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Old 01-22-2022, 08:36 PM   #1
bluec10
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Need help bleeding brakes

I installed a new brake booster and master cylinder and need to bleed the brakes.I bench bled the master cylinder - it wasn’t a new one but it was only used for a few hundred miles.

I put my vacuum pump on the right-rear brake and pumped up to 20psi pressure. No fluid came out after a lot of pumping. The mc is full of fluid.

The bleeder screw was well open.

Any ideas?
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Old 01-22-2022, 08:41 PM   #2
Steeveedee
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Re: Need help bleeding brakes

It has a dual master, right? Perhaps you triggered the shuttle valve? I'm guessing that you're working on the '69 in your signature?
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Old 01-23-2022, 12:07 AM   #3
Accelo
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Re: Need help bleeding brakes

Did you bench bleed the brake master cylinder? I always do this to confirm everything is working correctly.
I also leave the lines loose at the MC and pump the brakes till I get some seepage at the joint then I fully tighten the fittings.

Pump the brakes, see it that works. If not, it is easy to get the rod between the pedal and the MC out of adjustment when retrofitting brakes. As in it could be too long. Confirm you have some slack there.

Last edited by Accelo; 01-23-2022 at 12:21 AM.
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Old 01-23-2022, 12:16 AM   #4
Getter-Done
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Re: Need help bleeding brakes

Did you try (pushing or pulling) the button on to proportioning valve?
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Old 01-23-2022, 02:04 PM   #5
Jason Banks
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Re: Need help bleeding brakes

Just throwing this out there. I had the same problem, turned out to be the original rear brake hose from frame to diff was blocked.
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Old 01-23-2022, 02:29 PM   #6
jimijam00
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Re: Need help bleeding brakes

If you remove the vacuum pump, open the bleeder, and push on the brake pedal, does any fluid come out?
Quote:
Originally Posted by Accelo View Post
Did you bench bleed the brake master cylinder? I always do this to confirm everything is working correctly.
The second sentence of his post stated he did.
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Old 01-23-2022, 03:06 PM   #7
Accelo
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Re: Need help bleeding brakes

Oops, thanks for the correction
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Old 01-23-2022, 04:07 PM   #8
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Re: Need help bleeding brakes

Quote:
Originally Posted by Jason Banks View Post
Just throwing this out there. I had the same problem, turned out to be the original rear brake hose from frame to diff was blocked.
That's a good point. An easy way to verify would be to close the open bleeder and hook the vacuum pump to the other side. Of course, if it has the shuttle valve and it has moved, switching bleeders won't help. When the right front wheel cylinder on my truck started leaking, I just went to disc brakes (and rebuilt the front end, which it probably needed at 210k miles). No idea how old the rear hose was, so it was a no-brainer to change it out.
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Old 01-23-2022, 07:16 PM   #9
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Re: Need help bleeding brakes

Pull your bleeder screw all the way out and see if the hole is not plugged, you wont loose any fluid if you put the cover back on the MC .
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Old 01-24-2022, 09:20 PM   #10
Chevy Fan Always
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Re: Need help bleeding brakes

Make sure the button is pushed in on the proportion valve, you can use a c clamp. There is a tool made for it. In forbleeding.
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