front brakes won't bleed

saltshaker · #1 (**permalink**) 08-12-2009, 07:13 PM

Using a hand held vacuum pump I easily bleed the rear brakes. With the same hand held pump I can't draw a vacuum on the front brakes and I can't find a leak. Corvette style MC with a GM purporting valve....any suggestions?
Jon

bobcowan · #2 (**permalink**) 08-12-2009, 07:53 PM

Sounds like the cap is sealed, or the plunger is not fully retracting. Try pulling up on the brake pedal and see what happens.

LMH · #3 (**permalink**) 08-12-2009, 11:38 PM

Just a thought but you may have to prime the MC first. Then use the vac pump.
Larry

RICK LAKE · #4 (**permalink**) 08-13-2009, 04:14 AM

saltshaker You need to bleed the master first back into the fluid tank to remove all air from the master. It might be easier to just take the car and go to a garage with a pressure system and let them do this. Problem is the air want to stay in the system and goes to the highest location and is hard to remove. You can try using a short 2 pieces of brake line that will screw into the master and 2 plastic hoses to run to the fluid tank. they must stay under the fluid level to not suck air. Start pumping slowly. May take 2-10 minutes to remove all the air from the system. The tiny bubbles will be gone. Get the lines back on the master and then try your vacuum pump to remove the rest of the air. Tap on all the calipers with a small hammer to shake the air bubbles in them so they come to the top and will go out the bleeders. Cobra system is not a good gravity bleed system, master is lower than calipers. Rick L.

saltshaker · #5 (**permalink**) 08-13-2009, 07:30 AM

Rick, there are two bleeders on the MC...one above each line. i opened the rear one and was able to draw a vacuum 10 plus inch's but no brake fluid. As for the caliper, if I hold the pedal 1/2 was down I can draw 5 to 7 inch's of vacuum but it won't hold vacuum...
Jon

trularin · #6 (**permalink**) 08-13-2009, 08:06 AM

Remove the bleeder from the caliper and check it for clear passage.

While the bleeder is out, fuild will start to leak ( better to leave the master alone ). This is an indication the fuild is getting to the caliper.

I have seen guys put a tee in and never connect the front brakes ( they usually get interrupted or forget ). I have seen hoses pinched and not allow fuild. There are a good number of reasons why you are not getting fuild, but try this first.

Hey, it is just a suggestion.

saltshaker · #7 (**permalink**) 08-13-2009, 09:34 AM

Thanks, the MC has two bleeders on it....the rear when opened flows. The front
when opened won't. Probably a bad MC!
Jon

Tom Kirkham · #8 (**permalink**) 08-13-2009, 09:46 AM

Quote:

Originally Posted by saltshaker

Thanks, the MC has two bleeders on it....the rear when opened flows. The front
when opened won't. Probably a bad MC!
Jon

Can you post a picture? I have never seen a master cylinder with 2 bleeders. For that matter I have only seen 1 bleeder on a motorcycle master cylinder, never for a car.

patrickt · #9 (**permalink**) 08-13-2009, 11:12 AM

Quote:

Originally Posted by Tom Kirkham

Can you post a picture? I have never seen a master cylinder with 2 bleeders. For that matter I have only seen 1 bleeder on a motorcycle master cylinder, never for a car.

Some 1968-1973 Corvette Master Cylinders came with dual bleeder valves. They look like this:

trularin · #10 (**permalink**) 08-13-2009, 01:25 PM

Stupid as this may sound, remove the line from the MC and ask someone to gently push down on the pedal. Fluid should shoot out so use a rag.

Are you sure you put the balance bar in or the control rod to activate the MC?

This is nuts.

Reach into the footwell and push the rod. Fluid should come out.

Pull the darn MC and work it by hand.

patrickt · #11 (**permalink**) 08-13-2009, 01:31 PM

Quote:

Originally Posted by trularin

Stupid as this may sound, remove the line from the MC and ask someone to gently push down on the pedal. Fluid should shoot out so use a rag.

You might even put a Ziplock freezer bag around it just in case it performs like "Old Faithful" when he pumps the pedal and the geyser of brake fluid makes a bee-line for his paint job.

saltshaker · #12 (**permalink**) 08-13-2009, 02:14 PM

To be honest....there wasn't fluid in that side of the MC !!...
All four corners have been bleed and there aren't any leaks, but the pedal is soft. Do I bleed them again and using a vacuum system how much fluid should I draw from each caliper?
Thanks,
Jon

patrickt · #13 (**permalink**) 08-13-2009, 03:12 PM

Quote:

Originally Posted by saltshaker

To be honest....there wasn't fluid in that side of the MC !!...
All four corners have been bleed and there aren't any leaks, but the pedal is soft.

With the dual bleeders on the MC you can bleed it as well with an air tight plastic tube running back in to the reservoirs themselves (you don't have to undo the fittings).

saltshaker · #14 (**permalink**) 08-13-2009, 04:16 PM

are you saying that i can bleed the MC and forgo bleeding the calipers again?

patrickt · #15 (**permalink**) 08-13-2009, 04:29 PM

Quote:

Originally Posted by saltshaker

are you saying that i can bleed the MC and forgo bleeding the calipers again?

Maybe; but you won't know until you try. Put plastic tubing on both of your master cylinder bleeder valves and have the tubes run back in to the reservoirs. Then pump, pump, tap the MC with the back of screw driver, pump, pump, pump, until you see no more bubbles, then pump some more, tap some more, pump some more, and then tighten up the bleeder screws and carefully remove the plastic tubing that is full of fluid. If your pedal is still soft then you'll have to bleed all four wheels again.

saltshaker · #16 (**permalink**) 08-13-2009, 05:33 PM

thanks for the help...I have brakes, we'll see how good tomorrow. I have about 1.25" of travel till the pedal stops hard!
Jon

Tom Kirkham · #17 (**permalink**) 08-13-2009, 10:03 PM

Quote:

Originally Posted by patrickt

Some 1968-1973 Corvette Master Cylinders came with dual bleeder valves.

Thank you. I guess you can tell I have not worked on many Vetts.