Ok guys I am a complete rookie when it comes to brakes, my master cylinder was shot but before I removed it, my brakes were working now and then lol but they were working. I replaced the MC today and now my brake falls to the floor as soon as I touch it with the truck on or off (there was no fluid inside the power booster and i had already checked the vaccuum it was ok) So I am assuming that there is a lot of air within the lines from having taken it off to puting it back on. So my question is how exactly do I bleed the brakes? What size wrench is the "bleed valve" I cant seem to find one that works lol

Correct me if I am wrong

(i dunno if I need the truck on or off i believe I might need it on because I have power brakes?)

with the truck on/or off I am going to open my valve up a little bit and have someone press 3-4 times (which right now does absolutely nothing) and then have them press the pedal down (not quite all the way to the floor which is tricky) so then I will have the valve open until fluid comes out then I will close it and repeat this on all four tires (starting on passenger rear, driver rear, passenger front, driver front)

what am I missing?

 

Did you bench bleed the master cylinder? If you don't do this, you'll never be able to get all the air out of the system.

After you do this, start at the rear wheel on the passenger side. Slip some clear hose over the bleeder valve, and run the hose into a jar with clean brake fluid. With the valve closed, have a buddy push the pedal all the way down. Open the bleeder valve to let the air out, then close it back up. After you close the valve, tell your buddy to let off the pedal. Repeat this over and over until there is no more air coming out. Then move to the driver side rear wheel, do it again, then the passenger side front wheel, then finally the driver side front wheel.

Do this with the truck off. Use a flare wrench to open and close the bleeder valve. I can't remember the size off hand but it's SAE for sure.

 

It's a new master cylinder do I need to bench bleed still? and as a rook, how do you bench bleed?

it is 3/8 i just got it

 

Yes, you absolutely have to bench bleed the master cylinder especially because it's new. It should have come with a little booklet and a couple bleeder plugs in the box to do this. The point of bench bleeding is to get all of the air out of the tiny passageways inside the master cylinder. There should be an instruction sheet in the box, but if not, basically you stick the master cylinder in a vice by clamping onto the mounting flange (not the body of the MC). Then you plug off the flare fittings on the side with the plugs that came in the box, and you fill each reservoir about halfway. Then you take a rod or flatblade screwdriver or whatever works and you put it into the bore and push as hard as you can and hold it there for about 15 seconds. You'll see air bubbles come out. Then you back off slowly and wait 15 seconds again. Do this over and over until no more bubbles come out. You'll find that the more and more you do this, the harder and harder you have to push until you'll finally only be able to push it in an inch or so. Remember that the MC has to be level the entire time.

I forgot to mention when you're bleeding the rest of the brakes to make sure that the fluid level never drops too low. If the master cylinder sucks in air, you have to bench bleed it again. You have to bleed the rest of the system anytime you open it up.

 

It came with incomplete instructions and it didnt come with the bleed plugs? which it is a brand new one, so I guess i'll go and tell them at the parts store that they werent in there. so when the bleed plugs are in it wont let any fluid out of the MC and then I press on it and I will see the air bubbles in the reservoir come up and I do it like you said until their are no bubbles in the reservoir.

 

By Jove! I think he's got it!

 

P.S. Hope that didn't sound snarky, Just kidding, no offence intended

 

dont worry about it lol I am a complete rookie when it comes to brakes and much else lol

 

http://legacygarage.com/images/Pictu...20cylinder.JPG

 

Yah I am going to get a kit to do it like that, I was told by a friend just do it on the truck. Have someone watch it and add fluid if needed and just press the brake peddle down as needed

 

You can't bench-bleed it while it's in the truck. It won't be level. It's called bench-bleeding for a reason

 

The newer rear wheel cylinders are coming with metric bleeder screws, regardless of application. Ran into this when bleeding the brakes on my 76 Jeep.

 

Really? That sure does suck. I hate having to pick up another metric wrench everytime I replace something.

 

oh really? dang man :-( i was told by a bunch of diff people its ok to do it on the truck :-(

 

Normal bleeding is done with everything in the truck, but bunch-bleeding is a separate, additional procedure that has to take place with the MC out of the truck. When you asked your friend and he told you to watch the fluid as you do it, he's talking about bleeding the system itself. When you bench bleed an MC you don't lose any fluid because it circulates the fluid within itself. Bench bleeding is different, and only done when you replace the MC itself. Once you have the MC bench-bled, you install it, hook up the lines, and continue on with the normal bleeding procedure. You have to get the air out of the MC first, then bleed the brake lines. The only time you'd ever have to bench-bleed it again is if it drew in air.

There are two reasons that you have to bench bleed the MC with it out of the truck. First reason, If you think about it for a little bit, you can see that it makes sense that the MC has to be level for the air to be removed from the passageways inside. If the MC is not level, air bubbles can stay trapped in internal corners and not escape when you push the rod. If you look at the MC while it's installed in the truck, it's not level at all. It's angled by about 10 degrees or so. Second reason, the booster rod is not able to push the piston inside the cylinder in far enough to bench bleed the MC. In other words, when you bench bleed it, you have to push the piston in with your screwdriver so that the piston goes all the way in. The pedal itself is not always able to make the cylinder bottom out.

It's your truck, do it how you wish, but the fact that everyone here is showing you that it's done out of the truck, any instruction sheet you find is going to tell you to do it out of the truck, and the fact that it's called "bench" bleeding in the first place should tell you something