spongy brake pedal

Again, more issues with my 1989 GMC C1500 ext cab. Just yesterday I installed new front rotors, bearings and brake pads. I also replaced one of the rear wheel cylinders (it was leaking). After doing all this, I bled the brakes on each wheel, pumping the brakes about 6 times per wheel (I am using a "one man bleeder bottle with tube" since I have no helper) and made sure there were no air bubbles when done. I also bled the master cylinder (via the bleeder screw). I made sure the master cylinder never ran out of fluid. The brake pedal was hard/stiff when I was all done with the truck off. I started the truck when I was all done, and the brake pedal is really soft and goes almost to the floor....causing the brake light on the dash to come on.

What did I do wrong and what can I do to fix this issue....ughhhhhh!:banghead:

thanx.

Again, more issues with my 1989 GMC C1500 ext cab. Just yesterday I installed new front rotors, bearings and brake pads. I also replaced one of the rear wheel cylinders (it was leaking). After doing all this, I bled the brakes on each wheel, pumping the brakes about 6 times per wheel (I am using a "one man bleeder bottle with tube" since I have no helper) and made sure there were no air bubbles when done. I also bled the master cylinder (via the bleeder screw). I made sure the master cylinder never ran out of fluid. The brake pedal was hard/stiff when I was all done with the truck off. I started the truck when I was all done, and the brake pedal is really soft and goes almost to the floor....causing the brake light on the dash to come on.

What did I do wrong and what can I do to fix this issue....ughhhhhh!:banghead:

thanx.


System still has air in it or the M/C is gone and not pumping the fluid.

Could it be you blew a brake line now... follow every line and look for leaks. Its better for two people, one to pump the pedal and the other to go under the truck and investigate and look and listen for leaking fluid. If all is well maybe try bleeding them with the truck running... lol! since you had a hard pedal before you started the truck. If this don't work, take all the wheels off one by one and have someone depress the brake pedal slowly while you watch each brake function individually, being sure that the flex lines, bleeder screws, and wheel cylinders aren't leaking. If all is well still, than you still have air in your lines keep bleeding your brakes try 2 man method or you did let the master go dry and not notice it, hence you must bleed the master properly.
I think there is also something to be said about the pedal being hard before you start it and soft after... Can anyone else add to this...?

I did check the "check valve" on the brake booster and the line going to the throttle body, and they seem to be just fine with no air leaks. I also checked for line leakage and found none; nor at any of the cylinders. I noticed lately when the truck is off and I pump the brake pedal, it will get stiff but slowly work its way down, not all the way to the floor but about half way down. What do you suppose this means? When you say "bleed the master cylinder correctly"....what do you mean? The brake booster was also replaced just a couple years ago.

Bleeding your master properly, takes many minutes to perform properly.What you would be doing is flushing out tiny air bubbles (you cant really see them but you can kind of tell if the fluid looks white not clear) out of the master bore by repetively flushing it, or you can reverse bleed it, I guess using a brand new oil squirter can (be sure to clean it with brake cleaner first) filled with brake fluid and with a tube on it.Be sure theres no air in the tube either. Start from each bleeder screw and squirt back through the system, probally even the master bleed screw would work too. I mentioned earlier post it is possible it sucked in air; Look at the website provided in the title to get a description. Also your brake fluid should be new and not contaminated with the least bit of oil or exposed for too long to air, cause it asorbs moisture and will not compress. So if you used stale (opened to air more than a couple of days) brake fluid you should not rule this out either. This is the only explanation I can think to help at this time. Because - Sir to me it sounds like you are doing everything right. Hey Im having a problem bleeding my hydraulic clutch right now myself on my sierra. I havn't really ruled out every single possibility yet that I have just mentioned either, so were in this mess together! let me know how you solve this problem if you dont mind. Thanks SI16.

Did you bleed the Dump/Isolation Valve? It is next to the RWAL brake controller (drivers side of master) and has a bleeder screw on top.

