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I just finished plumbing this. Do I have to take it all back apart to bench bleed the master or is there maybe an alternate way to do it.
I think you should. Unless you have the means to jack the back of the car high enough to level out the bore of the master cylinder. Because at the stock position how else can you get air out of the highest point of it?
I think you should. Unless you have the means to jack the back of the car high enough to level out the bore of the master cylinder. Because at the stock position how else can you get air out of the highest point of it?
If you don't you may have trapped air bubbles at the most forward position in the master cylinder. No way to remove those. No fancy reverse bleeder system will remove them either, apart from (like Lurbie said) raising the rear end up really high to level out the master cylinder, bench bleeding is the only way.
Unless the Master cylinder is parallel with the ground you will not be able to remove all air from the master cylinder.
^^^ This ^^^
If it's at an angle like all of these cars, there's a part of each cyl inside it, that's above the line fitting; the air will go there, and will NEVER EVER come out by gravity bleeding. Or even, vacuum bleeding. You can bleed a gallon of fluid through it every single day for the rest of the century, and 2 gallons on Sundays just ... because, and it will STILL have air trapped up in there.
Part of the reason for doing this is to check for a defective master cylinder.
You don't really want to put everything together only to find out that the new MC is bad, and then you get to do the job all over again.
A tip for bench bleeding the master cylinder: Usually when you purchase a new master cylinder they come with plastic barb fittings and hose for attaching to the master's ports. Those fittings inevitably get lost or harden or mis thread-whatever- so buy the correct fittings and a length of 6" tubing for each of them. Loop it into a 270° curve so it can dump into the master below the fluid line. I made those years ago and I've used them many, many times. IMO way better than screwing around with some plastic barb and hose. Only trade off is that you have to carefully watch for bubbles in the water instead of the tube.
.......If it's at an angle like all of these cars .......
Yes sir , it's the angle of mounting that makes bench bleeding in the car all but impossible , I don't think someone could get the back of the car that far off of the ground without the nose being buried in the ground to make the MC actually perfectly level for the initial bleed . Your plenty old enough so I'll bet you remember when we used to be able to bleed a new MC right there on the firewall , specifically because in those days the MC did mount flat to the firewall with no angles to trap air and foil the process ....
Thanks guys I will take it apart and bench bleed it.
One more question. The whole brake system is pretty much dry, no fluid whatsoever. After I bench bleed the master and re install do I have to worry that since the lines are full of air when I hook them back up to the bled master that I will get air up in the master.... If that make any sense.
Because at the stock position how else can you get air out of the highest point of it?
Originally Posted by Tibo
Unless the Master cylinder is parallel with the ground you will not be able to remove all air from the master cylinder.
Originally Posted by sofakingdom
If it's at an angle like all of these cars, there's a part of each cyl inside it, that's above the line fitting; the air will go there, and will NEVER EVER come out by gravity bleeding. Or even, vacuum bleeding.
Originally Posted by OrangeBird
Yes sir , it's the angle of mounting that makes bench bleeding in the car all but impossible ,...
How does this account for my getting a thoroughly bled system then? New master. Lines. Calipers.
Set up the pneumatic bleeder. Drained several bottles of brake fluid through the components.
Done.
Maybe I was just lucky?
For the record, I don't recall whether or not I pumped the brake pedal while the system was being flushed but I do know the results.
Likely you have air in the system. Since it's equally divided among the wheels you might not be able to tell. When O Canada warms up and you're bored id bench bleed it and rebleed the system.
Isn't that the truth. Especially this part of O Canada.
Fact is that I did that wholesale braking upgrade about half a dozen years ago when I did the LS1 front/PBR rear swap. The master I used I think is from a disc/disc chassis with whatever prop valve was supplied (the Coupe was a V6 disc/drum). At first the rear brakes were practically nonfunctional however, to satisfy my curiosity a few months back (I drove it that way for the longest time without any problems), I put the car up on stands and tested the rears with the tires in the air. Rears stopped instantly and repeatedly.
Air in the system? I can't say.
What I've always thought though was that the braking upgrade, and the different caliper volumes both front and rear, it would make sense to also change the MC to the one used with this particular brake arrangement. A 4th gen version is what I'm thinking. Once I pull the trigger on that, I'll experiment again with the pneumatic bleeder vs bench bleeding and see where I end up.
In the meantime, I'm experiencing no ill effects from the method I used to bleed the entire system years back.
What I'd like to see is a cutaway of a 3rd gen master cylinder and see exactly where this air would be trapped and how it wouldn't be expelled if the fluid was drawn out. It would make sense that the brake pedal would have to be worked during the process.
Thanks guys I will take it apart and bench bleed it.
One more question. The whole brake system is pretty much dry, no fluid whatsoever. After I bench bleed the master and re install do I have to worry that since the lines are full of air when I hook them back up to the bled master that I will get air up in the master.... If that make any sense.
My experience is that dry lines make no difference in the bleeding process. Air isn't drawn back into the master on the release of the brake pedal.
(And if you've never tried a pneumatic bleeder, once you do, you'll never go back to the traditional method. My 2 cents.)
