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#1
07-25-2018, 07:51 AM
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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
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
07-25-2018, 09:19 AM
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No.
__________________
[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
07-25-2018, 06:34 PM
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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
07-25-2018, 06:59 PM
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No booster in this car.
__________________
[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
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
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/ Bolt-On Coil-On-Plug Tech for Fox-Body & SN95 Mustangs
__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.” ― Brian P. Cleary, You Oughta Know By Now
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#8
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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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.” ― Brian P. Cleary, You Oughta Know By Now Last edited by Mike D; 07-25-2018 at 10:17 PM. Reason: Meant "left" instead of "right"
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#9
07-25-2018, 08:17 PM
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Yes.
__________________
[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
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
07-25-2018, 11:19 PM
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I did not install it....so don't know...good thought though.
__________________
[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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#13
07-26-2018, 01:20 PM
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Ha ha!
__________________
[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
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
07-27-2018, 11:26 AM
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Sounds like you resolved this. What was the problem?
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