Brake Flush: How important is cycling ABS?

Looked up a bunch of threads for my impending brake flush using a Motive bleeder. Someone mentioned to cycle the ABS valves during the flush. I don't have a PST2 to activate the solenoids during the flush. Someone recommended flushing, then driving and stomping on the brakes to activate the ABS a few times, then doing a complete flush again. I also read (on a 993 thread I think) that just starting the car will get activate these brake solenoids and allow a flow. Do the 996's work this way? How important is this? I've not seen much info on this listed anywhere. TIA!

REAL good question. I've never had brake feel issues on my 996 from doing flushes with my motive power bleeder the standard way. However on my M3 I chased a soft pedal forever, rebuilt calipers, replaced lines, etc chasing what was ultimately air in the ABS system. Once I was able to use a dealer tool to cycle the ABS during the bleed process I finally got proper pedal feel back. Andy

so what do you need to cycle it? Durametric?

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I heard a PST2 since only the full monty Porsche computers can talk to the ABS and command actions. Thanks for the feedback Andy, good to see the comparison between your bimmer and p-car.

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I dont think Durametric will do that... Just bought one, but it's in transit still.

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On the M3, do you suspect that air got in the ABS system during your bleed sure that you shouldn't do a BMW bleed with a Motive?

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I've never cycled the ABS pump on any of my cars when I've bled the brakes with a motive pressure bleeder. On our E46 3-series, I have done this numerous times and the brake pedal is hard as a rock. I'd gather there is some air in the system in your case. - Anthony

we learned this in class but i can't remember the year and model. i think its an early c4 but i will look it up in my notes later today.

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That makes sense. I can't imagine how air would enter the ABS system just from bleeding that doesn't cycle the ABS valves. There must have been another problem with his car. As for the OP, I must stress that I do not know, but I have always thought that the quantity in the ABS system is likely pretty small and since the brake fluids are compatible and I am changing fluid more frequently than is really needed, that it makes little practical difference to bleed without opening the ABS. On the same theory, I don't bother with the clutch line bleed either.

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You should really bleed the clutch as well - it holds a decent about of fluid, and the clutch action is so much smoother if you regularly bleed the clutch. I do this on all of my cars when I bleed the brakes. - Anthony

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Can I bleed the clutch using the same DOT4 brake fluid? There is an article on renntech about bleeding the clutch and how doing it is slightly different than doing the brakes (must wait longer and slowly depress pedal, etc.).

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The clutch and brake fluid use the same reservoir. So if you don't bleed the clutch fluid, you still have some old fluid in that line.

I don't know how I missed this, but Loren on RennTech commented about this issue in his DIY for bleeding (which I read a couple times even! http://www.renntech.org/forums/index.php?showtopic=7064 ) Someone asked why the Porsche does not have a bleed valve on the ABS valve manifold like this person's Lexus's, and Loren replied that Porsche uses a PST2. Then that person asked if that meant if they had to take the P-car to a dealer to get the ABS fully flushed out, and Loren replied: "Most dealers do not both to bleed the ABS unless the system has been open (i.e. lines or components replaced). I have a PST (and PIWIS) and and I usually do not bleed the ABS on my own car." (I left Loren's typo in there, but it's obvious what he meant). If it's good enough for Loren, it's certainly good enough for me!!

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Oh!! Thanks ArneeA! My goal is to someday not be a P-car newbie.

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Exactly.

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Nothing wrong with Bleeding with the Motive on the BMW. As I look back I know exactly when I got my issue...it was a spur of the moment lapping day I did with the M3 that caused my issue. I was running street rubber, street pads and ATE Blue fluid (I've never had much luck with the ATE fluids). It was a combination of engaging the ABS on the street tires and overheating the street pads that led to air in the system. Moral. Make sure you've got good tires / brakes and fluid or don't go to the track.

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n/p good luck with it all. We all started somewhere, right?

I always was under the impressionthat ATE Super Blue was one of the best? Is it all hype? The numbers on the can are excellent. I was going to go to blue next time....

It sounds like everyone came to the correct conclusion that cycling the ABS during a normal bleed is not necessary. Actually the manual states as much. It is only necessary when air has been introduced into the system.

