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  #1  
Old 07-25-2018, 07:51 AM
t walgamuth's Avatar
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Location: Lafayette Indiana
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Brake bleeding question

I keep getting a soft pedal in my Cobra. The brakes have been bled three times. Bleed them and for a while a good solid pedal, then in a few days it is soft again. Any thoughts?

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #2  
Old 07-25-2018, 09:15 AM
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Sounds like a poor master cylinder internal seal. Fluid leaking past the seal into the back side of the piston.

You are using a pressure bleeder aren't you?
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  #3  
Old 07-25-2018, 09:19 AM
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No.
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #4  
Old 07-25-2018, 06:34 PM
A Talent for Obfuscation
 
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I remember having an Oldsmobile with an internal master cylinder leak. One second, all was well; the next second, the brake pedal thumped smartly against the floor with no braking action in sight. I did not delay repairs...
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  #5  
Old 07-25-2018, 06:59 PM
t walgamuth's Avatar
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No booster in this car.
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #6  
Old 07-25-2018, 07:00 PM
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Today when I went over to a buddy's place to take him for a ride it quit. No spark. We tested a bit and found no spark from the magneto. I am thinking of switching to a more modern distributor. I suspect the mag is because of no room with the four webers on it...?
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #7  
Old 07-25-2018, 07:51 PM
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Time to go to a "missing tooth" trigger wheel and either wasted spark or COP.


https://www.diyautotune.com/support/tech/customer/ford-edis/

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  #8  
Old 07-25-2018, 08:13 PM
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A quick and dirty check for a leak in the brake hydraulic system is to loosen the shortest brake line bleeder screw (usually the LEFT front) and watch for air bubbles. Don't pump the brakes or pressurize them, just let gravity do its work. When you have a clear drip/stream of fluid, tighten bleeder and try the pedal. If it is solid then you know you have air entering the system.

The usual culprit for air in the system with manual brakes is the master cylinder. Minute air bubbles enter the system and are forced to the shortest line during the cycles of compression and release.

The Cobra does have four wheel disc brakes, correct?
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Last edited by Mike D; 07-25-2018 at 10:17 PM. Reason: Meant "left" instead of "right"
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  #9  
Old 07-25-2018, 08:17 PM
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Yes.
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #10  
Old 07-25-2018, 08:36 PM
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I almost hate to ask: did you bench bleed the MC?
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  #11  
Old 07-25-2018, 11:19 PM
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I did not install it....so don't know...good thought though.
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #12  
Old 07-26-2018, 12:45 PM
A Talent for Obfuscation
 
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617 turbo's do not even need a distributor. Just a thought...
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  #13  
Old 07-26-2018, 01:20 PM
t walgamuth's Avatar
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Location: Lafayette Indiana
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Ha ha!
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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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  #14  
Old 07-26-2018, 03:53 PM
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I reread your first post. On second thought it cannot be the bench bleed because you at some point are able to get a strong pedal. I am thinking bad MC.
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  #15  
Old 07-27-2018, 11:26 AM
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Sounds like you resolved this. What was the problem?

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