Brake bleeding

[piecesparts]

OK; Put on a new master cylinder (due to it leaking at the rear seal) and new wheel cylinders and now all we get is air out of the brake lines. We bench bled the master to get it flushed of air and now the wheel cylinders are air/fluid mix on one shot and nothing but air on the next.

Any thoughts from the masters of disater on here.

[big blue 72]

gravity bleed them.best way to go.
one at a time till you get to the back. works like a charm

[68gmsee]

It's possible you are sucking in air from somewhere. Rubber hoses get cracked and should be replaced on these old trucks.

You didn't mention how long you pumped the brake to get the air out, but I know that in some cases you have to do it several times for each cylinder-probably more if you replaced the brake cylinders. I had one with mushy brakes and I think I must have gone through 2 cans of fluid to get all the air out.

[piecesparts]

Originally Posted by 68gmsee

It's possible you are sucking in air from somewhere. Rubber hoses get cracked and should be replaced on these old trucks.

You didn't mention how long you pumped the brake to get the air out, but I know that in some cases you have to do it several times for each cylinder-probably more if you replaced the brake cylinders. I had one with mushy brakes and I think I must have gone through 2 cans of fluid to get all the air out.

It is on my buddy's truck and he has gone through 2 quarts of fluid and is still getting air. He thinks the new Master Cylinder has a bad bleed check in it. He did NOT have any problems until he replaced the Master, due to the original leak. Now his wife has bent his ear hard, due to having to pump the brake pedal too much. Believe me, that is worse than the leak.

[WIDESIDE72]

Y'all mention going through 2 qts of fluid... Are you catching this fluid? If it is clean, I would pour it back into the system. A few yrs ago I decided to figure out how to bleed brakes without any help (without buying an expensive brake bleeder tool), and keep from wasting so much fluid bleeding brakes. I figured out if I went to the hardware store and bought a couple of feet of clear aquarium tubing. You may have to do some experimentation to figure out what size tubing is needed to fit over your bleeder screw. The rest of the stuff I needed could be found around the garage. I took a 1 liter clear plastic soda bottle and rinsed it out good. I drilled a hole in the cap just large enough for the tubing to pass thru, all the way in about 1" from touching the bottom. Pour some fluid in until the end of the tubing is covered. This way you won't suck air back in to the system. I took a 1 ft long piece of old electric fence wire I had in the scrap pile wire and wrapped one end around the neck of the bottle and tied the other end up under the truck near where I would be working to keep from spilling the bottle. I start at the right rear, then left rear, left front and right front. Break the bleeder screw loose a turn or two. Slip the other end onto the bleeder screw. Before I start bleeding, if there is any old fluid in the master cylinder, I take a coffee can, etc. and some paper towels or rags and sop all of the old fluid out, then refill with new fluid. Now you can get in the truck and pump the brakes a few times. Obviously, keep bleeding until you get all of the old dark nasty fluid out. Have a container handy to pour the old dirty fluid into. Since you are catching the fluid, if it is clear but you still have air bubbles, you can pour this fluid back into your MC. there is no reason to use half a gallon of fluid bleeding your bakes. Not to mention the old fluid will ruin the paint on anything under the truck, make a mess in general and is bad for the environment. Think of it this way. Don't let anything hit the ground that you wouldn't want to drink, because that is where it will end up (diluted, but still in the ground water).

[68gmsee]

Originally Posted by piecesparts

............. Now his wife has bent his ear hard, due to having to pump the brake pedal too much. Believe me, that is worse than the leak.

Tell him I know the feeling. My wife was definitely getting close to telling me to go you know where...

Re: bad master cylinders. I had an experience with that on my Tahoe. I exchanged the master cylinder twice for leaking and after the third time, I told them I wanted my money back. I went to another auto parts and never had any more leaks.