Push the brake pedal, crack the bleeder, tighten bleeder, release brake pedal. Wait 15 seconds (from the factory manual) and repeat until no air.

//2000CAYukon

UPDATE: I replaced my hydraulic clutch master and it bled in minutes. I wasted days outside bleeding a clutch master that was bypassing, so frustrating without wanting to spend the money and not knowing. (It was my first clutch to bleed, but it generally is all the same. Ive bled brakes hundreds of times) Well needless to carry on, its done now. On a different note if your brakes pump up and hold pressure than you start the vehicle and the pressure is gone. Where did the pressure go if you have no leaks? I would like to know this if you do solve this. Thanks in advance.

UPDATE ON MY BRAKE SITUATION......

I purchased a $30 vacuum pump tool from AutoZone today and followed the instructions for bleeding the brakes. I did the back brakes only, since that is where my problem is. The front brakes work great, and if it werent for them, I would have NO brakes at all. Once I pulled a decent vacuum from the bleeder screw on one of the back wheels, I loosened the bleeder screw and watched/listened as lots of air and little fluid came out. I repeated this procedure "literally" 21 times and got the exact same result each time. There is no way in hell there is that much air in just the rear brake lines. So......I went back to the AutoZone and purchased a set of "one man bleeder screws". Installed them and bled the rear brakes one at a time, making sure the fluid level never got empty. I pumped the brake (truck off) 5 times, refilled fluid and pumped another 5 times. I repeated on the other rear wheel. There was massive amounts of fluid on my garage floor when I was all done. I even hooked that vacuum pump up to the bleeder screw on the dump valve and bled it quite a few times. Satisfied by this point that I HAD to be done, I started the truck and depressed the brake pedal. :banghead: I wasted my f**king time and money. The front brakes still work great and grab well, but it is the rear brakes that have absolutely no pressure. If I pump the brakes with the truck off, the brake pedal will loose half of its pressure, until the front brakes grab.

There are absolutely no leaks anywhere, not the lines, master cylinder or wheel cylinders. The brake booster and check valve have been replaced within the last two years and I have also checked for vacuum leaks, which there are none. Where is the brake pressure for my rear wheels going and why? PLEASEEEEEEEEE HELPPPPPP

You do have brake material left on the shoes, the rear slack adjusters are adjusted inside the drum, Everything in the drum is on proper the wheel cylinders arent siezed or leaking and the drums are not worn out?

You have done everything right to this point?

Somebody earlier mentioned your master cylinder (m\c) could be bypassing, this is what I had to replace after all else failed for my system.

Have you bled brakes before? Because I don't count how many times i pump or anything. I do it by feel. Also after bleeding my brakes I never crack open a bleeder line cause you will let air back in the system.( If I read that right) My pedal in my truck goes half way down, when i start it. That sounds like its functioning normal. Does your brake light not come on any more? If your back brakes arent grabbing it could be the slack adjuster needs adjusting on the side that you replaced the wheel cylinder.

i think you still have air in them have you tryed bleeding them with truck running?? and the wheel cylinder you replaced sounds like that's all your problem..pull the dust boot back and see if you can see fluid as you might have got a bad cylinder..because thats the only 1 you replaced right?? so sounds like thats your only problem..

UPDATE ON MY BRAKE SITUATION......

