Complete brake failure !!

[W1NGE]

at least you can feather in a manual handbrake gradually - an electrical one is surely on or off which at speed would be rather dramatic and result in a spin quite likely

not sure (not had to try it - one for the Porsche Experience Day I think) - it may be progressive in application.

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[alexsas]

Did you have any brake “campaigns” applied recently? I had wpk0 that involves bleeding of brakes. I have just discovered they left all 4 dust caps on calipers dangling open. Probably not too serious, but what else can these “expert technicians” forget? Feel free to pm me with the name of your dealer to see if these could be the same…

 

[Singularity]

I think it is fairly standard on all newer cars with electronic parking brake that you can use that button as an emergency brake if the brake pedal fails. I just recently told this to my spouse in our Audi as we discussed this remote possibility. This is actually rather useful safety information that I think everyone should know.

I'm glad nothing serious happened in the case of the OP and I really hope Porsche investigates this asap. It's imperative to know if this was a one in a million failure or if there is a larger issue that can affect many Taycan's.

 

[Clive]

OK - so following pressure to the dealer from Porsche GB to determine cause quickly its been diagnosed as a split brake hose (nr side)

no evidence of impact or damage, just component failure

I think they need to start checking other cars ASAP ? this could be a killer

 

[Scandinavian]

OK - so following pressure to the dealer from Porsche GB to determine cause quickly its been diagnosed as a split brake hose (nr side)

no evidence of impact or damage, just component failure

I think they need to start checking other cars ASAP ? this could be a killer

wow! I thought all modern cars had a safety system with two separate system for brakes. That is what I had on a very old SAAB and Volvo, at least. So wonder how it could result in zero braking power?

And in case one circuit lost brake fluid a warning light would come on.

Was there no warning lights at all in the Porsche prior to the incident.

 

[Clive]

Opc casually suggest ordering and fitting a new pipe ………. no regard for the other 3 same age / same quality pipes on the car or the thousands of other Taycans that could have a similar failure

they honestly expect me put my wife and children in this car again without as much charging all the flexi pipes

i reckon there should be an immediate recall on all cars with this component, it should not fail at this age

 

[hifi239]

So I tried holding down the (P) button today at 30mph (no other cars). It works well. It stops the car vigorously and promptly, but also smoothly. It is a stand-alone, separate system. It does not also trigger regen, which is expected because this is a backup system and should remain simple. What it does do is apply electric servos to rear drum brakes, as with many other EV and ICE cars.

From that French site here, I got the parts diagram:

And the parts list description for 6 (servomotor):

I'm not going to play around too much, but it is probably a good idea to try this once or twice in a parking lot to get the feel for it and code your brain that this is an option.

 

[hifi239]

OK - so following pressure to the dealer from Porsche GB to determine cause quickly its been diagnosed as a split brake hose (nr side)

no evidence of impact or damage, just component failure

I think they need to start checking other cars ASAP ? this could be a killer

So it was the flex hose from the brake line (metal) to the caliper? If one of those blows out, which is contemplated as a possibility by all modern car designs, you will have pedal braking for a while until all the fluid empties out. It is puzzling because zero-brake should not happen immediately - lights should be coming on on the dash. Ask for the part and take a photo. For these it is most often road debris or corrosion and cracking over a decade in salt winters that can cause a failure. Or it could simply have been a defective part. I'm not so much worried about the split flex hose - that's not THAT crazy surprising. What is surprising is that you lost all braking because of one split flex hose. It absolutely shouldn't do that.

I stole this from a Macan forum here.:

With regard to the operation of dual circuit brakes and the pedal “going to the floor “ when a failure in one system occurs.
The master cylinder has two pistons , one for each circuit. When the brake pedal is depressed it pushes the first piston forward as well as applying the brakes on that circuit , the second piston is pushed by the brake fluid between the two pistons and applies the brakes in the second circuit.

The first piston is depressed mechanically by the pedal linkage and the second hydraulically as a result of the hydraulic lock formed when the brake pads in the first circuit contact the rotor.
If a failure occurs in the first circuit the first piston will move forward until it mechanically contacts the second piston and then braking will occur in the second circuit.

If the second circuit fails the first piston hydraulically pushes the second piston until the second piston contacts the end of the master cylinder. As the second piston can no longer move this gives the fluid no where to go but down the lines and apply the brakes in the first circuit.

