Dumb Mistake: Air in ABS System

NC_Taycan

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So they say misery loves company. Here's my misery.

HPDE coming up this weekend and my factory brake fluid is just over a year old and the Taycan has been to the track three times in the last year. So it's time to change the fluid.

It's not a difficult procedure. I've done it before on other cars. Unfortunately, I allowed myself to be interrupted between draining the master cylinder reservoir and beginning the bleed process - and forgot to top off the master cylinder reservoir with new fluid. Next thing you know, I've sucked air into the master cylinder and ABS system. Although I've refilled and bled the system as best I can, air in the ABS system requires a PWIS connection and process to open actuators in the system to complete the bleed procedure -> trip to dealer. Even in the off chance they get this done by Friday, am I going to trust this on a track this weekend? I don't think so.

I'm not even certain I can safely get it to the dealer. With the ABS system off-line, PSM, differential lock, and brake assist are all reporting as out of service. And the pedal is too soft, though I can stop the car.

Such a dumb move. It's going to cost me the HPDE cost plus at least several hundred dollars in labor at the dealer, plus the humiliation of explaining the mistake in the first place.
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991carreradriver

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So they say misery loves company. Here's my misery.

HPDE coming up this weekend and my factory brake fluid is just over a year old and the Taycan has been to the track three times in the last year. So it's time to change the fluid.

It's not a difficult procedure. I've done it before on other cars. Unfortunately, I allowed myself to be interrupted between draining the master cylinder reservoir and beginning the bleed process - and forgot to top off the master cylinder reservoir with new fluid. Next thing you know, I've sucked air into the master cylinder and ABS system. Although I've refilled and bled the system as best I can, air in the ABS system requires a PWIS connection and process to open actuators in the system to complete the bleed procedure -> trip to dealer. Even in the off chance they get this done by Friday, am I going to trust this on a track this weekend? I don't think so.

I'm not even certain I can safely get it to the dealer. With the ABS system off-line, PSM, differential lock, and brake assist are all reporting as out of service. And the pedal is too soft, though I can stop the car.

Such a dumb move. It's going to cost me the HPDE cost plus at least several hundred dollars in labor at the dealer, plus the humiliation of explaining the mistake in the first place.
Sh..t happens. I have done it myself, there is no end to the list of stupid things I have done. I bet the next flush you do, if anyone comes in the garage, you will throw them out....that's what I do!
 
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NC_Taycan

NC_Taycan

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Well after a few heavy bleeds (no obvious air expelled) and some very limited driving, all warnings are gone (PSM, all wheel drive, differential lock, brake assist), however the pedal feel is way soft and once the hydraulics engage, it's unpredictable. Appointment in the AM.
 
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NC_Taycan

NC_Taycan

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$1000 later ($330 for 6 more qts brake fluid, $700 labor - ouch) and it is back. Dealer has (as one would expect) a procedure for this, including pressure bleeding from the master cylinder and PWIS-directed actuation of the ABS valves. What I didn't know is that the Taycan brake system also has pressure differential sensors and these are used to check compressibility of the hydraulic fluid (which also tells if there is air left). The Taycan tech said he would be fully confident the braking is restored to spec.

So track day is saved, but my first few laps - maybe even full session - will be tentative - I need to convince myself all is well.
 

Dee

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Why did you want to change the fluid anyway after just one year?
Was it too moist or something?

Glad to see your day was saved though!
Thx for sharing! 🤭
 
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mikeva

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$1000 later ($330 for 6 more qts brake fluid, $700 labor - ouch) and it is back. Dealer has (as one would expect) a procedure for this, including pressure bleeding from the master cylinder and PWIS-directed actuation of the ABS valves. What I didn't know is that the Taycan brake system also has pressure differential sensors and these are used to check compressibility of the hydraulic fluid (which also tells if there is air left). The Taycan tech said he would be fully confident the braking is restored to spec.

So track day is saved, but my first few laps - maybe even full session - will be tentative - I need to convince myself all is well.
that is quite an ordeal .... hopefully things are ok now ..... have fun
 
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NC_Taycan

NC_Taycan

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Why did you want to change the fluid anyway after just one year?
Was it too moist or something?

Glad to see your day was saved though!
Thx for sharing! 🤭
Four track days = ~16 20 minute run sessions. Half my front pad is gone, so the brakes are being used (and any good track driver will tell you I'm not a good track driver if it took four days to use 50% of my pads). Braking in the most recent session felt a bit spongy. Many organized track events strongly suggest brake fluid to be < 90 days old anyway due to the propensity to absorb moisture that lowers the boiling temperature. So, was I being over-zealous wanting to replace brake fluid that is one year / 4 track days old? Maybe.