Thanks Ubermensch. I bled out the brakes and clutch, no problems. Used a total of 2000ml (four 500ml bottles) of Motul 5.1. I have some tips: Tip 1) I couldn't find a turkey baster small enough (or a syringe) to get into the reservoir to suck out the old fluid. So, I removed the interior cover in the trunk so I could see the reservoir and its level. I then put the Motive bleeder on it with NO FLUID inside, and simply pushed the old fluid out thru the right rear caliper, but not so much as to introduce air in the system. Question though: there is a small tube going from mid-reservoir into the cab (see attached). I was afraid of getting any air into this line (don't know what it's for, clutch?), so only pushed the fluid down to this point, not letting the level get lower than the tube. There was still a decent amount fluid left in the reservoir, so maybe it's best to suck it all out down past this tube using a syringe, thus allowing most of the fluid to be removed, but for old fluid to stay in that tube instead of air getting forced into it. Tip 2) So you don't round any of the bleed screws off with a line wrench or 12pointed end wrench, break them loose first with a 6point socket, and then close. If you do it with pressure applied, there's no fear of air feeding back into the system, just be sure to just crack them and close to minimize any spillage; I was able to do it with no leakage. Then you can put your tube and end wrench on the bleed screw and open it up easily . If you have 6pointed end wrenches, you've got more money for tools than I, and there's no need. ; ) Tip 3) Follow Loren's directions to a T!! I posted earlier in this thread, they're awesome and work like a charm (especially the part about how to bleed the clutch; I went thru a full 500ml on that, BTW.) My fluid was a bit dirty, only a tiny bit dark, but was green! Yikes! Happy bleeding!

ATE Blue is for all intents no better than the OEM fluid. Also leaves lovely blue stains on all that it touches. Use Motul RBF 600 -

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But telling people to use RBF 600 on a street car doesn't seem like that good of advice. I'd suggest Motul 5.1 for a street car, or if you don't want ATE superblue which does stain the reservoir, then use ATE Typ 200, which is the same thing but without the blue dye. - Anthony

I'd bleed brakes on a street car 1x per year anyway, so why not

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First, NEVER use the regular pedal method to do a brake flush these cars. The only time you ever use the pedal to bleed any part of the system is if replacing a master cylinder or a caliper. Then you only apply pressure to the pedal AFTER you open a bleeder. Because of the reverse flow valves in the ABS system, you can damage the system by traditional pedal bleading. Factory service manual (section 47-01-07) states to only pressure bleed at "approximately 1.5 bar" (yes that is correct: 1.5 bars/22 psi) of pressure. Using the Motive bleeder is a good way to bleed these cars. I normally pump to 25 psi then start bleeding. When the pressure drops to 20 psi, I pump it back up to 25 psi; basically averaging the recommended 1.5 bars. Motive recommends a max of 15 psi, but this is a much higher pressure brake system than most cars. Normally, I get a rock hard pedal right after bleeding. Fluid matters a lot. With Motul 600 or 660, it gets consistantly hard after every bleed. With ATE Blue or Gold, it is always soft (I don't recommend to ever use ATE as a result). AP551 is a good alternative if you are looking for a fluid just for the street that gives a great peal feel. If I feel any sponginess in the pedal, I will go out and get the ABS to kick in a couple of times. This is usually on a bumpy road where the ABS kicks in earlier. Remember, you need to get all the valves to activate. This means being able to lock up every corner. Getting the ABS valves to open will allow any air trapped near the ABS unit to purge into the reservoir. If it is still spongy, re-bleed them.

Peavy, that *is* the line to the clutch master cylinder. For those that care, you can also use a flare nut wrench on the bleeders, if you're concerned about rounding the corners of the hex.

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Durametric 6 is currently in beta and now also compatible with 9x6's. It DOES allow ABS cycling for the purposes mentioned by the OP. http://www.durametric.com/versionhistory.aspx JP

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I stand corrected, I downloaded the beta of 6 and it will indeed do that on the 996.

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My WAG is it is a good thing to exercise the ABS hydraulics to thoroughly remove the old brake fluid from every nook and cranny in the brake hydraulic system. The brake fluid picks up moisture at only one place I know of that is exposed to air and that is at the brake fluid reservoir. Yet when one bleeds old brake fluid the fluid that first comes out of the caliper bleed screw is often the nastiest looking of the fluid. This suggests to me that whatever enters the fluid at one point will migrate and contaminate the whole of the fluid over time. By exercising the ABS to flush the old fluid this ensures any contaminated fluid is removed from the system. Chances are you won't notice any difference in braking but over time this preventative brake fluid flushing/bleeding will prevent any premature failure or problems in the ABS system. Since AFAIK only a dealer service department has the diagnostics tools to cycle the ABS this implies brake fluid flushes/bleeds need to be done at dealership. However, I can understand the reluctance of some to do this. Perhaps every other fluid flush/bleed could be done at dealership. The others could be done at home under the shade tree. Not ideal but better than not doing any brake fluid flushes/bleeds or doing them and never cycling the ABS. Sincerely, Macster.

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Thanks Van. So I actually could have used the Motive bleeder with just air in it to push the fluid down in the resevoir to almost the bottom of the tank and still been OK, right? Since that line goes to the clutch master, and that line is sealed, no air could have been pushed down into that tube (I used the right rear caliper to bleed during this part). I didn't want to chance it, so pushed the fluid out with air just to the top of that tube, and then filled with clean brake fluid. Still purged with fluid in the Motive until it all came out clear, so should be good to go. As to the wrench, I do have line wrenches (flare nut wrench), but have even started to round stubborn bleed screws with them before (not on this car). When I pop on a true 6-point and they've come loose. Then back to the line wrench.