996-C2 (1999) Brake Issues

[BikePump]

As most of you know Carmine had some significant brake problems on Friday at DE that were mostly resolved on Saturday and didnt become apparent at all on Sunday.

The issue goes like this:
-Brakes have been flushed bled and tested - nice firm pedal no issues.
-20 min into the session the brake pedal isnt necessarily as hard as it was initially but no degradation in performance and the pedal travel has only increased by 1-2cm (think this is a brake cooling issue - will explain more later in the thread)
-all of a sudden (normally going into the brake zone at 10 for some reason) the pedal goes down almost to the floor. pumping will get me braking so i can stop the car but now the pedal is super long almost to the floor and unsafe and so i end the session. the brakes are unusable at this point
-check brakes in the pit - no bubbles when i bled and the fluid is the reservoir is correct level.
-when i head out for the next session - it all starts over again. this repeated 5 times on Friday.
-overnight i flush and bleed the fluid again
-saturday the major issue doesnt reoccur. strangely enough this is the exact same sequence of events and days that occurred at the August DE - including that on sat-sun there was no problem.

I have talked to many of you up and down the paddock searching for answers with nothing definitive. I am running PFC pads and slotted rotors and the rotors are one month old and the pads have 5 DE days on them. The prevailing theory is that there is an issue with the master cylinder - maybe an internal seal leaking and letting fluid blow past.

Today I was preparing to order a new master cylinder, seals , and booster - when something in the Pelican diagram struck me. There is a vacuum hose from the engine to the brake booster. It terminates on the driver side wheel well wall in the trunk and then there is a short hose from the surface mounted plate to the brake booster. One of the things I have noticed going into Turn 10 braking zone is that there does appear to but a subtle inflection in the brake pedal right when i get onto the pedal - feels almost as if the quick release of the throttle has "pulled" down the brake pedal a minor amount. It happens but more subtly into 3 but not into 5 or 1.

Could there be a vacuum issue at play here? your opinions are valued.

ps - sunday showed me that the small amount of fade that I am experiencing is due to overheating. Session 2 I was out in traffic the entire time and experienced the fade - while in Session 3 when I was driving in clean air the entire time I had zero fade - and I was driving quicker! going to have to address this over the winter with next ducting up front and a caliper rebuild

[N0tt0N]

Do you have ABS on Carmine?

[BikePump]

yes Carmine has ABS

[VA951]

Reading this I was thinking master cylinder as well but your mention of vacuum reminded me of an issue with Boxsters I heard about. Something along the lines of leaves clogging the body drains and water getting into the brake booster vacuum area and creating issues.
May be worth a look.

[HoodPin]

Make sure you don't have a high pressure leak somewhere. Had a situation once where the hose fitting on a caliper was failing. The Motive didn't provide enough pressure to get fluid leaking at the hose, but firm pedal pressure did. Any evidence of "wet" around any of the brake lines under the car?

[BikePump]

no evidence of any fluid leaks Tony.

[BlackTalon]

1. Not that it likely is the issue, but a small amount of pedal movement before the brakes engage usually means you should check the wheel bearings to see if one (or more) is loose.

2. Do you really name your cars? :lol:

[BikePump]

David - there are no bearing issues they have recently been replaced.

Pat named the car... :)

[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).

[Trak Ratt]

David - there are no bearing issues they have recently been replaced.

Not really "proof" and a lot less expensive than an MC! Disconnect the vacuum hose (plug the engine side) and see it duplicates the issue (low speed please)

[BlackTalon]

David - there are no bearing issues they have recently been replaced.Yeah, so were mine. And one front wheel bearing loosened on Friday. And the left front loosened at the August event. And at an event last season one of the rears was slightly loose. All were due to the bearing replacement work done by the shop not being quite perfect -- and they are a good shop. It happens, and is very easy to check for.

