Brakes go to floor

[sbhoney]

I am having a problem with my brakes on a 90 silverado. I have replaced the master cylinder, the booster, and blead the brakes 3 times. The problem is that while bleeding the brakes with the truck off I have a pedal. Once the truck is turned on the brakes go all the way to the floor. Does anyone have an idea of what is going on? Need help!!

[Thunderbolt]

Were you having these problems before you replaced the booster and the master cylinder ?? It is not uncommon to get a bad master cylinder. Are you sure there are no leaks ?? You may still have air in the system if you haven't blead enough fluid through it. Is the fluid level staying full or is it going down ?? Why did you change all the components to begin with ?? If you can shed a little more light on what lead you up to the point of replacing everthing such as were the brakes acting up. I am sure someone on this board can help you.

[sbhoney]

It all started while I was coming to a stop sign and the breaks went to the floor. When I got home I blead the brakes but then I noticed a leak at the master cylinder so I replaced that. Then I noticed a sucking noise coming from the booster so I replaced that since I read on a post that if you have a leaking master cylinder there is a good chance you could blow out the booster. Once that was done I blead the brakes again and the pedal felt fine until I started the truck. They once again went to the floor and I have no brakes. There are no leaks anywhere on the brake system. I have checked. If it was just are in the lines why would I have brakes until I started the truck? Help anyone

[Doug Rodrigues]

Are you sure that you've got all the air out? You start with the furthest line from the master cylinder: Right rear....Left rear.....right front...left front. Tell us what the final fix was so that we all can learn something.

[sbhoney]

yeas. Blead everything just as you said. No air left in this trucks lines. I will let you know when I find out.

[Doug Rodrigues]

Well this is a real puzzler? With the dual piston brake cylinder at least half the system should function: either the front or the back? Is it possible that both front half and back half failed at the same time? Or maybe half the master cylinder had gone bad and wasn't noticed followed by the other half which gave the impression that both halves failed? There is a flow divider under the chassis, but that thing never goes bad. Do you have ABS? I wonder if that could be the problem? Yeah, please let us know what you find. You have a rare problem indeed...something that most mechanics never experience!

[sbhoney]

Yeah really stumped. Brand new master cylinder and everything seems fine when the brakes are blead until I start the truck then straight down to the floor they go.

[sbhoney]

One thing I did notice when pumping the brakes was that the fluid was bubbling up inside the master cylinder. Not sure if this is suppose to happen.

[Doug Rodrigues]

Sure sounds like air in the lines. Okay, if it were me, in the absents of a pressure bleeder that clamps onto the top of the master cylinder, I'd go buy one of those $35 suction bleeders. The suction brake bleeder has a reservoir cup and a squeeze handle to apply suction. There is a tube that plugs on to the bleeder fitting at each brake station. If that didn't get it, the only other option is to give it to the dealer and pay whatever they want. I don't have a manual for your vehicle to check the trouble shooting list. I wonder if that manual addresses this situation? You might stop by the library and check the factory manual for your particular vehicle. Most librarys have such manuals available for you to research, but not to borrow. The copy machine is always nearby.

[Thunderbolt]

Doug, Do you think it would be worth removing the lines from the mastercylinder and connecting the 5 dollar bench bleed kit and bench bleeding the master alone and then bleeding the whole system again ?? If there are no leaks then it has to be air or a bad master cylinder I would think. It could be leaking out the back seal on the master cylinder, But I doubt it if the fluid stays full. I have gotten bad master cylinders many times. I have one for you, About fifteen years ago a guy brought me a truck and said he fixed a leak and replaced the master cylinder and gets no pedal. I tried bleeding the sytem, No luck, Pressure blead the system no luck. I raised it up on the hoist and started looking it over and here the guy spliced the line with a piece of fuel line and it was blowing up like a balloon when the brakes were applied.

[sbhoney]

I dont think I metioned this before but yes the truck had RWAL ABS on it. I actually have had two master cylinders on it. Took back the first one and got a second cause I thought it was bad. If it was the master cylinder why would I have brakes until I start the truck.

[Doug Rodrigues]

A fuel line for a brake line? Wow...that was a crazy thing for your "mechanic" to do. Hey, what I did only a few years ago for a suction bleeder, because I was out of town at a construction site and didn't have anyone available to pump the brakes for me....I made a jury-rig "suction bleeder." I stopped by a hardware store and bought 4 feet of clear tubing, actually three different small sizes of tubing because I knew one of the sizes would fit over the brake bleeder. I got a mayonaise jar out of a trash dumpster. After I found out which plastic line fit properly over the brake bleeder I drilled two small holes into the cap of that mayonaise jar. I slowly used larger drill bits until the tubes could be forced tightly into the holes. I pushed both tubes about 1" into the jar. With one tube in my mouth sucking, and the other tube on the brake bleeder, I was able to suck the air bubbles out of each brake line without too much trouble. Hell of a lot cheaper than spending $35 for the fancy squeeze handle suction pump. That's how I was able to replace my master cylinder without help from anyone else. With the one quart mayonaise jar you can start sucking until there is vacuum in the jar, and then open the bleeder valve and watch the fluid flow. Right before the flow stops completely, close the bleeder valve. Worked like a charm. Total cost for the homemade suction?: about 6 bucks.

[Doug Rodrigues]

Two master cylinders?.....Hummmmm. Well I have to admit, this one is out of my area of knowledge. I've never worked on an ABS system. I was long out of the car repairs racket before they were even invented. I still think that you should stop by the library and look into the shop manual....at least that's what I'd do next.

[vettemaan]

maybe its a broken brake pedal?

[Doug Rodrigues]

Yeah, probably will be something very simple, and simple to overlook. I'd be REAL curious as to what the final fix will end up being? This is guaranteed to be a "learning experience" for all.