Can't bleed front caliper !!! - Team Camaro Tech
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post #1 of 6 (permalink) Old Apr 15th, 19, 12:22 PM Thread Starter
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Dave
 
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Can't bleed front caliper !!!

I have a '68 with power front disc brakes and I am having a problem bleeding my driver side front caliper. I'm not using any kind of power or vacuum bleeder. Just a helper pushing the brake pedal.

In this restoration I've gone through the entire brake system.

All new hard lines and hoses.
New 5460346 casting double bleeder master cylinder.
Rebuilt original metering valve.
Rebuilt original distribution block.
Rebuilt original calipers, SS sleeved and rebuilt by Vette Brakes.

So I started with a completely dry system. The back brakes bled fine with no problems.

In my first attempt at bleeding the front brakes, I was getting air, air, and more air. This was my fault. Looing at the master cylinder more from the front than from the side, I thought I was keeping the fluid level plenty high and it turns out, because of the tilt of the master cylinder, what looked plenty high enough at the rear of the front chamber was not covering the port in the bottom, thus lots of air. I was out of fluid and had to quit for the day. Dumb mistake on my part!

More fluid in hand, and knowing I had to keep the fluid lever even higher, we tried again yesterday. The passenger side went fine. A few bubbles at first and them nothing but fluid. Great!

On the driver's side. A few microscopic bubbles at first and it worse not better.......An occasional bubble the size of a BB.....then bigger and bigger bubbles, some and inch or two long. The more I bled, the bigger the bubbles got! I could not get rid of them.

There are no leaks at any of the connections. I pulled the pads out to see if there were leaks at the piston bore seals. The were dry as a bone.

I have to be sucking in air somewhere but I have no idea where. I've pumped more air out that bleeder screw than the system could ever hold.

Any ideas ???

Thanks..Ö..Dave

1968, 327 210 HP, Power Steering, Power Disc Brakes, Custom Interior, 4 Speed, Console, Gauges, Tilt Wheel, Speed Warning, Fiber Optics, 10 Bolt 3.55 Posi Rear end......Owned since 1978.
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post #2 of 6 (permalink) Old Apr 15th, 19, 01:53 PM
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Re: Can't bleed front caliper !!!

If you have factory installed disc brakes you will have a hold off valve between the master cylinder and the distribution block.

I have factory disc brakes on my '67 and was having the same problem with air in the front brakes. After many hours of bleeding and several quarts of brake fluid I made up a steel line to bypass the hold off valve. With the valve out of the system I had no problem bleeding the brakes. This was going to be a temporary fix to see if the hold off valve was the source of the air getting into the system. It's been 15 years since I removed the valve. The brakes work so well without it I haven't bothered to replace it.



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post #3 of 6 (permalink) Old Apr 15th, 19, 03:41 PM
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Re: Can't bleed front caliper !!!

Did you bench bleed the master cylinder before installing it?
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post #4 of 6 (permalink) Old Apr 15th, 19, 07:05 PM Thread Starter
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Re: Can't bleed front caliper !!!

Yes, I did.

1968, 327 210 HP, Power Steering, Power Disc Brakes, Custom Interior, 4 Speed, Console, Gauges, Tilt Wheel, Speed Warning, Fiber Optics, 10 Bolt 3.55 Posi Rear end......Owned since 1978.
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post #5 of 6 (permalink) Old Apr 15th, 19, 07:17 PM
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Re: Can't bleed front caliper !!!



This is the original master cylinder in my '67. The car is a manual disc brake car and still has the original "AD" master cylinder. The hold off (metering) valve is missing in this picture but the bracket it still in place. I picked up the steel line from the MC to the distribution block at a local auto parts store. It came with the correct size ends and all I had to do was bend it into a "U" shape. This was really just a test to see if I was sucking air in through the hold off valve.

It proved without a doubt the air was entering the hold off valve. The odd part was the valve was completely dry on the outside. I still don't know how it was sucking in air without leaking a single drop, although I do suspect it was sucking the air in around the button on the back of the valve.

Anyway try bypassing your hold off valve and see if your brakes will bleed.

Steve

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post #6 of 6 (permalink) Old Apr 15th, 19, 07:25 PM
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Re: Can't bleed front caliper !!!

OP

Been there, done that. Front DS would not bleed. Used the buddy system to bleed.

What I found is my DS front brake line comes out of the distro block into a vertical 2 coil bend before going down to the DS brake. The top of this double loop was higher than the "out" of the distro block. air bubble would just "bounce" back and forth within the two coils as the pedal push just didn't carry enough volume to push it through the 2 loops in the hard line.

I used m Mighty Vac and bingo. First remove the bleeder screw and wrap threads in Teflon tape. You are sucking in air through the threads otherwise.

Normally a gravity bleed works for me but this 67 has the 2 coil line for DS....and no other line on the car has this.
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