I purchased a $30 vacuum pump tool from AutoZone today and followed the instructions for bleeding the brakes. I did the back brakes only, since that is where my problem is. The front brakes work great, and if it werent for them, I would have NO brakes at all. Once I pulled a decent vacuum from the bleeder screw on one of the back wheels, I loosened the bleeder screw and watched/listened as lots of air and little fluid came out. I repeated this procedure "literally" 21 times and got the exact same result each time. There is no way in hell there is that much air in just the rear brake lines. So......I went back to the AutoZone and purchased a set of "one man bleeder screws". Installed them and bled the rear brakes one at a time, making sure the fluid level never got empty. I pumped the brake (truck off) 5 times, refilled fluid and pumped another 5 times. I repeated on the other rear wheel. There was massive amounts of fluid on my garage floor when I was all done. I even hooked that vacuum pump up to the bleeder screw on the dump valve and bled it quite a few times. Satisfied by this point that I HAD to be done, I started the truck and depressed the brake pedal. :banghead: I wasted my f**king time and money. The front brakes still work great and grab well, but it is the rear brakes that have absolutely no pressure. If I pump the brakes with the truck off, the brake pedal will loose half of its pressure, until the front brakes grab.

There are absolutely no leaks anywhere, not the lines, master cylinder or wheel cylinders. The brake booster and check valve have been replaced within the last two years and I have also checked for vacuum leaks, which there are none. Where is the brake pressure for my rear wheels going and why? PLEASEEEEEEEEE HELPPPPPP
I would still consider air in the master cylinder. A quick story, a few years ago I was at a local repair shop where a friend worked, and watched as 2 techs spent ages trying to get all the air from a master, which can get trapped in little pockets, and be a you know what to get out. They tried quite a few ways to bleed it, and finally got all the air out of the master cylinder, when they ordered in a product called Speedi-Bleed from a local auto parts store. It was a little pressure bleeder that took about 5 minutes to hookup and within 15 minutes they had fully bleed the whole brake system including the master cylinder. Once the tool was hooked up, as soon as they cracked open the rear line from the master cylinder, you could hear the sound of the air pushed out, and they knew they had had it. The car was one of their contract police vehicles, so it was very important to get it done right before putting the car back on the road.

Watching that sold me on the tool, and I went and purchased my own Speedi-Bleed kit for my Toyota pickup, and have used it on many family vehicles. It gives a great pedal, though vacuum brake bleeder tools work good as well, but I think for overall use, and fluid flushing, this tool is hard to beat. Speedi-Bleed can be found at http://www.speedibleed.com (http://www.speedibleed.com)

Again, more issues with my 1989 GMC C1500 ext cab. Just yesterday I installed new front rotors, bearings and brake pads. I also replaced one of the rear wheel cylinders (it was leaking). After doing all this, I bled the brakes on each wheel, pumping the brakes about 6 times per wheel (I am using a "one man bleeder bottle with tube" since I have no helper) and made sure there were no air bubbles when done. I also bled the master cylinder (via the bleeder screw). I made sure the master cylinder never ran out of fluid. The brake pedal was hard/stiff when I was all done with the truck off. I started the truck when I was all done, and the brake pedal is really soft and goes almost to the floor....causing the brake light on the dash to come on.

What did I do wrong and what can I do to fix this issue....ughhhhhh!:banghead:

thanx.

Have you reset the proportioning valve? (Check Brake light) AKA Isolation/dump valve
It is located next to the Master cylinder between the Control module and the M/C (See Page 9-19 haynes repair manual. This valve when the light is on, also shuts off the brake fluid to half the system. (front or rear) If the light is still on, you must reset it first before continuing. Also when power bleading the system, Engine on, do not let the brake pedel to travel to the floor. This can trigger the light again.

The "speedi bleed" sounds like a great thing to have, but unfortanately my budget doesnt have room for that kind of expense. Both rear wheel cylinders are new and not leaking and I have cleaned the rear drums when I was installing the new wheel cylinders. The master cylinder is also new, but that doesnt mean there isnt air trapped somewhere in it.

My brake light is not on and the entire ABS system has been bypassed. I did however keep all the wires plugged into everything and like I said, the brake light does not come on at all.

When I find the exact problem, I will post here and let everyone know.....thanx all for your assist.

