Brakes for 1985 Ford F150

Hey everyone,

I am completely baffled by a brake problem I have with my truck. I completely lost brakes yesterday. I looked in the new master cylinder I replaced this year, and found the front reservoir completely empty. I traced all of the lines back only to find all intact. I bled all four brakes twice. I test drove the truck and the problem persists. Could my brake booster be bad? I can't figure out where the brakes would be leaking if I can't find a leak within the lines. I did notice that when I had my son step on the pedal, brake fluid leaked out past the gasket of the cover on the master cylinder over the front chamber. I am going to start with bleeding the system again, but am baffled by this problem.

Thanks for any help you can provide!

 

It wouldn't have anything to do with your booster if the front reservoir is empty. If the master was leaking out the back the booster could be transferring it to the engine through the vac source, but then your rear reservoir would be low.

You would have to have a leak in the system, either in the lines, calipers or wheel cylinders.

Run a couple master cylinder fills through it. The leak will show up on the ground.

Hope this helps,

Bob

 

it sounds like you may simply have a bad (or improperly sealing) gasket on the master cylinder. If it leaks when the pedal is depressed, there is a problem. If it leaks when you are stopping, the resevoir will at least partially empty.

The other thing I would look for is are the rear wheel cylinders leaking? Look at the backing plate from behind the wheels. If it is damp or wet at the bottom (not from your recent bleeding) you probably have a leaking wheel cylinder.

 

masterbobj,

You state "Run a couple master cylinder fills through it. The leak will show up on the ground." What exactly do you mean by this?
I am guessing that this front reservoir fills the rear brakes. If this is the case, should I take both drums off to see if the pistons are leaking there? I hate to do this because these are a pain to remove.

Thanks,

Todd

 

He means that if you run enough fluid through the system you will cause a leak big enough that fluid will make it to the ground and you'll only have to look up from the puddle to find your leak.

 

Mitch is on target. Some leaks take some time to show themselves. The leakage is absorbed by dirt and rust, etc on frame members or inside the brake drums. If you have a leak, finding it is more important than losing a little more brake fluid.

By running more leakage through will make its source easier to find.

 

Loosing all of the fluid in the front cylinder is pretty bad.
Brake fluid ussually leaves a tell-tale sign of dissolved paint.
Ckeck for dissolved paint at below your master cylinder and at the front brake pistons and rear wheel cylinders and backing plates.
It shouldn't be too hard to find.
Also check the front brake hoses for being wet.
You must have a pretty spongey brake pedal aye.......?
That's a sign of air in the system caused by a fluid leak.