Can't get any fluid to come out of the bleeders. New dual pot MC, converted to power with 8" dual diaphram booster, new wheel cylinders, new hoses and mostly new brake lines (remaining old ones were flushed and blown dry with compressed air). MC has been bench bled, I'm using a MityVac pressure bleeder pumped up to about 18 psi and the most I get is a little dribble out of the closest wheel cylinder. Tried pumping the pedal literally 75 times.....nothing. After 75 pumps you'd think that would at least fill up the lines but the fluid level didn't drop at all. I pop the cap, press the pedal and fluid spurts up from the bowls. I haven't bled that many brake systems. What am I doing wrong?
I take it you have clearance between the pedal pushrod and booster; but is there a chance the booster push rod is too long? What do you see thru the master cyl ports when you gently push the pedal with the cover off. Can check by loosening the master and add a couple body shims between it and the booster.
I've got a homemade adjustable pushrod between the pedal and booster...... Also, I had to machine a plunger slug to take up the space in MC bore cuz the master is a manual unit...... I've got 1/16" clearance between the booster rod and plunger slug.
I had trouble recently bleeding the brakes on an OT vehicle with dual mc and power booster. Screwed around for hours, then finally pull the MC out and put it in a vice and ran some tubes from the outlet ports, to the reservoir. Didn't take long to bench bleed the air out of the MC, then reinstalled it and the brakes bled just fine. Might be worth a try. It'll take you just a little while, and will probably fix it.
Most of the time if you can't get at least some fluid out of It is method rather than equipment. Pumping the brakes: 1. Master cylinder full with lid on and all bleeders closed. 2. have your helper pump the pedal ******** SLOWLY! no fast pumping it has to be slow and the pedal has to come all the way up every time. Then after they pump it several times tell them to hold the pedal down (until you say to pump again) and open the furtherst bleeder from the master cylinder brakeline wise. Close the bleeder and have them pump SLOWLY again and repeat checking the fluid level on a regular basis. Work your way around to the next furthest and so on and you may have to go around again more than a couple of times. Only a damned idiot would pump the pedal and run back and open a bleeder expecting to do a one man brake bleeding job. It just flat does not work. You can not pump bleed the brakes with an open bleeder valve, that just ****s air back in. It can be done half *** if there is a hose on the bleeder running into a bottle with the end of the hose covered with fluid so it tries to **** fluid back but that is still doing it half ***. Pressure bleeder if your pressure bleeder is similar to this one, the same basic step applies, do the furtherst first after you connect the bleeder and open the valve and it puts pressure on the system. Go around to the furtherst bleeder and open it and you should have air coming out and then fluid. Close that bleeder, check your pressure and move to the next. If all the bleeders are open you aren't going to get enough pressure on one line to push the air out and you may be getting as much air in as out. That plastic pressure bleeder kit using a weed sprayer tank has to have the tip of the tube that picks up the brake fluid below the fluid level. Works exactly the same as a weed sprayer. Now some questions: You do have the brake drums on and the brakes adusted? Yes I have seen the guy who tried to bleed brakes with the drums off. I also fixed his mess. As others said, you have to have clearance between the push rod and the master cylinder piston. You should be able to move the pedal with your finger tips and feel the slack before the pushrod pushes on the booster or master cylinder piston. The inlet ports have to be uncovered so that fluid will flow into the piston and then into the lines. If you aren't getting fluid flow with the pressure bleeder I am in belief like others are that your pedal push rod is pushing the piston far enough in that the inlet ports never uncover.
Do this as a quick test before you do anything else. unbolt the master cylinder and put matching flat washers on the bolts and put the master cylinder back on and see if you can get fluid to flow. That will let you know if your push rod isn't right or isn't adjusted right and you can go from there. You might just loosen the nuts a few turns, let the master cylinder slip forware and see if the pressure bleeder all the sudden works. That will let you know if the push rod is the problem.
Thanks guys! I'm gonna take another stab at it tomorrow. I'll try Mr48chev's methods first and if that doesn't work, I'll move on to squirrels recommendation and bench bleed it again.
After verifying master (bled ) & rod play, like other said . One time had one just could not get bled , ( master under floor) even with vac canister ,So added a rubber tire core to lid & pumped a few times with bicycle pump to pressurize the master & bled , Should of not been that difficult, brakes worked with no issues , wonder what ways said when someone spotted tire core in master cap.
Pedal return spring present? Required so that at rest there in nothing acting on the master allowing it to return to its proper position, uncovering ports etc. It can be that sensitive! 1/16" clearance between the master and booster sounds small but is quite large and certainly wasteful of valuable pedal travel and possibly adding to the bleeding problem. Chris
Take the brake lines off the mc but leave mc on car. Then use the clear tubes and fittings you used for bench bleeding,- oh wait, do you have that? Well most rebuilt mc's come with them.... Anyway connect the tubes to the outlets and stick other ends of tubes in open fluid filled mc reservoirs. Now as a friend slowly pushes brake pedal you can see if master cylinder is pumping fluid thru clear tubes back into reservoir. If not there is where to look, if yes at least you know mc is bled. I used to do it that way instead of bench bleeding- well you actually are bench bleeding- only on car- not on bench. Good luck!!
That’s good, if the MC is level, or else he’ll need to raise and support the car from the rear to level it out.
Even with new wheel cylinders, make sure the bleeders are clean. I have seen crud in new ones, I even saw a new one that wasn't drilled into the side hole deep enough.
I saw a picture somewhere recently.....don't remember where...........But someone had made an adapter for a master cylinder. I guess they used a top/lid off an old master cylinder just like the one being bled. They put a pipe sticking up out of the lid with a small shut off valve in it. Then above that was a reservoir that held a lot more brake fluid. You fill the master cylinder and then put the modified lid on it, and you have a reservoir with plenty of fluid above it. Open the valve, and as you bleed the brakes, the master cylinder never goes dry and needs more fluid added. Probably not helpful here but some of the creative guys might want to make one for future bleeding.
It's in the MC. If dragging pedal/linkage can over ride the internal spring pressure (by weight - not adjustment), the MC is defective.
I used a vacuum bleeder on my '41 when I replaced the hoses, some lines, wheel cylinders an master. I didn't have a pressure pot on hand so I went to Harbor Freight and bought a cheap air operated vacuum bleeder. Got fluid to all wheels and manually bled after that.
What exactly are you working on? Is it four wheel drum w/ DBL RSVR MC and BOOSTER? Any external valving at all?
I got one in a GM Metric caliper that was not drilled AT ALL! It was a straight-up bolt! I chucked it in the lathe and took care of it. The thought of trying to explain this at the parts store was too difficult to deal with.
Taking to chain parts house help... a must to avoid. I would have rather made a new one from scratch than done that.
The Jalopy Journal
