Brainz

I'm posting this for posterity sake. I hope it helps someone.

I was supposed to take my 997TT to the track today. In preparation, yesterday evening I switched from Hawk ceramic pads to Ferodo DS 1.11s (special thanks to Clark at Apex) and replaced the ATE Typ 200 with fresh Motul RBF600.

I used a pressure bleeder (dry method) to help bleed the brakes. It was all going well enough when I messed up and ran the master dry. No biggie, just keep flushing and any air in thebsystem it will pass on through, right? Except I never did see much air come through.

The pedal feel after bleeding was horrendous, and very strange: the pedal made a squishing noise when pressed and would sink to the floor at a quick rate (but not instantly). I could pump the pedal and get it to firm up, only to sink again to the floor. Despite re-bleeding, it wasn't getting better. I've had spongy brakes before (that needed bleeding) - - this was much worse - - it felt like a failed master cylinder.

Probably not my best idea, but I decided to see if driving the car might improve the pedal (I wanted to trigger the ABS). The braking matched the pedal feel: it would initially slow with pedal application, but as the pedal sank over the next half-second or so, the brakes would go away as the pedal went to the floor. If I pumped the pedal, I could get more braking (even to the point of lockup triggering ABS), but the braking force would decrease as the pedal eventually sank and there was no improvement in the pedal feel overall.

It was almost 10pm, I was tired, and I suspected that I may have damaged my master cylinder by over-stroking the pedal while bleeding (in conjunction with the power bleeder). Track day canceled...

I read the forums last night looking for a solution. There were a handful of people that had experienced similar issues. The solutions included new master cylinder, new ABS unit, caliper rebuilds, and rebleeding at the dealer (PIWIS has an ABS bleed mode). There was also commentary by several people that said they'd tried using the Durametric bleed mode to no avail, and that the car required dealer servicing.

With my track day ruined, I had time today to attempt another re-bleed. Although I have a Durametric, based on the forum feedback, I decided to use my iCarScan x431 scantool to trigger the ABS unit while bleeding instead.

I followed the instructions (which were clear enough in this case, though not always with the iCarScan tool):

- Fill brake master cylinder reservoir with your favorite flavor of fluid (use a turkey baster or syringe to remove old fluid first if needed)
- Attach pressure bleeder to the reservoir and pressurize
- Crack the brake bleeder and immediately run the iCarScan bleed mode for the appropriate wheel (which triggers the ABS valve and/or ABS pump) - - note unusual wheel sequence below
- Slowly pump the brake pedal while the ABS unit is being cycled and the caliper being bled
- When the cycle ends, bleed the other nipple on the caliper (without ABS cycling). I prefer to bleed the outside nipple first, and then move to the inside nipple after the ABS has cycled. This seems to capture the air on the inside nipple. Not sure it really matters.
- Be careful to not run your brake reservoir dry. I marked my catch bottle with a line at 250ml. The brake reservoir holds ~350ml, so don't go too far past the line on your catch bottle or you risk having to re-bleed again
- Repeat all the steps above for each wheel in the order specified: iCarScan said to do the following order: LR, LF, RF, RR

For whatever reason, bleeding on the left side with iCarScan did not trigger the ABS pump, but I could feel that a valve or something in the ABS was was opening and closing as the pedal resistance would change while pumping the brakes during the cycle. The right side calipers take longer and do trigger the ABS pump - - it makes a lot of noise and the pedal does all sorts of weird things while pumping, ranging from rock hard to pulsing/vibrating and sinking.

The end result was that after I bled each wheel, the pedal got incrementally firmer. And when I cracked the final (inside) bleeder nipple on the RR caliper, a long stream of air came out before the fluid flowed clear. Boom. Rock hard pedal with the engine off. The pedal did get a bit mushier when the engine was started, but that was "normal" and the sinking was gone.

I could have probably stopped there, but I'd used (cheaper) ATE Typ 200 to do the above ABS flush, since I really wasn't sure that was my problem and I was expecting to potentially have to replace the master cylinder (which would require yet more bleeding). But as the master cylinder appeared OK and I had enough RBF600, I elected to re-run the full ABS bleed procedure one more time to replace the fluid with RBF600.

Test drive confirmed it's all good now. Whew!

Lessons learned:

DO NOT let the master cylinder reservoir run dry. It appears that air can get trapped in the ABS unit and really mess up your brakes (at least temporarily).

