brake pedal to the floor off and on

[Randall]

Thanks Guru, I haven't changed the fluid in at least 4 years, but it isn't losing any, but I think you're onto something about the master cylinder

Thanks too Viper, I did the test you recommended and the pedal just stayed still mostly. If I pump it completely down and up it eventually does the squishy pedal symptom one every ten to fifteen times, so I'd like to think it can all be traced to the master cylinder but I am stumped because when I have had one fail before on different cars, they usually just fail and do not go back and forth between working great most of the time to not working. Anyway, thanks for the input!

 

[Randall]

with two jobs and almost no free time lately, I haven't had a chance to dive into this issue, but it is still there At the same time, my clutch has decided to fail, and first gear is no longer usable, so I've got a few other things on the burner. I still am totally stumped on what could be the cause, and due to a tight budget since I will need a clutch much earlier than anticipated, I refuse to just throw on a few different parts in hope of fixing this, maybe. Given what I have posted here in this thread, is there any other suggestions you guys out there might have?

Since the pedal issue happens when the car is sitting still with the engine off the same as when it's driving around town, it's very hard to pinpoint. I thought I was a SHO master, having owned 4 now, and fixing several different types of problems over the years, but this one has my butt kicked. I've searched this forum to exhaustion trying to find a similar issue and have had no luck.

If anyone knows of any tests to rule out various parts of the braking system please let me know, I am nearing a braking point of frustration (pun intended)!

 

[kevinspann]

Look at the booster, directly under the master cylinder - if it's wet there, the seals in the master cylinder are leaking.

 

[SeanMc]

If you talked with Eric, he is probably right. This happened to my parent's blazer recently (while I was driving it), and it ended up being both the master cylinder and the pump.

 

[auto.guru]

actually its easier to diagnose with it failing while the car is driving and is not driving.
this leads me to think the seals in the master cylinder are shot.... being as it doesnt make a difference if car is on or off.

 

[Randall]

thanks for all the replies, I bought a new Master Cylinder and should have it installed in the next few days. Eric felt the pedal after we dropped a new clutch in the car, and he said it had to be the MC. It was only 39$ at AutoZone with a lifetime warranty! Hope this fixes the problem!
Thanks again everyone!

 

[Randall]

Final update

Bought a new master cylinder from AutoZone after three attempts due to their system having the wrong info about SHO brake parts, got home, installed it, problem gone!

The brakes feel as if the whole system was replaced, the pedal feels better than most of the newer cars I drive at work!

Anyway, thanks for all the help guys, I really appreciated it!

(Just a tip for those of you who are going to replace a Master Cylinder with an aftermarket version--- Take the two roll pins that hold the reservoir onto the MC, take the large O-ring on the back of the MC, and buy lots of brake fluid!

It actually was much easier than I thought it would be to replace the MC, and if you have all the parts you need at the start of the job, given that the parts store actually knows what they are doing, it should be a breeze, especially with the Thexton 133 brake bleeding tool!

Thanks again all!

 

[icemaneric]

Glad you got it taken care of Randy, told you it was an easy job. All you need to do now is, replace the racing slicks you have out back.

 

[sdpatt]

I will add my case to this topic since it was through this discussion that I determined my master cylinder was also at fault for the identical symptoms. I replaced the the master cylinder (MC) with the remanufactured Fenco M2613 from AutoZone. The new part is the NM2613, with the "N" statnding for new. This part reuses the reservoir from the old MC. To remove the tank from the cylinder, tap out the roll pins from the side opposite the tank's plastic tab. I used the shank end of the appropriately sized drill bit to mate against the roll pins and tapped lightly with a hammer. The tank must be pulled with significant force to extract it from the rubber bushings on which it is mounted. There are two nozzles with ribbed ends that extend into the bushings. I used two hands on the tank and a foot on each end of the MC.

After careful "bench bleeding" with the supplied fittings and tubing before reinstalling, and purging any remaining air from the two brake line connections upon reinstallation in the car with the wife's help on the pedal, both per the good instructions packaged with the new part, I found the pedal to be as firm as before the swap without additional bleeding. I contentedly drove back to AutoZone and returned the core for my refund with the brakes working as designed. All seemed well on my return home as I slowed to pull into the driveway. Upon application of the brakes, the pedal once again sunk smoothly to the floor. How disappointing! And dangerous! I am still searching for the solution to my brake system malfunction.

 

[Aqua Roach]

Well check the master cylinder again, all the brake lines, the power-booster and even the calipers for any indication of leaks.

If it's the MC again, I'd be tearing some autozone employees a new one.

 

[sdpatt]

There have never been any leaks in the brake system. This happened shortly after replacing the front calipers and bleeding the system with full travel of the brake pedal to the floor. I recall one or two possible instances of this condition in the previous years since installing the '96 uprgade, but the occurances were so rare and non-repeating that I dismissed them. The only time I have added fluid to the brake system is when I bleed the brakes for track events. Never during a track session have I experienced this condition. The last two pedal to the floor events were at slow speed while turning into an alley (last night) or parking spot (this morning). The majority of the occurances have been at low speeds during approach to corners or in stop and go traffic. I have to think there is a relation between these effects. The rate of failure has been about 1 in 20 or 30 brake applications.

 

[Racer X]

Scott, do you still have the stock brakes?

If so, check the lower brake pad retention ear on the front knuckles. If there is a ridge worn where the pads are resting against, it's possible that the pads are hanging up against that ridge under braking, causing them to the ineffective. It would also cause the soft pedal until it's pumped up again.

*edit*
Just saw your latest post. Nevermind this.