I have a 95 GMC 1500 P/U 5.7 V8 and I have the same spongy brake padel. Replaced booster, master cylinder, bleed the master berfore connecting the lines...everything that was said here but still the same spongy brake padel. My next move was to take the truck somewhere to bleed the antilock system but now that I've read this post I don't think that is the problem, since you said that you have bypassed it. Same like you I've bleed the brakes like 20 times, went through 4 botlles of brake fluid but nothing...I've just read that by pinching the rubber hoses to each of the wheels(pinch the hose and make preassure by pressing the padel and when you release the hose if the padel goes down there is your problem) you can tell if there is a problem with that specific caliper or cylinder. Meenwhile if you fixed your system please let me know what and how... Or if anybody else has some more info....Meenwhile I'll keep you updated if I fixed mine or not.
Thank you.

ok then try this take 1 line off master cylinder and put bolt in it off the same threads bolt master cylnder put foot on brake and see how it feel's then take other line out and do the same after hooking up line you just had a bolt in.. let me no how it comes out.it'll tell you where the air is.because it has to have air in or..you got me..

I have a 95 GMC 1500 P/U 5.7 V8 and I have the same spongy brake padel. Replaced booster, master cylinder, bleed the master berfore connecting the lines...everything that was said here but still the same spongy brake padel. My next move was to take the truck somewhere to bleed the antilock system but now that I've read this post I don't think that is the problem, since you said that you have bypassed it. Same like you I've bleed the brakes like 20 times, went through 4 botlles of brake fluid but nothing...I've just read that by pinching the rubber hoses to each of the wheels(pinch the hose and make preassure by pressing the padel and when you release the hose if the padel goes down there is your problem) you can tell if there is a problem with that specific caliper or cylinder. Meenwhile if you fixed your system please let me know what and how... Or if anybody else has some more info....Meenwhile I'll keep you updated if I fixed mine or not.
Thank you.

Well, it isnt quite "fixed" yet.....it is still spongy and not like it should be, but I have half of a brake pedal and it stops the truck just fine. I have exhausted my efforts and cant take it to a brake shop because I have bypassed the factory settings (ABS). I have also tried "Scrapper"s idea by capping off the lines at the master cylinder. The pedal did get somewhat stiffer with less travel to the floor, which told me the problem was in the brake line itself. But bleed after bleed after bleed....no avail. Like I said, the truck stops and I am beginning to dump too much money into it already. Much more and it'll have a FOR SALE sign on it.:shakehead

Sounds like we are having similiar problems. My friend has a 94 Sierra and his brakes are spongey after bleeding its dozens of times. The pedal goes to the floor and is slow to return. The master cylinder has been replaced twice this year and the booster was just replaced along with both rear drum pistons. There isn't much left to try. I'm going to have him try the isolation method by capping off the lines, but if you have made any more progress with yours, the help would be great. Thanks

I would still consider air in the master cylinder. A quick story, a few years ago I was at a local repair shop where a friend worked, and watched as 2 techs spent ages trying to get all the air from a master, which can get trapped in little pockets, and be a you know what to get out. They tried quite a few ways to bleed it, and finally got all the air out of the master cylinder, when they ordered in a product called Speedi-Bleed from a local auto parts store. It was a little pressure bleeder that took about 5 minutes to hookup and within 15 minutes they had fully bleed the whole brake system including the master cylinder. Once the tool was hooked up, as soon as they cracked open the rear line from the master cylinder, you could hear the sound of the air pushed out, and they knew they had had it. The car was one of their contract police vehicles, so it was very important to get it done right before putting the car back on the road.

Watching that sold me on the tool, and I went and purchased my own Speedi-Bleed kit for my Toyota pickup, and have used it on many family vehicles. It gives a great pedal, though vacuum brake bleeder tools work good as well, but I think for overall use, and fluid flushing, this tool is hard to beat. Speedi-Bleed can be found at http://www.speedibleed.com (http://www.speedibleed.com)

The alternative is the "Speed Bleeder" valves to replace stock valves. They perform as advertised and well worth the price(about $7.00 apiece) that turn a two man job into a one man job.

http://www.speedbleeder.com/