[Vicegrip]

Originally Posted by Roo

Hmmmm....sure sounds like a master cylinder spool seal failure. With a well operating brake system, pushing the brake pedal pushes a spool inside the master cylinder bore which forces fluid from the reservoir through the lines into the brake calipers moving the pistons againt the brake pad backing plate.
The spool has several seals which separate the two halves of the brake system and force fluid into the lines. When the seals fail, pushing the pedal doesn't transfer as much fluid (or pressure) through the lines to the calipers resulting in reduced braking. Pumping the pedal may help as you're resetting the spool with fluid from the reservoir.
If you lost the vacuum boost on an otherwise good brake system, you would still have a functioning brake system. However, the pedal effort would be much higher (and the pedal wouldn't go to the floor).

This would be my first stop given the list of issues. Let us know what you find.

[BikePump]

Thanks Kurt - parts will be here for this weekend and I will be swapping out all of them. I wont know if it solves the issue at "track" speed until the Metro DE in 3 weeks so time will tell. Any way it goes I replacing the 15 year old parts cant be a bad thing.

[BikePump]

Quick update on the brake issue. Swapped out the master cylinder prior to the Metro DE weekend and had ZERO incidence of the brake pedal issue so it would seem to be solved. Still having some softer pedal than I would like and hopefully the rebuild of the calipers and new front rotors will address that over the winter.

Thankful that the super-scary thing is solved

[good hands]

Good to hear. GT3 MC seems to be the ticket to that soft pedal thing but it's not absolutely necessary. Drove a buddy's car that had it and it is definitely better.

[blipshift]

Question for y'all...everytime you flush a 996/7 with ABS, does it require a hookup to PWIS or Durametric? Or, if you get it pressurized, say with a motiv, and don't introduce air, the system stays closed? Soup to nuts, I'm trying to understand how the ABS gets bled. I'm not exactly clear what's going on and why, when it seems some systems require ABS manipulation to flush.

I went with GT3 MC and Booster. Was great for 2 track days. Third day I had ice pedal in 1 (pumping did not resolve the issue, the car slowed but the brakes weren't biting with full force)...twice. The only thing that seemed to work was setting the brakes after coming out of 10 by applying slight left foot braking while accelerating (enough to feel the brakes grab). And even then, I was braking around the 5 board...not the usual inside 3/2ish.

I'm almost positive there was air or old fluid still stuck in the system which worked its way to the calipers or somewhere in the ABS by the 3rd day. The system has been flushed 3 times with Durametric...after reading stuff all over the internet claiming Durametric cannot properly flush the ABS I decided to take it to a shop with a PWIS to see if that would fix my issue.

[Fumes]

Originally Posted by blipshift

Question for y'all...everytime you flush a 996/7 with ABS, does it require a hookup to PWIS or Durametric?

when I flushed 991 I did not use a Durametric and got advised I didn't need to. I had no issues.

you could try the gravel method -- others here will know better -- but I think idea is to go drive on a gravel road and brake a bunch to activate ABS a number of times in a row in hopes it moves some fluid through and dilutes the old fluid from the ABS (tiny amount) in the much larger amount of fresh fluid you just put in the system.

[blipshift]

Originally Posted by Fumes

when I flushed 991 I did not use a Durametric and got advised I didn't need to. I had no issues.

you could try the gravel method -- others here will know better -- but I think idea is to go drive on a gravel road and brake a bunch to activate ABS a number of times in a row in hopes it moves some fluid through and dilutes the old fluid from the ABS (tiny amount) in the much larger amount of fresh fluid you just put in the system.

I've flushed the 997 in the past with a Motiv and had zero issues. Which just confuses me more as to how this happens.

[987kmns]

Two things:

1a) I tried flushing the brakes on my 987 Cayman with the Durametric and I'm pretty sure the Durametric did not actually activate the ABS pump. I couldn't hear anything running and in theory I should have been able to, even though from a software perspective all seemed to work.

1b) With the above said, I don't think you need to flush the ABS on these cars to have good brakes. In theory, air can get into the ABS, but the likelihood of that happening is very small. When you do a normal Motiv flush, the ABS stays shut, so if there is no air in it to begin with, you won't be introducing any during the flush. For some reason I can't imagine air hanging around in the piping leading to ABS and being admitted in when the ABS in engaged. That sounds like a really low likelihood event.

2) I've had ice pedal events several times now and IMHO brake bleeding has nothing to do with it. I've had the best success in managing it by a very smooth, gentle, non-aggressive first application of the brakes. In your example above, if you start at the 5 marker with a very progressive application of the brakes you should be in better shape. You can still carry a little more speed deeper into the brake zone, but start applying the brakes earlier. I hope this makes sense. Other factors that affect ice pedal events are track conditions (green vs not green, hot vs cold, etc) and tires (new vs old, hot vs cold, and correct aspect ratios front to back).

[blipshift]

Originally Posted by 987kmns

Two things:

1a) I tried flushing the brakes on my 987 Cayman with the Durametric and I'm pretty sure the Durametric did not actually activate the ABS pump. I couldn't hear anything running and in theory I should have been able to, even though from a software perspective all seemed to work.

1b) With the above said, I don't think you need to flush the ABS on these cars to have good brakes. In theory, air can get into the ABS, but the likelihood of that happening is very small. When you do a normal Motiv flush, the ABS stays shut, so if there is no air in it to begin with, you won't be introducing any during the flush. For some reason I can't imagine air hanging around in the piping leading to ABS and being admitted in when the ABS in engaged. That sounds like a really low likelihood event.

2) I've had ice pedal events several times now and IMHO brake bleeding has nothing to do with it. I've had the best success in managing it by a very smooth, gentle, non-aggressive first application of the brakes. In your example above, if you start at the 5 marker with a very progressive application of the brakes you should be in better shape. You can still carry a little more speed deeper into the brake zone, but start applying the brakes earlier. I hope this makes sense. Other factors that affect ice pedal events are track conditions (green vs not green, hot vs cold, etc) and tires (new vs old, hot vs cold, and correct aspect ratios front to back).

All great observations. Something I forgot to mention, though...brakes at the start of the first event were hard and pedal initiated braking with little pedal depression. As time went by the pedal got longer.

Additionally, ice pedal only occurred when I didn't set the brakes. That being said, it wasn't the same feel as two days prior. Since it has a new mc and booster and calipers checked out it can only be air or faulty abs.

[blipshift]

For comparison I drove two other 997s to get a feel for their braking, one being CanAms. Completely different feel. The ABS only was activated when it truly needed to be whereas my abs system seems to activate if you look at it wrong.