Brake Problems 85 F150

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Mar 2, 2014 | 07:24 PM

85AustinTucker

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Brake Problems 85 F150

My truck has had a small leak from the master cylinder since I got it in November The brakes worked fine and i just wanted to get rid of the leak. I decided to replace both the master cylinder and booster. I have bled the brakes all day today and a couple hours Friday night. It seems to me that I have made no progress. After I bled a while l, I felt the brakes and they felt stiff. So I started the truck up and the pedal went immediately to the floor. I went through and bled all the wheels again and again. I started it up again and the pedal went to the floor. When I bought the parts at the store, the master cylinder and booster were already together. The guy said i didn't need to bench bleed the master cylinder and that we could do it with it already together and it would need more fluid to get them all bled. We did the RR, LR, LF, RF sequence many times. What could be the problem with why my brakes are still soft.

Mar 2, 2014 | 07:53 PM

Franklin2

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From: Virginia

Did you read the instructions with the setup? Most of them say bench bleed the master first. You will find that you may have to pump the master when it's mounted in the vise on the bench up to 30 strokes to get all the air out. Then you could have hooked it up, left the lines loose at the master, get someone to push the pedal one time and hold it, tighten the lines, and be good to go.

Now you have pumped all that air in the system, you will have to bleed it all again after you bench bleed the master. Just make sure you stop and check the master fluid level when bleeding the rear, it will not hold enough fluid to bleed the rear in one fill, i found this out the hard way, ran out, and had to start over.

Just make sure you DO NOT pull the rod out of the brake booster that goes into the master cylinder.

Mar 2, 2014 | 08:21 PM

85AustinTucker

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Thanks for your reply. Just so that I'm clear on what you are saying. I should take the master off and bench bleed it like I should have to begin with. Second, once we have all the air out, reconnect to booster and then pump the brakes once...hold the petal...reconnect the brakes lines....and we should be good? I'm assuming we need to go back and re bleed all for wheels and then hopefully we are good at that point. One more question...when I disconnect the master cylinder from the booster, you said to not remove the rod that goes into the booster. You lost me there. Can you re paint that scenario for me. We invested over 6 hrs today and really want to make our correcting our mistake as painless as possible. Thanks so much!!!! You dont know how much I appreciate your help. This site is awesome!!

Mar 2, 2014 | 08:27 PM

RL250

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From: Where the Army sends me

Blow by blow for you:
- unbolt master cylinder to include lines at master cylinder.
- gently pull master cylinder away from brake booster.
- there will be a rod sticking out of the booster. Leave it alone.
- bench bleed and re install master cylinder.
- re bleed lines.

Simple, but time consuming.

Mar 2, 2014 | 08:30 PM

85AustinTucker

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One last question....Bench bleed the master cylinder with the cap on and sealed? Just checking.

Mar 2, 2014 | 09:11 PM

Franklin2

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From: Virginia

The master usually comes with plastic plugs. Screw them in tight so they seal, leave the cap off, and slowly push in on the master with something like a screwdriver. You will see bubbles come up into the fluid and the master plunger will move. If it moves a lot, it has a lot of air in it. As you keep pumping slowly, the plunger travel will get shorter and shorter as more air gets out of it, till you can't hardly move it at all. Then you are done. Don't push too hard, you can pop the plastic caps out.

I confused you by mentioning pushing the pedal down and re-connecting the lines. That is what you could have done in the beginning. Forget what I said, you need to go ahead and re-connect the lines after you install the master, and then start your bleeding procedure again like you did before, get someone to push the pedal down and hold it, open a bleeder, close the bleeder, tell them to lift and then push and hold again.