brake pedal to the floor off and on

[Randall]

Hello,

The other day while just driving normally, I was nearly smashed by a semi truck as when I came to a red light, my brake pedal went nearly all the way to the floor out of the blue. It caught me off guard, but I let off the brake and pumped it quickly, and the car stopped just in time, and the pedal stayed about an inch and a half from the floor. I immediately pulled over and checked the brake fluid, which was full to the brim, and the vacuum hose to the booster was intact and fine. What was funny is that the brakes acted normally again immediately after that incident. I drove it back to work, and through maybe 20 different stops, it was fine. Then, as I came to a stop at the light near my work, it happened again. This time I just let all the way off the pedal and it was like a reset button, and the pedal worked normally. It has happened a few more times at random since, and "pumping" the brakes seems to not make a difference half the time. It never goes all the way to the floor, as it stops and gets firm at about an inch and a half from there.

Still, this is alarming, and I have no idea what it could be. I talked to Eric Dominguez, and he thinks it may be the ABS motor/pump. I need your help in finding a way to diagnose this ASAP as this is my only car currently, and although I am still driving it, I would much rather be able to solve this and no longer have the "white knuckle" experience continue.

Additional info: Probably unrelated, but the clutch pedal suddenly changed it's feel while driving on the freeway a week ago, and now it's really hard to shift into all gears.

Also, during one or two of the stops where the pedal became squishy, I heard a clicking noise from the front of the car on the driver's side. I think it's really weird how this comes and goes, but any advice is appreciated!

thanks!

 

[93rev2sev]

Sharp car. Send it to Michigan when you're done with it...LOL...


I'd also guess the ABS pump is at fault. Did you feel any sort of pulsation when the pedal dropped? That would be the ABS pump cycling. It basically think's you're sliding when it does this. The first thing I'd do is put it on jackstands with the wheels removed and inspect all of the ABS sensor rings.

If it had only happened once, I'd say the rear brakes could be the cause. You can lose all rear brake functionality and hardly notice a difference if you drive "normal". In addition, you could pop a rear brake hose and not lose fluid....but then your foot wouldn't go to the floor and it certainly wouldn't happen more than once.

Nope. Your problem MUST be electronic. For there are no parts of the brake system that can fail, allowing the pedal to go to the floor and then return to normal.

 

[Randall]

Thanks for the advice! I hadn't thought of that yet about eliminating it to electrical, but that makes total sense! Is there a way to run a diagnostic on that ABS pump? I've got no light coming on for the "anti lock".

Thanks!

 

[Randall]

So, I am still afraid to drive the car, and I need a little more help if possible. All I really want is to be able to narrow the problem down to what component is bad. Right now, I think it is possible that the ABS pump could be bad, the master cylinder possibly, the booster possibly, or something I have yet to think of....
Anyway, is there any certain way to eliminate the booster or the master cylinder from being bad?
Thanks!

 

[93rev2sev]

Did you feel any pulsations in the pedal when this occured?

 

[zach44102]

Surely you would of noticed if you had a caliper sticking right? I just know from my experience when i had my pedel go to the floor I had a caliper sieze and my brake fluid started boiling.

 

[Randall]

I didn't feel a pulsation really, just a super soft pedal down to about an inch and a half above the floor board. I did hear a clicking noise twice during the soft pedal incidents that I could feel in the pedal, but it was more of a click or two and that was it each time.

No, I don't think I have a seized caliper, I did check the rotors out and they appear fine, and also, this pedal stuff only happens at about 1 in 20 stops. Really weird. I am going to try and short the diagnostic pins for the ABS and see if I get anything, no Anti Lock lights yet though, and yes the bulb works.

Thanks for the help so far guys, you're great!

I still am not sure how to rule out a possible bad Master Cylinder or Booster yet, but I know for sure there is no sound of a vacuum leak at the booster, and with the pedal working at about 90% of the time I think it's safe to say it's not the booster. Any more help is greatly appreciated!

 

[Randall]

Ok, so I ran a self diagnostic on the Anti Lock system through shorting the two pins in the red connector, and even though my light is not on at all, there were 4 codes!!!

Here they are in order that they came out:

22-Left hand front inlet valve
44-left hand rear sensor
43-right hand rear sensor
63-Pump motor speed sensor

Does this make any sense to anyone here when combined with the issues I am having?

 

[Randall]

ping... anyone?

It is still happening at the same rate, about one in every 20 stops, and it seems more common at slow speeds. I just need some help in figuring out how to deal with the codes I pulled, and if I have a bad ABS pump or motor. Any tips are appreciated!

 

[ViPER1313]

I can't help with your ABS codes, but how are the condition of your wheel bearings and front axle nuts? Does the soft pedal happen directly after you take a corner (ex.. coming off of a highway offramp?) Try this out in a parking lot - make several semi-quick 360-degree left circles and then hit the brakes, then do the same while turning right. Does the pedal remain firm after both?

It is just something else to think of, because a loose front axle nut or bad wheel bearing can cause symptoms like you describe (it would be pronounced after a corner though.) The loose bearing allows the caliper piston at that wheel to depress while taking a corner, and when you straighten the wheel the piston is actually some distance from the rotor. When you hit the brakes, you are greeted by a soft pedal (because the piston has to come back out towards the rotor.) Hit the brakes again, and they firm up (because the piston is now at the rotor's surface.) This happened on my Talon a few times before I figured it out - it was quite a scary feeling. It took me a while to realize it was only happening after left cornering. The right-front wheels axle nut was finger-tight - tightening it resolved the issue completely.

 

[93rev2sev]

This can happen when one of the tone rings gets caked with dirt/grease/mud or gets damaged. The ABS pump will activate when it's not supposed to.

