The Stovebolt Site Forums The Shop Area Engine Shop Why is this happening?

Can anyone tell me why, after I have applied the bark several times on my 1948 1 1/2 ton truck, the fluid wants to run out of the breather holes in the top of the master cylinder filler cap?

The brakes are spongy to begin with, and that is the only spot where I detected fluid loss. Thanks for any advice.

Have you checked the wheel cylinders yet? You might have a siezed one, or maybe a blockage of rust/crud in one of the lines.

Just a thought-I'm sure others more "in the know" will chime in.

Best of luck

Regards,
Wannabe

You have air in the lines. To bleed this air out you need some one to help you. Start with the power brake booster [some have 2 bleed ports] then the left front, then right front, left rear, right rear. Make sure the master cyl does nor run out of fluid while bleeding. The helper person needs to pump the brakes till they have a good pedal, hold it till you open the bleeder, then let you know when the pedal is all the way to the floor. You close the bleeder, repeat this till there is not any air coming out the bleeder, then go to the next wheel. As I mentioned before, do not let the master cyl. run out of fluid.
I hope this helps you have good brakes.

It can be difficult to bleed the air out on the larger trucks.The brake lines are often higher than the master cylinder, complicating the bleeding.Most of us don't own a power bleeder so I have a cheapo alternative.I use a rubber stopper with a tube through the center that fits into the master cylinder opening. An old coffee can with a similar tube soldiered or epoxyied onto the bottom is hung from the steering wheel with a wire. A length a hose connects the can to the stopper.Fill the can with fluid and bleed the brakes as Racecarldad explains. The can keeps the MC full and acts to keep the brake fluid above the level of the brake lines.A friend reported good success by bleeding the brakes with one of those hand held bleeding pumps. Instead of sucking the fluid from the wheel cylinder screw, he uses the pump to force fluid into the bleeder and out through the master cylinder.I have never used a pump ,so I can't say for sure it works.

You have received some good advice on getting the air out of the system to correct your spongy brakes. No answer on your first problem, though, about fluid running out of the breather holes in the cap.

Each time you press the pedal, a small jet of fluid squirts out the tiny hole in the bottom of the reservoir. In most cylinders, that jet of fluid hits the bottom of the cap. Because of this, caps are made with baffle systems to turn the fluid back into the reservoir. Original GM caps have a stamped sheet steel baffle pressed into the bottom of the cap. Aftermarket caps vary in design, but all have some sort of baffle. Yours is missing or damaged, I'd guess.

Joe

The other day I had topped off my brake fluid and figured let's feel the pedal. So I did with my hand while my head was still down there and the cap off. A squirt of fluid went straight up passed my ear and missed me by inches.

As with Tony, I wondered if the gasket might be missing from the filler hole.

Not sure if mentioned in racecarldad article but if your fluid is new you can attach a small hose to the bleeder and direct to a container for immeadiate resuse. If old fluid is present the hose will stop the fluid going everywhere. Hope this is of assistance.

Just wondered, I don't have a bark on my half ton, did that just come on the big trucks?

Just for everyones information Mighty Vac makes a new LARGE Fluid Extractor that you can buy a Brake fluid addapter for. I got one of these for many reasons ( draining differential, gear box ). Anyways this is a great tool, even used it the other night to test my wiper motor befor intstalling it. This is just a giant vacuum pump with a very large catch container aprox 6 liters. Nice tool!

First of all, thanks to all of you for your ideas and suggestions. Hopefully this will solve my problem. You have been great, regardless.

As for Grant's question, yes the bark is only on the big dogs (actually, that error proves that spellcheck is nothing but a pain in the exhaust pipe, o rthat I am too quick to say okay.)

I know some guys dont go to the lounge but I just posted a thread about brake bleeding that can be done single handed apparently. I guess I should have posted it here.

Grant, I think you need the dog option to get the bark. They came standard on bigger trucks.

All seriousness aside, I use a 1- man bleeder tool which is a little transparent bottle with a magnet on it and a hose. You connect the hose to the bleeder, open it, and pump until the air comes out. The bottle fills with brake fluid, and you just empty it out (I never re-use mine). It works great and only costs $5 at your flaps. You don't get any fluid on your paint that way.

Darn it, I spent 99 cents more on my bleeder kit
It still works great

I have been [censored] ever since I read the other thread. I paid $7.99

A _magnet_? where's the fun in that ? you're supposed to use an old pop botle and tie some wire around the neck and then make up a loop that goes over the axle and lets the bottle hang where you can easily see the bubbles coming out the hose , then bump it with the bleeder wrench or your elbow , splashing brake fluid all over you and the freshly painted backing plate , etc.....