[BikePump]

i wish that i could make this happen at low speed David that would make my life easier. Unfortunately it will only occur after heavy use on track.. never ever on the street

[BikePump]

Yeah, so were mine. And one front wheel bearing loosened on Friday. And the left front loosened at the August event. And at an event last season one of the rears was slightly loose. All were due to the bearing replacement work done by the shop not being quite perfect -- and they are a good shop. It happens, and is very easy to check for.

it was actually something that Dirk checked after the first time this occured on Friday - all was well

[BlackTalon]

Gotcha. I was just throwing that out there as something that could be happening in addition to the main problem since it seemed the pedal normally 'drops' a little.

BTW, do you have any brake cooling other than factory scoops? Are you running stock wheels? Are the wheel spokes sufficiently open for good expose of the caliper? Have you removed the sheet metal dust shields on the insides of the rotors?

[BikePump]

Gotcha. I was just throwing that out there as something that could be happening in addition to the main problem since it seemed the pedal normally 'drops' a little.

BTW, do you have any brake cooling other than factory scoops? Are you running stock wheels? Are the wheel spokes sufficiently open for good expose of the caliper? Have you removed the sheet metal dust shields on the insides of the rotors?

David - there is work to be done on the cooling - the ancient underbody work is tattered and the shield do need to be removed - all part of the winter improvement efforts. The nature of this issue may be heat related but we have ruled out issues at the calipers - the loss of pedal is so complete and not a fade

[Chopper Dropper]

I suspected MC problem, but also bearings (had that happen) pushed and pulled on all wheels, no movement. Agree vacuum would just give a hard to push pedal but not a long pedal. There was no loss of fluid from reservoir or evidence of leaks. There was no fade as such as pedal did not go down slowly but just went right down, bled several times and no bubbles. Mike did a good job handling the issue, I heard "BRAKES" no panic from either of us coming into T10, he did miss the apex though!!!
Dirk

[BikePump]

well the MC and booster and a seal kit are on their way - time will tell

[racer]

old fluid stuck in ABS module? Just throwing it out there. But frequent flushing of the system might be slowly purging out the bad fluid?

Is this a two driver car? is the second driver experiencing similar issues or is it the driving style of one of the drovers? ;)

Maybe the MC is the issue. Rebuilding/replacing a potentially 15 year old component may not be a bad idea.

[good hands]

Did you go GT3 MC ?

[BikePump]

Did you go GT3 MC ?

did not - yet. $100 vs $550 was a no brainer given that i dont know its the right issue

[Vicegrip]

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]

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]

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]

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.

[BMAN]

Are you running stock calipers and rotors?

What pads?

What booster # did you put in?

One possibility is that you've got too much booster for the stock caliper and rotor which can trigger ice mode and you could be overheating your pads giving a longer pedal feel.

If you haven't already, consider a booster with less aggressive ratio. PCA Club Racing just approved 996.355.923.90 booster with 997.355.910.30 Master Cylinder.

[Croc R]

One possibility is that you've got too much booster for the stock caliper and rotor which can trigger ice mode and you could be overheating your pads giving a longer pedal feel.

If you haven't already, consider a booster with less aggressive ratio. PCA Club Racing just approved 996.355.923.90 booster with 997.355.910.30 Master Cylinder.

BMAN, how would the above advice translate for a Cayman? A few weeks ago, I was at the advanced DE in connection with the Club Race at Daytona. After being amazed at how well my brakes were working the first 2 days (because I too have had ice pedal problems in the past), I got ice pedal going into the bus stop on Sunday. This was because I was going deeper into turn 1 before braking, thus using the brakes harder. (Incidentally, I hit 155 on at least one lap before braking for turn 1.)

[BMAN]

BMAN, how would the above advice translate for a Cayman?

I can't speak to it's effectiveness but from what I understand it's the raced Caymans that started experimenting with lower ratio boosters and had success. I believe ITC has a different booster called out in their build sheet, compared to PCA, but it's basically the same concept.

