Brakes not working - brake pedal sinks

[tookien]

Hello,

I have trailblazer 2007 4.2L.

I recently did some work on the front end (right wheel. replacing ABS sensor and some other suspension parts).

Negative battery terminal was disconnected before I started.

I had to take the caliper off to do the work and disconnect the brake hose.

I had the brake hose lightly crimped to prevent the fluid coming out - but not crimped enough as much of the brake fluid eventually leaked out.

I put back the front wheel together along with the caliper, reinstalled the brake hose clamp to the caliper with the washer.

I forgot that much of the brake fluid leaked out before I had someone pump the brakes to bleed the air out of the system while I was working the bleeder valves at each wheel.

Realizing that air is probably in the system, I went through many many many rounds of more than 1.5 quarts of brake fluid while bleeding out air from all 4 wheels.

No signs of leaks anywhere, especially at the front right wheel caliper, brake hoses and brake line where I did the work. Also, at the master cylinder the fluid stays at the same level when the brake pedal is pumped.

(I'm familiar with bleeding the brakes process as I have done it many times successfully)

The brake pedal still sinks down to the ground with no eventually resistance built up.

The brake pedal feels spongy, and I can hear lots of air noise when it's pressed.

I thought it might be the Master cylinder (my suspicion is it failed when bleeding the brakes with little brake fluid), but I'm just not sure about that as the brakes were working perfectly fine before I did the work.

The car has the ABS, which I had disabled many months ago as my front right ABS sensor needed to be replaced, which I did during this job.


The brake pedal just continues to sink to the floor with virtually no resistance.

I attempted to drive the car to see if there is any braking at all. There is some braking force applied at the end but just barely enough to stop.


Would appreciate any help.

Thank you

 

[clinebarger]

Bench bleed the master cylinder with port plugs!! Then attempt to bleed at the wheels.

 

[tookien]

thank you for the help.

I will give that a try.

 

[tookien]

Now that I think about it, the car was on jack stanks on the right side while I was bleeding the brakes.

I think the fact that it wasn't leveled may have prevented the air from escaping.


Going to perform another round of bleeding and if it doesn't work, then I will attempt to bleed the M/C.

 

[chrome]

Two immediate areas you will need to look at, the master cylinder and the ABS unit.

As advised, you need to bench bleed the MC first, and ensure the lip seals are still good. Then you need to bleed the ABS unit according to the procedure specific to your vehicle. It sounds like you still have plenty of air in the system.

 

[artbuc]

Hope you didn’t damage your brake hose. I never heard of crimping a brake hose but then again, I am not a mechanic. After you get your system fully bled and operable, keep an eye on the problem wheel to make sure pads are releasing properly which will not happen if your brake hose is collapsed.

 

[Ducked]

THINK I disagree with master cylinder as first focus, 4WIW

It seems the OP has air in the system, so I'd get that out first (which you'll have to do eventually anyway).

I'd do that with an upward fill from all 4 corners, using an enema syringe, and cycling to help dislodge air bubbles.This does not waste/consume any brake fluid

Once you think you have an air free system, if youve still got a dead pedal, its likely youve torn the seals by pedal-pumping with a dry system.

Though I did it for years, I now think pedal-pumping is a daft and risky way to bleed brakes anyway, even when fluid-filled.

Get a syringe.

Full disclosure, I know SFA about ABS systems, never having had one, but since the OP says he's disabled his (can you do that?) MAYBE its not involved.

 

[Snagglefoot]

Not sure if you are working with a vacuum bleeder. If not, it would help.

 

[das_peikko]

Did you re-use your old brake hose washers? If so, that could be your problem. Those are one-time items.

 

[Dallas69]

Never crimp a brake line.
Sounds like you need a pro.

 

[Ducked]

Originally Posted By: Dallas69
Never crimp a brake line.
Sounds like you need a pro.


Yeh, get a pro to crimp your brake lines, then you wont feel bad about having done it yourself, and you won't get lectured about it.

It probably is a bad idea to clamp a brake hose, though I used to do it and it never caused me a problem.

(I had a special tool for it, so somebody made a special tool to do what you should never do.)

Be that as it may, your reported symptoms don't appear to be caused by damage to a brake hose.

 

[MarkM66]

Double and triple check for no leaks.

Gravity bleed it. If that doesn't work, pressure bleed it.

 

[Ducked]

Originally Posted By: Snagglefoot
Not sure if you are working with a vacuum bleeder. If not, it would help.


Vacuum/pressure bleeders probably work just fine.

I'll probably never know, since they cost 50-a few hundred times more than a syringe.

Which works just fine.

 

[tookien]

Ducked,

Do you mean torn the seals of the master cylinder?

thanks

 

[Ducked]

Originally Posted By: tookien
Ducked,

Do you mean torn the seals of the master cylinder?

thanks


Yes.

Its said to happen when using the pedal pumping method of brake bleeding, because its very easy to exceed normal pedal travel and chew up the seals on a corrosion/wear lip inside the cylinder bore. Doing it dry would probably greatly increase this risk.

Still, you don't know for sure that's whats happened, and I think its worth filling the system with fluid first to see if that fixes it. I'd do this upward with a syringe, because its easy and it avoids the risk of further damage.

 

[JMJNet]

Brake hoses can collapse internally.

So it will not be leaking but it is just clogged.

 

[tookien]

The brake fluid is present in all 4 calipers, while bleeding.

The fluid is filled to the top.

I make sure the fluid is filled in the master cylinder.


The car is now level so I will go through bleeding process again, to see if that purges any air.

If that doesn't work I'll bleed out the master cylinder.


I really really don't want to disconnect the lines going to the M/C or ABS module, because there is always surprises with corrosion given that I live up here in rust belt.

 

[tookien]

As for the brake hose.

I've done enough of brake jobs to know that a clogged/broken brake hose would not cause this issue.

Crimping the brake hose does no damage to it. I always use a vice grip (lightly crimped) and cloth/material between the grips to prevent shredding or cracking. This always worked for me.

If it was a clogged brake hose no brake fluid would come out during bleeding.
If it was broken, it would show sign of leaks.

None of these symptoms is present.

Not to mention, I have bleed the brakes on this car before without any issues.


The symptom remains that the brake pedal just goes down without any build up of resistance during the brake bleeding process.

I need to:

1) replace the banjo washer at the caliper I took off with a new one on the right front wheel
2) bleed out at each wheel when the car is level now (it was on jack stands before on the right side)
3) bleed out the master cylinder

 

[tookien]

Does anyone think the ABS module needs to be bleed out?

 

[das_peikko]

Originally Posted By: tookien
Does anyone think the ABS module needs to be bleed out?


Not unless you disconnected the ABS module.

I think the old banjo washers are killing you. They take up an impression every time they're clamped on. When the new impression doesn't line up with the previous impression, you'll get air entering through the previous impression. I've had it happen to me before I was educated about banjo washers.