How is air getting into my lines?

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Hilderbrand1983

Hilderbrand1983

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1967 Dodge Dart 270 /6

I just swapped out the master cylinder and the wheel cylinders for the front brake drums (9"). I also installed new hardware, self-adjusting screw assemblies, and new shoes for the front brake drums. I proceeded to bleed the brakes, which went fine for the rear brakes and the front passenger brake. However, the front driver's-side brake has given me a little problem.

When I bleed the brake, a bunch of air jets out of the bleeder, followed by fluid. I bleed it correctly and get it squared away, but the pedal feels squishy. So, I have my buddy pump the pedal until it feels firm, then have him press and hold it down. I open the bleeder, and again, a bunch of air shoots out, followed by brake fluid.

This happened five or six times before I gave up. I don't want to drive the car until I can figure out what's going on.

I can't find any leaks (in that there's no brake fluid dripping from the car), but the hoses and lines are pretty old and crusty. The connections are all tight. The only part I can't test or inspect easily is the little box that distributes brake fluid to the wheel cylinders[EDIT: Just found out this is the "proportioning valve"].

Thoughts?
 
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Don't press the pedal so far on the bleeding, but just do 1/3 or so pumps.
When everything returns from the pedal press they can suck air in around the cups in the brake cylinders.
You might want to disassemble that wheel cylinder to make sure there isn't any manufacturing garbage in it.

Other than that, a power bleeder should solve it.
 
No, that's a distribution block. There's no proportioning valve on a drum brake system. I have always had the best luck on older vehicles by simply gravity bleeding.
 
RustyRatRod said:
No, that's a distribution block. There's no proportioning valve on a drum brake system. I have always had the best luck on older vehicles by simply gravity bleeding.
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You talking to me?
You talking to ME? :D

I have had master cylinders return from a pump and suck air in around the cups before the piston seal in the master cleared the return port.

On ones that are being a pain I sometimes use a squeeze bottle with a plastic hose on it to fill it from the wheel cylinder up instead of from the master down.
 
TrailBeast said:
You talking to me?
You talking to ME? :D

I have had master cylinders return from a pump and suck air in around the cups before the piston seal in the master cleared the return port.

On ones that are being a pain I sometimes use a squeeze bottle with a plastic hose on it to fill it from the wheel cylinder up instead of from the master down.
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Me too, but in that case the air would be transferred to both right and left of whichever side of the M/C was sucking air.
 
RustyRatRod said:
Me too, but in that case the air would be transferred to both right and left of whichever side of the M/C was sucking air.
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No, I meant a vacumm on a wheel cylinder cup letting air into that one cylinder and not the master itself.
That's when you keep getting air out of one cylinder over and over and over.
 
TrailBeast said:
No, I meant a vacumm on a wheel cylinder cup letting air into that one cylinder and not the master itself.
That's when you keep getting air out of one cylinder over and over and over.
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Yup, that would do it. .....and this is exactly why I would much rather rebuild my own original American made than trust chinkesium knockoffs.
 
Try adjusting the (front) shoes up nice and tight and then bleed them. You might have trouble with brake hardware, IE shoe return springs, something like that. The idea is this:

Drum masters have a residual valve which is supposed to keep a small positive pressure in the system. (Why I don't like vacuum bleeders). This is to keep air from coming INTO the wheel cups during the return. The wheel cups MUST be spring return via the brake return springs to keep the cups expanded. If the master tries to return, and if pressure drops off in the system, air can come in around the cylinder cups.

Some sort of damage in one cylinder could certainly be a problem, a burr on the cylinder wall or some such.
 
Cheap wheel cylinders? RRR said it about the Chinese stuff. I could never get cheap wheel cylinders to bleed properly.
 
Thank you! I always wondered WHY drum systems had residual valves! Learn something new every day!!
 
67Dart273 said:
Try adjusting the (front) shoes up nice and tight and then bleed them. You might have trouble with brake hardware, IE shoe return springs, something like that. The idea is this:

Drum masters have a residual valve which is supposed to keep a small positive pressure in the system. (Why I don't like vacuum bleeders). This is to keep air from coming INTO the wheel cups during the return. The wheel cups MUST be spring return via the brake return springs to keep the cups expanded. If the master tries to return, and if pressure drops off in the system, air can come in around the cylinder cups.

Some sort of damage in one cylinder could certainly be a problem, a burr on the cylinder wall or some such.
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^^^What he said^^^

Any drum system I have ever had trouble bleeding has always turned out to be a bad wheel cylinder. Ive also seen on 2 occasions, the spring in the middle of the two rubber cups inside the wheel cylinder, missing. Also, the residual pressure valves can cease to operate if the system was left dry and open to elements too long.

Rusty is right about the cheap chinese knockoffs. I rebuilt my original wheel cylinders. The kits were like $5 or $6 each from Rockauto. Now I can't say the kits weren't made in china, but I know my quality control is a hell of a lot better!
 
I had a similar sitch with my 65 Dart. All the wheels bled fine except the left front. The brake line went from the "D" block down and around the frame member and up to the support clip; made a "U" bend down about an inch or so to the flex line connection. The flex line to the wheel cylinder had a slight uphill turn for it to flex. All these high points in the line to the wheel cylinder seemed to trap air I was constantly getting out, and then seemed to reappear. What I did was separate the flex at the hard line, bleed there and then re-connect. Then bleeding the flex line and wheel cylinder went much better. I used a hand operated pressure bleeder which made things easier than frustrating an assistant at the pedal; and I could pump to my heart's content. Do NOT trust anything out of the box for brakes. I've had wheel cylinders with metric fittings or bolts for domestic iron; I've found manufacturing debris in NEW parts, even ones that were made in the USA regardless of price or lifetime warranty. QA is just not dependable these days.
 
