Bypassing ABS for Blake Fluid Flushes

[TD in DC]

Hello All:

I use Castrol SRF brake fluid, and I regularly bleed/flush my brakes to maintain optimum performance. I understand that a significant amount of fluid can remain trapped in the system due to the ABS system. This is undesireable since having a mixture of cheaper fluid with a lower boiling point pretty much negates the benefits of paying for such an expensive brake fluid like Castrol SRF.

I have heard that you can manually trigger the ABS system while flushing the brake fluid in order to get a complete flush. Is this true? If so, how do you do that?

Thanks,

TD in DC

[kam]

I want to know how too.

Somebody suggests that you could bleed the car once and then go out for a drive to engage the ABS a couple of time.

Go back and bleed it for a second time. It would probably work but I don't want to bleed it twice.

[Loren]

The only way I know to do it is with a PST2 or PIWIS tester. It is one of the items in the ABS control section.

Sorry the pic is a little fuzzy - but you get the idea.

[TD in DC]

I know you can do it with the PST2 or PIWIS tester, but I have heard numerous times that there is another very easy way to do it without any special testers or Porsche equipment. I cannot believe I forgot the specifics of the rumor.

[TD in DC]

OK, I remember the rumor. :lightbulb: Supposedly you can jump pins on the ABS relay. In order to know which pins to jump, you need to check out the wiring diagram. Can anyone illuminate this topic a little further?

Thanks,

TD

Edited September 15, 2005 by TD in DC

[Loren]

If your car has PSM then the ABS return pump is controlled through the PSM controller and the relays (pump and valves) are inside. If you have a non PSM car then the relays are inside the ABS controller.

If you want the diagram let me know which one (with or without PSM).

[TD in DC]

I have PSM. Can you please provide the diagram and explain how I can both get to the relay and "jump" the appropriate pins?

As always, I appreciate your help Loren.

TD

[kam]

I can't wait for the answer and hope that the procedure of doing it is not too involve.

[Mitty]

I don't have PSM and would like to see that diag too.

Thanks!

[wwest]

Just get all four wheels off the ground, run the car at ~5MPH with PSM. Without PSM simply and apply the brakes while "running".

With a C4 have someone hold a front tire, CAREFULLY, in place

[frank320]

Just get all four wheels off the ground, run the car at ~5MPH with PSM. Without PSM simply and apply the brakes while "running".

With a C4 have someone hold a front tire, CAREFULLY, in place

<{POST_SNAPBACK}>

No offense, but this sounds like an accident waiting to happen for the weekend DIYer without proper lifting equipment... :eek:

[djantlive]

ditto, most ridiculous advice given I've seen. How is someone going to be able to hold a rotating tire/wheel weighing 40lbs?

Just bleed the fluid and be happy that it's done. The drop of fluid inside the ABS unit can't possibly compromise the litre that you just replaced.

[wwest]

It's a simple matter to hold a front wheel "still", virtually no effort, due to the open front diff'l the opposite wheel will simply rotate twice as fast.

[SPIKES]

so how do we do this. i was told today that the car has to be "running"..he did not define running...i assumed car idling while pumping/bleeding the brakes?

how much fluid is in the abs unit?

[wwest]

This first came up when I had Lexus flush the brake system on my 92 LS400 recently. The technician explained that the way he activated the Trac system was by running the car in gear on a lift. The rear wheels turn, the front doesn't and the trac system activates because it thinks the rear wheels are slipping.

[0586slb]

I think your concerns are un-necessary. You mention that the poorer quality fluid apparently left in the ABS pump is a worry because of its lower boiling point. The temperatures in the front luggage compartment are not going to creep much above ambient - no where near the boiling point of the fluid. Its only the fluid in the caliper that has a chance to reach the boiling temperature of the fluid. Because the fluid travels minute distances along the brakeline, it would take decades for the fluid to end up in the caliper, if at all.

Under normal braking, the ABS/PSM unit has straight through passages - it has to, so that if the unit fails electrically, braking will be as conventional. When it intervenes, it just closes a valve in the line it wants to modulate, then a piston either relaxes very quickly (when a wheel locks) or activates to build pressure in the caliper it wants to brake. The fluid that gets in the piston and valve orifices will be negligible

[SPR]

So then assuming what you just wrote in a non PSM can you could just pull the abs fuse and then turn the car on and bleed the system?

[TD in DC]

0586slb

You are joking around, right? Of course I am not worried about temperature in the luggage compartment! However, I, like many of those who frequent this board, actually track our cars and thus fluid boil can be a real possibility. Why else spend the extra $$$ for SRF?

Also, with a modern ABS system like that on our cars, there is an amount of fluid that is trapped in the system, and which will not come out with a normal bleeding of the brakes. It is more than a few drops.

Is this reason to panic? No.

Does this mean bleeding the brakes without activating the ABS is worthless? Absolutely not.

However, when a dealer flushes your system, he or she DOES activate the PSM using Porsche electronics, which I do not have. I have been told that you can do it yourself at home, and I am trying to figure out if there is a safe way to do so.

I will report back when I learn more.

[SPR]

I understand the rationale. However I find that when the dealer bled my system after I had a clutch put in, and subsequent to that when I complained about it. I did a better job when I did it myself afterward. I always bleed the clutch line though. Dunno