer, air pressure would prevent the flow into the reservoir

This post doesn't address the braking performance, but I think it does mean I should double check that the reservoir is not over full.

  • Did you do anything to the break fluid when you installed the new pads? Top it up? When was it changed the last time? Do you run the normal fluid as recommended by VW or did you use any performance fluid? – Daniel Mar 19 at 0:46
  • Also maybe of interest: youtube.com/watch?v=6hlK81gxe7U – Daniel Mar 19 at 0:47
  • 1. Didn't do anything to the fluid other then use a turkey baster to remove some of the excess - I left the reservoir open and removed fluid as needed when I compressed the pistons. I did add a little bit of the removed fluid back. I don't know when the fluid was last changed, but not since I bought the car with 87k miles on it – as far as I know, it's running OEM fluid, which is either DOT3 or DOT4 - I'd have to check the manual – Mako212 Mar 19 at 6:11
  • 2. To the video, that's interesting, however it doesn't sound like the same condition. With the exception of the two noted examples, the brakes/rotors perform far better than the OEM ones I replaced. Stopping distance is significantly reduced, and the braking is firm and consistent. – Mako212 Mar 19 at 6:13
  • I would check the vacuum line and check valve to the brake booster, as well as the master cylinder itself. – SteveRacer Mar 22 at 4:05

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