Brake Failure
 

I took my 1998 Boxster out for a longer than usual drive today — 20 miles? As I was finishing the drive, I began smelling something — burning smell. Sure enough, within a minute, I got the “Brake Pad Wear” light. But, as I got ready to turn, I had no brakes whatsoever and the brake pedal went to the floor. I only had about 200 yds to get home and I managed to get her in the driveway. Upon only a cursory inspection, all pads looked more than ample, but there was definitely smoke coming from the driver’s side wheel well. Of note, the passenger side rotor was almost cool to the touch and obviously wasn’t providing much braking. But then again, I was on an 8 mile long straight road with no traffic and very little need for braking. Reservoir is full of brake fluid. After cooling, the brake pedal pressure seems normal. Any thoughts? Stuck caliper on the driver’s side?

Yes, that sounds like the correct conclusion. Sticky caliper. As a result you seem to have boiled your fluid giving you the spongy pedal, otherwise you'd still be able to brake, but with a strong pull to the passenger side.

Rebuild the caliper and change the fluid. The pads are likely glazed up and the disc potentially warped. The glazing will wear off but the disc might need replacement.

One thing I do wonder though is which light came on. Hot brakes should not trip the wear indicator.

Good info…thank you.

That’s definitely the light that illuminated. Odd, right?

Before you smelled smoke, did you feel any pulling on one side or the other when braking? It's possible you actually have a problem with the passenger side not braking at all and putting all the load on the driver's side causing it overheat. Don't assume your problem is only on the driver's side.

Well, it doesn't hurt to double check indeed, but my bet is on a sticking caliper.

- Try to rotate both wheels (off the ground). If the suspect side is already dragging, you know enough
- If both rotate freely, take the car for a short drive, feel both brakes (don't touch). If one side becomes warmer than the other, take the wheel of the ground and check for a dragging brake again. But typically if one side becomes hot while the other doesn't you have found a sticky caliper.

Also check for a bad hose. Once you find your "sticking" caliper, take the wheel off, pump the brakes a few times to build up pressure, then release them. The suspect caliper should remain stuck and prevent the rotor from spinning by hand. Then open the bleeder screw. If a bunch of fluid squirts out and the rotor can then spin, your problem is the hose. If fluid drips out, but the rotor is still stuck, then you have a bad caliper. Good luck.

I get your point, butr what could cause the hose to get bad, it should behave lake a not return valve then ... !?

It can break internally and either cause a bulge, resulting on low pressure on that side, or cause an internal obstruction which keeps pressure on the caliper even after you've released the brake. Yes, like a one-way valve.

The inner lining of the brake hose can deteriorate over time and a "flap" develops inside the hose. If the loose end of the flap is in the direction of the caliper it will flatten itself against the wall of the hose when the brake fluid is flowing outward as normally happens when you step on the pedal. However, it will impede the return fluid flow when you release the pedal inasmuch as the flap is now perpendicular to and obstructing the flow in the direction the fluid is attempting to travel. Pressure on the brake pads will not be fully released and they will not retract from the disk, causing the disk, pads, and fluid to heat up the the point that the fluid boils resulting in the pedal going to the floor without apparent resistance as well as the smoke from the caliper.

The next morning the brakes will work fine (for a while) because everything has cooled and enough time has elapsed for the fluid to seep past the point of the obstruction back into the master cylinder.

I've never had it happen on my Porsche, but one of my pick up trucks had the same problem some years ago. I, too, was convinced it was probably a frozen caliper til an old hands-on mechanic who'd spent his life working on cars explained it to me.

Replaced the brake hose (actually replaced ALL the brake hoses) and the problem was remedied, never to return again.

Interesting, thanks.

After 25 or so years, I thought it a good idea to replace brake lines to avoid this trouble! That's quite a long time for any product, regardless of mileage, and this is a high-stress application.