For the last 2 months I've been pumping my brake pedal about 3 or 4 times to stop. The first 3 pumps would go right to the floor and trigger the "Brake" idiot light on the dash. By the 4th pump, the pedal is firm and the brakes have pressure, so the "Brake" light on the dash goes off. If I continue to pump for 6 or more pumps, the pedal gets VERY hard and the brakes don't grab any easier, they actually don't grab as well. If I push down REAL hard at this point, the truck stops quick. I think the rear brakes lock up and the front don't.
There is also a fluid leak at coming from the brake booster. Right where the master cylinder and booster meet together, at the bottom.
Also, the front reservoir in the master cylinder has been slowly disappearing. This is the smaller reservoir. I've topped off the fluid 4 times. The first 2 times, it helped with building pressure. The last 2 times didn't help.
The truck has also been pulling to the right for the last 4 months. Not a big deal, I just have to keep the wheel straight and don't let go. Well, today that issue showed its ugly face. The right front brakes didn't seem to let go. They really pulled the truck to the right, and eventually started smoking while I got it home. BUT, when I applied the brakes, the truck would straighten out and NOT pull to the right. 2 year old NAPA calipers and pads! They weren't rebuilds either, I went brand new to AVOID problems. I had them on the other truck and put them on the current truck about 5 months ago. When I put them on, I put a bunch of grease where they slide on the caliper bracket so they wouldn't stick.
The truck is sitting in the driveway waiting for the rotor and caliper to cool. I pulled the wheel off so it could cool quicker. It was so hot that I spit on it, and it boiled and evaporated so fast I didn't even see it.
Any ideas? I'm thinking proportioning valve because it's only the front brakes with issues right now. I'm waiting for it cool so it doesn't burn my hands even with gloves on. I'll get on it as much as I can now. I'll report back later. Thanks for the help guys.

 

I'll be waiting for an answer on this to, mine is doing the exact same things. No leaks tho, and original calipers. And my brake light doesn't come on. Although the pedal does go far in the floor, after a couple pumps, she comes up hard. I was thinking air in the system but we'll see what others have to say.

Where would be the proportioning valve anyway?

 

The proportioning valve is attached to a bracket, attached to the frame rail directly below the master cylinder.

 

That's the valve? It looks more like just a T to direct fluid to different wheels....

I'm asking that cause I got a problem with the brakes on my F150, air is all bleeded out and still no brake pedal when the engine is running. I think the kids that owned before me, had a cup under the leaky brake like and were collecting the fluid and putting it back in the master. The master was messed up, so I'm wondering if the propor. valve ain't stuck.... I'll have to go knock on it with a hammer see if it makes a differents.

 

I had this happen on my f250 gasser. Turned out the rear brakes weren't adjusted correctly.

 

BlueOvalBud,
Sounds like you need a new master cylinder, and probably a new booster as well. Supposedly its good to swap them together if the master has been leaking into the booster (but don't quote me on that). Once the leak is fixed, you can start working on any other issues.

Check to see if the rears are adjusted right, or leaking. The front sounds like a sticking caliper, even though it was new, could still develop problems. Might need to pop it off and see if the pistons move easily. Did you replace the front hoses? Bad hoses can collapse or have chunks break loose internally and hold pressure in the caliper even after you take your foot off.

Also, stepping on the brakes would apply pressure to the other side, so then the brakes would be applied evenly (even if one side was sticking) and cause it to travel straight.

So in summary, replace the master cylinder and booster, and check everything else closely, then report back.

 

Thank You tecgod,
I figured I'd be replacing the master cylinder/booster at the same time. If I replaced the Master Cylinder and didn't touch the booster, it wouldn't be long before I had to replace the booster as well...especially with the fluid leak coming from it. Yikes!
The caliper was so tight, I couldn't budge the wheel. I took the caliper off and pulled the pads out. I took a small block of scrap wood with my C-Clamp and pressed the pistons back in. Stubborn! So I pulled the cap off the master cylinder in case I was pushing air back through the lines. I also used a 3/8" wrench and opened up the bleeder screw to try and relieve pressure. I was able to crank the pistons back into the caliper.
I put it all back together and continued using the truck this afternoon, all seemed OK.
Nope, didn't replace the hoses. I figure they're original, and better than than the NAPA ones I had at the time.
When I replace the master cylinder/booster with a Carquest product, I'll throw some Carquest brake hoses on at the same time. When these inferior NAPA calipers fail in about a year, I'll get some Carquest calipers.

Any ideas on the proportioning valve? Would it cause pressure to stay at the caliper?

 

Sounds like you have several problems that are causing different symptoms. The smaller area of the reservoir is for the rear brakes. I would be willing to bet that you have a blown rear wheel cylinder. The truck pulling to one side with brakes not applied and then straightening out when you apply brakes would lead me to think that you have a bad flex hose going to one of the front calipers. What happens if the inner lining of the hose brakes down and acts like a check valve, not allowing pressure to release the brake fully. It straightens out when you brake because the other side now has pressure too. Change the master cylinder and both front rubber brake hoses. Pull the rear wheels off and make sure you haven't blown a wheel cylinder and inspect brake lines going to rear brakes. Also these old trucks have vacuum assist brakes and has a vacuum pump. If you pump the brakes too much you will deplete the vacuum and you will only have manual brakes. Your vacuum pump may be getting weak. You can check this by plumbing a vac guage into the vacuum manifold. It should be pulling close to 25 inches of vacuum.

 

Well it sounds like about 10 pumps before you are loosing vacumn, so I would think your pump is good. As far as pulling to the right and getting Hot, if your caliper released when you opened the bleeder I will second the hose and it will happen again.

The brakefluid leaking out at your booster is coming from the master cylinder. There is no fluid in your booster, but if the master cylinder has been leaking for 2 months I would go ahead and replace it.

 

When you buy the master cylinder, get one with the reservoir already on it. They are a @#$@# to change. When I changed my master I thought I would save a few bucks and get one without the reservoir and just reuse my old one. It would have been well worth the extra few dollars to buy one with it already attached. Also make sure you bench bleed it before you put it on, it takes a while.

 

I didn't even know they sold masters without the resevoir. lol

 

tecgod13 it looks like you and I were posting at the same time and you beat me. Your post wasn't there when I started my post. LOL Looks like we were thinking the same you were just a faster typer.

 

My 93 f250 7.3 idi is giving me issues with the brakes - hoping someone can steer me in the right direction.

90% of the time brakes work fine - nice, steady application. But sometimes it is as if I don't have power brakes. I am pushing hard on the petal (just like in the older 'pre power' vehicles I have driven) and I do get a firm response and good braking but it seems like I am doing all the work manually.

Not seeing any leaking - reservoir is full.

What is failing? What should I look at/for?

 

Most likely a vaccum leak or a bad vacuum pump.

 

yup, sounds like the vacuum pump is dead. the brakes feel good on the first application because the pump has time to draw a vacuum. then if you hit them again the pedal gets hard because the pump can not recover that fast.
you need at least a constant 19 inches vacuum for the brakes to work properly, a new pump should hold around 23-24 inches vacuum.