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Old 11-28-2018, 06:54 AM   #1
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Master Cylinder, Booster, or both???

My brake pedal feels a bit soft. The brakes work well, just not a hard pedal
It manifests most when I am at the track. Its not fade, or brake lines , or air in the lines.

I have done a full flush and bled the lines a few times. Fluid is fresh Motul 600 and new pads. I don't have any fluid loss either

Sometimes the pedal is rock hard for a couple of time on the pedal, but most of the time it just feel soft. It doesn't bottom out and if I pump it it gets a little harder, but still not what it used to feel like, rock hard.

Like I said, the brakes work well, just doesn't feel right and it causes me to brake much earlier than I would normally at the track.

I'm thinking it may be the booster or the master cylinder or both

Thoughts??
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Old 11-28-2018, 09:32 AM   #2
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Likely the master cylinder; you can verify this by testing your line pressures if you have the equipment.
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Old 11-28-2018, 09:36 AM   #3
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Following, as I sometimes have that same thing. I'm hoping for me that it is just a stubborn air bubble somewhere in the system, I am about to put new pads so i am going to do a bleed with the motive, also with a helper pressing the brake pedal a few times for each bleed nipple, and I'm going to do this with the pistons pushed all the way in (due to the pad change) and see what I get...
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Old 11-28-2018, 09:55 AM   #4
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i've heard about guys having issues like this. not me personally, of course. it tends to become more of an issue as our equipment gets older. apparently it can be quite an issue when it happens in the 'heat of the moment' so to speak. i've heard that the following is a good solution:

https://www.viagra.com/taking/tips-for-taking-viagra

don't let a soft 'brake pedal' get you down, my friend!
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Old 11-28-2018, 11:27 AM   #5
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I only take it for heart related issues, and the fact that they are hidden in my dresser is irrelevant.
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Old 11-28-2018, 11:30 AM   #6
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Quote:
Originally Posted by The Radium King View Post
i've heard about guys having issues like this. not me personally, of course. it tends to become more of an issue as our equipment gets older. apparently it can be quite an issue when it happens in the 'heat of the moment' so to speak. i've heard that the following is a good solution:

https://www.viagra.com/taking/tips-for-taking-viagra

don't let a soft 'brake pedal' get you down, my friend!
"The most common side effects of VIAGRA: headache; flushing; upset stomach; abnormal vision, such as changes in color vision
(such as having a blue color tinge) and blurred vision; stuffy or runny nose; back pain; muscle pain; nausea; dizziness; rash."

Side effects? I experience those same symptoms every time I wrench on the car.
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Old 11-28-2018, 11:44 AM   #7
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... and sorry for the hijack! i've noted the same; bled brakes, exercised the abs pump to work out any bubbles, and pedal still feels softer than before. thought perhaps poor recollection or using them differently, old pads mean more piston travel, stickier tires changing abs engagement and brake behavior (car seems harder to get into abs than previous) ... dunno.
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Old 11-28-2018, 08:36 PM   #8
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did some research. 996 guys complain about brake feel, and 987 guys really complain about brake feel. apparently the soln is a gt3 master cylinder. did some searching and found the following:

996.355.910.00 - standard 9x6 MC

996.355.910.50 - 996 GT3/GT2/TT MC - bigger piston that stiffens pedal. expensive and only oem available (unless you want a used unit of a wrecked turbo).

997.355.910.30/TRW PMN166 - 997 GT3 MC - even bigger piston, and the trw part is much less $ than the oem part (but currently sold out everywhere).

notes:
- does not work with cars that have psm - will cel
- will bolt right up, however some variation (m10 vs 12) in brake line fitting size. soln is this:

https://www.ebay.com/itm/Brake-Line-Thread-Adapter-Male-M12-x-1-Bubble-Female-M10-x-1-Bubble/331605500736?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

- other options are the boost assist; 9x7 have more than 9x6 which is why they have poorer pedal feel than our cars. gt3s have less which makes them stiffer. apparently boosters will interchange but are different dimensions (ie, gt3 unit is deeper) which means they may impact bits around them, require massaging brake lines, etc.

so, if your MC is working fine and you think you need a stiffer pedal then perhaps convert. if you MC is failing and you have to replace it, consider a GT3 unit for even better pedal feel because the increase in cost (new 986 unit vs gt3 unit) is incremental.
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Old 12-07-2018, 12:48 PM   #9
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A Meyle 1145320008 will also fit and is lower cost than the others
Its a direct replacement for the stock part $71 at F C P euro and has a lifetime warranty
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Old 05-08-2019, 01:10 AM   #10
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can anyone point me at the precise part number / name for a brake booster upgrade (the 2004 one that's sold as a kit with the pedal and all). Shouldn't there be a sticky thread with all the absolute must-do's and must-have's? Like LN plain bearing replacement, this brake booster, roof top with glass window, ECU vacuum sealing kit, drain plugs locations etc?

cheers
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Old 05-11-2019, 07:14 PM   #11
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Coming off the brakes I feel the pedal travel upwards stick like there is undue friction somewhere in the mechanism. My initial impression was brake master cylinder. Any thoughts? What am I feeling? Is it GT3 time? Brakes work but feel is mushy
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