Please Help!!!! Brake Issues

[3000gt93]

1) Truck is on = mash brakes = extremely soft pedal = takes forever to stop = Need help

97 2 door tahoe
OK, I have replaced the master cylinder, 2 rear wheel cylinder, shoes, and pads. Everything put on correctly.

The problem is that i can only bleed my brakes when the truck is off. When I crank the truck, I will pump the brakes and when I bleed them, I have no pressure to the rear, However the front pressures are normal. When the truck is OFF, everthing works great. Also when i pump up the brakes when the truck is ON, a gushing sound is heard at my master cylinder. If i leave the top off the master cylinder and mash the brakes it will blow fluid everywhere(is that normal??) If i didn't know anybetter i think Have a faulty ABS Brake Modulator Valve.

Any suggestions would be GREATLY appreciated.

[j cAT]

Originally Posted by 3000gt93

1) Truck is on = mash brakes = extremely soft pedal = takes forever to stop = Need help

97 2 door tahoe
OK, I have replaced the master cylinder, 2 rear wheel cylinder, shoes, and pads. Everything put on correctly.

The problem is that i can only bleed my brakes when the truck is off. When I crank the truck, I will pump the brakes and when I bleed them, I have no pressure to the rear, However the front pressures are normal. When the truck is OFF, everthing works great. Also when i pump up the brakes when the truck is ON, a gushing sound is heard at my master cylinder. If i leave the top off the master cylinder and mash the brakes it will blow fluid everywhere(is that normal??) If i didn't know anybetter i think Have a faulty ABS Brake Modulator Valve.

Any suggestions would be GREATLY appreciated.

i believe you will need a scan tool that will force the abs on so that the brakes can be bled. whenever bleeding brakes by brake pedal keep cover on. brake fluid on rubber and paint will be very bad ....you could try to suck air out of rear brake lines with the proper tool.have cover off if you do it this way. how did this occur anyway?

[3000gt93]

well i have owned the truck for 4 years and i love it(BTW GM needs to start making the 2 dooor version again). Anyway, the brakes have always been weak. Gradually they have gotten worse over the years. When I replaced the shoes on the rear a few years ago, they were hardly worn.
I just can't figure out why my brake pedal has to go to the floor before it will stop. Even after the pedal is to the floor it takes forever to stop. I thought that i had air in the system but a mechanic bleed my brakes for me and it did not resolve my problem. The only things left to replace are my brake booster, and ABS Brake Modulator Valve.

Basically i have to press my brake pedal 1/2 way before my truck even attempts to stop.

[j cAT]

Originally Posted by 3000gt93

well i have owned the truck for 4 years and i love it(BTW GM needs to start making the 2 dooor version again). Anyway, the brakes have always been weak. Gradually they have gotten worse over the years. When I replaced the shoes on the rear a few years ago, they were hardly worn.
I just can't figure out why my brake pedal has to go to the floor before it will stop. Even after the pedal is to the floor it takes forever to stop. I thought that i had air in the system but a mechanic bleed my brakes for me and it did not resolve my problem. The only things left to replace are my brake booster, and ABS Brake Modulator Valve.

Basically i have to press my brake pedal 1/2 way before my truck even attempts to stop.

brake pads are made of many different materials. MR.GM does not tell aftermarket manufactures what the secret mix is, and as a result brake problems like yours abound as owners use different brake manufactures pads in the vehicle. so as you apply brake pedal pressure vehicle does not slow as expected. now because you replaced the master cylinder , i believe you will require a scan tool to force on abs , to properly bleed system or maybe using vacuum bleed equiptment. you have air in abs abs needs to be bled.pedal to floor is air soft pedal is air hard pedal brake booster vacuum /diaphram. with a good brake pedal and vehicle does not slow as expected poorly designed brake pads.....""if you have brake drums rear you must replace the drums if the shoes are wearing only on 1/2 of the shoe as the drum diameter has grown too large to be effective in creating a large enough friction surface"".......

[G.A.S.]

You need to properly bleed the system

[3000gt93]

THANK YOU ALL VERY MUCH FOR THE REPLIES!!!! today i am taking my truck to GM. I will inform you'll of the results after they bleed the system.

[3000gt93]

alright..... "sigh"......

The brakes were bled (by a mechanic) and there is no air to be found in my brake lines. He bled the abs module as well. Sadly, I still have a spongy pedal and very poor brakes.

I left out an important peice to the puzzle. I have owned the truck for about 4 years now. In that time, my ABS has NEVER worked. I am saying that because my pedal has never vibrated nor do i ever here that ABS motor run.

I have not seen my check engine light come on either.
I did UNPLUG my ABS unit today after i got the truck home and that did not help. I read where may help.

Could the bypass valve be stuck??
Could the ABS unit be stuck therfor Venting air???
I know there is someone out there with the answer.
Please help!!!!!!

[zambiti]

their was a recall on the abs, i had a truck same as yours an had the same problem it was just this $2 part from the junk yard right by the brake fluid resivwar thirs is this little bolt you could say that had a pin tiny poke in it their for loosing just enough pressure same sympton as you have someone press the brakes follow the lines as they do that and check for the slightest leak

[3000gt93]

is this part on the ABS unit? or is it down on the frame somewhere?

[j cAT]

Originally Posted by 3000gt93

is this part on the ABS unit? or is it down on the frame somewhere?

the question is did this occur gradually or after you/others worked on your vehicle? do you service your vehicle or others like oil r/r etc.... it is and does occur, repair service shops put the wrong fluid in brake res. or fluid that is conntaminated i.e. used same container for different fluids.............just something to think about........

once again do you have drum brakes? if so did you adj brake shoes ? is the shoe contacting the drum completely?

[3000gt93]

Problem solved!!!!!!

There was air in the abs unit!!!!! The brakes are excellent now. Apparently you need a power bleeder to force all the air out of the system. Thank you all for the help. Very helpful forum....