99 brake sticking issue

[Rick Norwood]

How is your brake pedal? Obviously, the pressure is not being released from the calipers, keeping them engaged, at least partially, when you release the pedal.

Old Master, When you say you suspect the master cylinder, do you mean it is sticking? You also say the Push Rod may be the problem, do you mean bent, kinked, broken, binding? Please clarify.

I have seen master cylinders leak back past the "O" ring seals internally and fill the Vacuum Booster full of brake fluid, and this Forum is full of threads with Squishy pedal complaints, but I've never seen one stick in the pressurized position that keeps the calipers locked. But I guess I've never seen a rotor turn red either. I still gotta think the problem is in the ABS unit. Whatever it is, this is a strange one. Keep us posted on this one for sure.

[burnchassis3]

It did not do it today on the way home .
The pedal feels fine/normal..I had someone else drive it ,and they said the brakes felt very good.
Thats the problem,they are good untill they are bad.
lol
However I do feel a VERY hard pedal sometimes,BUT a soft/normal pedal most of the time.
Makes me also wonder about the booster....possibly a vacuum leak? Could an air leak cause this?
Occasionaly I do hear a slight hissing from under the dash just above brake pedal...but i just thought it was vent related.
Thanks to all!
CS

[Rick Norwood]

I still think you need to bleed the ABS unit with a scanner, and then bleed the cylinders again.

"they are good until they are bad" will get you in a wreck are get someone hurt.

Please have this checked out at a reputable shop if it is beyond what you can do on your own.

[BlazerLT]

Were the caliper pins replaced and lubed up?

[burnchassis3]

New ,and lubed yes....and stopping isnt the problem....its never had a problem stopping....ever.

[BlazerLT]

Are both sticking, or just one? Maybe it is a bad caliper?

[old_master]

Originally Posted by Rick Norwood

...Old Master, When you say you suspect the master cylinder, do you mean it is sticking? You also say the Push Rod may be the problem, do you mean bent, kinked, broken, binding? Please clarify...

Passages in the master cylinder, and/or ABS unit for that matter, could be restricted with debris. Something might be floating around in there and occasionally gets caught in the wrong place. There may be a deteriorated or distorted seal, burrs on the piston, or burrs in the bore.

The push rod could be out of adjustment, (too long) damaged, or not seated correctly in the master cylinder or booster. If the master cylinder has never been removed from the booster, it's highly unlikely the rod developed a problem on its own. If the booster is contaminated with brake fluid, due to a leaking seal on the master cylinder, that could also be a possibility. These are things that could cause the symptoms he is experiencing. Without knowing the complete repair history of the vehicle, and without the advantage of being able to look at it, all possibilities should be checked before replacing a boat load of expensive parts unnecessarily.

[Rick Norwood]

Originally Posted by BlazerLT

Are both sticking, or just one? Maybe it is a bad caliper?

I believe he said both sides were sticking.

This tells me he is either terribly unlucky, amazingly consistent or there is an upstream problem with the ABS unit or the Master Cylinder. The wheel cylinders are apparently not releasing all the way, so something is keeping pressure on them, however slight.

I agree with Old Master in that he needs to Bleed the ABS system using a Scan tool. If nothing else, this is a good place to start, it certainly won't hurt.

[burnchassis3]

Originally Posted by old_master

Passages in the master cylinder, and/or ABS unit for that matter, could be restricted with debris. Something might be floating around in there and occasionally gets caught in the wrong place. There may be a deteriorated or distorted seal, burrs on the piston, or burrs in the bore.

The push rod could be out of adjustment, (too long) damaged, or not seated correctly in the master cylinder or booster. If the master cylinder has never been removed from the booster, it's highly unlikely the rod developed a problem on its own. If the booster is contaminated with brake fluid, due to a leaking seal on the master cylinder, that could also be a possibility. These are things that could cause the symptoms he is experiencing. Without knowing the complete repair history of the vehicle, and without the advantage of being able to look at it, all possibilities should be checked before replacing a boat load of expensive parts unnecessarily.

