Brake Anomaly
#2548810
09/11/18 03:05 PM
09/11/18 03:05 PM
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Joined: Jan 2003
Posts: 25,808 Rio Linda, CA
John_Kunkel
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Joined: Jan 2003
Posts: 25,808
Rio Linda, CA
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My '57 Dodge has upgraded manual brakes, later rear with drum brakes and front disc conversion using a factory tandem MC. After the conversion I bench bled the new MC and thoroughly bled the system and had a good firm pedal. I've been driving it occasionally with no brake problems.
So, the other day I jump in and back it out of the garage, apply the brakes and the pedal is way low and spongy. I check the fluid level and look for signs of a leak; fluid level is correct and no leaks.
I have a friend operate the brake pedal while I observe the fluid in the reservoir, rear reservoir shows a normal slight burble in the fluid surface as the pedal is applied but the front reservoir (for the rear drum brakes) has air bubbles rising. Slowly pumping the pedal produces rising air bubbles with each stroke. So, today I sat in the car and slowly pumped the brake pedal numerous times and now the pedal feel is just like it was before the incident.
I'm at a loss to figure where the air in the front reservoir came from, the MC has no RPV so I installed one (10 psi) in the line to the rear brakes. How can air suddenly appear in a system that's sealed tight? Any thoughts?
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Re: Brake Anomaly
[Re: Andrewh]
#2548910
09/11/18 06:18 PM
09/11/18 06:18 PM
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Joined: Jan 2003
Posts: 25,808 Rio Linda, CA
John_Kunkel
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Rio Linda, CA
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Fluid level remains the same, all rubber hoses are brand new and dry.
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Re: Brake Anomaly
[Re: John_Kunkel]
#2548933
09/11/18 06:56 PM
09/11/18 06:56 PM
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Joined: Nov 2003
Posts: 36,040 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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I'm at a loss to figure where the air in the front reservoir came from. How can air suddenly appear in a system that's sealed tight? Any thoughts? I'm thinking a loose fitting/line/hose that is allowing air to be sucked back up in there on the return stroke.
live every 24 hour block of time like it's your last day on earth
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Re: Brake Anomaly
[Re: John_Kunkel]
#2548934
09/11/18 07:04 PM
09/11/18 07:04 PM
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Joined: Nov 2003
Posts: 36,040 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,040
Lincoln Nebraska
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Slowly pumping the pedal produces rising air bubbles with each stroke. Yeah either the air is still in there (& I wouldn't think so as there ain't no magic to bleeding) & especially with the amt of the bubbles (from what it sounds like) that it (air) is being drawn back in somehow.
live every 24 hour block of time like it's your last day on earth
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Re: Brake Anomaly
[Re: John_Kunkel]
#2548939
09/11/18 07:19 PM
09/11/18 07:19 PM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
About to go away
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About to go away
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Posts: 14,889
up yours
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One thing we learned in the Navy was that watertight did not mean airtight.
IOW, air leaks in easier than a liquid. Probably woulcn't hurt to put a wrench on all connections and retighten them.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Brake Anomaly
[Re: John_Kunkel]
#2549113
09/12/18 04:45 AM
09/12/18 04:45 AM
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Joined: Dec 2009
Posts: 20,640 in a cattle trailer down by th...
Guitar Jones
Paddle faster! I hear banjo music!
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Paddle faster! I hear banjo music!
Joined: Dec 2009
Posts: 20,640
in a cattle trailer down by th...
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The air most likely came in from a wheel cylinder.
"Follow me the wise man said, but he walked behind"
'92 D250 Club Cab CTD, 47RH conversion, pump tweaks, injectors, rear disc and hydroboost conversion. '74 W200 Crew Cab 360, NV4500, D44, D60 and NP205 divorced transfer case. Rear disc and hydroboost conversion. 2019 1500 Long Horn Crew Cab 4WD, 5.7 Hemi.
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Re: Brake Anomaly
[Re: Guitar Jones]
#2549257
09/12/18 03:58 PM
09/12/18 03:58 PM
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Joined: Aug 2011
Posts: 2,861 Pattison Texas
CSK
master
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master
Joined: Aug 2011
Posts: 2,861
Pattison Texas
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The air most likely came in from a wheel cylinder. This ^^^^^^ I have had this happen more than once, also VERY common on c3 vett calipers to suck air
Last edited by csk; 09/12/18 04:00 PM.
1968 Charger COLD A/C Hilborn EFI 512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim 2020 T/A 392 Stock 11.79 @ 114.5
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Re: Brake Anomaly
[Re: Guitar Jones]
#2549295
09/12/18 05:44 PM
09/12/18 05:44 PM
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Joined: Jan 2003
Posts: 25,808 Rio Linda, CA
John_Kunkel
OP
Too Many Posts
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OP
Too Many Posts
Joined: Jan 2003
Posts: 25,808
Rio Linda, CA
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The air most likely came in from a wheel cylinder. The RPV is supposed to prevent that. The notion that the air was always there, trapped somehow, isn't consistent with the pedal being firm after the original installation.
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