 

[sdpatt]

RacerX, I had found a simliar post of yours in a search this morning and plan to perform a detailed inspection of the brakes to check for the items you mentioned. I will also check the anti-rattle springs. The front brakes are the '96 upgrade and the calipers are the second set of remanned units that have been installed. As I stated in my last post, there may have been one or two occurances of this condition over the last 4 years with the first set of calipers on the '96 upgrade. The caliper brackets had a smooth channel where the pads slide IIRC from applying the hi-temp brake grease during installation of the latest calipers.

The booster and vaccum check valve seem to be working as I had forgotten to press the brake pedal to release the vacuum in the booster before trying to remove it last night. Even an hour after engine shutdown, there was still a significant vacuum holding the master cylinder to the booster. I felt the resistance to move as I grabbed the MC to pull it from the booster after removing the two nuts and heard a noticeable vacuum release sound from the O-ring when the seal was broken.

I have checked for loose wheel bearings with the 12 and 6 o'clock test at all four corners. The fronts and rears have a few track sessions on them and they have been replaced in the past at the usual signs of wear. I currently do not see or hear the same evidence that indicated their previous failures.

 

[sdpatt]

Engine off - pedal to the floor

Doing more testing, I find that with the engine off, I can push the brake pedal to the floor on occasion. The pedal is usually hard when pressed, but after about 30-50 pushes, it will sink quite easily to the floor for 1-3 presses and then be hard again. What components could be causing this? My thoughts point toward the master cylinder leaking past the seals, but why would the remanufactured unit behave so similarly to the master cylinder that had been on the car for 20 years?

This finding should remove the ABS system, caliper bracket ridges, loose wheel bearings and system leaks from the equation? If one of the calipers or brakes lines was leaking, there would be brake fluid on the ground and the level in the reservoir would decrease. I will be quite perturbed (but maybe a little releaved) if I have to replace the master cylinder again.

 

[Randall]

So sorry to hear that you're still dealing with this issue! What a nightmare! It still somehow sounds like the MC is bad, maybe the new one is faulty already. Do the pedal drops happen at the same amount as they did with the original MC, or more or less than before? On the brightside, you do have a lifetime warranty on that part, so although it will cost you time and labor to swap another one out, the part would be free.

After dealing with the same issue as yourself for a few months, I tested everything and even swapped a few parts until the MC ultimately solved the issue, which has not returned. Just like you, when I saw that the pedal was failing without the car even running, I realized it had nothing to do with the electronics/ABS parts, and that just left calipers, lines, and the MC. You've said you have no fluid leaks, so that pretty much points to the MC again being the culprit. I had the exact same results as you with the 1-3 bad pedal pushes every 30 or so with the car off, and also the pedal failures happening at slow speeds or on turns into spots. I too have the '96 brake upgrade, so maybe there is something to that. I did have a bad wheel bearing, but replacing it didn't solve the issue. It was only after the new MC went on that things returned to normal. I know I haven't seen this car in person, but I strongly suspect you got a bad/defective MC from autozone that may have even been tested before being boxed up, but like we have experienced, the unit acts normal for 20-40 uses, then suddenly fails.

Good luck on this, I hope you can find a solution soon!

 

[Shovert]

Unsure if this helps and not reading it in this thread. Thought I would mention.
http://www.taurusclub.com/forum/118-suspension-handling-brakes/151194-95-sho-brake-headache.html
http://www.shoforum.com/showthread.php?t=109034&highlight=bleeding+brakes
If ABS acts like this I would rather trust my own skills so I would remove all. I had a neighbor wreck his truck because ABS failed. Maurice
http://www.shoforum.com/showthread.php?t=84461&highlight=bleeding+brakes

 

[auto.guru]

id have to agree... this sounds like a bad MC off the shelf...
even i have been fooled with brand new parts.

3 different starters from autozone... till i finally went to the junkyard and got one. Havent changed it since then

 

[sdpatt]

To make it even more probable that the newly installed master cylinder is faulty, it was a remanufactured part that may have been "on the shelf" for an undeterimined length of time. It does have a lifetime warranty and I now will be developing experience in the master cylinder replacement process. It wasn't too hard the first time, but there is nothing fun about working with brake fluid outside of its normally closed system. The Fenco M2613 looked to be in good shape externally and was packaged with the requisite fittings and tubing to allow an effective and clean bench bleed where the fluid dischared from the ports is routed back in to the top of the reservoir. What Fenco can't control, is the length of time the dry seals have been sitting in a dusty box on a auto parts store shelf. I will be updating this topic with the results of the second MC replacement to keep my old SHO rolling. And stopping!

 

[Nessa]

id have to agree... this sounds like a bad MC off the shelf...
even i have been fooled with brand new parts.

3 different starters from autozone... till i finally went to the junkyard and got one. Havent changed it since then

Going to try not to derail the thread, but since it was brought up:

Is it very common for new parts to fail? I mean you said it's happened, but does it happen often? Bought and installed a new brake light switch (myself, thank you very much), and it's still not working right, even though it's better. Not that I was looking for help on that, just curious about how common new part failure is.


ETA: Also, hope that fixes your brakes! That's scary.

 

[auto.guru]

on a personal basis i would say it happens anywhere from 10-20% of the time for parts that have been reman, or sitting on the shelf for a great deal of time. I also break down a lot - so im buying parts more often than others lol.

i often "shopped" around from carquest, advanced, autozone, auto supply, napa... you name it. So its possible i got the cheapest part from a certain store just because it has sat on the shelf for so long. With any part that can be "tested" - i buy it and test it before i walk out of the store. Just to be sure.