2005-2014 Mustangs Discussions on the latest S197 model Mustangs from Ford.

Cap off when bleeding brakes/pedal-pump clutch bleed?

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Old Apr 10, 2008 | 12:11 AM
  #1  
ohnoesaz's Avatar
ohnoesaz
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Default Cap off when bleeding brakes/pedal-pump clutch bleed?

Yeah.... Gonna bleed brakes with speed bleeders this weekend. I know you fill the resovoir up when it gets low, but do you leave the cap off during the whole process?

And same question for when you jack the driver front corner up 12" and pump the clutch to bleed it, after clutch work, if needed.

Spanks you!
Old Apr 10, 2008 | 01:02 PM
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Default RE: Cap off when bleeding brakes/pedal-pump clutch bleed?

ORIGINAL: ohnoesaz

Yeah.... Gonna bleed brakes with speed bleeders this weekend. I know you fill the resovoir up when it gets low, but do you leave the cap off during the whole process?

And same question for when you jack the driver front corner up 12" and pump the clutch to bleed it, after clutch work, if needed.

Spanks you!
Master cylinder cap must be in place when bleeding brakes. If you were to push in the pedal with the cap removed, you'd have a mess on your hands. Same for the clutch.
Old Jun 10, 2010 | 06:44 PM
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Originally Posted by rlh6805
Master cylinder cap must be in place when bleeding brakes. If you were to push in the pedal with the cap removed, you'd have a mess on your hands. Same for the clutch.

False statement. The cap does NOT need to be in place to flush the system. I can fill the reservoir to the top, leave the cap off, and bleed the system by pumping the pedal. NOTHING will come out of the top of the reservoir.
Old Jun 10, 2010 | 06:52 PM
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ive never left the cap on, i just noticed i need to go slow.
Old Jun 10, 2010 | 09:32 PM
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You'll love the speed bleeders. Makes the job soooo easy.
Old Jun 11, 2010 | 04:57 PM
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Never worked with speed bleeders. But from my own experience, I've left the cap off while pumping the brakes and nothing has come out.
Old Jun 11, 2010 | 10:59 PM
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speed bleeders and always leave cap off... just did mine a month ago or so (once a year deal for me, run clean fluid in)
Old Jun 12, 2010 | 12:42 AM
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One word of advice, be very careful when you install the speed bleeders. They're partly hollow, so they can break off more easily than the original bleeder screws. On the other hand, you have to get them tightened enough that they seat properly and don't leak. Just be patient and turn them in slowly. They're great time saver.
Old Jun 12, 2010 | 09:25 AM
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Originally Posted by Unleashedbeast
False statement. The cap does NOT need to be in place to flush the system. I can fill the reservoir to the top, leave the cap off, and bleed the system by pumping the pedal. NOTHING will come out of the top of the reservoir.
Cap on, cap off.
No difference.
Older cast iron master resivoirs would kinda spit fluid if
let get low while pumping up the brakes to have the
friend pop the bleeder.
The S197 is not like that.
So you now have the Russell speed bleeders?
Maybe clue us in on the thread size or the Russell
part # so we can all get them without doing all the
searching you had to do to come up with the S197s
OEM caliper bleed screw thread sizes?
Old Jun 13, 2010 | 01:12 PM
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The big reason to have the cap on while you're bleeding the brakes is to minimize the exposure of the brake fluid to ambient air. Brake fluid is hygroscopic, so it'll absorb water out of the atmosphere if left exposed to the air. Obviously, this is much worse on a humid day, but typically, water in the brake fluid is one of the main reasons it needs to be bled and/or flushed as often as it does (assuming you don't track the car), so it make sense to minimize the amount that gets absorbed to begin with.

Just my 2 cents...



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