When either system fails it greatly extends how far the pedal must be pushed to operate the other system giving the impression of going to the floor. And the brakes being ineffective as only two wheels are braking and not four wheels.
For the pedal to go to the floor it would require both systems to fail, the result would be zero brakes.

When a brake line fails and hydraulic pressure is lost, the brake warning light will not come on as the reservoir is still full of fluid.
The light will come on after pumping the brakes enough times to lower the fluid level in the reservoir and trigger the light.
The reservoir is also divided internally to prevent a leak on one circuit completely draining the reservoir. Thus leaving one circuit with sufficient fluid to operate.

 

[Clive]

So it was the flex hose from the brake line (metal) to the caliper? If one of those blows out, which is contemplated as a possibility by all modern car designs, you will have pedal braking for a while until all the fluid empties out. It is puzzling because zero-brake should not happen immediately - lights should be coming on on the dash. Ask for the part and take a photo. For these it is most often road debris or corrosion and cracking over a decade in salt winters that can cause a failure. Or it could simply have been a defective part.

flex pipe bust - so no pressure in the system and all fluid pumped out = no brakes other than the very light effect of the regen

dealer agree it’s not damaged at all, it has just burst under pressure

yes parts can fail but not on 3yr old £137k cars with full dealer service history. A part like this should be specified to cope with double the max pressure it should ever experience

this component is not good enough - all taycans fitted with it should be recalled before someone is killed

i will be selling this car immediately when i get it back

 

[andix]

That can only happen if a mechanic made a mistake.
Had this in an Audi once, and the mechanic assembled sth wrong.
Not a structural or systematic problem.

 

[Clive]

That can only happen if a mechanic made a mistake.
Had this in an Audi once, and the mechanic assembled sth wrong.
Not a structural or systematic problem.

it’s never been taken apart , i’ve owned this car from new and it’s has nothing other than routine opc service

the hose has failed under pressure, it’s either faulty or spec is too low

Porsche have a big problem here imo

 

[Vercingetorix]

Dual braking system was mandated here in the USA in 1967. I just cannot see the whole system failing. It would take 2 separate failures. My best guess is this might be related somehow to being a right hand drive car?

 

[Scandinavian]

flex pipe bust - so no pressure in the system and all fluid pumped out = no brakes other than the very light effect of the regen

dealer agree it’s not damaged at all, it has just burst under pressure

yes parts can fail but not on 3yr old £137k cars with full dealer service history. A part like this should be specified to cope with double the max pressure it should ever experience

this component is not good enough - all taycans fitted with it should be recalled before someone is killed

i will be selling this car immediately when i get it back

I can understand that you will sell the car directly. I have not looked how the brake hose is done in the Taycan, but will surely check now to see if there is any kind of rubbing against something. Any sign of abrasion will mean braided hoses to replace the existing ones.

I am still very surprised that it happened as described. I thought the design of the two circuits were more robust than to suddenly loose all braking power with out any warning signs. Very scary one Way or the other.
I also think you should ask for and get a very detailed explanation from either the Porsche Centre or rather from Porsche GB. They must share the root cause and also explain in detail why a dual circuit system fails so catastrophically.

 

[Scandinavian]

it’s never been taken apart , i’ve owned this car from new and it’s has nothing other than routine opc service

the hose has failed under pressure, it’s either faulty or spec is too low

Porsche have a big problem here imo

Again a part like that can have a very rare manufacturing fault and could fail, but why a dual circuit system fails beats me.

 

[hifi239]

flex pipe bust - so no pressure in the system and all fluid pumped out = no brakes other than the very light effect of the regen

dealer agree it’s not damaged at all, it has just burst under pressure

yes parts can fail but not on 3yr old £137k cars with full dealer service history. A part like this should be specified to cope with double the max pressure it should ever experience

this component is not good enough - all taycans fitted with it should be recalled before someone is killed

i will be selling this car immediately when i get it back

As others have said, thank you very much for taking the time to respond to all these questions. One thing many of us learned as a result of your misfortune is that there is an emergency brake in these cars. I've been on the board and other places for a year and never heard of a brake failure. Maybe others have? That would suggest maybe not a bad design but a bad part. But who knows. I apologize if you said, but on which corner was this flex line located? I would not be surprised if the part was shared with other Porsche models like the Panamera.

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