Btw, the booster on my 996 Cup is also a low ratio, by design.

I think it's worth a try. Probably won't cure the problem but hopefully would settle it down.

I hit 155 on at least one lap before braking for turn 1.)

Nice! That sounds like fun.

[BikePump]

Are you running stock calipers and rotors?

What pads?

What booster # did you put in?

One possibility is that you've got too much booster for the stock caliper and rotor which can trigger ice mode and you could be overheating your pads giving a longer pedal feel.

If you haven't already, consider a booster with less aggressive ratio. PCA Club Racing just approved 996.355.923.90 booster with 997.355.910.30 Master Cylinder.

Brian
I have slotted rotors up front and pfc pass along with the stock master cylinder . I do think the soft pedal is potentially related to hear build up. The front calipers were poorly painted at some point in its past and I am guessing that they have never been rebuilt. Hoping new seals and maybe Pistons depending on their condition will have apositive impact. Likely also put a better cooling rotor up front - open to recommendations

[BikePump]

Brian
I have slotted rotors up front and pfc pass along with the stock master cylinder . I do think the soft pedal is potentially related to hear build up. The front calipers were poorly painted at some point in its past and I am guessing that they have never been rebuilt. Hoping new seals and maybe Pistons depending on their condition will have apositive impact. Likely also put a better cooling rotor up front - open to recommendations

Ohh and the brake booster is the stock unit right now

[BMAN]

I do think the soft pedal is potentially related to hear build up.

Is your pedal still soft? I thought the MC changed helped. Considering it never got above 40degrees at the last event, cooling should not have been a problem.

You might consider adding some cooling around your exhaust tips.....umm well where your tips used to be. :p

[BikePump]

the mc absolutely helped - got rid of the suprise "no brakes" issue. the pedal got a little softer than the rock hard one i started with but after a couple of initial bleeds (the system did get substantial air when i replaced the mc) it stayed consistent at a little soft but i want it bak at super-firm. i do know that cooling was an issue at the previous DE when it was hotter - in clean air i had no issues but when following there was softening

[blipshift]

997 GT3 MC/Booster. SRF. PFC-11. Stock C2 Drilled Rotors and Calipers. Street Tires.

Last PCAP SPM event the car ran well, no braking issues, ran a 1:26.019 on Bridgestone Potenzas.

PCAP Day one: Pedal started very firm and stayed firm until last run. A little ABS happiness but the car was stopping around 2.5ish into 1.
Day two: Pedal started slightly less firm than day before. No issues.

Following Track day 2 weeks later: Pedal retained a slightly longer throw and slightly less firm feel as from last time on track. 4-5 laps into session 1 when I had clear track and car had warmed I pushed into one hit the brakes and got some (~3/4 of full pedal) but not enough braking. Upon pumping the brake nothing happened, still had some but not full brake. Pucker-factor was high, but fortunately I was able to retain control and not hit anything. Went back in to check things over, everything looked fine, took it back out. Was mindful of previous event so I backed up my brake point to outside of 5 board. Another few laps, another brake issue. Lots more space to maneuver but never-the-less the braking was not optimal. Brought it back in for the session. ---should also point out that this was only a noted issue in 1. Although, I have a suspicion that it may have also occurred heading into 5 but most speed had already been bled off so it was a non-factor and a bit indistinguishable at the slower speed.

Talked it over with some folks in the paddock, made a phonecall, and reluctantly took it back out for the next session but this time set the brakes with left foot braking while accelerating out of 10, and kept brake point clear outside the 5 board. No issues to report with that regimen. If truly ice pedal, I think it should have occurred regardless of setting the brakes, no? To try and describe what the pedal felt like...It reminded me of ABS coming on but without actually braking.

Just picked the car up with a PIWIS flush. Pedal feels solid, good throw, ABS seems to be less chatty (as best as I can tell on the street, at least)