Need Brake Help
Thread Starter
Heel & Toe
Joined: Aug 2010
Posts: 15
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Need Brake Help
I have been trying to bleed the brakes on my 73 and simply cannot get any fluid to either front caliper. I replaced the calipers, rotors,hoses, and due to a butchered flare nut the crossover steel line to the right. The fluid did drain completely from the from the front half of the master cylinder but I did do a bleed the master on the car (I think?). I am using a Mighty Vac and can get fluid through the rears okay just nothing to the front. I searched and read about the proportioning valve needing to be centered but when I put a line into a jar with fluid I get air bubbles so I am coming to the conclusion if I get air I should get fluid. Any thoughts?
Team Owner
Joined: Mar 2002
Posts: 24,160
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Sounds like you're air locked at the MC. What was your procedure for bleeding the MC? Simply pulling the hardlines at the MC and pumping the pedal doesn't work because on the upstroke the piston will suck air back through the port. You have to either get a proper bleed kit which will let you run a line from the port back into the reservoir, or you can "burp" the MC. The latter requires a helper. Open the port on the pedal's downstroke, then cover it with your thumb on the pedal's upstroke. That'll force the piston to pull fluid from the reservoir instead of air from the port. Keep doing that until you get a solid squirt of fluid on the downstroke. It's messy but it works.
Thread Starter
Heel & Toe
Joined: Aug 2010
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Thanks for your reply. I pulled the hardline and used a bleeder kit running the fluid back into the master and pumped the pedal. The level did drop slightly and no air bubbles after a few pumps so I thought i was good. I then reinstalled the hard line. As I pull vacuum on the left front I hear some gurgling noise like it wants to do something but no fluid.
Thread Starter
Heel & Toe
Joined: Aug 2010
Posts: 15
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To be honest I haven't checked the brake light. I have read the whole "sticky" on brake bleeding a bunch of times and I'm still way confused on the whole proportioning valve/switch. All four lines for each wheel come out of this thing so if one of the front failed you would think the other should still work. I did send some air (compreesed air can) back up through one of the lines in an attempt to check the switch and I did get bubbling at the master cylinder. I am not saying it is not off center, just not sure what to do about it. If air is used, at what kind of pressure we talking, and exactly where is this air applied. I'm soooo confused!!
Team Owner
Joined: Mar 2002
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The hydraulic valve in the distribution block is designed to block off flow to the front or rear brake circuit in the case of pressure loss. Its usefulness is suspect at best and a lot of us have plumbed them out completely.
But if you can blow air from the wheel cylinder line to the MC then this probably is not your issue.
It can take a lot of pumping to fill up empty calipers. Maybe you just need to keep at it? You say you're getting air out of the bleeder, so something has to be taking that air's place! Remember, open bleeder, pedal down, close bleeder, pedal up ... repeat ad naseum. If you don't close the bleeder on the upstroke, you'll just bounce the air around.
But if you can blow air from the wheel cylinder line to the MC then this probably is not your issue.
It can take a lot of pumping to fill up empty calipers. Maybe you just need to keep at it? You say you're getting air out of the bleeder, so something has to be taking that air's place! Remember, open bleeder, pedal down, close bleeder, pedal up ... repeat ad naseum. If you don't close the bleeder on the upstroke, you'll just bounce the air around.
Team Owner
Joined: Mar 2002
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Put the MityVac away, call your wife, and have her give it a good honest 50 pedal strokes while you open and close the bleeder before you go bonkers trying to diagnose a problem which may or may not even exist. Like I said, these calipers hold a lot of fluid, and bringing dry ones to life is an exercise in patience.
Another thing you might try is to just remove the bleed screw altogether, fill up the MC, then come back in a half hour or so and see if the fluid level in the MC res. has dropped. (gravity bleed)
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Le Mans Master
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From: charlotte north carolina
i always thought that the "proportioning" valve on the early cars was nothing more that a fancy distribution block that had a slide switch inside to warn of uneven pressure. i didn't think that fluid could pass between the front and rear reservoir.
Drifting
Joined: Jun 2007
Posts: 1,404
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From: Ansonia/NYC CT
Gravity bleed it. Get a lawn chair, and a decent book, or a buddy and a couple beers, whatever, and just sit back and relax for about 30 minutes or so. After about 45, if nothing comes out, and the reservoir has not gone down, then something is up.
Thread Starter
Heel & Toe
Joined: Aug 2010
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Based on my backyard brake job, the rear or back half of the master never changed even with the front wide open and I have fluid to the rear calipers no problem. I did leave the right front open for an extended time hoping for a gravity bleed, but maybe not long enough. I'll crack it open when I get home tonight and see what happens, or doesn't. I think I'll open up the steel to hose flare nut also just to know if fluid is or isn't that far. Thanks everyone.
Thread Starter
Heel & Toe
Joined: Aug 2010
Posts: 15
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Well, I spent some time on the brakes last night and have come to the conclusion the proportioning valve is off center or just plugged up. I tried gravity bleeding and nothing. Got my 20 year old kid out there pumping the pedal and ran the cycle every bit of fifty times and nothing. I then pulled the hose apart where it meets the steel line and could get just a minuscule amount of fluid using the mighty vac (no threads,right off the steel line). Last question, replace the valve or try to recenter it?
Team Owner
Joined: Mar 2002
Posts: 24,160
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Well, I spent some time on the brakes last night and have come to the conclusion the proportioning valve is off center or just plugged up. I tried gravity bleeding and nothing. Got my 20 year old kid out there pumping the pedal and ran the cycle every bit of fifty times and nothing. I then pulled the hose apart where it meets the steel line and could get just a minuscule amount of fluid using the mighty vac (no threads,right off the steel line). Last question, replace the valve or try to recenter it?
[PERSONAL OPINION]If that doesn't work, plumb the f'king thing out. They cause way more problems than they solve.[/PERSONAL OPINION]
To recenter it, with the engine idling hold the brake pedal down as hard as you can until you feel a bump. Now if the hard lines are full of air, this may not work. In that case, you can also try to open a rear bleeder (and close the fronts) to reduce pressure in the rear circuit, and slowly stroke the pedal down until you feel a bump. This is tricky, and you very well may end up blocking off the other circuit until you get a feel for it.
good luck!
Team Owner
Joined: Mar 2002
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