’11 Cayman 987.2 master brake cylinder fail during bleeding?

After installing braided SS brake lines, new rotors and power bleeding the brakes, I’m wondering if my brake master cylinder is suddenly failing. I’d like to hear your thoughts. I have 105k miles on my ‘11 987.2 base Cayman 6MT. Brake pedal travel has always been a bit long (like others have noted) but fine for street use with the OEM pads. It was time to get new rotors and bleed brakes, and I thought it prudent to move to braided SS lines (Goodrich). After rotor and line replacement I bled brakes with power bleeder (replacing the old OEM fluid with ATE 200 DOT4 and using RR-LR-RF-LF patern, outboard nipples first). Afterward brake feel was very mushy and the pedal wouldn’t hold under light-moderate force. I bled again, this time pumping the pedal while pressure bleeding each caliper. With the engine off the pedal was stiff, though it did have a slight stutter early in its movement, like a pop from a slight pressure release. With the engine running and booster operating, though, it was mushy and the pedal still wouldn’t hold under moderate pressure. It also continues to have that slight stutter early in pedal travel. i have not yet triggered ABS when bleeding (I have a Durametric). There is no leaking at the calipers nor under the master cylinder . If it was just a mushy pedal, next step would be to bleed air from the ABS system with the Durametric. However, with the stutter and the pedal not holding, I’m thinking it is a master cylinder that has failed during my maintenance. I don’t believe fluid levels went too low in the reservoir, but there’s always the potential it did when I suctioned old fluid out and put a little ATE in to start the bleeding. Thoughts?

Assuming you have chosen the right fluid, german cars are very particular as to what fluid to use, then my guess is you still have air in the system. The only difference between engine running and engine off except the brake boost. With the extra force from the brake boost the brakes are "mushy" so that sounds like air somewhere in system to me. ABS is a good place to start.

Thanks RickH, seems to be the consensus of folks I’m talking to. I’ll give bleeding the secondary (ABS) circuit a shot, just means burning through anther ~$20 quart of ATE and finding a helpful soul around the shop to lend their leg to the cause. Not really sure the final pedal “pump ‘n hold” is necessary when using a power bleeder, but I’ll stop thinking and just follow directions (ref: Nuke LaLouche). Never had issues with bleeding and ABS before, but have never dealt with master cylinders in modern 4wheel ABS cars (just older ones).

If air got into the the ABS you need to bleed the ABS circuit. If the system drained completely during the line change this would happen. I seriously doubt there's anything wrong with your master cylinder other than it's not a GT3 unit Bleed it again with the Durametric and you should be good to go.

I strongly doubt the problem is your master cylinder . As already mentioned flush again and pay attention to the ABS pump.

How much pressure did you use on the pressure bleeder? The first time I bled the brakes on my 07 I ended up with a mushy pedal. I increased the pressure and bled again and got good brakes.

I did the ABS secondary bleed process with a Durametric. Brakes are still very soft and long, though I can get he fronts wheels to trigger ABS at parking lot speeds. I pressured to 2bar at the start of each caliper. I used the Brake Bleed activation selection for each caliper, but the pump was never triggered. Once I began a bleed, I pumped the pedal for ~20secs while the Durametric was in Start for that corner. It never gave any directions while bleeding, so I selected Stop manually then closed the nipple. I then bled the inside of the caliper without the Durametric. Since the pump never triggered during the bleed cycles, I went around and did it again, this time triggering the pump via Durametric for ~20secs while pumping the pedal. I’m wondering if I should have waited during the first cycle of ABS bleeds for Durametric to give me directions, rather then manually hitting Stop. Could I have stopped too soon to let Durametric do it’s thing? I called Durametric but they didn’t want to tell me how to use it to bleed brakes (liability, I guess). I also looked online for a better description but no use. Any insites on how the Durametric responds during bleed operations? I’ve never had this much difficulty with a bleed (though ATE is sure making out in fluid sales!). Thanks.

Sorry to drag this up, did you solve this? When driving did you notice any unusual behaviour? I found a similar problem, soft pedal feel, ok at medium speed but at low speed brake performance really poor. My mechanic suspected vacuum pump failure, so we replace which seems to have improved things, but after a relatively short drive the problems return. What did you do to solve the problem?

Once I got it on the road it was fine. No issues on street or track, though I would like to put in the GT3 master cylinder for better response.