BOPE

When I flush the brakes on my motorcycle, I use a computer program that activates the ABS circuit to ensure that the fluid that is trapped there is flushed from the system.

So I was wondering how folks flush the brake system on their 991.2? Is a computer program or other device or method used to ensure all the fluid from the ABS circuit is released and flushed?

Thanks!
Jason

plenum

My understanding is that the only proper way to completely flush whether .1 or .2 991 is using PIWIS tool to open and close each of the dampers in the system. I don't know of any other electronic tool available that would perform this same process.... Most of us simply do a "best effort" brake flush forcing the fluid through the system out each caliper valve until fluid color changes.... I've done this countless times and never had an issue with my 991's.
Cheers!

polobai

Another option is to flush as above and then “activate” the abs by coming to a sudden stop. Once that happens, you flush again.

worf928

The 991 workshop manual does not direct use of PIWIS for scheduled brake fluid replacement. According to the WSM, PIWIS is needed only if the ABS pump is replaced.

FWIW.

BOPE

That's all well and good, but the fluid in the ABS circuit does not get flushed without some sort of tool/software activating the ABS to release the trapped fluid. So, without some means of triggering the ABS valves, you're not getting a complete brake fluid flush.

Jason

bkrantz

The way I look at it, we never get 100% fluid replacement no matter what, short of separating all components and lines, flushing with solvent, and drying. The key question is the volume of fluid isolated in the ABS part of the circuit, and what percent this is of the total system. Same as with oil changes.

BOPE

Indeed, when changing the oil in a 991.2 there appears to be a considerable quantity of "dirty" oil that remains in the oil cooler and the oil lines that connect it to the engine. But this oil is immediately circulated with the "clean" oil when the engine is started. So dilution is the solution in this case.

However, the brake fluid in the ABS circuit will not circulate with the fluid in the remainder of the system unless the ABS valves are activated and the brake pedal is depressed multiple times as the ABS valves are being cycled. This is best achieved with the use of device to activate the ABS valves.

How much fluid is trapped in the ABS circuit is unknown to me. But my concern is that stagnant fluid harboring moisture in a delicate circuit is harmful, hence my query for a program/tool/device to more effectively flush the brake system.

Jason

BOPE

Deleted duplicate post.

991.1 Guy

I agree with "activating the ABS manually" to flush the fluid. I have done it on several other cars with good results. Fill and bleed the system, then drive and brake hard enough to activate the ABS several times and re-bleed. Most tracked cars never have to worry about this since ABS is activated frequently.

BOPE

Good point about track cars activating ABS times during a run to help distribute the brake fluid beyond the ABS circuit.

Since I don't track my car, I think I'll continue my search for a tool that will manually activate the ABS system.

Jason

Sidvicious7

Have you tried reaching out to a technical advisor at a Porsche dealership? I normally make calls seeking advice on technical related issues at Porsche dealerships and Indy shops with moderate success when I need feedback beyond this forum.

worf928

Does the modern Porsche ABS pump feature cavities that are completely closed off from the rest of the brake fluid supply? Or, is the supply-side of the valves open to the fluid supply with the pressure-side closed-off via the valves?

dr bob

Unfortunately, the fluid in the ABS chambers only cycles internally when the ABS is "activated". To actually move fluid through both major chambers, you'll want to have upstream pressure, downstream bleed path open while cycling the ABS unit. So the dirty fluid has a place to go. No good opportunity to do that while driving.

Jack F

I believe, here is a vid that addresses your question.

BOPE

Indeed, the Autel tool works very similar to the one I have for my motorcycle. I plan to contact Autel to ask if they have a tool that will bleed the ABS on a 991.2.

Thanks for posting the video!

Jason