I’m a one month owner of my first Porsche- 2006 Cayman S (with chrono and PSM). The previous owner (since 2011) had not flushed the brakes in years and hadn't tracked it. I’ve always done maintenance and most repairs on my vehicles since my ’67 Mustang in high-school. So, I read up on the job, bought me a Motive power booster, filled the master cylinder reservoir, attached the Motive (dry) and boosted to 15 psi. I started the flush on the RR caliper. I flushed the outside and then the inside bleeder valve (approx. 200ml/100ml). Moved to the LR caliper and didn’t have room to work, so started the car to move it, and when I pressed the brake, it went clear to the floor. The second pump stopped the car. I checked the reservoir and it was low, just barely covering the bottom of the reservoir. I finished the LR, RF, LF flush of outer and inner bleed valves, keeping a better eye on the reservoir. The only air bubbles were in the LF, and they cleared up quickly. Once completed, the pedal would build pressure when pumped and hold (didn't sink to the floor) with the car off. I then took it for a short drive during which I would have to pump the brake once, then it would firm up and be able to stop the car. I then flushed the outside bleeders for each caliper by the old pedal pump method- pump 3-5 times, hold, open bleeder valve, drain, close valve, release brake.

The next day I tried to follow the maintenance manual, picking up after the motive pressure procedures. It states “Check the brake system for residual air by the amount of brake pedal travel. Repeat the bleeding procedure if necessary. Operate (pump) the brake pedal at the same time as described below. This will remove the remaining air bubbles from the primary circuit. Open the rear right bleeder valves, then fully rapidly depress the brake pedal hard several times. Hold the brake pedal for 2 to 3 seconds after each depression, then release slowly. Continue bleeding until the brake fluid emerging into the collection bottle is free of bubbles and foam.” This was confusing, as it appeared to direct us to open the bleeder valve and then pump the pedal, with the Motive pressurized. So we attached the Motive, boosted to 25psi (the maintenance manual called for 2 bar) and completed the pedal bleed by the same method I described above. And removed the Motive.

The pedal would go to the floor, then the next pump would hold midway (it wasn't spongy) while the car was not running. As soon as the car was started the pedal would sink to the floor. When we pumped the pedal while running and held it, it would slowly sink to the floor. Another thing we saw was that brake fluid was very slowly leaking from the seals between the reservoir and master cylinder, only after the car was running while pumping the brakes. Is the vacuum booster causing high pressure in the reservoir due to possible seal damage?

My understanding is that I could have damaged the master cylinder piston seals when the pedal went to the floor the very first time. But I don’t understand why it went to the floor the first time without any resistance.

I am hoping someone can provide some advice on what my next step should be. I am hesitant to install a new mc by myself- with my epic brake bleed failure my mojo is down.

 

Sounds like you have air in the line to the rear caliper. That's why I don't like trying to use the motive dry, the resovoir just doesn't hold enough fluid.

One you get air in, its a long line to fully flush. Will take more fluid than you think to fully flush it end to end.

Don't know about the seal between the MC and booster, but its not uncommon to develop leaks on an old MC that's put to the floor the first time. You can get some minor corrosion in the bore just beyond normal range. One you drag the the piston seals over the rough area you can get seepage.

Changing the MC on these is a piece of cake. Id change it out and run 2 full bottles of fluid through the system using the motive the "correct" way.

Your mojo is still good.

 

Do you think it’s just air In the line with the pedal going clear to the floor when the car’s running? I’ve always had the pedal stop before hitting the floor when it’s been air. But, I’ve never had a MC fail before.

 

your master cylinder is fine. Its not some ancient car with rust or rough surface in the MC so that the seal would be damaged. I wouldn't make a habit of it, but its a non issue.

Your reservoir to MC seals are leaking because you have the motive at 25psi. Wayyy too much. 15 is perfect.

