Black76

I replaced the 2 front flex hoses. Now when having the wife pump the brakes and hold i open the screw on caliper and get nothing . my question is does the car have to be running to build up vacuum when bleeding the brakes .

Grumpy 427

Bleeding brakes takes time. Correct way to do it is to start with the inner bleeder screw first. Have wife pump up the pedal 3-4 times. keep foot on pedal then crack bleeder screw open with her foot hard on pedal, open screw her foot goes to the floor. Leave foot to floor till you close bleeder screw. Repeat till no more air comes out of bleeder screw. Then do outer bleeder screw on same caliper. Then do other side. Make sure you leave cover sitting on brake booster, but keep eye on fluid level. if you empty the master your really screwed and need to remove that then bleed the master and start over.

Black76

does the engine need to be running to do this and when i open the bleeder screw i get nothing

Roadking

No. Attach a clear line to the bleeders and crack the bleeder about a quarter turn and walk away for an hour or so. Make sure the master is full. There is alot of air the fluid has to over come. Take your time. C3 brakes are a no rush job. That's been my experience with them. My $.02

...Roger...

Bench bleed the master cylinder.

7t9l82

the front chamber on mine ran dry i filled it up took off the front line pumped it twice worked like a charm.
have something to catch the fluid and rinse any spillage quickly

Black76

no matter how much we pump the brakes i cant get anything out of the bleeder screw

7t9l82

i had the same problem, it was a collapsed line. try taking the hose off the hard line. if not there is a block which people refer to as a switch it may be stuck. bleed a rear caliper if your working on the front. the switch is what some call a proportioning valve, but its not. I'd open all the bleeders and let it go for an hour or so just check it once and a while.

njfl

Trouble shoot by moving from the bleeder screw, back to the point even before it goes into the caliper and see if you have fluid there. If you remove the hose from the hard line and nothing comes out, your problem is that you have an air block in the master cylinder and need to bleed the master cylinder.

LancePearson

If you have power assisted brakes you may also have lost the power booster check valve from the vacuum from the engine. When that happens you get no brakes as well. Last time in mine had that happen so the mechanic just replaced the brake booster check valve. I think it is the little round thing on the front of the booster housing that the vacuum hose goes into but not completely positive. Check your books. It keeps the vacuum in the booster is my understanding which allows the brake pedal to work. No check valve working correctly and mechanic says no pedal. I'm no expert but when they did, it works great now with new front calipers which was the original issue.

The thing with these things is when you put new in any part of a system like the brakes, it now is stronger than the other parts and if they are at all weak the imbalance will eventually break them down until you've replaced it all. Now I just do things in pairs or the whole system rather than nickel and dime it one at a time if it's old equipment in the system. Cheaper in the long run.

Lance P.

...Roger...

The master will not pump air.

LancePearson

here's the diagram for mine...and you can see the check valve which is available from the vendors. This is from Zip's site.

Lance P.

Black76

Thanks for the diagram . does the engine have to be running for the check valve to work . I have both front bleeder screws open and i pump the brakes get no fluid out

LancePearson

I am far from a brake expert but have read a lot here as I have all new brakes and proportioning valve on my 76 since last Oct. to July but one method is gravity bleeding...use the search function as there is a good description of that on the forum. In order to initially get vacuum in the vacuum brake booster the engine has to run and the check valve has to be working to use that. I believe this is what's normally called a "power brake."

Here it is right off the forum..I saved it but haven't tried it myself yet. No need at present for me.

Lance P.



"It's possible you got some air into the master, and thereby got some air into the fronts.

Have you ever ever used the gravity--bleed method? Short version:

Car up on jack stands, no wheels.
attach small tube to each bleeder valve (1/4" ID?), long enough to get to the bottom of a clear receptical, like a small pop bottle. (one bleeder valve on each caliper or 8 in total on wheels)

fill each receptical 1/4 with clean brake fluid.

crack open each brake bleeder.

open the master cylinder.

Keep the master filled as the brake fluid slowly migrates out of each bleeder.

DON'T mow the grass, grill a burger, watch a baseball game, or listen to your wife while the fluid is flowing. If you do, the MC will run dry, and you'll have to start all over again.

Walk around the car as the brake fluid is flowing and watch for little bitty bubbles coming out of the hoses.

Once the bubbles stop, close all the bleeders. Replace the MC cover.

Step on the brakes. The pedal will go to the floor. SLOWLY let it up, and slowly depress it again. Might have to do this 2-3 times before the peddle gets hard.

If it doesn't get hard, go inside, find your wife, tell her how that skirt/dress/shorts/swimsuit makes her look sooooo skinny,

then ask her to come pump the brakes for you.


She'll probably do it anyway.


Good luck."


However, everything I've ever read or seen or watched says you don't start bleeding the front brakes whatever method you use, power or gravity, but you start with the line that is furthest from the master cylinder which on my 76 is the right rear and bleed it until no bubbles come out. Bleed both sides, both calipers on each wheel as you have four pistons on each wheel on my 76. Then do the drivers side rear, same way. Then do the passenger's side front, same way, then do the driver's side front, same way. I never have seen the mechanic open more than one bleeder at a time either. I do not know how to bleed the master cyclinder but it also must have no air in it and it's diaphragm must not be ruptured or pushing the brake pedal, power or other, just pushes nothing.

Gravity bleeding takes time and I believe if you do it right you can open each wheel caliper that the bleed hose is hooked to into the bottle of brake fluid reservoir but you must be sure the master cylinder remains full the entire time. When air is out, move the bleed hose on each wheel to the caliper on the other side. patience as it takes time.

My 76 also has a proportioning valve between the mc and the lines to rear and lines to front to complicate it a bit further. Any air in the system anywhere makes brakes worthless until you get it out.

In the meantime while you are figuring it out, you can tell your wife it is all her fault for pumping the pedal the wrong way but there is a way she can make it up to you.........grins.

I have the mechanic do mine because he's usually replacing something and he machine bleeds but gravity works at home for many.

noonie

In a worst case, the bleeder screws can have crud blocking the holes, take them all the way out and make sure you can blow thru them.
The engine does not have to be running to bleed or pump the master.
Make sure the master is full and gently loosen the front line at the master, to test for pressure while pumping. If good, then go to both sides of the prop valve and so on down the front system till you find the cause.

Black76

Im getting fluid to the back wheels nothing to the front could the master cyclinder be bad

LancePearson

If memory serves the proportioning valve does that. If there's an issue it blocks off either front or rear so the other half can work. Your proportioning valve may not be working right if your system has one. They failed on mine and it literally shut the back brakes down so the car couldn't move then relaxed as pressure eased. if you lose pressure on the front the valve is supposed to shut the front system off so the back can still give you braking....and vice versa in theory.

Ralphbf

Loosen the hard line coming from the master cylinder.

Step on the break pedal.

If you get break fluid to squirt then the MC is okay.

Tighten the hard line before removing your foot from the pedal
or you will suck air into the system.

If the fluid squirts, move farther down the line and try it again.

Repeat until you can not get fluid to squirt.
Then you have found the problem.

It could very well be a bad Master Cylinder or if your lucky,
a MC that needs to be bleed.

Ralph

Black76

Ralph

thanks for the comments how do you bleed a master cyclinder

dannyman

Black76;

I know the following thread used to be a sticky.

http://forums.corvetteforum.com/c3-t...fo-please.html

Read (post #3) thoroughly to answer all your questions, and disregard the rest of the thread.




Dan