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