Working on a older 60's vehicle but is off topic here. It is one of them GM's with the master at a drastic angle from the factory. All parts are new, master, proportioning valve and hard and rubber lines. I have been able to get the rear to bleed just fine, but not the front. this is a disc, drum setup and all factory components. I am using a pressure bleeder, and no fluid comes out of the lines or master. I have bench bled the master and it did that fine. The only way I can get fluid out of master is by pressing pedal. Even with the pressure bleeder hooked up and 7 psi, when I crack/take off the line to the front nothing comes out. I was thinking the proportioning valve was the problem, but cant get past the master at this point. I do have factory manual, and it gives me tips, but none of that is working, I am leaning towards bad master but not sure. Is there a way to check master?
What kind of gasket does your pressure bleeder have at the master? Rubber can squeeze down and close off the disc brake half of the cylinder.
Will it gravity bleed? Open the bleeders and walk away for about an hour. See if anything runs out. Make sure to leave the lid off.
I had that thought so I rotated the top and same thing, it is a rubber gasket but totally open in the middle.
If it bench bled but won’t bleed installed, I’d be looking at the pedal/rod/master clearance. I can’t give you a good reason, but that’s what’s changed. Including the booster to master rod if it’s power brakes.
to do this the rear of the car would be 6ft in the air, and with a pressure bleeder it shouldn't matter.
“I have bench bled the master and it did that fine.” “I was thinking the proportioning valve was the problem, but cant get past the master at this point.” I lean towards the proportioning valve, but your statements don’t add up?? Regardless, I’ll guess that when you pressure bled the rear, the internal valve (brake warning light switch) moved and closed off the front circuit in the proportioning valve.
When I bench bled, I was pushing the plunger, if I dont push plunger or pedal nothing will come out of master for the front brakes. Gravity and pressure bleeder, does nothing for me. I have thought the same about the brake light switch, but that is located on the frame, and is not part of the master.
If fluid will come out of the master when the pedal is pressed why not bleed it that way? Agree there could be something else going on though, as has already been suggested. Chris
There is another procedure to get the air out of the system on a angle mounted master cyl system when raising the car to level the master cly. would be unsafe.There was a tech service bulletin from GM for this problem with this mount style master.
You don't show the combination valve because it's covered, but I'll bet there's a small button at the front end which is the hold-off or metering bypass. This has to be pushed to allow low pressure bleeding, as they normally require about 100 psi to open for fluid movement to the front discs.
I agree on the combination valve, that is one of the things it says in the manual. It doesn't move far but it does move. That is one of the things I did first. Thanks
I would absolutely do it that way if I had another person. Wife is gone for 10 days, and guy that owns car cant get here until next Thursday.
Is this a brand new master, and booster? It's possible the rod between master and booster, or booster and pedal is wrong or out of adjustment, and not allowing the master to fully retract it's piston. If that happens they wont ever bleed as the outlet in the bottom of the master cylinder is blocked. Since it bench bled fine I'd be double checking those rods to ensure nothing is too long.
Loosen the master cylinder from the booster and slide it forward to see if fluid will flow out the ports, even if the internal rod is the same length, it could still be wrong for the new setup. Try to find a service manual for the car or truck the master cylinder came off of and see if there is a cross sectional drawing to show how it works inside. There could be a pressure differential spring/valave that won't let fluid out till a certain pressure is met.
That Utube up there with the bottle and tube implies you need brake fluid in the bottle, (I like a glass jar.) The liquid can be anything, even water. Or beer.
Gravity bleeding is a nonsense thing perpetuated by people who have never done brake jobs who want to sound like experts. I have done brakes since 1962 and did them for a living for a number of years sometimes doing as many as five brake jobs a day and never once heard about "gravity bleeding anywhere until someone here on the HAMB claimed that you could do it but it is all too obvious that it will not work simply because there are too many spots in any brake system where air could be trapped. Leave that for the guys down at the spit and whittle club to BS the new guys with.
If there is no blockage and reservoir is full and above the bleed, physics and gravity will make you a liar
That could well be the issue right there. If the inlet port from the reservoir to the cylinder is covered no fluid will flow. I'm not out ruling the concept that the piston in the proportioning valve is stuck to one end and not letting fluid flow . Back in my early days of doing mechanic work as a job I had the pressure differential valve in a combination valve go to one side and actually break the tip of the brake warning light switch and ended up having to take the whole valve apart to get that chunk of plastic out and then make a trip to the dealer to buy a switch out of my pocket at lunch. My screw up I fixed it and the parts house across the street didn't have one. If that valve/piston is stuck to one side that may be the issue.
I am no expert but I would be willing to bet your Chinese replacement master cylinder is no good and was assembled incorrectly. When you are bleeding it on the bench I assume you are taking the threaded lines and flipping them right back into the reservoir and watching air come out into the fluid in the reservoir correct? How far is your pedal stroke when you are pressing it with the end of a screwdriver or however you are driving the piston and once you put it inside the car how far is your pedal stroke, I got a feeling it's less or more and I got a feeling the piston seal is getting in the way and blocking the port just as the picture above my post shows on the diagrams of the master cylinders. I used to sell car parts at Kragen's 20 years ago and the rebuilt master cylinders usually didn't have the problem (The brand was cardone) but the Chinese replacement ones were terrible although They looked great, I would say one out of 10 were defective right out of the box. I can't imagine the quality has gotten any better. In my personal wrenching experience I have a Chinese c3 Corvette style (I think that's 1968 to 1982 right?) That has the two equal reservoir sizes that sits at a hell of an angle anyways on the car anyways I replaced The master father's 1978 Corvette and I was having almost the exact same problem with the front brakes, My buddy came over and unbolted it and said take it back... Long story short, I bought that one from AutoZone They took it back without an issue and they had to order another one 24 hours later I got the new master and It bled correctly and it is still on the car.
While this is generally true, there are some vehicles that it will work on. I have a '99 F150 that all you have to do is fill the reservoir, walk away a few minutes, come back and refill it a time or two, tighten up the bleeders and you're done. I also know for sure if I tried it on a couple of my other vehicles, I would be waiting to refill the reservoir a year later. I'll take something if they're giving it away.
Gravity bleeding is pure bravo-sierra. I have never seen it work. I'm glad someone said it. I am also in the bad-master camp.
Sorry to ruffle your feathers. But you sir are wrong! Sounds like all you did was replace brakes for a living while I am actually a competent mechanic in all facets of automotive repair. Gravity bleeding is a great way to get the bleeding process started and then to be finished by pressure bleeding. Maybe you should read a book on fluid dynamics rather than hanging around the spit wittle club. I can’t believe the nerve of people on this site.
Ardinger , you are spot on. letting a brake system get started bleeding from gravity while attending to other tasks was the norm for me. Works about every time. You might have to pump it a few times to get things flowing.
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