Hello everyone

I'm just finishing up my complete brake job, MC, lines, rotors, drums, hardware, the whole 9 yards. Today I went to bleed the brakes and ran into a problem with the front brakes. No matter how much I bleed them, I get a bunch of air at the end. I can't pull the pin on the proportioning valve either, so if that solves the problem I need a way around it

If I bleed both front calipers at the same time, will that flush the air in the front lines out? Its not a problem with the MC either, the rear brakes were solid fluid.

Thanks in advance!

 

That metering valve pin needs to be pulled to bleed all the air from the system.

 

How much should it move? Maybe I'm just not noticing it. My manual says it only moves a 1/16" or something like that. And should it slide out semi easy? Does it click when its open? And lastly should it have a rubber boot on it? I'll take a picture a little later and yall can tell me if somethings amuck

 

The pin only moves out 1/8" or so; there is no click. Its purpose is to bypass the front metering valve that delays fluid to the front brakes so that fluid can move right through as you bleed. You must hold it open while you bleed the fronts; I usually do this by wedging a small pair of needle noise pliers there.

 

Do you wedge the pliers inbetween the rubber piece and the body of the proportiong valve then? And is the little pin kinda hard to pull? Like what kinda spring pressure are we talking valve spring or springs in a carb?

 

That's correct, I wedge the tip of the pliers in between the raised end of the valve tip, and the rubber boot after it's fully extended. It shouldn't take much pressure to pull it out.

 

Right now it feels like theres a coil over spring behind it. I've gone at it with the long nosed pliers, stub nosed and the vise grips and I'm getting no movement. Soaking it with PB blaster now.

My manuals said something about over 6800 GVWR you push the pin in, mines got an 8100 GVWR, so should I still be pulling it out?

This is how far it should stick out untouched, right?

 

What kind of vehicle is this? Some of the heavier-duty trucks had a different valve that required the pin to be pushed in and not out, as your manual describes. Your valve does look different than what I'm used to.

Take a look at this post from a very old thread regarding the issue:

https://www.ford-trucks.com/forums/7...ml#post5655283

 

I took the little rubber boot off so that might make a difference in the way it looks. I have a '78 F250 4x4 with a 8100# GVWR. I'll see if it moves in when I get back to the ranch. Thanks for takin the time with this I really appreciate it!

 

Well I think I may have bled the MC wrong...finally got now bubbles but the pedal is still kinda squishy

The technique I was using was push the punch the punch in 1" or so until the bubbles stopped coming. I'm reading now that I should've kept going until it was next to impossible to push it more than 1/8 of an inch?

 

That's correct. The MC isn't fully devoid of air until you can't push the cylinder in past 1/8 inch.

It can take quite a while to get to this point - the MC will appear to be free of bubbles for a few strokes, only to let some more through if you keep going. Sometimes it helps to tilt the MC and bench bleed it at a couple different angles (forward and back, in addition to level) to get it completely bled. If you were still able to push it in a full inch with the outlets capped while you were bench bleeding it, it's still full of air.

 

Wait what do you mean when you say the "outlets capped"? I had two little male nipples shoved in the ports that my dad was holding tight when I was doing this. Are you talking about if I had a bench bleeding kit?

And when I started, should I have been pushing more than just an inch? Should I have been pushing the punch until it bottomed out?

 

Are the calipers on the correct side? Bleeder screw on the top? Ive done it myself.

 

When you buy a new master cylinder, it should come with a bench bleeding kit. This can be as simple as two plastic threaded plugs. With this type of kit, you install the plugs, fill both reservoirs with brake fluid, and slowly depress the cylinder until it bottoms out. Hold it there for 15 seconds, then slowly let it back out. Wait another 15, then do it again. You must do this over and over until the cylinder will not compress more than 1/8 of an inch.

The other type of bench bleeding kit has two fittings with hose barbs that run back into each reservoir.

The method you are describing to bench bleed the MC is incorrect and will not work. Even if you were to get fluid to your calipers, the pedal will never be firm enough. Compressing the cylinder in only an inch or so does not fully compress it; you must bottom it out, and keep going until you cannot push it in past 1/8 of an inch. When you first start the process, the cylinder compresses quite far and is easy to push, as you're simply compressing air. As you repeat the process and the bubbles work their way out of the cylinder, you start trying to compress brake fluid, which of course does not compress. The more the clyinder becomes primed with brake fluid and the less air exists in the cylinder, the harder it is to compress - until the MC is completely bled and cannot be compressed further.

You also must have a complete seal at the ports - it's very easy for air to sneak in. The bench bleeding process relies on the ports being completely sealed off, so that fluid can bypass back through into the reservoirs to push out air. Pressing against them by hand won't do.

A final note, bench bleeding is typically done in a vise on a bench (hence the name) with the MC level - but as I mentioned previously, sometimes it helps to try a few strokes at a forward and backward tilt once the MC seems to be done - this can help grab the last few bubbles. I recommend going back and forth until none of the 3 angles have any bubbles at all.

 

Yes, that two threaded plug is the kit I had. That makes so much more sense now! Thank you for the nice, easy, kind "you done f***ed up now"

But really, thank you for the constructive criticism, it's really nice to still see that in the world.

I did do the original bleeding in the vise and did the little 3 way method that I've seen in some of your other posts.

As far as the "perfect seal", should I put some teflon tape on the threads to ensure a better seal? One of the plugs leaked IIRC.