[piecesparts]

Originally Posted by WIDESIDE72

Y'all mention going through 2 qts of fluid... Are you catching this fluid? If it is clean, I would pour it back into the system. A few yrs ago I decided to figure out how to bleed brakes without any help (without buying an expensive brake bleeder tool), and keep from wasting so much fluid bleeding brakes. I figured out if I went to the hardware store and bought a couple of feet of clear aquarium tubing. You may have to do some experimentation to figure out what size tubing is needed to fit over your bleeder screw. The rest of the stuff I needed could be found around the garage. I took a 1 liter clear plastic soda bottle and rinsed it out good. I drilled a hole in the cap just large enough for the tubing to pass thru, all the way in about 1" from touching the bottom. Pour some fluid in until the end of the tubing is covered. This way you won't suck air back in to the system. I took a 1 ft long piece of old electric fence wire I had in the scrap pile wire and wrapped one end around the neck of the bottle and tied the other end up under the truck near where I would be working to keep from spilling the bottle. I start at the right rear, then left rear, left front and right front. Break the bleeder screw loose a turn or two. Slip the other end onto the bleeder screw. Before I start bleeding, if there is any old fluid in the master cylinder, I take a coffee can, etc. and some paper towels or rags and sop all of the old fluid out, then refill with new fluid. Now you can get in the truck and pump the brakes a few times. Obviously, keep bleeding until you get all of the old dark nasty fluid out. Have a container handy to pour the old dirty fluid into. Since you are catching the fluid, if it is clear but you still have air bubbles, you can pour this fluid back into your MC. there is no reason to use half a gallon of fluid bleeding your bakes. Not to mention the old fluid will ruin the paint on anything under the truck, make a mess in general and is bad for the environment. Think of it this way. Don't let anything hit the ground that you wouldn't want to drink, because that is where it will end up (diluted, but still in the ground water).

Been doing that, that two quarts is a single used around and around. We just need to get to the point that there is no more air.

[MotorSeven]

I just went thru the exact same thing. It took over 30 min of pumping/bleeding to get the system clear of air. Then i found that my right caliper was toast(almost melted the paint on my rallys), so i opted to replace both along with the bearings. Now i have air in the system again because i was flying solo. I think i will try the gravity thing.......

RD

[garold99]

Originally Posted by big blue 72

gravity bleed them.best way to go.
one at a time till you get to the back. works like a charm

Explain this please, thanks

[MotorSeven]

Ok, got mine done. The person pumping has to pump slow, then hold the pedal down while you crack the bleeder slightly, then close. Then the pedal should then be let up very slowly. If you open the bleeder too much, the proportioning valve opens & you get more air in the system. RR first, LR, RF then LF. I didn't have to do the gravity, which is just opening the bleeder & leaving it open until the fluid is driping out on it's own.

RD

[68gmsee]

Originally Posted by MotorSeven

........... If you open the bleeder too much, the proportioning valve opens & you get more air in the system. RR first, LR, RF then LF........

I've always had my helper slowly depress the pedal as I open the bleeder valve. I usually open it enough to get a good stream to come out as the pedal is going down. Then I tell the helper to hold the pedal down and I tighten the valve. I repeat as often as I need.. That's always worked for me.

[WIDESIDE72]

What I refer to gravity bleeding means to connect some form of catch can to every wheel cylinder, fill the MC, crack the bleeders open and let it set for several days.

[68gmsee]

Originally Posted by WIDESIDE72

What I refer to gravity bleeding means to connect some form of catch can to every wheel cylinder, fill the MC, crack the bleeders open and let it set for several days.

Maybe this is a dumb question but I've never tried this technique....

How do you keep the master cylinder from emptying itself out and basically wind up with the lines full of air again?

[1968SWBBigBlock]

68gmsee - you will need to check the fluid a couple of times a day - based on my sons school books the gravity bleed should not take more than several hours - & accordingly seems to be a good way to bleed

[Pont406]

Did you replace copper washers when you install new wheel cylinders?

[piecesparts]

YEP on the washer thing. It just seems that the more he tries to bleed the more air that keeps coming out of the lines. Almost as if there is a leak somewhere else and the air is pulled back in when the master is stroked.

[LONGHAIR]

Gravity bleeding should only take a few hours, just be sure to "babysit" it. You don't want the master cylinder to run dry.