| Brake Pedal Slowly Goes To The Floor [message #368576] |
Wed, 26 January 2022 08:54  |
Tom Katzenberger
Messages: 399
Registered: June 2019
Location: Kingsville, MD
Karma: 4
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Senior Member |
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Good Morning all,
My situation is as follows:
Components: I have installed my 3rd new P30 Master Cylinder on a new 6 Disc brake system. All lines have been replaced with stainless steel solid and braded where needed. I installed a new combination valve which has the piston removed so it no longer proportions from front to rear. I have Dave Lindsey's sensitized brake booster with a summit back up vacuum pump.
Problem: After bench bleeding and making sure the plunger is not depressed more than 1" I still have the the brake pedal slowly sinking while under steady pressure.
I am looking for the wisdom of the members on this site. Again and as always, all opinions and thoughts are welcome and appreciated.
Thank you all.
Sincerely,
Tom K.
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D., Micro Level, Howell EBL-EFI Spark Control, Macerator, York Air Compressor, 6 Wheel Disc, Quadra Bag, Onan W/Bovee Ignition
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| Re: Brake Pedal Slowly Goes To The Floor [message #368589 is a reply to message #368576] |
Wed, 26 January 2022 23:03  |
Rick Staples
Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA
Karma: -1
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Senior Member |
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Tom, If you aren't losing fluid from the system, it is almost certainly a defective/damaged master cylinder. The classic test of a master cylinder involves first "stabbing" the brake pedal (stepping on it hard and fast). This will often cause a worn piston cup to momentarily seal and hold pressure. Then release the pedal and rest your foot lightly on it and slowly push down. A bad master will seep fluid back into the reservoir, and the pedal will sink.
HTH
Rick Staples
Rick Staples, '75 Eleganza, Johnstown, CO
"Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien
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| Re: Brake Pedal Slowly Goes To The Floor [message #368590 is a reply to message #368589] |
Thu, 27 January 2022 06:14 |
Christo
Messages: 108
Registered: April 2019
Location: Weymouth, MA
Karma: 0
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Senior Member |
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I don't believe that stabbing the pedal works on the cursed P30 MC because it uses poppet valves rather than the piston cups you mentioned.
Christo Darsch
GMC Nor'easters
1977 Eleganza II - "The Komet"
3.50 Power Drive, Disc Brakes, Alcoas
Weymouth, MA
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| Re: Brake Pedal Slowly Goes To The Floor [message #368592 is a reply to message #368576] |
Thu, 27 January 2022 08:52 |
Tom Katzenberger
Messages: 399
Registered: June 2019
Location: Kingsville, MD
Karma: 4
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Senior Member |
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Guys,
That is also what I thought and was my experience in the past.
Rather then installing another P30, I am looking at the 2 stage master and the Hydro boost. The 2 stage master is the easiest and cheapest so I will try that first.
I am really not interested in installing a 4th P30.
Take care and I will report back.
Thanks again guys,
Tom K.
Tom & Oki Katzenberger,
Kingsville, Maryland,
1977 23' Birchaven, 455 C.I.D., Micro Level, Howell EBL-EFI Spark Control, Macerator, York Air Compressor, 6 Wheel Disc, Quadra Bag, Onan W/Bovee Ignition
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