That said, repeated 1.3 g deceleration of a 5100 lbs vehicle from 150 MPH to 30 MPH will overheat any brake system, though proper carbon ceramic pads (Turbo S or PCCB upgrade) with high-temp fluid will fare the best. So see above over-zealous comment.

What will be interesting is if I notice the same this weekend, given new (but Porsche OEM) brake fluid and (knock on wood) all air bled from the system. If my last posts are tonight, we may have missed some bubbles...
 

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Sorry to hear about the ordeal. You’re definitely not alone. Brake bleeds are easy to mess up! If you’re just occasionally hitting the track, consider just doing a partial bleed just to get the dark, heat affected fluid out of each caliper. Most HP brake fluids have wet boiling points high enough that the fluid in your reservoir is still ok after a year or two. Makes bleeding process quicker and harder to mess up.

Your story got me thinking, normally if you’re dealing with a soft or low brake pedal on the track, you can lightly pump the brake pedal with your left foot on the straights to get a taller, firmer pedal. But with the regen and by-wire braking, curious how that would work on a Taycan.
 

Dee

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Four track days = ~16 20 minute run sessions. Half my front pad is gone, so the brakes are being used (and any good track driver will tell you I'm not a good track driver if it took four days to use 50% of my pads). Braking in the most recent session felt a bit spongy. Many organized track events strongly suggest brake fluid to be < 90 days old anyway due to the propensity to absorb moisture that lowers the boiling temperature. So, was I being over-zealous wanting to replace brake fluid that is one year / 4 track days old? Maybe.

That said, repeated 1.3 g deceleration of a 5100 lbs vehicle from 150 MPH to 30 MPH will overheat any brake system, though proper carbon ceramic pads (Turbo S or PCCB upgrade) with high-temp fluid will fare the best. So see above over-zealous comment.

What will be interesting is if I notice the same this weekend, given new (but Porsche OEM) brake fluid and (knock on wood) all air bled from the system. If my last posts are tonight, we may have missed some bubbles...
So you didn't measure the amount of moisture?
They say to change it <90 days but that's just guessing.
You can actually measure the quality (data vs feelings!).
Anyway, it's nice you share the story, just to prevent people changing theirs...
Have fun! 😁👍🏻
 
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NC_Taycan

NC_Taycan

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Your story got me thinking, normally if you’re dealing with a soft or low brake pedal on the track, you can lightly pump the brake pedal with your left foot on the straights to get a taller, firmer pedal. But with the regen and by-wire braking, curious how that would work on a Taycan.
The addage "check your brakes coming into the braking zone from a high speed straight" doesn't apply with regen. Regen-only deceleration in a Turbo or Turbo S is about 0.8 gs (reasonable guess, not scientifically measured). You'd dump way too much speed too early. But from a safety perspective on the first few laps or under a yellow, it's still prudent.
 
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NC_Taycan

NC_Taycan

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So you didn't measure the amount of moisture?
They say to change it <90 days but that's just guessing.
You can actually measure the quality (data vs feelings!).
You know the answer. Of course I didn't. Did you measure CD and lift before/after your cool custom diffuser? It's a hobby. We hobbyists sometimes do things for non-data-driven reasons.

The tech inspection "requirement" for brake fluid < 90 days old is intended to also cover track-only cars that will be pushed much harder than I intend to push mine. 1 year seems reasonable to me.
 
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Dee

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Did you measure CD and lift before/after your cool custom diffuser? .
No, I didn't.
No need to cuz it doesn't change the function of the diffuser (downforce) but it only changes the drag.
Fins are vortex generators and help to reduce drag so CD value will probably a tiny bit lower and that's always good but that's another story/thread.

Anyway thx for answering my question.
If my way of asking was a bit annoying, I apologize, it was a sincere question. 😉
 

bsclywilly

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The addage "check your brakes coming into the braking zone from a high speed straight" doesn't apply with regen. Regen-only deceleration in a Turbo or Turbo S is about 0.8 gs (reasonable guess, not scientifically measured). You'd dump way too much speed too early. But from a safety perspective on the first few laps or under a yellow, it's still prudent.
I was referring to pumping brakes lightly while still at full throttle, not a brake check. This is done to get more fluid in the circuit to compensate for pad knockback or boiled fluid. My question, more directly, is will the brake-by-wire system recognize that if you're applying brake pressure while still on the throttle and directly engage the hydraulic circuit? I can think of some fail-safe scenarios where this would make sense. I'm not expecting an answer, it's just a thought I had.
 
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NC_Taycan

NC_Taycan

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No, I didn't.
No need to cuz it doesn't change the function of the diffuser (downforce) but it only changes the drag.
Fins are vortex generators and help to reduce drag so CD value will probably a tiny bit lower and that's always good but that's another story/thread.

Anyway thx for answering my question.
If my way of asking was a bit annoying, I apologize, it was a sincere question. 😉
Not annoyed at all.
 
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