The MC has never been removed..I have never had to add any fluid as if the booster was leaking.
My only concern with having to bleed the abs is : this happened before anything was tampered with at all..Stock calipers,lines,abs,MC,and booster and always full of fluid.
Now ,If I do need to bleed them now ,Why did it happen before to begin with? this is the real problem..Not to sound defiant but,I dont think bleeding the ABS will make a difference.
Im leaning more towards a vacuum leak causing the booster to think/function differently??
Can anyone rule out the vacuum leak possibility? Like I said earlier I do occasionally hear a hissing from under the dash above the brake pedal...but I always thought it was vent related.
Thanks as always.
CS

[old_master]

If the master cylinder goes dry, for any reason, air is injested into the ABS unit. Using the scan tool is the only way to "force" solenoids to operate within the ABS unit so it can be bled. Without using the scan tool, it is impossible to bleed the accumulator. Bleeding the system may not make a difference with your problem however, it must be bled before you can continue with an accurate diagnosis of what the problem is.

If there is a vacuum leak in the supply line to the booster or the diaphragm in the booster leaks, a hard pedal and reduced power assist would be the result.

[burnchassis3]

How hot is brake fluid supposed to be? after a couple hours of sitting at 70*F my fluid in my MC is 128*F.
Is that normal?

[Rick Norwood]

I do not know nor in all likelihood will anyone of us on the Forum be able to tell you why this problem existed prior to all the work you did. As Old Master says, we need to fix the obvious issues to properly diagnose the real culprit.

Since the engine runs at 190° - 195° it is not too far out of the realm of reality that the brake fluid temperature would increase to 128°. I assume the hood was closed when you did this test.

I do not believe that any type of vacuum leak would cause the rotors to turn cherry red. You could disconnect the vacuum line and still have brakes, but this would only affect the pedal.

The only logical thing that comes to my mind is that there is a defect somewhere in the ABS unit itself. Either the pump runs continuously or there is a sticking valve or something else is wrong.

Lets stop and re-think this a minute. You have both front rotors turning cherry red after driving the truck. This tells me the calipers are staying pressurized while driving with no pressure being applied to the brake pedal. I admit I do not have intimate knowledge of GM's ABS systems, but basic common sense tells me that the fluid/pressure is not releasing back into master cylinder. Something is either stuck, plugged or inoperative. Perhaps there is a bad solenoid.

[burnchassis3]

Its at the shop now ..the shop manager seems to be sure its the hoses.
So were replacing the hoses at the calipers,and bleeding the unit...if this dont fix it ill let you all know again.
Thanks for all who posted for me.
I will be sure to post a follow up.
CS

[burnchassis3]

ok heres the story...Its not just 1 thing ,or it may be just 1 thing,but everything in the brake system that has a rubber seal is, or could be destroyed.Including ,but not limited to abs system. master cylinder,all hoses,and seals.
At some time someone has put something other then brake fluid in my master cylinder possibly causing all of the seals and hoses to collapse possibly.
The fluid was to hot beacuse it was burning from the hot brakes ,between the burnt fluid, and possibly the power steering fluid that was proposed to have been put in there.It has caused black residue through out my system.

So if this problem ever arrises for someone again...1st question should be:

Is the rubber seal on your masrer cylinder ok/normal ? or is it swollen?
Because if yours is swollen you too have a contaminated brake system and you need to flush it right away before it ruins everything in your system.If it is swollen in the least bit...that means its contaminated.
thanks to all for posting.
im sure I'll have more questions as I change the entire brake system until it goes away.
Starting with the ABS brain box,and master cylinder.
CS

[burnchassis3]

Well I figured I probably had to replace the entire braking system,but I didnt know where to start.
I started by replacing the fluid,Sucked all of it from the MC,and replaced it with new,then bled the brakes for 2 hours! I ran 3 bottles of synthetic fluid through the lines close to 96 ounces...all 4 tires
That was 3 days ago,and it has not happened again(yet).
I could have gotten really lucky....or not.
But for now i'm not going to replace anything....except fluid I will clear the MC of fluid everyday after I drive it for awhile...that seemed to help alot!!
AGAIN
Thanks to all who helped me out!
CS