Lark327

The brake fluid in the 72 I bought last year was of unknown age so I decided to flush and bleed. I used a one person vacuum bleeder and was careful to keep the master fluid full. It seemed to work as always except now I have no pedal at all. Any thoughts? I'm reading about a brake pressure switch and two bleeders on the rear calipers. I only bled one bleeder on the rear. There was a second bolt the size of a bleeder. Are you supposed to put a bleed nipple in there? Its manual brakes and they worked fine before.Thanks

MelWff

the rear calipers have a bleed screw on the top of each half of the caliper, at least from the factory they do.

0Willcox Corvette

I don't have much faith in those vacuum bleeders, but then I've never given them much of a test either. I have a pressure bleeder here and my suggestion is for you to find someone or a shop that has one. It is by far the best way to bleed the brakes... takes about 30 minutes from start to finish but when completed we always have a perfect pedal.

Typically.. you start with the right rear, then driver rear, then passenger front then driver front.... But you also bleed every bleeder on each caliper moving from the furthest from the master cylinder to the closest.

Willcox

DUB

First off you need to better explain what you meant by you 'decided to flush' the system.

Explain in great detail what you did to 'flush' the system. Knowing if you used any solvents or to the liquids to clean it and all that stuff. Do not leave anything out.

OR...bleed out the system again and make sure bleed BOTH bleeders on your rear calipers....and see what that does for you.

I also have a pressure bleeder and I would be lost without it.

DUB

Lark327

By Flush I meant to get most of the old fluid out of the system. I didn't use anything but DOT 3/4 brake fluid. I removed most of the fluid in the master so I could wipe out the inside as there was some residue. I then filled both chambers with brake fluid and then bled from the furthest to the closest to the M/C using the vacuum pump. I bled until clean fluid came out. I used a little over a quart of brake fluid. So I am confused because the brakes worked before, and I didn't think I did anything to introduce air, but apparently I did because if I pump the pedal several times I will get a little pedal but it is still way down to an inch off the floor. I only bled one nipple on each rear because there is only one nipple on each caliper. There is a second bolt that looks like a plug in place of a bleeder.

maj75

Sounds like you are missing two bleeders in the rear calipers. If so, that side of the caliper is full of air and you will get a bad pedal like you describe. Buy new bleeders and install in place of the bolts that are there.

A picture of the rear caliper bleeders would help to make sure we are all on the same page!

Jeff_Keryk

1 word: Motive Bleeder. I guess that's 2...
Seriously, I have done full brake jobs on 3 of these cars. I have worked many car's brakes, and generally brakes are pretty easy.
The only way I was able to get a pedal was with the Motive Bleeder. Also, adjusting your idle mixture screws for highest vacuum helped as well.
That's my experience. If you live near Silicon Valley, you can borrow mine.

kansas123

By "most of the fluid" do you mean you left just enough fluid in the master cylinder to keep from introducing air into the lines? Or do you now need to bleed the master cylinder?

If you took most of the fluid out of the master cylinder then you might have to remove it and bench bleed it.

Lark327

The bottom holes in the MC were covered and I filled the MC back up before bleeding so I don't think there is any way I could have introduced air into the master.

Sluefoot

You do NOT have to remove the MC to bleed it...can be done right on the car..I helped a friend do just that a few days ago, and worked fine.

Krystal

I can almost GUARANTEE this is all about the bleeders on the back brakes. Those two extra bleeders on the inside trip up lots of people the first time......don't ask how I know.....blew through a LARGE BOTTLE of new fluid before we noticed what we were doing wrong the first time .... more than just few years age. ......

Best part?

You probably have bleed out all but that back half of the rears.......just do them first and the pedal will probably come back without having to go to all 4 corners again. 5 minutes more and .......DONE!!

Lesson learned for life.

Sluefoot

with Krystal....I'm also convinced it's the "OTHER" bleeders that need to be taken care of....>GOOD LUCK!

Gale Banks 80'

It sure sounds like the Master has lost its prime. This can be confirmed by putting a clear hose on on any Caliper bleeder and running it straight up. Have a helper, or work on the left rear and just use a broom handle to move the brake peddle. Open the bleeder 1/4 turn and push the peddle. Did You get Fluid, Air or nothing ? Another thing to look at is the Master itself. When it is stroked are there any bubbles or is there a small wave in the center. Try tapping the Master, any bubbles ? Try stroking the master just a little bit looking for bubbles.

DUB

Thanks for your reply to my questions about the 'flush' and YES...I do what you did countless times where I remove about all of the fluid and clean out the reservoir and add fluid. Literally...all that is needed is a drop on the ports inside the reservoir and the system can not get air in it ESPECIALLY if the brake pedal is NOT pressed. It is not like air is going to be able to travel downwards.....right?

You are AWARE they you are bleeding the air out of your calipers from the TOP bleeders. This 'bolt' you are referring to is NOT to be touched because it is there because GM flips that housing so they can use it on the other side when making calipers. And with this 'bolt' being on the bottom of the caliper...if it were removed.... how are you going to get air from the top of the caliper to flow downwards.

AS mentioned...You need to bleed the rear caliper ON the top of BOTH halves of the caliper...and on the front calipers. There is only one bleeder as you know and it is on the inside of the caliper at the top... pointing horizontally.

I doubt you lost your prime due to you did not run the master cylinder dry.

DUB

Lark327

Thanks for that reply. Now Inunderstand that there is a bleeder on each side of the caliper. The wheels are on the car now so I will have to look this weekend but I assume you are saying there is another bleed on the inboard side of the caliper. I totally missed that. Thanks.

73TexasVette

Which Motive Bleeder would fit the MC on a 73' vette the best?

Lark327

To bring closure.... First I bled the master cylinder. Then I gravity bled the rear brakes, both bleeders on each wheel, then the front. I got some pedal but not nearly enough. Then I used a vacuum bleeder on the rear brakes. The problem is you get a lot of bubbles from the nipple so not really sure if you're getting air out of the caliper too. I did pull a lot of fluid through. Checked brakes and was back to no pedal. What??? So before calling it a night I went back and gravity bled the rears again. Fluid looked clean with no bubbles, then all of a sudden on the outboard bleed nipple on the rear drivers side, a huge amount of air came out. Finished up and checked the brakes. Rock hard pedal. I promptly threw my cheap vacuum bleeder in the trash.

revitup

"I promptly threw my cheap vacuum bleeder in the trash."
Good move.

dembo

Welcome to the brake issues world (see my thread)
I ordered MVP-0105, it seals well with just one C clamp in the middle of the plate.
Nick

Snoopysvet

Bleed the brakes in this sequence....

Left rear inner
Left rear outer
Right rear inner
Right rear outer
Left front
Right front