No. Hook it up. Fill the master and crack open front and rear bleeder on the longest lines (especially front)
Then use a sucker type bleeder to get all the air out. Only after do the pedal bleeding. This way the mc will not over travel and potentially damage the internal seal. Easiest done with 2 people.
I'll experiment again with the pneumatic bleeder vs bench bleeding and see where I end up
It's not really a this-or-that option, more like step 1, step 2. I don't think anyone here would disagree that pressure bleeding is awesome. We're just saying that air will remain in the front of a master cylinder bore if step 1(bench bleeding) isn't done first.
So if you were to get the master cylinder level while in the car, lets say by the way of a steep drive way, would the air not naturally work it's way out into the lines? Then re bleed the lines after?
So if you were to get the master cylinder level while in the car, lets say by the way of a steep drive way, would the air not naturally work it's way out into the lines? Then re bleed the lines after?
What happens when you fart in the bathtub? Sorry, couldn't resist.
The air bubble is always going to rise to the top in a liquid.
In the brake system, it needs to be forced out.
But like you, I also was thinking of parking the car on the appropriate incline to level the master cylinder. Then pressure bleed.
Think of this:
Do the OEMs bench bleed each master cylinder before it's installed?
Just a question to stimulate the conversation. I've personally observed the bleeding apparatus in operation but I don't recall ever seeing any plant employee working on an individual component. The brake system is assembled as a whole and pressure bled in one shot.
Just saying...
Yes you do. Disconnect lines at master coonect bleeders to master probably those plastic pieces that were in it run some rubber hoses form the bleeders back in to the master fill with fluid pump it till no more bubbles reconnect the lines bleed the wheels starting at right rear left rear right front left front.
You can forgo the bench bleed and bleed from the wheels but it will take forever to get all the air out and you will probably have to do it again several times when you discover you didn't , and by that I do not mean gravity bleed.
Manufacturing, masters probably come pre-charged and the system is pressure bled before attaching to the vehicle
Think about that statement. If you haven't been in the auto manufacturing environment then it's not likely you'll understand the processes involved. In mass produced vehicles, like our third gens, there are little if any preliminary steps taken.
New masters are shipped dry just like you buy them from NAPA (for obvious reasons). The OEMs install them this way as well.
Originally Posted by LS2Swapped92
Is saving 30mins worth risking your life and car?
However, I'll leave it at that.
I don't want to create any concerns regarding safety.
Last edited by skinny z; Mar 16, 2018 at 08:21 PM.
To be done properly, they must be bench bled, not a big deal and only takes a couple minutes. If skinnyz got lucky and didn't have to, props to him but this is not usually the case.
As for the rest of the lines being dry, it doesn't matter as long as the master is not allowed to run dry during the rest of the bleeding process. Done it a millions times.
I see two problems. The first being, when installed, our third gen master cylinder reservoir inlets are on a lower plane than that of the highest point of the end of the master cylinder bore. Using his own theory that the air wants to go up, it will never exit the MC bore because it went up to the end of the bore instead. The second is that he mentions using water in the catch can at the calipers.
Think about that statement. If you haven't been in the auto manufacturing environment then it's not likely you'll understand the processes involved. In mass produced vehicles, like our third gens, there are little if any preliminary steps taken.
New masters are shipped dry just like you buy them from NAPA (for obvious reasons). The OEMs install them this way as well.
However, I'll leave it at that.
I don't want to create any concerns regarding safety.
I happen to work in the automotive/aerospace manufacturing sector. Don't claim to know exactly what they did in the 80s. TONS of things have changed since then. However, it stands to reason they probably did one of these:
1) Hooked the line assemblies to the masters and precharged them
2) Pressure bled the system on an inclined spot in the assembly line
3) Did everything manually
Maybe if someone has an assembly line video or someone here actually worked on that line we'd know for sure. Until then it's all speculation
Ah, there is the key, they pull a vacuum first. Now that makes sense. Get rid of the air before adding the fluid. I like it!
Not only is the M/C an issue, but prop or combo valves can also hold air. Last car I did was a bunch of new lines, added a prop valve, entire system was empty. Bench bled the M/C but had a heck of a time getting the air out of other system parts.
That's why I said... crack the bleeders and use a vac can in the 4 corners to pull fluid in and only start pumping the oedal for that last bit if firmness.
You HAVE TO evacuate the ENTIRE MC in the process; GOTTA get the air out of those corners that are ABOVE the line fittings. That's why a vacuum bleeder system, where the vac is applied at the bleeder screws, CANNOT work; unless it pulls the system down to near deep-space level through them, WITH A CAP ON, and then fluid is introduced perhaps through a petcock sort of arrangement at the top, or through 4 such at the bleeders.
But ONE WAY OR ANOTHER, the air MUST be removed ENTIRELY from the MC, before fluid is added.
Yes sir , it's the angle of mounting that makes bench bleeding in the car all but impossible , I don't think someone could get the back of the car that far off of the ground without the nose being buried in the ground to make the MC actually perfectly level for the initial bleed . Your plenty old enough so I'll bet you remember when we used to be able to bleed a new MC right there on the firewall , specifically because in those days the MC did mount flat to the firewall with no angles to trap air and foil the process .... 
