Master Cylinder won't pump fluid - Chevelle Tech
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post #1 of 22 (permalink) Old Jul 26th, 19, 6:35 PM Thread Starter
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Master Cylinder won't pump fluid

I'm trying to bleed my brakes; just installed LS1 brakes on all 4 corners of a 67 Chevelle.

I have the bleeder screw at the passenger side rear cracked open and connected to a reservoir of fluid with a clear hose. All other bleeder screws are closed and the system seems tight - no leaks.

As I pump the brake pedal, the master cylinder reservoir does not change - no fluid is going down the lines.

I've disconnected the line going to the rear of the car and blew 30 psi air through it.

I checked the rod between the booster and the master cylinder- it seems to have plenty of stroke ; about 1-1/2".

Do I need a hand vacuum pump to get the fluid moving to the rear brakes ?


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post #2 of 22 (permalink) Old Jul 26th, 19, 6:41 PM
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Open all the bleeders then once it starts dripping close them and do one at a time.
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post #3 of 22 (permalink) Old Jul 26th, 19, 6:47 PM Thread Starter
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Re: Master Cylinder won't pump fluid

Quote:
Originally Posted by Jasons 69 Chevelle View Post
Open all the bleeders then once it starts dripping close them and do one at a time.
Thanks, I'll go try that; I need to see some fluid start to move ! LOL

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post #4 of 22 (permalink) Old Jul 26th, 19, 6:52 PM
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Re: Master Cylinder won't pump fluid

If your using the original distribution block the valve may be off center restricting fluid movement. There is a bleeding tool to aid in bleeding your brakes.
https://www.ebay.com/itm/Combination...0AAMXQVT9TBk9g


Good Luck


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post #5 of 22 (permalink) Old Jul 26th, 19, 7:09 PM Thread Starter
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Re: Master Cylinder won't pump fluid

Quote:
Originally Posted by PCB67SS View Post
If your using the original distribution block the valve may be off center restricting fluid movement. There is a bleeding tool to aid in bleeding your brakes.
https://www.ebay.com/itm/Combination...0AAMXQVT9TBk9g

Master Power Brakes Combination Valve Video - YouTube

Good Luck
Thanks but I removed the distribution block because of the rear disc brakes.

I cracked open all 4 bleeders and the MC still won't pump.

Wondering if I need to pull a vacuum on one line at a time to help the fluid move down the line.

I'm using Dot 5 silicone fluid and I think it's a thicker viscosity.

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post #6 of 22 (permalink) Old Jul 26th, 19, 7:38 PM
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Just open them up when I first did mine it took about 4 hours to start dripping no need to pump. When you pump with the bleeders open it will suck air back in threw the bleeders.
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post #7 of 22 (permalink) Old Jul 26th, 19, 8:47 PM Thread Starter
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Re: Master Cylinder won't pump fluid

Quote:
Originally Posted by Jasons 69 Chevelle View Post
Just open them up when I first did mine it took about 4 hours to start dripping no need to pump. When you pump with the bleeders open it will suck air back in threw the bleeders.
Thanks. Just got back from Harbor Freight with a Mity-Vac hand pump.

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post #8 of 22 (permalink) Old Jul 26th, 19, 9:33 PM
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Re: Master Cylinder won't pump fluid

Quote:
Originally Posted by nashville beth View Post
Thanks. Just got back from Harbor Freight with a Mity-Vac hand pump.
Yeah, sometimes that's needed to get things started.

I can HIGHLY recommend speed bleeders from Dorman, 12706 for the LS F-body calipers. I had a stubborn bleeding job like this and they worked great-they allow you to quickly pump the brake pedal.

If this is the original disc/drum master, it may have a residual pressure valve in it for the rear section which will hold like 5psi in the line and cause the rear pads to drag.

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post #9 of 22 (permalink) Old Jul 26th, 19, 10:45 PM Thread Starter
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Re: Master Cylinder won't pump fluid

Quote:
Originally Posted by paul bell View Post
Yeah, sometimes that's needed to get things started.

I can HIGHLY recommend speed bleeders from Dorman, 12706 for the LS F-body calipers. I had a stubborn bleeding job like this and they worked great-they allow you to quickly pump the brake pedal.

If this is the original disc/drum master, it may have a residual pressure valve in it for the rear section which will hold like 5psi in the line and cause the rear pads to drag.
I hope the master doesn't have anything "built-in" to hold pressure. It came as part of a "booster -master cylinder- proportioning valve" combo from the Right Stuff.
It had a disc-drum proportioning valve that I swapped out for a disc/disc PV.

So I wouldn't think the MC would also have a residual pressure valve ?

I disconnected the 1/4" rear brake line before the rear axle flex hose and started pulling vacuum there. It wouldn't hold a vacuum but I did start getting a trickle of brake fluid through the line.

I have to go out of town so I'm admitting defeat right now.

I will check out those speed bleeders. Thanks

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post #10 of 22 (permalink) Old Jul 26th, 19, 10:50 PM
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Re: Master Cylinder won't pump fluid

Quote:
Originally Posted by nashville beth View Post
I hope the master doesn't have anything "built-in" to hold pressure. It came as part of a "booster -master cylinder- proportioning valve" combo from the Right Stuff.
It had a disc-drum proportioning valve that I swapped out for a disc/disc PV.

So I wouldn't think the MC would also have a residual pressure valve ?

I'm sure it's correct then.

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post #11 of 22 (permalink) Old Jul 27th, 19, 2:19 PM
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Re: Master Cylinder won't pump fluid

was that the one from from Wrong Stuff or Online Boob?
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post #12 of 22 (permalink) Old Jul 28th, 19, 8:38 PM
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Re: Master Cylinder won't pump fluid

My guess is the rubber line at the rear end is swollen shut. I had a similar problem and I started at the master cylinder and had someone pump the brake while I cracked the next fitting in line. If it has pressure coming out of the MC, go to the next fitting in line and so on. When I got to the hard line to rubber line junction near the rear, I had fluid/pressure. When I went to the junction where the rubber line connects to the T fitting on the rear end, no pressure. So the rubber line was the culprit. $15 at NAPA and the brakes work better than ever.

I often forget the car is 50 years old. If you never replaced that line before, I recommend it to anyone even if you don't have symptoms yet.

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post #13 of 22 (permalink) Old Jul 28th, 19, 9:45 PM Thread Starter
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Re: Master Cylinder won't pump fluid

Quote:
Originally Posted by Tom Mobley View Post
was that the one from from Wrong Stuff or Online Boob?
It's from the "Wrong Stuff"

Quote:
Originally Posted by Greg Owens View Post
My guess is the rubber line at the rear end is swollen shut.
I replaced all the lines except for the 1/4" steel running from front to back. Blew air thru it in both directions.

I'll be back thursday to try again and will report back then.

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post #14 of 22 (permalink) Old Jul 28th, 19, 11:00 PM
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Re: Master Cylinder won't pump fluid

I don't see any mention of bench bleeding the master cylinder.
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post #15 of 22 (permalink) Old Jul 29th, 19, 10:38 AM
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Re: Master Cylinder won't pump fluid

Quote:
Originally Posted by Jasons 69 Chevelle View Post
Just open them up when I first did mine it took about 4 hours to start dripping no need to pump. When you pump with the bleeders open it will suck air back in threw the bleeders.
Quote:
Originally Posted by lkmarsh View Post
I don't see any mention of bench bleeding the master cylinder.
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