Have you inspected them yet? Because I told you to do that already. If someone gives advice and you ignore it, don't expect more advice. It's really unbeleivable that so many people do this.

 

[Randall]

Thanks Viper, I tried that and it didn't seem to help or hurt the situation, I did have the wheels off and I didn't notice the spindle nuts being loose, but I can easily check that again. It seems to happen mostly on straight stretches at low speeds, so it makes very little sense. I seem almost certain its the ABS pump, so my next step is going to be just to replace it.

What happened 93rev? Did you have a bad day or something?
I don't like being called out when it's not warranted.
I did take your advice, and I thought it was helpful! I have easy access to a lift, so taking the wheels off and on is a snap. I pulled off the wheels and checked for any obvious signs of damage to the wiring at the sensors, and even sprayed a full can of brake cleaner spray on the sensors/rings to clean them and it made no difference. I agree with you that a lot of people ask for help and then ignore it, but I've been on this forum for quite some time, technically longer than you even, so give me the benefit of the doubt, huh

 

[93rev2sev]

Well...there's no doubt now that you reported your findings.

Moving along...

I've seen tone rings with hairline cracks in them that allow the ring to slip on the axle. Tap them with a screwdriver and a hammer to eliminate them as your culprit.

While you're tracking this down, disconnect a sensor to disable the ABS so you don't rear end anyone.

 

[auto.guru]

why has no one offered the suggestion of a brake booster???

jeezz. my old dodge daytona had a brake booster go out on it and it acted exactly like this. i mean... to the nose hair. It always clicked when the pedal squished to the floor, not sure what the clicking was, but i remember it.

get your brake booster checked before you do anything else. How to test? i have no clue. But thats where i would start. Junkyards work best

 

[Randall]

Thanks Rev, you've been a star in my book for a long time

I just had the wheels off again, and I missed your post before I did it, but I'll check again as the driver's side front did appear to have a crack in it. All of the sensors were intact and free of grease upon initial inspection, but I sprayed them down anyway. Then today, I took the wheels back off just to make sure I didn't miss something like Viper mentioned where a wheel nut could be loose - - but they were nice and tight too.

Anyway, thanks so much for the tip about disconnecting the sensors, I never thought of that, and you're right, it can be scary even when you're ready for the pedal to work or not. I have noticed that when the pedal goes down to near the floor that if I use much force, the front driver's side tire skids audibly, and yet still no ANTI LOCK light! I will disconnect the rear sensors, and thanks again for your advice, I really do appreciate it!!

Auto guru, I also was thinking it could be the booster, but I ran a vacuum pump to the large check valve and there was no leaking or spikes in pressure, so I think it may be good. When I have had one fail in the past, they get loud and vacuum pressure seems to fall off at idle, but it does have nearly 200,000 miles on it! Thanks for the suggestion!

 

[auto.guru]

see i never checked mine in the daytona.... so i couldnt tell you about falling vacuum at idle. But if this is an intermittent issue wont your falling vacuum be intermittent as well? it could be, and it may not be. Who knows....

And you wont get an ABS light when your pedal reaches the floor. The ABS system comes on when it detects wheel slippage. Thus it reads all 4 tires and uses that info to pulsate the brakes.
But when your pedal is to the floor, you trip a sensor, and it clicks. This is one of the clicks youve been hearing - and it turns on that brake light on the dash. When you activate that light, it shuts down the ABS system.

WHY?
well think about this. If your braking and locking up your wheels, thats a harsh force. Now think about the ABS pump pulsating the brakes - from locked to unlocked - to locked - to unlocked very very fast. Thats alot of sudden inertia that has to go somewhere. Your tires are going to get chewed up faster than belief, you are going to break lug nuts depending on your speed, or your CV halfshaft is going to break. Either way all that momentum and force has to go somewhere and something is gonna break.

Thats why you put your foot to the floor and lock em up. What would you rather do? lock your tires up and stop or break your halfshaft and be stuck in the road?

 

[Randall]

Okay, major update here!!

I removed the 40 amp fuse from the distribution box for the ABS motor and the Anti Lock light came on, but the exact same problem persisted. Then I kept the engine running and pumped the brakes repeatedly while stopped, and it still happened at about 1 in 15 tries, usually two in a row.
Then, I turned the car off, and repeated. I got the same results, even with no engine running, about 1 in every 15 complete pumps, the pedal goes down to nearly the floor.


Now I am totally stumped again, but at least it seems it is not the ABS pump/ motor. Does anyone have any ideas with this new info?

 

[auto.guru]

youve got to be losing brake pressure in your lines somewhere....
a leak maybe?
its got something to do with the psi drop off... we know that now

 

[auto.guru]

whens the last time you changed the brake fluid???
ill bet money your master cylinder is starting to take a ******* on you. It sounds like the seals are shot, and like to "leak" after repeated use.

You could replace your seals, but im unsure they sell those separate. You might have to buy or get a whole new one

 

[ViPER1313]

why has no one offered the suggestion of a brake booster???

jeezz. my old dodge daytona had a brake booster go out on it and it acted exactly like this. i mean... to the nose hair. It always clicked when the pedal squished to the floor, not sure what the clicking was, but i remember it.

get your brake booster checked before you do anything else. How to test? i have no clue. But thats where i would start. Junkyards work best

I had a bad brake booster on my 97 Taurus - the pedal would not go to the floor, but would become very stiff if you depressed it 2 times in quick succession. You could also hear a hissing down by the brake pedal, and there was a clicking noise involved when you pressed the pedal as well. If I recall correctly, the way to check for a bad brake booster is to press the brake pedal to the floor with the motor running and then shut the motor off. If the brake pedal immediately starts to push back against your foot when the car is turned off, it means the booster is leaking somewhere internally (it should hold vacuum.)