Nashvegas

Took the 2013 Carrera S 991.1 out to a thing this morning, a 20 min high speed highway run to a Cars & Coffee. Got off highway exit ramp. Brakes normal. Turned onto a small side road for a few hundred yards. Goosed it in 2nd, then as I was slowing down (rapidly) at traffic light w revs quite high, the brake pedal went right to the floor and had almost no brakes. Very soft pedal all the way to floor. Pumped brake once and regained braking and stopped at the light halfway through the intersection. Pulled off. No trail of fluid behind car. Restarted car. Brakes completely normal.

Um... what ... the... heck. This was unexpected.

Fluid was flushed (allegedly) at Porsche dealer in Dec 2023.

Obviously something is up. I hadn't been braking to a degree enough to overheat fluid prior and my highway offramp stop wasn't overly aggressive just prior to the side road. I've noticed a bit of soft spot at top of brake pedal recently (when compared to my other cars) but have read here it's sort of normal for a 991.1 Carrera S.

Should I just have the brake fluid changed ? Any other ideas?

No leaks or brake fluid warning light and level in reservoir is good. Fluid looks clear/clean.

The only thing I could think was some weird vacuum booster or master cylinder issue ... I was in Sport+ and the car was at maybe 6500 RPM's slowing down in 2nd.

Had plans to go on a mountain run with a couple guys after but tapped out as I don't have any confidence in the brakes just yet... under different circumstances could have been disastrous.

Mike Murphy

That’s only happened to me on the track. And I was using my brakes really hard and then came off the the track and that’s when my brakes boiled. To think that can happen on the street would seem to require a lot of brake usage.

I would get the braking system inspected.

I guess it’s possible you have air in the line or the fluid is quite low.

JimEb

Hydraulic brake systems are simple, just fluid in a close system. In order to achieve what you described you would need either change in fluid properties (ie; boiling, air), loss of fluid (leak) or change in volume in the system (pad/caliper shifted).

Pumping the brakes sounds like it got the system filled back up and got them working again. Makes me lean toward something changed in the volume of your system. Did you have a stuck caliper piston that suddenly freed itself? Did a brake pad's friction material break off?

Bud Taylor

But there is a small rubber hose that goes to top of master cylinder which gives up. Air in the system does wierd things. You can see it because the connection end splits.

As this is brakes I would make sure I know what happened to not die. Any good wrench will be able to track it down.

worf928

With a 2013, it’s about the right time for the seals on the piston inside the brake master cylinder to be damaged from a rusted inner cylinder due to the first brake flush being done in ‘23.

jfischet

this makes the most sense to me based on conditions. were the pads changed in Dec too?

Nashvegas

Thanks for the thoughts gang. Agree it is probably something simple. Good ideas above.

Today I put the 991 on top of the stacker for a peek (it's usually parked underneath)... Checked all 4 corners. Nothing amiss I could find. (I did not remove wheels so could not verify all pad portions were intact). No evidence to indicate something coming apart or burning up or fluid loss.

Brake fluid's been changed every year or two since new at dealers. Only like 20 something k miles on the car. Pads front and rear are genuine Porsche, rears replaced about 5500 miles ago of street driving, friction material thickness is good where I could see it. Have no service history on front brakes ever being done but surely they were... (or maybe not?).

After my inspection, I went about 50 yards down the block and hear loud grinding from right rear wheel as I slowed down from maybe 15mph to 0 at the first stop sign-- definitely a new noise. Pedal felt normal though. This grinding noise did not repeat and rather annoyingly a podcast was on (Spikes Car Radio and they were playing intro music loudly on so coudn't hear it 100%).

So I've scheduled a dealer visit on their website. I love a good mystery. I'm sure they'll change fluid and tell me it's fine.

Mike Murphy

A loud grinding noise hopefully reveals something interesting.