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Well, I guess Ima little late to the party, So I'll just throw this in.
What I sometimes do is pinch the flex line at the offending corner, as the helper lets the pedal up. Then as he pushes fluid out I can feel it under my hose-pincher, as the fluid goes by. I and my pincher become the on-location residual valve.
Party On!
 
AJ/FormS said:
Well, I guess Ima little late to the party, So I'll just throw this in.
What I sometimes do is pinch the flex line at the offending corner, as the helper lets the pedal up. Then as he pushes fluid out I can feel it under my hose-pincher, as the fluid goes by. I and my pincher become the on-location residual valve.
Party On!
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Would you be willing to double as my line lock? :D
I can yell pretty loud.
 
Don't OPEN the bleeders, just crack them off the seat the tiniest amount that will allow fluid out. Push the pedal gently only a little ways down until you can feel that you're no longer spurting air, then tighten.
Had to learn this a long time ago when I could never get an assistant for brake bleeding.
 
I wouldn't kink a high pressure fluid line much less pinch it with pliers.
 
hose-pincher
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NEVER pinch hydraulic hose. Even though brake hose could be classed as low or medium pressure hydraulic hose; you can damage the inner liner with pinching or kinking. This "shortcut" is only done by less-than-stellar or un-informed mechanics.
 
TrailBeast said:
Would you be willing to double as my line lock? :D
I can yell pretty loud.
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You think one tire will hold; I cant reach both sides. I work for Pepsi's
NEVER pinch hydraulic hose. Even though brake hose could be classed as low or medium pressure hydraulic hose; you can damage the inner liner with pinching or kinking. This "shortcut" is only done by less-than-stellar or un-informed mechanics.
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RedFish said:
I wouldn't kink a high pressure fluid line much less pinch it with pliers.
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Guys; special tool; Been doing it many decades no comebacks, relax . I didn't say clamp it off with a Visegrips. Teachers teach all kinds of stuff, some total BS,probably to protect their own asses from newbies using Visegrips. I can only imagine.
But since you mention it, this method is not acceptable on high-performance type hoses which may have non-rubber inner-liners; you know,the braided stuff; which I totally love, and highly recommend.
 
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Special tool? I've seen pinch off tools for cooling systems and fuel line "advertised" as for brake line clamps; but that does not make it right. YMMV, and it's your iron, your life but the right way is just plug it. Golf tees work pretty good or a female fitting just screwed hand tight.
 
When the shop charge is 6 or 7 or 8 times what the customer's wages are, I ain't got all afternoon. I got two weeks to two months work ahead of me at all times. People come to have me fix their stuff. Not some " less than stellar,un-informed", upstart, novice.That's why I used to get the big bucks; I know how to get things done, and in a timely fashion, and it don't come back. And I make tools too.The kind that work.
My bosses got rich off me, and I never had a slowday.I fix everything. I can overhaul nearly anything on your pre EFI; car, pick-up, farm-truck, and from the flywheel back, your hiway tractor, your ditch-witch, powershift anything less than 6 ft tall, your outboard motor,your snowmobile, ATC, motorcycle, golfcart, lawnmower, chainsaw or bicycle. Your sewing machine your electric tooth brush and your hairdryer. I can rewire your house,install your plumbing, heck I can build the whole house.Or your garage.or your garden shed.I can build your kitchen cabinets, install your shower and hack down your dead trees. I can drive just about anything with rubber tires, and probably fix it when it breaks. I do engines, trannys, and diffs. I do brakes suspension and steering.I do electrical, and hydraulics.
I don't cook,clean or vacuum. I have a helpmeet for that.
I am a mechanic, oldschool kind.
OOPs I was a mechanic.

I'm semi-retired now, so leave me alone, it's past nap time, lol
 
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I've never seen a stock brake hose that didn't have some sort of metal braided inner. I have never pinched a hose off. It's not a good practice, I don't care who endorses it. It can and probably will permanently damage the brake hose.
 
Hyup every afternoon from 3:30 to 5ish. It get's harder to sleep through the night, with the wifey making all kinda ugly sounds next to me, as she gets older. So I needs me some make-up sleep, after my shift ends at 3PM. After that Ima good 'til about 1AM. Then more nap-time. Then up at 5/5:30, to see my Honey off to work. Then a little keyboard work here to scare the arthritis away, and then off to work at 8:30. So I'm still getting my 6 hours or so.
Hah, I got no gutters on my house. Tore 'em all off, when I built a wrap-around deck .And a carport. And a Balcony.
 
AJ/FormS said:
Hyup every afternoon from 3:30 to 5ish. It get's harder to sleep through the night, with the wifey making all kinda ugly sounds next to me, as she gets older. So I needs me some make-up sleep, after my shift ends at 3PM. After that Ima good 'til about 1AM. Then more nap-time. Then up at 5/5:30, to see my Honey off to work. Then a little keyboard work here to scare the arthritis away, and then off to work at 8:30. So I'm still getting my 6 hours or so.
Hah, I got no gutters on my house. Tore 'em all off, when I built a wrap-around deck .And a carport. And a Balcony.
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Try that with (not ours but our Daughter's) 1 year old twins in the house. :D
Right now it's waaaaa, waaaaa, waaaaa,waaaaa
 
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