Brake Pedal Randomly Goes to Floor

[Snowball]

Hello,
New to this site.
Have a 2003 Vibe all wheel drive that I've owned for about 15 months.
About a year ago after just got the car on the road the brake pedal suddenly went to the floor.
Diagnosis was master cylinder. Replaced Master cylinder with new one, bled system and was fine for about a year.
Then a couple weeks ago the pedal suddenly went to floor again a couple times in a row, then has been fine since.
Seems odd that this could happen twice in a year with two different master cylinders.
My question is could this be anything else in the brake system other than the master cylinder ??
Thanks

[Caretaker]

I would hope that whomever did the master cylinder and brake work first checked to ensure that none of the brakes were constantly rubbing, causing the fluid to overheat and thus allow the brake pedal to go to the floor.

[zbyers]

Have you bled the brakes again to ensure there is no air in the system?

I know that little check valve on the brake booster is important, and if bad, can provide the symptoms you've mentioned. It's a cheap part to buy and install yourself to eliminate that as an issue. My old Volvo had a bad check valve, and replacing that solved my soft pedal.

[andrewclaus]

"Never underestimate the power of coincidence." I think the Car Guys said that. I think you somehow got a poorly rebuilt master cylinder. It's not an expensive or difficult item to replace. I'd do it again, perhaps from a different source. And of course, get everything else--each wheel cylinder, every hose, the vacuum booster--checked by a professional. The soft pedal happened to me once (master cylinder failure), and I hope it never does again.

[Snowball]

Ok, so my 2003 Vibe AWD did it again !!
So I've now had it two years, I've lost the pedal 3 times with three different master cylinders on the vehicle (one that was on it when I bought it and two remanufactured units).
Not consistent loss of pedal, it'll go for months or more and then Once will go to floor with no brakes.
Is this a common issue with Vibe/Matrix's ?
Do I need to go to a New (not remanufactured) Pontiac or Toyota master cylinder ??
Or is that Check Valve a definite possibility to cause something this serious ??? (I will be replacing the check valve anyway)

Thanks for any help,
Jeff

[zbyers]

Not a common issue. If it's not the master cylinder, then it could be the brake booster.

[andrewclaus]

A failed booster will only cause loss of braking power, not sponginess. There is still a direct mechanical connection from the pedal to the master cylinder through the booster, so it will work as a manual system with loss of vacuum. You should get two or three power braking operations after you turn off the engine, and that's a simple test of your booster.

A bad booster diaphragm will cause loss of manifold vacuum and may cause rough engine idle, but it will not introduce air into the brake hydraulic system.

If the booster has failed structurally or has come loose from the firewall, that would be a problem, but it wouldn't be intermittent.

I'm not familiar with ABS actuators, but I read that a failure could cause spongy/unresponsive pedal. And you should get a warning light.

Has the brake light (red) or ABS light (yellow) ever come on during these problems?

Have you replaced the brake fluid?

I'd go back to post #2 and check for dragging brakes.

I'd try to find a good OBD-II reader that will read chassis codes, and see if there are any pending ABS codes.

[Caretaker]

I'd go back to post #2 and check for dragging brakes.

Ha, ha....come on; nobody ever listens to me. I almost killed a kid on a bike after a brake job "expert" over tightened my emergency brake causing my brake fluid to boil and total loss of brakes.

[Snowball]

No dragging brakes.
No dash lights.
No codes.
And yes, the fluid has been changed.

The pedal isn't great at the best of times. Sitting in park it isn't very solid, will lower and lower.

Could the Check Valve cause such a serious issue cuz it looks original ?

Thanks again.

[andrewclaus]

Easy test for the check valve--remove the vacuum hose from the manifold and try blowing though it into the booster. The check valve should prevent that.

Try the pedal test with the engine off, car safely parked. If it still feels soft, it's not the vacuum boost system.

If the pedal slowly goes all the way to the floor, it's probably the master. If it goes part way then stops, it may be a stuck wheel piston or caliper.

Conversely, try starting the engine with the brakes on. If the pedal depresses a little when engine starts, the vacuum system is working correctly.

[Snowball]

Ok, so this is an ABS Vibe.

Check valve seems fine, blew into it and air didn't go anywhere.

Pedal is solid when vehicle is off and then drops quite a bit when holding foot on brake and then starting vehicle.

Thanks

[Snowball]

Also, would anyone know for sure if this part number 18M390734 ACDelco master cylinder would fit on my 2003 Base AWD Vibe with ABS ?
It says on some websites it does, but just wanna make sure.

Thanks

[andrewclaus]

The parts system I use comes up with this Toyota number for my '07 w/ABS: 47201-02300. I don't have a cross-reference.

Good luck with it.