Cayenne 958 Brake Bleeding?
 

Hey guys,
Having an issue with my cayenne. We've bled the brake system 7 or 8 times now, no air is coming through to the calipers but the pedal is still soft.

With the car off, if i stomp the brake pedal really fast and hard, its hard and stays in place.
If I pump it once and press it a second time, it's hard and stays in place.
If I put my foot relatively lightly on it, like I was stopping at a light - the pedal slowly goes to the floor.

I'm thinking master brake cylinder is gone - any other ideas?

Should add that it's a MY2011 Cayenne Diesel. I've tried bleeding the ABS pump too by loosening the lines on it in a similar way to how the nipples on the calipers are done, some air came out of there too but not much.

I can't even see a part number on the master cylinder, it just says TRW on it but no part number.

What's you method of bleeding the brakes? Are you using the push the brake pedal down method to bleed the brakes?

We tried both the break pedal down method, and pressure bleeding it (the "tire method").

Does the master brake cylinder need to be bled somehow maybe as well?

I've been using for the last couple of years a pressure bleeder that connects to the master cylinder. Once you crack the caliper bleeder it's squirts out nice and force fluid past the abs unit without issues. If you done it this way first I'm surprised you have a problem. Loosening the lines by the ABS pump wasn't a good idea but... Doing the foot pump method on newer cars seems to cause issues. Hence why I got the pressure bleeder with all the adapters.

Have you tried to use a pump to suck the fluid from the caliper end?

I don't think you have a master cylinder problem. I think it's a bleeding issue with ABS. I had a friend with a GM that had a similar issue and I borrowed a TECH II to go threw the ABS pumping program. I don't know if Porsche has this with their PIWIS.

We tried pressure bleeding as well using the tire method. I read that vacuum bleeding works poorly on porsches for some reason. That being said - there's nothing but fluid coming out on the calipers, today I ran at least a liter of fluid through each one. There's no porsche dealership or even service here so it's hard to find someone with a PIWIS tester to turn on the bleed mode... It doesn't look any different then any other cars brake system other then that there are two nipples on each caliper, though.

Don't know if this is helpful but ya never know. One thing I noticed was there are 2 bleeders.

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Bleeding the brake system (and replacing hydraulic unit)

Information
Observe brake fluid quality. Use only new DOT 4 brake fluid.
This brake fluid is available under the following part numbers: Quantity supplied: 1 litre = 000.043.203.66; 30 litres = 000.043.203.67.
There are two bleeder valves on the brake caliper. Brake fluid must be drained at both bleeder valves. Observe specified sequence: Bleed the outer bleeder valve first.
Open the cap -1- on the reservoir -2- .



Brake fluid reservoir

Connect bleeding device to the reservoir -2- .
Switch on the bleeding device. Bleeding pressure is approx. 2.0 bar.
A second mechanic is required. Continuously pump the brake pedal slowly during the bleeding process. 4.1. Continue changing the brake fluid at the brake calipers. Observe the sequence specified on the Porsche System Tester: Front left/Front right/Rear right/Rear left.
Open each bleeder valve until clear, bubble-free brake fluid emerges.
Use a transparent hose and a collecting bottle to check the escaping brake fluid for cleanliness, absence of air bubbles and to determine the amount of brake fluid used. 6.1. Only when replacing the hydraulic unit:
Bleed the secondary circuit using the Porsche System Tester. To do this, select >>PSM>>Maintenance/repairs >>Bleeding hydraulic unit << in the control unit overview.

Then bleed the right-hand side of the vehicle manually again: Front right/Rear right.
Tighten the bleeder valves to the specified tightening torque -- 47 Tightening torques for brake hydraulic system - section on "Technical values" and remove the bleeder hoses.
Switch off the bleeding device and remove the adapter at the reservoir. The brake fluid level in the reservoir must be between the MIN and MAX markings after filling and bleeding the vehicle -1- . Correct the brake fluid level if necessary.



Min/Max markings for brake fluid

Remove the Porsche System Tester.

Hey Guys,
We figured it out. Writing up here in case anyone runs into this issue.

In my case, it was either the servo or the brake pump - we replaced both, managed to find a used servo/pump together for $130 - part number matched exactly. After replacing it, we bled the system using a combination of pressure bleeding and traditional stomping on the brake pedal - no computer was needed, and brake pedal is nice and firm now.

Piwis comes handy because you can cycle the Abs pump

Yeah, but where do I get PIWIS...

I live in Poland, and my city has no porsche dealership (or rather, one is being built right now but it will be a bit still). There is one shop in the city that has one of these as far as I know, and they wanted some absolutely absurd money to bleed the brakes (6x what any other shop wants to do such a procedure).

I'm quite familiar with the BMW software used for coding and diagnostics - ISTA, NCS Expert, etc but was unable to find anything for porsche at all (that would work on a 958). Even durametrics can't cycle the ABS pump as far as I know.

Jak bus mieszkal w Kanadzie pomogl bym mam piwis 2

21 lat tam mieszkałem - w Vancouver :)

It's been a while but iirc yes