86 Brake System Troubles

Good Morning Everyone,
My name is Nick, I'm a college student in Tennessee (soon to be Texas) and I have and 86 F-150 XLT Lariat with the 302. Ive been trying to figure out brake issues I've been having. I replaced both front calipers a few weeks ago since the bleeder screws on both were in rough shape, bled the brakes and that did no good. Last week I replaced the brake booster and that also did nothing. When I'm bleeding the brakes the pedal is very firm by the time I'm done, but when I turn the truck on and go to give it a test drive, the pedal softens back up and it takes the pedal all the way down to the bottom of the travel until i feel the brakes. Might I have a vacuum problem? Problem with my master cylinder? Any input would be helpful as this is my first "project vehicle".
thanks,
Nick

Nick - Welcome to the forum.  Glad you joined.  

You may have missed the email that asked you to do an intro post in the New Members Start Here folder - after reading the guidelines.  The main purpose of that is to ensure everyone reads the guidelines as we hold everyone to them.  So can you assure me you have read them?

And, I always ask in the intro posts where the person lives.  That's 'cause we have a map (Bullnose Forum/Member's Map in the menu) and can add you if we had a city or zip.

On your brake issues, I'm not sure you really told us what the issue is you've been trying to solve.  Maybe it is that your brake pedal goes down when you start the engine?  If so, that is to be expected to some extent as the engine's vacuum provides a lot of boost to your pedal pressure, and if there is any air in the brake fluid then it will get compressed.

But it sounds like your brake pedal goes down too much?  If so, then you may have air in the system rather than a vacuum problem.  Apparently there is plenty of vacuum, which is causing the air to be compressed.

Have you bled the rear brakes?  Has the master cylinder been replaced and maybe it wasn't bled properly?

Gary,
Thanks for the response. Yes I did read the forum introduction over the weekend when I joined, but my apologies, I never made my intro post. It should but up now.
As for my problem, I've been having my neighbor who knows more than I do assist me in bleeding the brakes, which we've done about 3 times, front and back starting from furthest from the cylinder. My issue is that my pedal is very soft and has a very long travel before I feel any braking. One problem that I was having before I replaced the brake booster was that my pedal would not return to the forward position after it was pushed down, I would have to put my foot under it and pull it back up after I was done braking. With the new booster it returns on its own, but the pedal is still spongy and long. The master cylinder is still the stock one, but it has 2 new front calipers. I've noticed that there are some vacuum hoses that were not connected in the engine bay, but they didn't seem to trace back directly to the braking system, but I was wondering if they would still affect the brakes. I guess my main question was does this sound like it could be a vacuum issue or a problem with another component that I have not replaced yet, such as the master cylinder which is not leaking anywhere from what I could see. I was going to continue to recheck all my replacement parts but wanted to throw my problem out there to see if there was something obvious I was missing.
Thanks again,
Nick

Nick - I did see your intro just now.  You are good to go.

On the brakes, it is actually a leaking master cylinder that usually does in the booster.  Masters can leak out the push rod area and that gets sucked into the booster and ruins it.  So I'd normally recommend replacing the master when you have to replace the booster.

But was the inside of your booster wet or damp?  If not, maybe the master isn't leaking.  However, the master can still be bad as the pistons can leak internally and cause a soft pedal.  So it sure wouldn't hurt to replace it, although you'll have to bleed everything again.

Also, there's an adjustable push rod between the booster and the master that sometimes needs tweaking as they can be changed accidentally while a booster or master is being changed out.  You can read about it here: Documentation/Driveline/Brakes and then the Master Cyl's & Boosters tab and the the Push Rod Adjustment tab.

Having said all that, if it was me I'd be considering replacing the master cylinder with a later model one with a plastic tank.  I like them much better than the old ones for three reasons.  First, you can see how much fluid you have.  Second, they don't leak out the top like the cast iron ones do.  Third, it is pretty easy to rig up a pressure system to allow you to pressure-bleed the system, which allows you to do it single-handedly.

I'll let you digest that and then ask questions....

How were the brakes BEFORE you changed the calipers?  Were they working properly or more properly then?  

When the truck is running the booster is working to multiply the pressure you apply to the pedal.
If you have mushy brakes the two most common reasons are that the rear brakes are out of adjustment and the rubber hoses (one at each caliper and one from rear crossmember to axle) are expanding when under pressure.

Rear self adjusters often don't.
You can use a brake spoon through the backing plate to get them to where they should be.
But this is a good opportunity to pull the rear wheels and have a look.
Randy posted some before and after photos the other day.    

Did you properly lubricate the new calipers so they slide nicely?

My understanding is that to adjust the rears, you can put the parking brake on while driving and tap the brake pedal. Ive done this on other vehicles, obviously not around other drivers. I dont know if the Fords are different because my parking brake doesnt fumction.

The pawl is meant to turn the adjuster when you apply the brakes in reverse.
But most people aren't aggressive enough when backing up, and then they seize.

Better to use a spoon anyhow.