Jet.Fuel.Only

People always want to comment that bleeding the brakes isn't enough, you need to bleed the ABS module too! Is that the case? In this video I have a full fluid exchange procedure on my Porsche using the Motive Power Brake Bleeder, in addition I discuss when you actually need to bleed the ABS and how you can do it.

skl

Interesting- I have the isoft 2.0 and will be bleeding the brakes on my 981 spyder in the next week or so, so I guess I'll find out if it will in fact work on my car to bleed the ABS module. Will report back when I'm done. I've bled the brakes on several cars using my Motive system and always done it "dry." I'll try the "wet" way this time so I don't have to keep topping up the reservoir. And I'll see if I can bleed the ABS... never have to worry about that on my 914's

(but I guess it won't work on my T as it is a dot 2)

Jet.Fuel.Only

Yeah report back! The sketchy thing is the iCarsoft calls for 29psi in the Motive bleeder. That’s max on the gauge. Someone else reported getting it done at 20 psi or so and I tried 24 so maybe that was the issue.

skl

29psi??? Man, at that pressure I'll have the whole damned car covered in towels in case of a leak somewhere!!!!!! I've always done it before at 15 and even that makes me nervous!

Tommy L Garage

I tracked my 981 Cayman and never bled the ABS. Always used the wet method and had no issues.

IXLR8

That is what the Porsche Service Manual calls for. I have never even used 20 psi.

KNSBrakes

I have a PIWIS 2 that I have attempted to bleed brakes with. It works sometimes. I found this out when going into the braking zone at VIR and locked up a front right wheel.

My new procedure for bleeding ABS is to bleed the brakes, then go on a loose surface road and activate ABS, then bleed again. This is my preferred method.

--Aaron

skl

Interesting suggestion- but do you "circulate" brake fluid throughout the system when the ABS is activated or does it just increase the hydraulic pressure in the appropriate lines? If the later, you wouldn't get "new" brake fluid throughout the system. Are we all just guessing???

KNSBrakes

It worked for us for multiple endurance races, including having the ABS module off and apart before this years 24 hours of VIR.

--Aaron

skl

Thanks. Now I need to figure out how to activate the system as I don't drive on gravel roads that often, like never, unless I'm in my Bronco!

Tier1Terrier

Great video on flushing the brake fluid but I’m afraid I’m still not 100% clear on when to flush/bleed the ABS module and if it’s even necessary. I get that if the the ABS module is connected to the main brake system but how and when can air be introduced into the module? Seems like this is a very ambiguous task and there does not seem to be a consistent explanation anywhere that I have see so far.

Autobahnschreck

A look into the factory service manual reveals: ( this applies only for changing the brake fluid )
Yes, they recommend 29 psi ( 2,0 bar) pressure for bleeding. This reads quite high, and I even heard of exploded brake fluid reservoirs when doing this on older cars. What a mess this must be.
I have been successful with around 20 psi (1,5 bar) on the brakes, but I have PDK. The rationale may be, if you bleed the clutch circuit, you may need a higher pressure to open the check valve to achieve flow.
In the video it is emphasized to bleed the inner valves of any caliper first. Porsche says, choose the sequence of calipers and their valves to be bled as you like.
Do you need to bleed the ABS unit ? Porsche requires it only after replacing the ABS unit.
And finally, my opinion about circulation of fluid through the ABS unit: either releasing brakes by ABS, PSM, or by PTV (torque vectoring) action requires a certain re-flow of fluid to- and through the ABS unit. There will be an exchange of fluid between the ABS and the "conventional" parts of the hydraulic system, how much, remains to guessing. Use your PTV, PSM and ABS.

Out of curiosity, some time ago after changing the brake fluid I determined the water contamination of the fluid sucked out of the reservoir and the fluid drained from the calipers (by measuring its electrical conductivity).
I expected no big difference, if any, the water content in the reservoir to be higher because of the air venting needed for the reservoir . To my surprise, the water contamination in the calipers was much higher. I believe this is caused by the permeability for humidity of both brake hoses and dust boots. I thus do not care too much about sucking out fluid from the reservoir before starting the bleeding at the calipers.