Ideally, if you are going to bleed your own brakes you should probably have have a scan tool that can activate the bleed cycle on the ABS if for no other reason than to save your bacon if you do get air in the system. I'll plan on using the iCarScan going forward as it was straight forward to use and took no extra time versus the "normal" method of bleeding the brakes.

If I'd known what I was doing and/or not waited until the night before, I wouldn't have missed my track day...

jayzbird

Agree the best way to avoid accidentally running dry when dry bleeding is to use a measured catch bottle. Motive sells these, 500ml I believe albeit with no markings, so mark them yourself and you’ll always know just how much fluid you’ve removed.

Petza914

A few years ago I did the same thing using the Motive dry. Took something like 3 or 4 more bottles of fluid to resolve ir, and didn't have success until doing the abs activations with the Durametric. Usually now, I dump about 6 bottles of fluid into the motive and do all the cars one right after the other. With my open wheel designs, I can access the bleeders with the cars on the ground just by rolling them back and forth by hand a bit, and have all the cars running RBF 600 now. I used to renew the fluid every spring, but bought a brake fluid moisture measuring tool and after a year they're still reading only 1% so probably going to move to a 2 year cycle.

RABjr

Excellent writeup. As long as you don't run low in fluid in master cylinder the ABS cycling isn't necessary- correct?

Petza914

Corect.

Brainz

Correct, and as noted above, one helpful way to avoid running the master reservoir low is to put a 250ml mark on your catch bottle. That should give you ~100ml of safety margin.

But don't get distracted, like I did, and move to the next corner without first refilling the reservoir... Doh!

I avoid the wet method primarily because I despise cleaning the pressure bleeder, and I'm always concerned that I the pressure bleeder could pump brake fluid some place I didn't want it if the tubing were to rupture.

Wayne Smith

My first Motive failed, leaking brake fluid everywhere. Fortunately I never trust brake fluid so everywhere was only into a garbage bag I had the Motive in to act as a secondary containment chamber. The mess would have been enormous otherwise.

I pledged to only use my second Motive dry after that. But constantly removing the Motive from the master cylinder for refills got old quickly.

So I picked up a vacuum system. I can use an adaptor cap to place the brake fluid jug upside down on the master cylinder and this acts as an auto refill. Makes bleeding a breeze and works on all cars.

ManoTexas

Thanks Brainz, takes personal strength to post failure as well as success, and you achieved both! And great advice I from which I can learn since I’ll be flushing brake fluid in next few weeks. I’ve done far worse things working on cars. However I won’t admit to the total debacle of changing a clutch master cylinder on an Audi 25 yrs ago, I’m not as mentally strong as you.

Tman-Wa

Thanks Brainz for the write-up. I thought I had really messed my master cylinder up: https://rennlist.com/forums/987-981-...w-owner-2.html, but followed your procedures after purchasing the iCarScan and had the same successful end results.👍👍

Brainz

That's great! Glad you got it sorted.

rickster997

I had this same problem on my 997.2 GTS after a shop replaced my master cylinder. They kept saying it was normal. I actually went on track thinking I could engage the ABS and after the first session it went back to normal. Do you have a link to the iCarScan x431 you purchased?

I watched them do it... they did not do "- Slowly pump the brake pedal while the ABS unit is being cycled and the caliper being bled", I wonder if that was the issue.

rickster997

https://www.obd2tool.com/goods-10333...SABEgJtZ_D_BwE

Is this it?

Tman-Wa

that’s the one I ordered. Took about a week. $203.66 out the door.

Brainz

The link you posted looks right for iCarScan. That version has 7 vehicle marques, mine is older and the licence only covered 5. I did Porsche, MB, BMW, VW and Toyota. You get free software updates for 1 year, but the device keeps working thereafter - - you just wont get the latest software (which is usually for new cars anyway).

If your mechanic didn't pump the brake while the ABS unit was cycled, it may not have moved the air out of the ABS.

For you guys with the latest iCarScans - - see if you can adjust the TPMS settings (eg: lower the pressures from the factory warning level). My older iCarScan has the menus for programming, but I could never get it to work. Would be great if they fixed that in the latest software.

Tman-Wa

“That version has 7 vehicle marques,”
Actually only 5 vehicles, plus a General OBD2 and one other non vehicle. I can add the other vehicles anytime before the year is up.
I don’t have TPMS on my car sorry.