You will need to run a boat load of fluid through it. Use the motive, use the foot method, but I wouldn't combine them at once. I typically flush with motive, and do a final bleed manually.

Worst case, you may need the abs unit bled, but I doubt it.

Don't panic.

 

Thanks for the input! Only the final flush that I performed was at 25psi. The initial was at 15-18. Here's the snipit from the workshop manual.

 

Like others mentioned, I cant imagine the MC is damaged, most likely air got in somehow. Worst case pay a few hundred and take it to a indie shop to do a flush of the brake fluid.

 

I hate to give you my opinion of what happened, but *if* you get air out of all the calipers and you still have this issue, what you've done is the same thing I did a few months back, which is run the reservoir so low that you got air into the ABS. The only way to resolve that is to get someone that has the Porsche computer that can cycle the ABS pump to get the air out of it. No amount of bleeding will get the air out of the ABS. When I did it I got the car to the dealer along with 5-6 bottles of fluid and they charged me $300 to do it.

 

Maybe I’ll go find some a drive to activate the ABS (in the pacific NW it’ll rain in a day or so, and with summer tires still on, I should be able to activate it). And then do the full flush again and see what happens. The last thing I want to do is put a new MC in and still have the problem. The input seems to point to MC change being the last step after more Flushing/bleeding and ABS activation.

 

I tried that method too. The second time I got up to 35 mph on a deserted road and jammed on the brakes, the rear driver’s side tire locked sending the car almost sideways. It was at that point that I limped to the dealer with my tail between my legs admitting defeat. Wasn’t worth trying to fix it that way IMO so I decided to not make a bad situation worse.

 

Yikes. I don’t need that excitement. Got enough these days. I’ve got to go back and read some more posts, as I don’t remember if the Durametric will do that. I don’t have one, but could reach out to the local PNW PCA.

 

I'm pretty sure EZ99B5 gave you the right answer. Durametric is supposed to be able to actuate the ABS pump but from reports I've read (never tried it myself) that function doesn't work right. Can't hurt to try, I guess.

25 PSI is not a problem. As you noted, manual specs 2 bar (29 PSI) and that's what I've used without issue. I know folks like to use the Motive dry but if you use the wet method you'll pretty much eliminate the risk of running the MC dry. I do the bleed with the Motive full and it works great.

 

Old guy weighing in here, but I've got to say that if there's one thing on a car that I want to be perfect, it's the brakes. Bite the bullet, find a good shop and get everything on the brakes back to spec. You'll thank yourself the next time somebody blows a STOP sign in front of you and you have to make a full-on panic stop.

 

That's not going to work. The ABS is also the PSM modulator - and there are 4 separate pumps in the unit. Only the one where the wheel is locking up will be activated. *Each one* has to be bled while activated - and bled from the wheel it's associated with. The best way to do this is to hook up the motive bleeder, pressurized to 5PSI with brake fluid in it so the reservoir CAN'T GO DRY, (5PSI doesn't destroy the reservoir seals or even worse - pop the reservoir off the master brake cylinder (I've seen that happen and it's not a happy thing to see..) Then go around to each wheel, open the bleeder and activate the modulator.

iCarScan has a function to activate the ABS/PSM modulator - you don't need to visit the dealer.

For the OP - dunno if there is a master-cylinder rebuild kit so you can get the reservoir seals. If not - a new master cylinder might not be a bad idea. And as someone pointed out - it's not uncommon for a neglected brake system to have corrosion/rust in the last inch of travel of the master cylinder since the piston seals normally never travel there, and water in the brake fluid will tend to accumulate in the stagnant fluid. One way to avoid that is - use a pressurized bleeder, and when bleeding the master cylinder DO NOT take it all the way to the floor. A 2" block taped to the back of the pedal will avoid this if you're doing the old fashioned 2-man bleed (one at the pedal, one on the bleeders.)

 

iCarScan tool is on the way. Thanks for the helpful input.

 

Great - let us know how it works out!